ROUTE Exam Guide v3.3 [PDF]

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The Online

CCNP ROUTE

642-902 Exam Guide No filler. No hype. Exam-focused. “A portable, comprehensive guide with everything you need to get up to speed and pass the ROUTE Exam - the first time.” www.ccnpguide.com 1|Page

Introduction I started www.ccnpguide.com as a way for me to capture technical notes as I prepared for the three major CCNP Exams – SWITCH, ROUTE, & TSHOOT. As I began sharing my notes with the world, I immediately started to receive feedback on the SWITCH exam’s focus areas and how difficult it was. What I realized was that the exam prep resources available (read: Cisco Press Books) were not even covering all of the exam topics, including some that you were required to configure in live simulation scenarios. First-time fail rates seemed normal and a big part of that was because the some of the simulation scenarios required you to know some extremely specific protocol configuration details that most network professionals just wouldn’t know off the top of their heads. I began to tailor my notes to include topics that were not being covered in “official” exam guides and trimmed down those that just were not necessary. The feedback was overwhelmingly positive from the online community! The problem is, of course, that the notes were not formatted well for off-line consumption and didn’t include enough lab/scenario-based examples. This guide is an answer to the countless requests to create a portable, comprehensive, and exam-focused ROUTE prep guide. I’ve refined the online notes even more to focus exclusively on exactly what Cisco expects you to know on exam day. I have also included a Simulation Scenario section at the end. Here’s my recommendation. Read through this manual a few times and make sure you understand each chapter. After you feel comfortable with the details in each chapter, go to the Simulation Scenarios section and run through the three scenarios until you can solve them off the top of your head. That may mean running through them ten times each, but trust me – you’ll thank me when you sit for the test. If you have questions, exam feedback, or want to reach out to me directly - shoot me an email at [email protected]. I promise you’ll get a response.

Best of luck.

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Routing Basics

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EIGRP

11

OSPF

29

Route Filtering & Redistribution

52

BGP

59

VPNs & IPSec

73

IPv6

77

Simulation Scenarios

88

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Routing Basics 4|Page

Static Routes In order for routers to forward packets to remote networks, they must know how to reach them. There are two options: static or dynamic routes. Static routes are manually configured on each router. They are used for a couple of reasons: • •

where there is only a single path to a network (a.k.a. stub network) when connecting to an ISP and configuring it as a default (static) route

There are a number of problems with implementing static routes network-wide. Some include: • • •

failure to scale well does not automatically react/recover to changes in the network tedious to configure for large networks (see point 1)

To configure a static route: R1(conf)# ip route prefix mask address|interface [distance]

The prefix and mask is the destination network and subnet mask. You can use an address to define the IP address of the next hop towards the destination network or specify a local router interface that the router will use to send traffic out to the destination network. The optional distance keyword can be used to manually define the administrative distance for the route.

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Static Default Routes One of the most common uses of static routes is for creating a default route. There are often cases when you want to forward packets that are not defined in a specific route out an interface or towards another router. A common example is when connecting to an ISP. If traffic is destined for an address range not defined within your organization (i.e. your coworker’s Facebook updates), then it makes sense to configure a default route towards your ISP or other organization.

To configure a static default route: R1(conf)# ip route 0.0.0.0 0.0.0.0 address|interface ]

Floating Static Routes There are some circumstances when it makes sense to use a static route as a backup to a dynamic routing protocol. In order for this to work, however, the default administrative distance value on the static route must be raised so it will have a lower priority than the dynamic routing protocol (see administrative distance section below).

Dynamic Routing Dynamic routing protocols can dynamically respond to changes in the network. The routing protocol is configured on each router and the routers learn about both each other and remote networks. Examples of modern dynamic routing protocols include:

• • • • •

RIP v1,2 (ok, maybe this isn’t very “modern”) EIGRP IS-IS OSPF BGP

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Distance Vector vs. Link-State Distance Vector When routers run a distance vector dynamic routing protocol, they periodically send information about their known routes to their connected neighbors. This is how the router knows whether changes have been made to the network. They compare their routing table against the information they receive from their neighbors – if it matches, they’re good. If not, they update their routing tables to reflect the changes. RIP is an example of a distance vector routing protocol.

Link State Link state routing protocols operate differently. Routers send information about the state of their links to the entire network (or area) that they are a part of. In this way, each router understands the entire network topology and must run an algorithm every time a network change is announced to recalculate the best routes throughout the network. This makes link state routing protocols much more processor intensive. The second major difference in link state routing protocols is that updates are only sent if a change on a router’s link occurs. This helps keep bandwidth utilization low, unlike distance vector protocols which send out reoccurring updates regardless if a change has occurred. OSPF and IS-IS are examples of link state routing protocols.

Advanced Distance Vector Advanced distance vector is the title Cisco gives to EIGRP, which borrows the best attributes of both distance vector and link state designs. EIGRP does not send periodic route information; instead it sends updates only when changes occur (like link state protocols). Also, EIGRP forms neighbor relationships with its directly connected peers and only updates them – not the entire network (like distance vector protocols).

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Classful Concepts IP routing protocols are either classful or classless and that determines how they present route information.

Classful Classful routing protocols (like RIPv1) do not include the subnet mask in routing updates. When an update is sent, the packet contains only the major network information depending on whether it is a class A,B, or C address. For example, a route to network 172.16.10.0/24 would be advertised as 172.16.0.0/16 because its classful boundary is a class B address. Obviously if you have broken your major network boundaries up into smaller subnets that are more granular than the major classful boundaries, this will not work well and that’s the reason almost all modern routing protocols are classless. Another classful routing example is illustrated on the right.

Classeless Classless routing protocols (like RIPv2, EIGRP, OSPF, IS-IS, and BGP) include the subnet mask in routing updates allowing for VLSM support and supernetting.

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Administrative Distance Routers need a way of determining which path to use to a destination network if two or more routing protocols are in use and both advertise a route. Administrative distance is Cisco’s answer. Cisco has assigned an administrative distance (AD) to each routing protocol that outlines which protocol a router will prefer. The AD values can be between 0 and 255 with the lowest values being used for routing.

Default AD values

For example, if router R1 receives a route to network 10.10.200.0 from both EIGRP and OSPF, the router will compare the administrative distance of the EIGRP-learned route (90), to that of OSPF (110). The router will then add EIGRP’s route to the routing table because its AD is lower (90 < 110).

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Summary

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EIGRP

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EIGRP Characteristics Fast Convergence EIGRP uses the DUAL algorithm to converge very quickly. It does this by knowing neighbor router’s routing tables and predefining primary and secondary routes to every destination network.

Triggered Updates EIGRP uses partial triggered updates to its directly connected neighbors rather than periodically sharing its entire routing table. This saves link bandwidth because updates are only sent if a change is incurred, only the changes are sent in the update, and lastly – the updates are only sent to a routers’ affected neighbors. Very efficient!

Multicast EIGRP sends route updates, hellos, and queries to its neighbors using the multicast address 224.0.0.10 so end hosts are not affected. Hellos are sent out every 5 seconds by default to learn about new neighbors and make sure existing neighbors are still available.

VLSM Variable length subnet masking is supported by EIGRP because it is a classless routing protocol. That means subnet masks are included in route updates.

Protocol Independent Enhanced Interior Gateway Routing Protocol supports more than just IPv4. It supports IPv4, IPv6, IPX, and AppleTalk.

Terminology Feasible and advertised distance EIGRP’s DUAL algorithm determines the best route to a particular network by using distance information, known as cost or metric. DUAL determines the lowest cost path by adding up the cost to the destination network. Neighbors exchange the cost to every route they know of when a neighbor adjacency is formed. A router then uses that information to calculate their own cost to the same network by adding the cost between themselves and their neighbor, then adding that to the neighbor’s advertised cost.

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So, (the cost between neighbors) + (the neighbor’s cost to the destination network) = the total cost to the remote network, or the feasible distance. The cost the neighbor advertised to the remote network is known as the advertised distance. See the diagram below.

Successor Think of the successor as the active, or primary, route to a destination for EIGRP. The successor is actually the neighbor router that has the least-cost path to a destination network (a.k.a. has the lowest feasible distance). Successor routes are added directly to the routing table. You should also know that multiple successors can exist if they have identical feasible distance values.

Feasible Successor This is more like the backup route EIGRP chooses to a destination network. The feasible successor feature is what makes EIGRP convergence so unique and so fast. It always tries to find a backup route. In the event that the successor fails, it can immediately switch over to the feasible successor (backup) route with very little delay. To qualify as a feasible successor, the AD must be less than the successor’s FD. This helps ensure a loop-free layer 3 path.

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Tables Neighbor Table EIGRP discovers neighbors by sending out hellos every 5 seconds. When a routers receives a hello with the same AS number defined, it forms an adjacency and adds the local interface it used to reach it as well as the neighbor’s IP address to the EIGRP neighbor table.

Topology Table When routers form an adjacency, they exchange route information. That information is transferred to the EIGRP topology table, which contains all the destinations advertised by a router’s neighbors. There are two different types of entries in the topology table, active and passive. Now you may think that the active entry is the preferred or “actively-in-use” route, but surprisingly, the opposite is true. The route in the topology table that is in the active state signifies that it is “actively” looking for an alternative path to a destination because the successor has failed and no FS exists. Obviously this is not an ideal scenario. If a router’s successor route becomes unavailable, but has a feasible successor – the FS will immediately become the successor and there is almost no delay incurred. This is the primary reason EIGRP convergence times tend to be some of the fastest of all the dynamic routing protocols. If, however, a router’s successor becomes unavailable and does not have a FS to the destination, it will send query messages to all of its neighbors asking if they know of a path to the destination. The neighbors will either respond with a path or forward the query to all of their neighbor routers until a path is identified and relayed back to the original requester or no more neighbor routers exist. During the time the router is waiting back for a response, it is unable to forward traffic to the destination network, which can hurt EIGRP’s convergence time.

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Passive entries represent routes that have at least a single successor and perhaps a feasible successor. They are what you should see in a normal, stable topology. Notice the “P’s” in the output from the show eigrp topology command below. They indicate that the entries in the EIGRP topology table are in the passive (read: normal) state.

R1#sh ip eigrp topology IP-EIGRP Topology Table for AS(1)/ID(10.1.1.1) Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply, r – reply Status, s – sia Status P 10.1.3.0/24, 1 successors, FD is 156160 via 10.1.100.3 (156160/128256), FastEthernet0/0 P 10.1.2.0/24, 1 successors, FD is 156160 via 10.1.100.2 (156160/128256), FastEthernet0/0 via 10.1.200.2 (2297856/128256), Serial1/0 P 10.1.1.0/24, 1 successors, FD is 128256 via Connected, Loopback1 P 192.168.100.0/24, 1 successors, FD is 156160 via 10.1.100.3 (156160/128256), FastEthernet0/0 P 10.1.100.0/24, 1 successors, FD is 28160 via Connected, FastEthernet0/0 P 10.1.200.0/24, 1 successors, FD is 2169856 via Connected, Serial1/0

EIGRP Messages Hello EIGRP hello packets are sent out every 5 seconds by default using multicast address 224.0.0.10 to maintain and discover neighbor relationships. On slower (T1 and below) and NBMA links, hellos are sent every 60 seconds to conserve bandwidth. EIGRP hello packets also contain a hold timer which lets the router know if a neighbor is down. The hold timer is set to 15 seconds normally (~3 unresponsive hellos), and 180 seconds for slower WAN links. When a router receives a hello packet from another router with the same AS (Autonomous System) number, it automatically forms a neighbor relationship (also known as an adjacency).

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Update During the EIGRP start-up process on a router, an update message is sent out to its neighbors containing the contents of the router’s routing table. The only other time an update packet is sent is when network changes occur on a router and it then sends out an update message to its neighbors who the route change would affect.

Ack Acknowledgement packets are sent in response to update, query, or reply packets.

Reply When a router responds to a neighbor router looking for a route (query), it sends it in the form of a reply.

Query When EIGRP loses its successor route and does not have a FS, it sends out a query message to all of its neighbors asking if they know a path. (See topology section above)

Graceful Shutdown When an EIGRP process is shut down, the router sends out “goodbye” messages to its neighbors (ironically in the form of hello packets). The neighbors can then immediately begin recalculating paths to destinations that went through the shutdown router without having to wait for the hold timer to expire.

EIGRP Metrics There are 5 descriptives EIGRP uses to calculate it’s metric, although Cisco generally does not recommend tuning these metrics unless you have a very specific purpose. You should be aware that only the bandwidth and delay numbers factor into the default formula. • • • •

•

Bandwidth – the lowest bandwidth value between the source and destination Delay – the cumulative delay along a series of links Reliability Load MTU

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EIGRP Configuration Step 1

Define EIGRP as the routing protocol with a predefined Autonomous System ID. Routers will not form a neighbor relationship if their AS numbers do not match.

Example: R3(config)# router eigrp 1

Step 2

Define the attached networks you want to participate in EIGRP Add each network to the EIGRP process with the network prefix mask command. The mask is an inverted mask, like ACLs use. Example, a /24 mask would be 0.0.0.255.

The network prefix/mask command tells the router which local interfaces will then participate in EIGRP. This can be very useful if you do not want specific interfaces to participate in EIGRP. Using the mask statement will define how you want the routes summarized if you turn off auto summarization. If you choose not to use the mask, EIGRP will assume the networks are part of the major networks (class A,B,C boundaries) and could cause potential problems.

Example:

The output of R3′s running configuration can be seen below. R3(config-router)#router eigrp 1 R3(config-router)# network 10.1.100.0 0.0.0.225 R3(config-router)# network 192.168.100.0 0.0.0.3 R3(config-router)# network 192.168.100.4 0.0.0.3 R3(config-router)# no auto-summary

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Example: R3#sh run | begin router eigrp 1 router eigrp 1 network 10.0.0.0 network 192.168.100.0 0.0.0.3 network 192.168.100.4 0.0.0.3 no auto-summary

EIGRP Verification show ip eigrp neighbors //

Displays EIGRP neighbors a router has discovered.

R3#sh ip eigrp neighbors IP-EIGRP neighbors for process 1 H Address Interface 1 0

10.1.100.2 10.1.100.1

Fa0/0 Fa0/0

Hold Uptime SRTT (sec) (ms) 13 00:12:23 737 14 00:12:29 535

RTO

Q Cnt 4422 0 3210 0

Seq Num 21 22

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show ip eigrp topology // R3#sh ip IP-EIGRP Codes: P r

Displays the output of the EIGRP topology tables including successor and feasible successor routes.

eigrp topology Topology Table for AS(1)/ID(192.168.100.5) – Passive, A – Active, U – Update, Q – Query, R – Reply, – reply Status, s – sia Status

P 192.168.100.4/30, 1 successors, FD is 128256 via Connected, Loopback15 P 10.1.3.0/24, 1 successors, FD is 128256 via Connected, Loopback3 P 10.1.2.0/24, 1 successors, FD is 156160 via 10.1.100.2 (156160/128256), FastEthernet0/0 P 10.1.1.0/24, 1 successors, FD is 156160 via 10.1.100.1 (156160/128256), FastEthernet0/0 P 192.168.100.0/30, 1 successors, FD is 128256 via Connected, Loopback11 P 10.1.100.0/24, 1 successors, FD is 28160 via Connected, FastEthernet0/0 P 10.1.200.0/24, 2 successors, FD is 2172416 via 10.1.100.1 (2172416/2169856), FastEthernet0/0 via 10.1.100.2 (2172416/2169856), FastEthernet0/0 show ip eigrp topology

show ip route //

Shows the IP routing table entries for all routing protocols.

R3#sh ip route Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2 E1 – OSPF external type 1, E2 – OSPF external type 2 i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2 ia – IS-IS inter area, * – candidate default, U – per-user static route o – ODR, P – periodic downloaded static route

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show ip route continued… Gateway of last resort is not set 10.0.0.0/24 is subnetted, 5 subnets C 10.1.3.0 is directly connected, Loopback3 D 10.1.2.0 [90/156160] via 10.1.100.2, 00:14:46, FastEthernet0/0 D 10.1.1.0 [90/156160] via 10.1.100.1, 00:14:55, FastEthernet0/0 C 10.1.100.0 is directly connected, FastEthernet0/0 D 10.1.200.0 [90/2172416] via 10.1.100.2, 00:14:46, FastEthernet0/0 [90/2172416] via 10.1.100.1, 00:14:46, FastEthernet0/0 192.168.100.0/30 is subnetted, 2 subnets C 192.168.100.4 is directly connected, Loopback15 C 192.168.100.0 is directly connected, Loopback11 show ip route

show ip route eigrp //

Displays the EIGRP routes that the routing table is using.

R3#sh ip route eigrp 10.0.0.0/24 is subnetted, 5 subnets D 10.1.2.0 [90/156160] via 10.1.100.2, 00:16:49, FastEthernet0/0 D 10.1.1.0 [90/156160] via 10.1.100.1, 00:16:57, FastEthernet0/0 D 10.1.200.0 [90/2172416] via 10.1.100.2, 00:16:49, FastEthernet0/0 [90/2172416] via 10.1.100.1, 00:16:49, FastEthernet0/0

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Additional EIGRP Configuration Options EIGRP Default Routes Defaults routes make life easier in many situations. They can decrease the size (and complexity) of the routing table by providing a path to all unspecified destinations. One option is to use a static default route with the ip route 0.0.0.0 0.0.0.0 interface/address statement as discussed in the Routing Fundamentals page. This must be configured on every router that will use that default route. Another option if you are running EIGRP is to use the ip default-network network-number command in global configuration mode. Any network that is reachable within the local router’s routing table is eligible to be used by EIGRP as a default route. Once configured, EIGRP will advertise the route to its EIGRP neighbors as a default route.

** If you want to use this method in conjunction with a static route – you will have to first redistribute the static route into EIGRP. ** Once you use the ip default-network command to define a default route for EIGRP, the router creates a static route in the configuration without notifying you. That means in order to remove the default route, you must use the no ip route command instead of no ip default-network.

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Summarization EIGRP summarizes routes by their major classful boundaries, which can be problematic and cause specific subnets to not be advertised correctly.

To disable automatic summarization: R1(config)# router eigrp 1 R1(config-router)# no auto-summary

It is also possible to manually summarize routes with EIGRP out specific interfaces. Under the interface configuration mode, use the ip summaryaddress eigrp autonomous-system command:

R1(config)# intferface s0/0/0 R1(config-if)# ip summary-address eigrp 1

10.1.2.0 255.255.255.0

EIGRP over WAN Networks EIGRP + MPLS MPLS defines the customer’s WAN routers as CE, or customer edge routers and the carrier’s border routers as PE, or provider’s edge routers. The CE routers appear to each other as directly connected peers. When CE West sends information to CE East, PE West intercepts the data, strips the Ethernet frame, encapsulates it into a MPLS packet, and forwards it over the service provider’s network to PE East. PE East strips off the MPLS information, reencapsulates it into an Ethernet frame and forwards it on to CE East.

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This transparent transport allows an EIGRP neighbor relationship to form between the two customer routers.

EIGRP + Frame Relay Let’s face it; frame relay is a dying WAN technology. Other, more current WAN options like MPLS and metro Ethernet have taken over, but Cisco thinks it’s important for us to understand the underlying framework of how frame relay works. Frame relay works using switched, virtual circuits through the service provider network. One of the advantages of Frame Relay is that it allows multiple logical circuits to be configured on a single physical interface. Each VC is identified with a locally-significant DLCI, or Data-Link Connection Identifier. The layer 2 virtual circuit must then be mapped to a layer three neighbor, which can be either dynamic or static. Frame relay is able to emulate point-to-point links by using multiple subinterfaces on a single physical interface (often used on hub-and-spoke topologies). This allows neighbor’s to be identified as down much more quickly for two reasons: 1. The default timers are shorter (5 sec hold timer, 15 second dead timer). 2. The subinterface is marked down whenever its local DLCI goes down.

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Static To configure frame relay statically, configurations must be done on the interface level. The broadcast descriptive is required at the end of the statement because frame relay defaults to a non-broadcast medium. Also, static mappings can be applied to both multipoint interfaces as well as subinterfaces on a single physical port. R1(config-if)# frame-relay map ip remote-ip-address local-dlci broadcast

Dynamic Dynamic mappings use inverse ARP. In this case, routers only form EIGRP neighbor relationships with other routers they connect to using a frame relay virtual circuit.

No IP split horizon When running EIGRP on frame relay multipoint subinterfaces, a major communication problem can occur. Split-horizon is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned. When a hub and spoke frame relay topology exists, multipoint subinterfaces are configured on the hub router. The issue is that split horizon is enabled by default, so in the example below, if R2 learns routes from R1, it cannot then pass those on to R3 because split horizon would prevent the advertisement from going out the same physical interface. This results in R2 being able to communicate with the spoke router’s networks, but R3 and R1 are unable to communicate with each other.

To remedy the situation, split horizon must be disabled on the R2’s EIGRP hub interface.

R2(config-if)# no ip split-horizon EIGRP as-number

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Managing EIGRP Bandwidth There are two important points to remember when running EIGRP over WAN links. The first is that EIGRP assumes that WAN interfaces run at T1 speed (1544 kbs). The second is that EIGRP will allocate up to 50% of a link’s bandwidth for EIGRP control traffic. These two combined can be problematic on links that are slower than a T1 (like a 64k fractional T1 for example). In that situation, EIGRP messages could choke out data traffic quickly. To control that, the bandwidth command should be used in WAN links to tell EIGRP what the actual link bandwidth is.

R1(config)# int serial 0/0/0 R1(config-if)# bandwidth 64

EIGRP is often used on frame relay for this reason alone. The ability to control the routing protocol’s usable bandwidth so simply makes it a popular choice.

More EIGRP options Passive Interfaces

Unicast

Not to be confused with the passive (healthy) topology table entries, interfaces with the passive-interface command applied do not allow any routing updates or hellos out the interface. For EIGRP, this means that the router will not form adjacencies with connected routers on that particular port.

EIGRP uses multicast address 224.0.0.10 when sending messages to its neighbors. You should be aware that EIGRP can also use a unicast address when communicating with a specific neighbor. To configure it:

R1(config)#router eigrp 1 R1(config-router)# neighbor ip-address R1(config)# router eigrp 1 R1(config-router)# passive-interface gig 3/1

The IP address used must be in one of the same subnet ranges as one of the router’s interfaces.

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EIGRP load balancing Out of the box, EIGRP will automatically load balance across equal-cost paths with no special configuration. EIGRP is unique, however, in its ability to load balance across unequal-cost paths with a single command. The variance command allows unequal-cost load balancing over up to 6 different paths. But here’s the key, it only works when the cost of the path is lower than the variance number multiplied by the best metric.

Here is an example scenario. R1 will by default use the path through R3 because it has the lowest metric. To enable unequal-cost load balancing, we can use the following command:

R1(config)#router eigrp 1 R1(config-router)# variance 2

The variance command multiplies the best cost (10,000) by 2 (20,000) and will begin load balancing across all paths with a FD less than or equal to that – which includes the path through R2(15,000). This will load balance the traffic in proportion to each path’s metric.

Maximum-paths By default, Cisco IOS will load balance across 4 equal-cost paths only. Using the maximum-paths command, you can configure the router to load balance over up to 16 paths. Setting it to 1 disables the load balancing.

R1(config)# maximum-paths number-of-paths

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EIGRP Authentication EIGRP supports authentication of its messages using an MD5 hash. When configured, if an incoming EIGRP packet’s hash does not match the local hash, the packet is silently dropped.

Authentication configuration steps: 1. Configure a key chain to group the keys (read: passwords). 2. Create a key(s) inside the keychain. The router will look inside the keychain and compare the keys against incoming packets. 3. Enable authentication and assign a key to an interface. 4. Indicate MD5 as the authentication type.

Example: R1(config)# key chain TEST R1(config-keychain)# key 1 R1(config-keychain-key)# key-string samplepassword R1(config-keychain-key)# exit R1(config)# interface gig 1/12 R1(config-if)# ip authentication mode eigrp 10 md5 R1(config-if)# ip authentication key-chain eigrp 10 TEST

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EIGRP Stub Routing If a router is a spoke in a hub-and-spoke router topology, it is considered a stub router. It is not a transit router and usually has only a single neighbor router, sometimes two. Within EIGRP you can define a router as a stub router to limit the EIGRP queries. This saves bandwidth and prevents neighbor routers from requesting alternate routes when a path fails. If you have many spoke routers, this can dramatically improve EIGRP reconvergence time. The EIGRP stub router still receives all route updates from its neighbor(s) by default.

R1(config)#router eigrp 1 R1(config-router)# eigrp stub [receive-only | connected | static | summary | redistributed]

EIGRP Stub Options

Cisco EIGRP Best Practices: •

Summarize routes when possible.

•

Limit the network depth to 7 hops.

•

Limit the scope of EIGRP queries

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Cisco Chapter 3:

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OSPF

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Open Shortest Path First (OSPF) •

OSPF, or Open Shortest Path First, is a link-state, open-standard, dynamic routing protocol. OSPF uses an algorithm known as SPF, or Dijkstra’s Shortest Path First, to compute internally the best path to any given route.

•

OSPF is classless and converges fairly quickly, using cost as it’s metric. A router running OSPF creates its own database which contains information on the entire OSPF network, not simply neighbor’s routes like EIGRP. This allows the router to make intelligent choices about path selection on its own instead of relying exclusively on neighbor information.

•

OSPF routers do form neighbor relationships though. They exchange hellos with neighboring routers and in the process learn their neighbor’s Router ID (RID) and cost. Those values are then sent to the adjacency table.

•

Every router is responsible for computing its own best paths to all destinations within an OSPF domain. Once the SPF algorithm selects the best paths, they are then eligible to be added to the routing table.

Link State Database Once a router has exchanged hellos with its neighbors and captured Router IDs and cost information, it begins sending LSAs, or Link State Advertisements. LSAs contain the RID and cost to the router’s neighbors. LSAs are shared with every other router in the OSPF domain. A router stores all of its LSA information (including info it receives from incoming LSAs) in the Link State Database (LSDB). I apologize if the acronyms are starting to pile up. OSPF, architecturally speaking, is more complicated than its counterpart EIGRP – and the long list of acronyms and definitions is part of that.

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Areas OSPF is different from EIGRP in that it uses areas to segment routing domains. This helps partition routers into manageable groups if the layer 3 network begins to get large. It all starts with area 0. Every OSPF network must contain an area 0, sometimes referred to as the backbone area and every additional area must be physically connected to area 0. From there, other areas are optional. Note that the SPF algorithm only runs within a single area, so routers only compute paths within their own area. Inter-area routes are passed using border routers.

All link state databases must match within an OSPF area. This means that the more OSPF-enabled routers are configured for the same area, the more LSA advertisements that must be sent out. After you reach about 50 routers, the high levels of LSA traffic and numerous routing table entries can become a problem. That is why Cisco recommends limiting an OSPF area to no more than 50-100 routers.

The following three factors determine the maximum number of routers: • • •

How easily the area’s subnets can be summarized The type of areas being used The number of external LSAs being injected

An added bonus of partitioning out your OSPF network into areas is that it is a natural fit for a hierarchical IP scheme.

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Area Types Backbone area Another name for area 0

Regular area Non-backbone area, with both internal and external routes

Stub area Contains only internal routes and a default route

Not-So-Stubby area (NSSA) Contains internal routes, redistributed routes, and optionally a default route

Totally Stubby Area Cisco proprietary option for a stub area

Totally Stubby NSSA Cisco proprietary option for NSSA

Router Roles Internal: All interfaces in a single area (routers 1,4,5 in diagram above)

Area Border Router (ABR): Have interfaces in two or more areas (routers 2,3 in diagram above)

Backbone: At least one interface assigned to area 0 (routers 1,2,3 in diagram above)

ABRs contain a separate Link State Database, separating LSA flooding between areas, optionally summarizing routes, and optionally sourcing default routes.

Autonomous System Boundary Router (ASBR): Has at least one interface in an OSPF area and at least one interface outside of an OSPF area.

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OSPF Metric Each interface is assigned a cost value based purely on bandwidth. The formula is:

Cost = (100Mbs/bandwidth)

Higher bandwidth means a lower cost!

Let’s run through some common examples quickly:

T1 line | 100,000 / 1544 = 64 10 Mbps | 100,000 / 10,000 = 10 100 Mbps | 100,000 / 100,000 = 1 1000 Mbps | 100,000 / 1,000,000 = .1 1 (OSPF still uses 1 for this, see explanation below)

The cost is then accrued at each hop along the path based on the link’s bandwidth. Unfortunately, OSFP was written when 100Mbs was considered fast. Because of that, it assigns the same cost to any interface with speeds higher than 100Mbs. To OSPF, a Fast Ethernet interface is weighted the same as a Gigabit Ethernet interface, both a cost of 1.

To fix that problem, you can use the auto-cost command under the OSPF process.

R1(config-router)# auto-cost reference-bandwidth 1000

Another option is to simply change the cost on a per-interface basis with the ip ospf cost command (using any number between 1-65,535).

R1(config-if)# ip ospf cost 35

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Link State Advertisements LSAs contain a sequence number and a Router ID. Sequence numbers are 32 bits, starting with 0×80000001. The sequence number increases if: • •

a route is added or deleted a LSA ages out

The largest sequence number is always the most current. The default time that LSAs are aged out is 30 minutes. When an LSA enters a router, it checks it against its internal Link State Database (LSDB). • • •

If it is new, it is added to the LSDB and the SPF algorithm is re-run. If it contains a Router ID (RID) that is already in the database, entries with an older sequence number are discarded. If it receives an older version (according to its sequence number), it discards the LSA and sends back the newer version to the original sender.

The command show ip ospf database will display the sequence numbers and age (in seconds) for each entry.

LSDB Overload In large OSPF networks, if major network changes occur, a flood of LSAs will immediately hit the entire network. The number of incoming LSAs to each router could be substantial and bring the CPU and memory to its knees. To mitigate that scenario, Cisco offers what it refers to as Link Sate Database Overload Protection. Once enabled, if the defined threshold is exceeded over one-minute time period, the router will enter the ignore state – dropping all adjacencies and clearing the OSPF database. Know that this is a drastic response because routing will be disrupted during that period.

R1(config-router)# max-lsa number

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LSA Definitions

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OSPF Messaging OSPF uses several different types of messages to maintain neighbor relationships and correct routing information.

OSPF Packet Types Hello Discovers neighbors and works as a keepalive. Link State Request (LSR) Requests a Link State Update (LSU), see below.

Link State Update (LSU) Contains one or more complete LSAs. Link State Acknowledgement (LSAck) Acknowledges all other OSPF packets (except hellos).

Database Description (DBD) Contains a summary of the LSDB, including RIDs and sequence numbers.

OSPF sends the five packet types listed above over IP directly, using IP port 89 with an OSPF packet header. Multicast address 224.0.0.5 is used if sending to all routers, address 224.0.0.6 is used for sending to all OSPF DRs.

OSPF Neighbors Hellos are sent out periodically using multicast on OSPF enabled routers. The router forms an adjacency with a peer router when it sees its own Router ID in the neighbor field of another router’s hello message. That indicates there is direct, bi-directional communication on the same subnet.

Note: On multi-access links, adjacencies are only formed between the router and the DR and BDR.

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All of the following fields in an OSPF hello message must match for an adjacency to form: • • • • • •

hello timer dead timer area ID authentication type password stub area flag

As with many network protocols, hellos act as a form of keepalive or heartbeat. With OSPF, if four consecutive hellos are not received (the dead time), the router is considered down.

Point-point interfaces: hellos every 10 seconds, 40 second dead timer Nonbroadcast multiaccess (NBMA) interfaces: hellos every 30 seconds, 120 second dead timer

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OSPF States There are 7 different OSPF states when forming neighbor relationships. Take the time to learn the states and their corresponding functions.

1

Down State OSPF has not started and no hellos have been sent.

2

Init State Hellos are sent out all OSPF-participating interfaces

3

Two-way State A hello is received from another router with its own RID in the neighbor field. All other required elements match and the routers become neighbors.

4

Exstart State Routers determine which one will begin the route exchange process with the other.

5

Exchange State Routers exchange DBDs.

6

Loading State Routers compare the DBD to their LS database. LSRs are sent out for missing or outdated LSAs. Each router then responds to the LSRs with a Link State Update. Finally, the LSUs are acknowledged.

7

Full State The LSDB is completely synchronized with the OSPF neighbor.

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OSPF Configuration OSPF configuration is not too complicated, but has some important syntax distinctions from EIGRP. First, it is configured from router configuration mode and requires a process ID appended to the router ospf command. The process ID is only locally significant, so don’t worry if it doesn’t match on other OSPF routers.

R1(config)# router ospf process-id

The next step is to determine which router interfaces you want participating in OSPF. Just like EIGRP, the network statements define which local router interfaces will participate.

R1(config)# router ospf 10 R1(config-router)# network 10.1.1.0 0.0.0.255 area 0 R1(config-router)# network 10.9.9.0 0.0.0.255 area 1

In the example above, interfaces in the 10.1.1.0/24 subnet will participate in OSPF area 0. Interfaces in the 10.9.9.0/24 subnet will participate in OSPF area 1. Unlike EIGRP, the subnet wildcard mask in the network statement is not optional because OSPF is classless by default. Let’s do another example…

R1 has six interfaces, all within area 0: • • •

GigabitEthernet 0/0: 192.168.100.1/24 GigabitEthernet 0/1: 192.168.101.1/24 GigabitEthernet 0/2: 192.168.102.1/24

• • •

GigabitEthernet 0/3: 192.168.103.1/24 Serial 1/0: 10.100.100.1/30 Serial 1/1: 10.100.100.5/30

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The simplest way to configure OSPF an all interfaces into area 0 would be to use this command: R1(config-router)# network 0.0.0.0 255.255.255.255 area 0

A second option is to break up the 10. and 192. networks into different statements: R1(config-router)# network 10.0.0.0 0.255.255.255 area 0 R1(config-router)# network 192.168.100.0 0.0.3.255 area 0

The third way to configure the interfaces to participate in OSPF:

R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)#

network network network network network network

10.100.100.1 0.0.0.0 area 0 10.100.100.5 0.0.0.0 area 0 192.168.100.1 0.0.0.0 area 0 192.168.101.1 0.0.0.0 area 0 192.168.102.1 0.0.0.0 area 0 192.168.103.1 0.0.0.0 area 0

All three approaches achieve the exact same result. The configuration you choose is up to you.

Interface Configuration An alternative configuration option is to configure an interface to participate in OSPF directly. The [ ip ospf process-id area area-id ] command takes precedence over the more common network commands.

R1(config)# int gig 0/1 R1(config-if)# ip ospf 10 area 0

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Router ID The SPF algorithm uses a Router ID to identify hops along a path. The problem, of course, is that routers don’t have a generic “router ID” built in. The designers of OSPF decided to use the highest IP address assigned to a loopback interface as the Router ID (RID) by default. If no loopback is configured, it will use the highest IP address assigned to an active interface when the OSPF process begins. OSPF will not change the RID, even if another interface with a higher IP address comes online unless the OSPF process is restarted. This helps keep the network stable and happy. Note: The clear ip ospf process command will also force the OSPF process to restart, but will cause an outage – so use it with caution.

Loopbacks are preferred for use as a router ID because they are virtual interfaces and are not affected by links going up and down. To configure a loopback interface, first create it and assign it an IP address.

R1(config)# int loopback 0 R1(config-if)# ip address 10.100.100.1 255.255.255.255

Static RIDs It is also possible to manually define a static Router ID within OSPF with the router-id command.

R1(config)# router ospf 10 R1(config-router)# router-id 10.100.100.1

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DRs & BDRs SPF works by mapping all paths to every destination on each router. It uses the RID to identify hops along each path and uses bandwidth as a metric between those hops. This whole system works really well when routers are connected with point-to-point links and OSPF traffic is simply sent using multicast address 224.0.0.5. It doesn’t work well, however, when a router is connecting to multiaccess networks like an Ethernet VLAN. Multiaccess OSPF links require a Designated Router (DR) be elected to represent the entire segment. Another router is then elected as the Backup Designated Router, or BDR. On that specific multiaccess segment, routers only form adjacencies with the DR and BDR. The DR uses type 2, network LSAs to advertise the segment over multicast address 224.0.0.5. The Non-Designated routers then use IP address 224.0.0.6 to communicate directly with the DR.

Elections 1. When the OSPF process on a router starts up, it listens for hellos. If it does not receive any within its dead time, it elects itself the DR. 2. If hellos are received before the dead time expires, the router with the highest OSPF priority is elected as the DR. Next, the same process happens to elect the BDR.

Note: If a router’s OSPF priority is set to 0, it will not participate in the elections. 3. If two routers happen to have the same OSPF priority, the router with the highest Router ID will become DR. The same is true for BDR.

Once a DR is elected, elections cannot take place again until either the DR or BDR go down. This essentially means that there is no OSPF DR preemption if another router comes online with a higher OSPF priority. In the case that the DR goes down, the BDR automatically is assigned the DR role and a new BDR election occurs. Be aware that a router with a non-zero priority that happens to boots first can become the DR just because it did not receive any hellos when the OSPF process was started – even though it may have a low OSPF priority.

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The default OSPF priority is 1 and Cisco recommends manually changing that on routers you want to become the DR and BDR. Remember that DRs are only used on multiaccess links, so they are only significant on an interface level. A router with two different interfaces connected to two different multiaccess links will have separate DR elections for each segment.

To set the OPSF priority, use the ip ospf priority command on the interface connected to the multiaccess segment. Values can be between 0-255.

R1(config)# int gig 0/1 R1(config-if)# ip ospf priority 255

OSPF over the WAN Routing protocols assume both broadcast capabilities and full mesh connectivity on multiaccess networks. For OSPF, there are a few points to consider: •

Full mesh environments can use physical interfaces, but often times subinterfaces are used

•

Partial mesh environments should be configured using point-to-point subinterfaces

•

Hub-and-spoke environments should elect the hub as the DR or use point-to-point subinterfaces – which don’t require a DR

•

Frame Relay and ATM maps should include the broadcast attribute

•

In multiaccess environments, the DR and BDR should have full virtual circuit connectivity to all other routers

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Summarization First, it’s important to note that running the SPF algorithm on a router is extremely taxing on CPU resources and can easily consume them all. The reason is because OSPF has to compute the best path to every destination within its area. Avoiding running the algorithm whenever it isn’t required is a big win. Summarization has two important benefits for OSPF. It prevents topology changes from being passed outside an area – thus reducing the number of routers re-running the SPF algorithm. It also consolidates many routes in to a single statement, reducing the memory load and database size on OSPFenabled routers. There are two types of route summarization, inter-area and external.

Inter-area Summarization (LSA Type 3) This occurs on ABRs to summarize routes between areas. This really only works well if the networks contained within an area are subnetted contiguously so that they can be easily summarized into a single statement. The new summary route’s cost will be equal to the highest cost route within the summary range. After the command is entered, the router will automatically create a static route pointing to Null0.

Example: ABR-R1(config)# router ospf 10 ABR-R1(config-router)# area 2 range 10.100.0.0 255.255.0.0

In this example, the summary network 10.100.0.0/16 is summarized from area 2.

External Summarization (LSA Type 5) This occurs on ASBRs for routes that are injected into OSPF via route redistribution. After the command is entered, the router will automatically create a

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static route pointing to Null0.

Example: ASBR-R1(config)# router ospf 10 ASBR-R1(config-router)# summary-address 192.168.0.0 255.255.0.0

In this example, an external network has been summarized into 192.168.0.0/16 and is injected into OSPF via a single type 5 LSA.

OSPF Passive Interfaces Like EIGRP, OSPF supports the use of passive interfaces. The passive-interface interface command disables OSPF hellos from being sent out, thus disabling the interface from forming adjacencies out that interface.

OSPF Default Routes Default routes are injected into OSPF via type 5 LSAs. There are multiple ways to inject default routes into OSPF, but Cisco recommends using the default-information originate command under the OSPF routing process.

R1(config)# router ospf 10 R1(config-router)# default-information originate [always] [metric metric]

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If the always keyword is not used, OSPF will advertise a default route learned from another source, like a static route. If the always keyword is present, a default route will be advertised regardless if the route exists in the routing table. Another option is to use the area range and summary-address commands discussed in the summarization section above. Using these will result in the router advertising a default route pointing to itself.

Stub and Not-So-Stubby Areas Stub areas are another way to simplify route information that gets advertised. Area 2 in the diagram below shows an example.

The ABR in a stub area drops all external routes and instead uses a default route of 0.0.0.0 (R3 in this example). That is, they do not know about any non-OSPF route information outside their own area. A Cisco proprietary version of a stub area is a Totally Stubby Area, or TSA. TSAs do not accept any external routes from non-OSPF sources AND they do not accept routes from other areas within their OSPF autonomous system. If a router needs to send traffic to a route outside of its own area, it sends the traffic using a default route. *ABRs use default routes in Stub and Totally Stubby areas.

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Stubby areas are made into Totally Stubby Areas by appending the no-summary keyword.

Example: R5(config)# router ospf 10 R5(config-router)# area 2 stub no-summary R5(config-router)# area 2 stub default-cost 8

The example above sets area 2 as a totally stubby area. The default-cost command is optional and in this case changed the default route cost from 1 to 8.

Stub Limitations • •

Virtual links cannot be included Cannot include an ASBR

•

The stub configuration must be applied to every router within the stubby area

•

Area 0 cannot be a stub

Bullet point 3 is extremely important! If two routers are connected, but one does not have the stub statement configured, the hello packets will be dropped and they will not form a neighbor adjacency. Both R3 and R5 above would need the configuration.

NSSAs Not-So-Stubby Areas, or NSSAs were an addendum to the original OSPF RFC and defined a new special LSA, type 7. NSSAs are very similar to stubby areas, but they allow the use of ASBRs in the area – something stub areas prohibit. External routes are advertised by the ASBR as type 7 LSAs and the ABR then converts them into type 5 external LSAs when it advertises them to adjacent areas.

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NSSA is configured using the area area-number nssa command as can been seen in the example below. Using the no-summary keyword turns the area into a Totally Stubby NSSA. A Totally Stubby NSSA does not accept external or summary routes from other areas. Lastly, the NSSA ABR does not by default advertise a default route back into the area. The default-information-originate option does just that.

R4(config)# router ospf 10 R4(config-router)#area 1 nssa [no-summary] [default-information-originate]

The table below should help recap the different area type behaviors.

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OSPF Virtual Links OSPF has strict rules around how areas connect and where they can be located. More specifically, every area must be physically connected to area 0 and area zero must be ‘contiguous’ – meaning it cannot broken into multiple, connected area 0s. Virtual links were developed as a band-aid to situations that temporarily must violate those requirements. Virtual links connect areas that do not connect directly to area 0. It can also connect two area 0s together! Keep in mind that Cisco recommends virtual links be a temporary workaround to a shortterm problem, not a permanent design. The diagram below illustrates an example when a virtual link could be used. Let’s pretend Company ABC and Company XYZ just announced a merger and now their corporate networks must do the same. In this case, both routers R1 and R2 have now become ABRs and the virtual link configuration will be applied to them. The command area area-number virtual-link router-id is applied to each ABR. Note that the area used in the command is the transit area that the virtual link resides in. Also, the RID identifies the RID of the OTHER router at the end of the link!

Example: R1(config)# router R1(config-router)# R2(config)# router R2(config-router)#

ospf area ospf area

20 1 virtual-link 10.30.30.30 20 1 virtual-link 10.50.50.50

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OSPF Authentication Out of the box, OSPF does not authenticate its protocol’s messages or route updates. OSPF does, however, support two message authentication options: • •

Simple Authentication - using plaintext keys MD5 Authentication – using a secure hash

Matching authentication methods and keys must be configured on each interface on a segment. Theoretically, different passwords could be applied to different router interfaces – the routers on the other ends of those links would just be required to have matching information.

Simple Authentication Example: R1(config)# int fa0/1 R1(config-if)# ip ospf authentication-key KEY123 R1(config-if)# ip ospf authentication R1(config-if)# exit R1(config)# router ospf 10 R1(config-router)# area 0 authentication

MD5 Authentication Example: R1(config)# int fa0/1 R1(config-if)# ip ospf message-digest-key 1 md5 KEY123 R1(config-if)# ip ospf authentication message-digest R1(config-if)# exit R1(config)# router ospf 10 R1(config-router)# area 0 authentication message-digest

** The 1 in the ip ospf message-digest-key 1 md5 KEY123 statement above is a key number.

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OSPF Verification The OSPF neighbor table can be viewed using the show ip ospf neighbor command. It shows the status of the OSPF database loading process, status of neighbor adjacencies, as well as DR and BDR assignments. •

To show which OSPF routers are being used by the routing table, issue the show ip route ospf command.

•

The show ip ospf command displays the RID, counters, and timers.

•

To see which router interfaces are participating in OSPF (and their area assignments), use the show ip ospf interface command.

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•

Cisco Chapter 4:

642 902

Route Filtering & Redistribution

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Redistribution is necessary when routing protocols connect and must pass routes between the two. This can happen in a number of situations, but some examples include:

• • •

Organizations transitioning routing protocols Businesses merge, and so must their networks OSPF or EIGRP is used at the access and distribution layer of an enterprise and BGP is used in the core

The challenge to redistributing routing protocols is that each routing protocol uses its own metric and they are not compatible with each other. Furthermore, there is no magic algorithm than can automatically translate metrics between, say RP and BGP. To deal with this dilemma, a new seed metric is used as a starting point when redistribution is configured.

Configuring Redistribution To configure redistribution between routing protocols, the redistribute protocol command is used under the routing protocol that receives the routes.

R1(config-router)# redistribute protocol [AS or process-id] [metric metric-value]

The process-id field above is the AS number for RIP, EIGRP, BGP. For OSPF, use the process ID. Also, both RIP and EIGRP require the use of the metric keyword!

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EIGRP Redistribution Example: R1(config)# router eigrp 10 R1(config-router)# redistribute ospf 20 metric 1000 100 255 1 1500

The example above shows OSPF being redistributed into EIGRP with a metric of 1000 100 255 1 1500. That is a lot of different numbers for an EIGRP cost! That’s because EIGRP redistribution metric requires you to input all of the metric calculation manually: • • • • •

bandwidth delay reliability loading MTU

You can perform a show interface on the outgoing router interface prior to see what values the router is currently using.

OSPF Redistribution Example: R1(config)# router ospf 100 R1(config-router)# redistribute eigrp 10 subnets

The example above redistributes EIGRP routes into OSPF. The subnets keyword at the end of the redistribute command is extremely important! Without this keyword, OSPF will redistribute networks at their classful boundaries – not something most administrators want. If you don’t use it the IOS will even give you a warning. Make sure to include it.

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Distribute Lists Distribute lists are access lists applied to the routing process, determining which networks are allowed into the routing table or included in updates. They essentially act as a filter.

Think: access list applied to routing = distribute lists

When creating a distribute list, use the following steps:

Step 1

Identify the network addresses to be filtered and create an ACL – permitting the networks you want to be advertised.

Step 2

Determine if you want to filter updates coming into the router or leaving the router.

Step 3

Assign the ACL using the distribute-list command.

Incoming Distribute List R1(config-router)# distribute-list {acl-number | name} in [interface-type number]

Outgoing Distribute List R1(config-router)# distribute-list {acl-number | name} out [interface-name | routing-process | AS-number]

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Route Maps When a routing update arrives at an interface, a series of steps occur to process it correctly. The diagram below outlines those steps and serves as a foundation for the rest of this route redistribution and filtering section. Route maps are extremely flexible and are used in a number routing scenarios including: • • • •

Controlling redistribution based on permit/deny statements Defining policies in policy-based routing (PBR) Add more mature decision making to NAT decisions than simply using static translation When implementing BGP PBR

Route maps allow an administrator to define specific traffic and then take automated actions against it to control how routing information is processed and forwarded. Route maps uses logic similar to if/then statements in simple scripting. In route map terms, it matches traffic against conditions and sets options for that traffic.

NOTE: If you have downloaded the Switch Exam Guide, you will notice the similarity between the syntax structure of route maps and VACLs.

Each statement in a route map has a sequence number, which are read from lowest to highest. The router stops reading statements when it reaches its first matching statement. Understand that there is an implicit deny included in all route maps. If traffic does not match any statement, it is denied.

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Basic Route Map Configuration R1(config)# route-map {tag} permit | deny [sequence_number]

That is how all route maps begin. Permit means that any traffic matching the match statement that follows is processed by the route map. Deny means that any traffic matching the match statement that follows is NOT processed by the route map. Remember the difference.

Match & Set Conditions •

If no match condition exists, the statement matches anything (similar to a ‘permit any’).

•

If no set condition exists, the statement is simply permitted or denied with no additional changes made.

•

If multiple match conditions are used on the same line, it is interpreted as a logical OR. In other words, if one condition is true, a match is made. For example, the router would interpret ‘match a b c’ as ‘a or b or c’.

If multiple match conditions are used on consecutive lines, it is interpreted as a logical AND. In other words, all conditions must be true before a match is made. A router would interpret the following example as match a and b and c:

route-map EXAMPLE permit 5 match a match b match c

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Important route redistribution match conditions ip address Refers to an access list that permits or denies networks

length Permits or denies packets based on length (in bytes)

ip address prefix-list Refers to a prefix list that permits or denies prefixes

metric Permits or denies routes with specific metrics from being redistributed

ip next-hop Refers to an access list that permits or denies IP next hops IP addresses

route-type Permits or denies redistribution based on the route type listed

ip route-source Refers to an access list that permits or denies advertising router IP addresses

tag Routes can be labeled with a number that identifies it

Important route redistribution set conditions Metric Sets the metric for redistributed routes Tag Tags a route with a numbered identifier

Route Map Verification Use the show route-map command to verify route maps and PBR entries are filtering as expected.

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Cisco Chapter 5:

642 902

BGP

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BGP, or Border Gateway Protocol is an external, dynamic routing protocol. It is most often used between ISPs and between enterprises and their service providers. BGP is literally the routing protocol of the Internet because it connects independent network together, enabling end-to-end transport. Scalability and stability are BGP’s focus, not speed – as a result it behaves very differently than most other routing protocols. BGP is recommended whenever multihoming is a requirement (dual ISP connections to different carriers), when route path manipulation is needed, and in transit Autonomous Systems.

A Quick Overview •

Routers running BGP are called BGP speakers.

•

BGP uses autonomous system numbers to keep track of different administrative domains. 1-64511 are public, 64512-65535 are private.

•

BGP is used to connect IGPs, interior gateway protocols like OSPF and EIGRP. Routing between Autonomous Systems is referred to as interdomain routing.

•

The administrative distance for eBGP routes is 20, iBGP is 200.

•

BGP neighbors are called “peers” and must be statically assigned.

•

Peers receive incremental, triggered updates as well as keepalives using TCP port 179.

•

BGP is sometimes referred to as a “path-vector” protocol because its route to a network uses AS numbers on the path to the destination.

•

BGP uses its path-vector attributes to help in loop prevention. When an update leaves an AS, the AS number is prepended to update along with all the other AS numbers that have spread the update. When a BGP router receives an update, it first scans through the list of AS numbers. If it sees its own AS number, the update is discarded.

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BGP Databases Like most modern routing protocols, BGP has two separate databases – a neighbor database and a BGP-specific database. Neighbor Database Lists all of the configured BGP neighbors (to view – #show ip bgp summary). BGP Database Lists all networks known by BGP along with their attributes. (to view – #show ip bgp).

BGP Message Types There are four different BGP message types. Open After a BGP neighbor is configured, the router sends an open message to establish peering with the neighbor.

Keepalive BGP peers sends keepalive messages every 60 seconds by default to maintain active neighbor status.

Update The type of message used to transfer routing information between peers.

Notification If a problem occurs and a BGP peer connection must be dropped, a notification message is sent and the session is closed.

Internal vs. External iBGP, or internal BGP is a peering relationship between BGP routers within the same autonomous system. eBGP, or external BGP describes a peering relationship between BGP routers in different autonomous systems. It is an important distinction to make. In the diagram below, R1 and R2 are eBGP peers. R2 and R3 and iBGP peers.

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BGP Next-Hop Self When you have BGP neighbors peering between autonomous systems like R1 and R2 above, BGP uses the the IP address of the router the update was received from as its “next hop”. Routers that receive an update from an eBGP neighbor must pass the update to its iBGP neighbors with-out modifying the next hop attribute. The next-hop IP address is the IP address of the edge router belonging to the next-hop autonomous system.

For example, let’s say R1 sends an update to R2 from its 10.1.1.1 serial interface. R2 must keep the next-hop IP set as 10.1.1.1 when it passes the update along to R3, its iBGP peer. The problem is that R3 does not know about 10.1.1.1 and so it cannot use it as its next hop address.

The neighbor [IP address] next-hop-self command solves the problem by advertising itself as the next-hop address. In this example, it would be applied to R2 so any updates passed along to R3 would use an R2 address as the next-hop.

R2(config)# router bgp 65300 R2(config-router)# neighbor 10.2.2.2 next-hop-self R2(config)# exit

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BGPs Synchronization Rule The BGP synchronization rule states that a BGP router cannot use or forward new route updates it learns from iBGP peers unless it knows about the network from another source, like an IGP or static route. The idea is to prevent using or forwarding on information that is unreliable and cannot be verified. Remember, BGP prefers reliability and stability over using the newest, fastest route. This means that iBGP peers will not update each other unless an IGP is running under the hood. To remove the limitation, use the no synchronization command under BGP configuration mode. Recent versions of IOS have it disabled by default, but it is important topic to understand.

Resetting BGP Sessions Internet routers running BGP have enormous routing tables. When a filter is applied, like a route map, changes to BGP attributes occur. Those changes could affect many of the routes already in the routing table from BGP. Because BGP’s network list is usually very long, applying a route map or prefix list after BGP has converged can be disastrous. The router would have to check the filter against every possible route and attribute combination.

To make matters worse, if it were to apply the filters and pull routes back from neighbors, those changes could then cause another reconvergence – and on and on. In an effort to avoid that scenario (BGP loves stability), BGP will only apply attribute and network changes to routes AFTER the filter has been applied. All existing routes stay unchanged.

If the network administrator decides that the filter needs to be applied to all routes, then the BGP instance must be reset – forcing the entire BGP table to pass through the filter. There are three ways to do this: • • •

Hard reset Soft reset Route refresh

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The hard and soft reset options aren’t discussed here because they are not directly relevant to the exam. You should know though, that both options are extremely memory-taxing on the router as all the routes must be recomputed. Route refresh was developed to solve the high memory problems, while still forcing a reset. The clear ip bgp [ * | neighbor-address] in command performs the BGP route refresh.

BGP Configuration Enabling BGP Like other routing protocols, BGP must be enabled with the router command. Make sure to include the AS number. R1(config)# router bgp autonomous-system-number

BGP Peering Each neighbor must be statically assigned using the neighbor command. If the AS number matches the local router’s, it is an iBGP connection. If the AS number is different, it is an eBGP connection.

R1(config-router)# neighbor ip-address remote-as autonomous-system-number

If a router has a long list of directly connected neighbors, the BGP configuration can start to get long and difficult to follow – especially as neighbor policies are applied. Peer groups solve that.

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Peer groups are groups of peer neighbors that share a common update policy. Updating an entire group of neighbor statements can then be done with one command. Much easier for large BGP networks. Think of a peer group as a logical grouping of routers that are grouped under a single name to make changes faster and configurations shorter. Like OUs in Active Directory. Peer groups not only reduce the number of lines of configuration, but they reduce overhead on the router. A BGP update process normally runs for each neighbor. If a peer group is configured, a single update process runs for all routers in the group. Notice that this means that all of the router inside a peer group must be either all iBGP or eBGP neighbors.

Basic Neighbor Configuration Example:

Peer Group Configuration Example:

R1(config)# router R1(config-router)# R1(config-router)# R1(config-router)#

R1(config)# router R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)#

bgp 65300 neighbor 10.1.1.1 remote-as 65300 neighbor 10.1.2.1 remote-as 65300 neighbor 10.1.3.1 remote-as 65300

bgp 65300 neighbor MINE peer-group neighbor MINE remote-as 65300 neighbor 10.1.1.1 peer-group MINE neighbor 10.1.2.1 peer-group MINE neighbor 10.1.3.1 peer-group MINE

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BGP Source Address R1 in the diagram has two different options when it comes to peering to R2. It can peer to the physical interface IP address, 10.1.1.2 or it can peer to R2′s loopback interface, 192.168.2.2. If a peer relationship is made using the physical interface as the source address, problems can occur if the interface goes down. In this scenario, even if R2′s 10.1.1.2 interface drops, it still has connectivity to R2′s networks via R3 and R2′s other physical interface. Even though an IGP would still show R2′s network as accessible, the BGP peer relationship would drop because R1 cannot reach its peering address with R2. Most implementations recommend using a loopback address as the BGP source address for this reason. Remember that the loopback address must be added to the IGP running for this to work. This way, if R2′s 10.1.1.2 interface fails, R2 will still be reachable.

The update-source command accomplishes this. Here’s an example:

R1(config)# router R1(config-router)# R1(config-router)# R2(config)# router R2(config-router)# R2(config-router)#

bgp 65400 neighbor 192.168.2.2 neighbor 192.168.2.2 bgp 65400 neighbor 192.168.1.1 neighbor 192.168.1.1

remote-as 65400 update-source loopback0 remote-as 65400 update-source loopback0

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Defining Networks Network statements in BGP are used differently than in other routing protocols like EIGRP or OSPF. EIGRP and OSPF use the network statements to define which interfaces you want to participate in the routing protocol process. BGP uses network statements to define which networks the local router should advertise. Each network doesn’t have to be originating from the local router, but the network must exist in the routing table. The optional mask keyword is often recommended as BGP supports subnetting and supernetting.

Example: R1(config)# router R1(config-router)# R1(config-router)# R1(config-router)# R1(config-router)#

bgp 65300 neighbor 10.1.1.1 remote-as 65300 network 10.1.1.0 255.255.255.0 neighbor 10.1.2.1 remote-as 65300 network 10.1.2.0 255.255.255.0

Understand that by default a BGP router will not advertise a network learned from one iBGP peer to another. This is why iBGP is not a good replacement for an IGP like EIGRP and OSPF.

BGP Path Selection Unlike most other routing protocols, BGP is not concerned with using the fastest path to a given destination. Instead, BGP assigns a long list of attributes to each path. Each of these attributes can be administratively tuned for extremely granular control of route selections. BGP also does not load balance across links by default. To select the best route, BGP uses the criteria in the following order:

1. 2. 3. 4. 5. 6.

Highest weight Highest local preference Routes originated locally Path with the shortest AS path Lowest origin code ( i < e < ? ) Lowest MED

7. eBGP route over iBGP route 8. Route with nearest IGP neighbor (lowest IGP metric) 9. Oldest route 10. Neighbor with the lowest router ID 11. Neighbor with the lowest IP address

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Controlling Path Selection The most common method of controlling the attributes listed above is to use route maps. This allows specific attributes to be changed on specific routes. Before we get into route maps, let’s first discuss the three prominent attributes, weight, local preference, and MED.

Weight On Cisco routers, weight is the most influential BGP attribute. The weight attribute is proprietary to Cisco and is normally used to select an exit interface when multiple paths lead to the same destination. Weight is local and is not sent to other routers. It can be a value between 0-65,535. 0 is the default. In the example below, if you want R2 to prefer to use R1 when sending traffic to 192.168.20.0 then the weight attribute could be raised on R2 for R1.

R2(config)# router R2(config-router)# R2(config-router)# R2(config-router)#

bgp 65100 neighbor 10.1.1.1 remote-as 65100 neighbor 10.2.2.1 remote-as 65100 neighbor 10.1.1.1 weight 100

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Local Preference • • •

Local preference is not proprietary to Cisco and can be used in a similar fashion to weight. It can be set for the entire router or for a specific prefix. Local preferences can range from 0-4,294,967,295, with 100 being the default value. Unlike weight, local preference is propagated to iBGP neighbors. Using the diagram above, if an administrator wanted R2 to use R1 when sending traffic to 192.168.20.0, the configuration would look something like this:

R1(config)# router bgp 65100 R1(config-router)# bgp default local-preference 500

After the local preference is raised on R1, it will be shared with R2 and R2 will begin using it as its best path to the distant network (assuming the weight is the same of course). If you want to set the local preference on specific prefixes, route maps are usually the best option. Below is an example of the local preference being set using a route map:

R7(config)# router R7(config-router)# R7(config-router)# R2(config-router)#

bgp 200 neighbor 10.10.10.1 remote-as 100 neighbor 10.10.10.1 route-map lp_example in exit

R7(config)# access-list 7 permit 10.30.30.0 0.0.0.255 R7(config)# route-map lp_example permit 10 R7(config-rmap)# match ip address 7 R7(config-rmap)# set local-preference 300 R7(config-rmap)# exit R7(config)# route-map lp_example permit 20 R7(config-rmap)# set local-preference 100

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MED The MED attribute, or multi-exit discriminator, is used to influence which path external neighbors use to enter an AS. MED is also much farther down on the attribute list compared to attributes like weight, local preference, AS path length, and origin. The default MED value is 0 and a lower value is preferred. A common scenario for MED is when a company has two connections to the same ISP for internet. Weight or local preference could be used to send outgoing traffic on the higher bandwidth link, but local preference is not shared with routers outside an AS. MED could be set on one router so ISP routers prefer that path in.

To set the MED on all routes: R1(config-router)# default-metric value

Here’s an example using a route map to influence incoming paths to 10.30.30.0/24 using MED: R7(config)# router R7(config-router)# R7(config-router)# R2(config-router)#

bgp 200 neighbor 10.10.10.1 remote-as 200 neighbor 10.10.10.1 route-map med_example out exit

R7(config)# access-list 7 permit 10.30.30.0 0.0.0.255 R7(config)# route-map med_example permit 10 R7(config-rmap)# match ip address 7 R7(config-rmap)# set metric 50 R7(config-rmap)# exit R7(config)# route-map med_example permit 20 R7(config-rmap)# set metric 150

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Verification It’s important that you understand and are able to interpret the show ip bgp command output. It displays the contents of the local BGP topology database- including the attributes assigned to each network. It is perhaps the most important BGP verification and troubleshooting tool! Because BGP uses many attributes and sources routes in a number of ways, the output of the show ip bgp command can be a bit overwhelming if you don’t know what you are looking for.

R1# show ip bgp BGP table version is 21, local router ID is 10.0.22.24 Status codes: s suppressed, d damped, h history, * valid, > best, i – internal Origin codes: i – IGP, e – EGP, ? – incomplete Network Next Hop Metric LocPrf Weight Path *> 10.1.0.0 0.0.0.0 0 32768 ? * 10.2.0.0 10.0.22.25 10 0 25 ? *> 0.0.0.0 0 32768 ? * 10.0.0.0 10.0.22.25 10 0 25 ? *> 0.0.0.0 0 32768 ? *> 192.168.0.0/16 10.0.22.25 10 0 25 ?

Attributes Here’s a breakdown of some important fields you should consider remembering: * An asterisk in the first column means that the route has a valid next hop. s (suppressed) BGP is not advertising the network, usually because it is part of a summarized route. > Indicates the best route for a particular destination. These will end up in the routing table.

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i (internal) If the third column has an i in it, it means the network was learned from an iBGP neighbor. If it is blank, it means the network was learned from an external source. 0.0.0.0 The fifth column shows the next hop address for each route. A 0.0.0.0 indicates the local router originated the route (examples include a network command entered locally or a network an IGP redistributed into BGP on the router) Metric (MED value) The column titled Metric represents the configured MED values. Recall that 0 is the default and if another value exists, lower is preferred. i/e/? The last column displays information on how BGP originally learned the route and are referred to as origin codes. i - Entry originated from an Interior Gateway Protocol (IGP) and was advertised with a network router configuration command. e - Entry originated from an Exterior Gateway Protocol (EGP). ? - Origin of the path is not clear. Usually, this is a router that is redistributed into BGP from an IGP.

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Cisco Chapter 6:

642 902

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VPN tunnels and IPSec are two topics covered on the exam, but not in great detail. You’ll need to know enough to verify a sample configuration and answer straightforward questions on both technologies. Let’s start with IPSec.

IPSec Basics IPSec allows the establishment of a secure connection between two hosts. The IPSec protocol sets up a unidirectional SA (security association between the two endpoints). Because the association is unidirectional, an SA is created on both ends, resulting in two SAs per IPSec tunnel. IPSec tunnels are often used as a backup to a WAN link failure. If a point-to-point WAN circuit drops, an IPSec tunnel can be configured to automatically be established over the internet to the remote site. When the primary WAN circuit comes back up, the IPSec tunnel is disconnected.

Floating Static Routes Configuring an IPSec tunnel to activate when a primary link drops is commonly implemented as a floating static route. The idea is to configure to IPSec VPN as a static route, but with an administrative distance higher than that of the WAN routing protocols’s AD. If the primary route is active, the backup link is not placed into the routing table because its AD is higher. If the primary route goes down, the static route becomes active. To configure a floating static route, make sure you define a higher AD value at the end: R1(conf)# ip route prefix mask address|interface distance_value

VPN Tunnels One major problem with standard IPSec sessions is that they do not support broadcast or multicast traffic. If you want to use an IPSec VPN in an “always on” fashion, then the tunnel needs to allow routing information to pass through. Of course dynamic routing protocols use broadcast or multicast to send hellos and updates, creating a dilemma. To get around this issue, a “tunnel within a tunnel” approach can be used. A generic tunnel can be configured within the IPSec tunnel to allow routing protocol information (along with all the other traffic). There are generally four ways to do this paired with IPSec:

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DMVPN and GET VPN Both allow the creation of secure, “on-demand”, multipoint tunnels. Virtual Tunnel Interface (VTI) A secure, “always-on” tunnel that supports multicast traffic. This allows routing protocols to operate within it.

Generic Routing Encapsulation (GRE) GRE tunnels may be the most common of the bunch – they are also the default tunnel mode on Cisco routers. GRE tunnels support many layer 3 protocols but perhaps most importantly allow multicast traffic across the tunnel – granting dynamic routing protocol traffic.

Be aware that GRE tunnels add an additional 20 byte IP header as well as a 4 byte GRE tunnel header.

Branch Office Connectivity The CCNP ROUTE exam covers several unusual topics related to managing and configuring the connectivity between an HQ site and a branch office. You need to be familiar with some of the underlying technologies used. Cisco ISR routers are often a good choice for branch sites as they support a wide variety of incoming services. In smaller offices, a single ISR may be used for a both remote connectivity and inter-VLAN routing. In that case, know that an Ethernet Switch Module would be required for the ISR router.

DSL DSL, or Digital Subscriber Line, can be used as a backup WAN connection to a branch office. DSL uses frequencies not used by TDM phone systems on a phone line – allowing the extra bandwidth to be used for data connectivity. Asymmetrical DSL has higher downstream bandwidth than upstream, while with symmetric DSL they are both the same rate. There are two primary methods for pushing L2 data across a DSL line: PPPoE Point-to-Point Protocol over Ethernet is the most common method and encapsulates PPP traffic into Ethernet frames.

PPoA Point-to-Point Protocol over ATM is less common and routes PPP traffic over an ATM network between the customer and the DSL service provider.

** Both options can be configured on a Cisco router to terminate the DSL connectivity. PPPoE is especially helpful because it this frees the user computers from running PPPoE

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Cable Broadband cable providers also provide internet connectivity which can be used for WAN backup or Internet connectivity for telecommuters. The internet signal is carried on the same line that the television is carried, but a cable modem allows the data traffic to be separated. The international standard for sending data over a cable system is Data Over Cable Service Interface Specification (or DOCSIS). Many different versions of the standard are used throughout the world. Cable system connections are typically not terminated directly into a Cisco router. Instead, a cable modem demodulates the incoming signal and converts the traffic to Ethernet frames, which a router can process.

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Cisco Chapter 7:

642 902

IPv6

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IPv6 IPv6 is an important topic – and not just for the exam. The growth of web-based services and diminishing IPv4 addressing will continue to push organizations towards IPv6, especially on web-facing networks.

Basics IPv4 addresses are 32 bits long and are represented in dotted-decimal format. IPv6 addresses are 128 bits and are in hexadecimal format. The first 64 bits of an IPv6 address are reserved for the network portion and the last 64 bits are used for the host portion.

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IPv6 Shorthand The ability to shorten IPv6 addresses is very important to understand because it makes reading and writing them much easier. There are two ways to condense an IPv6 address.

1. Leading zeros can be removed in any section.

2. Sequential sections of all zeros can be shortened to a single double colon.

0021:0001:0000:030A:0000:0000:0000:0987E Can be abbreviated as:

This can only be used once per address though! Using the same example address above, it can be further shortened to:

21:1:0:30A:0:0:0:987E

21:1:0:30A::987E

Unicast, Multicast, & Anycast Unicast Unicast is for sending traffic to a single interface. In IPv6 there are actually two different unicasts types, global unicast and link-local unicast. Multicast Unlike IPv4, IPv6 addressing does not support broadcasts. Instead, it has replaced it with multicast (which is a more efficient variation). This is used for sending traffic to a group of devices. Anycast IPv6 supports another, new packet type – anycast. Anycast allows the same address to be used on multiple devices for load balancing and redundancy. Technically, it is used for sending traffic to the nearest interface in a group. While multiple devices may be running the same anycast address, only one will be used per packet sent.

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Be aware that with IPv6, an interface can be assigned multiple addresses. Here is the list: • • •

Unicast address Link-local address loopback (::1/128)

• • •

All nodes multicast (FF00::1) Site-local multicast (FF02::2) Solicited-nodes multicast

•

Default Route (::/0)

Address Assignment In IPv6, there are three different ways devices are assigned an IP address: •

manual configuration

•

stateless autoconfiguration

•

DHCPv6.

Manual Address Configuration The first thing to know about manual IPv6 address configuration is that addresses assigned to a router interface use the address/prefix-length notation instead of the address mask notation. This is so much easier than typing 255.255… after every IP address! • •

Make sure you first enable IPv6 routing with the ipv6 unicast-routing global configuration command. Use the ipv6 address ipv6-address/prefix-length command to assign an address.

An example of an interface configured with an IPv6 address: R1# conf t R1(config)# ipv6 unicast-routing R1(config)# int gig 1/1 R1(config-if)# ipv6 address 21:1:0:30A::987E/64

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Manual Network Assignment Another way to manually configure an IPv6 address is to configure the network and allow the host portion to be auto-populated based on the device’s MAC address. This can work well because MAC addresses are 64 bits long – the exact same length as the host portion of an IPv6 address! An example with the network portion defined:

R1(config)# int gig 1/1 R1(config-if)# ipv6 address 21:1:0:30A::/64

Note: Some systems have a 48 bit MAC address. In this case, it flips the 7th bit and inserts 0xFFEE into the middle of the MAC address. This modified version is called an EUI-64 address. To do this, add the keyword eui-64 to the end of the ipv6 address statement.

Stateless Autoconfiguration Stateless autoconfiguration allows a device to self-assign an IP address for use locally without any outside information. Remember that interfaces using IPv6 will often have more than one IPv6 address assigned, and in this case stateless autoconfiguraiton will generate a link-local address in addition to any other manually assigned addresses. Link-local addresses are created by starting with the prefix FE80:: and appending the device’s MAC address. Since every MAC address should be unique, it works well for auto-generated local IP addresses. Link-local addresses are not routable within packets and are used for administrative purposes within the local segment. For example, most IGPs use linklocal addresses to for neighbor relationships and the link-local address is listed as the next-hop address in the routing table. Once a router has created an IPv6 link-local address using stateless autoconfiguration, it uses NDP to make sure it is actually unique within the local network. NDP stands for Neighbor Discovery Protocol. NDP uses ICMP packets as part of the neighbor discovery process. To configure stateless autoconfiguration, use the ipv6 address autoconfig command.

R1(config)# int gig 1/1 R1(config-if)# ipv6 address autoconfig

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IPv6 Routing Static Routes The configuration for IPv6 static routes is identical to IPv4, except for the ipv6 route keywords (instead of ip route) and the addresses will obviously look different. Other than that, it is exactly the same!

An example of a static IPv6 default route:

An example of an IPv6 static route with a next-hop address:

R1(config)# ipv6 route ::/0 serial1/1

R1(config)# ipv6 route 2003:2:1:A::/64 2003:2:1:F::1

To view the IPv6 routes in the routing table, use the command show ipv6 route.

IPv6 EIGRP •

There are many differences in the way EIGRP is configured and with IPv6. It still sends hellos out every 5 seconds to its neighbors, but when running EIGRP with IPv6 addresses, it uses the multicast address FF02::A.

To Configure IPv6 EIGRP: R1(config)# ipv6 unicast-routing R1(config)# ipv6 router eigrp AS R1(config-rtr)# router-id ipv4-address R1(config-rtr)# no shut R1(config-rtr)# exit R1(config)# interface type number R1(config-if)# ipv6 eigrp AS

•

EIGRP messages are exchanged using the link-local address as the source address and perhaps the biggest difference is that there is no network command! Instead, EIGRP routing is enabled on each participating interface.

•

Also, EIGRP running IPv6 requires a router ID be configured. The format is that of an IPv4 address - 32 digits and it can be a private address (non-routable) with no issues.

•

The last major change is that the EIGRP process starts in the shutdown state. You have to issue a no shut to bring it up on the router.

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OSPFv3 •

•

OSPFv3 is an updated version of OSPF designed to accommodate IPv6 natively. Most of the configuration and function is identical to its predecessor, but a few changes were made – starting with messaging. OSPFv3 uses the multicast address FF02::5 and FF02::6, but like EIGRP, it now uses its link-local address as the source address in advertisements. Also, it’s possible to run multiple instances of OSPFv3 on each link.

•

Like the IPv6 implementation of EIGRP, a 32 bit router ID must be manually created. It will not automatically create one based on highest loopback or interface address. The RID that is assigned will then be used to determine the DR and BDR on a segment (highest wins).

•

OSPFv3 has dropped its native authentication options. Instead, it relies on the underlying authentications built into IPv6, like IPSec.

Configuration The configuration is now done on each individual interface. The following is an example configuration:

To Configure OSPFv3: R2(config)# ipv6 unicast-routing ! R2(config)# ipv6 router ospf 100 R2(config-rtr)# router-id 10.10.10.1 R2(config-rtr)# area 1 stub no-summary R2(config-rtr)# exit ! R2(config)# interface gig1/1 R2(config-if)# ipv6 address 2003:2:1:2::1/64 R2(config-if)# ipv6 ospf 100 area 0 ! R2(config)# interface gig1/2 R2(config-if)# ipv6 address 2003:2:1:A::1/64 R2(config-if)# ipv6 ospf 100 area 1 R2(config-if)# ipv6 ospf priority 30

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MP-BGP MP-BGP, or multiple protocol BGP, was outlined in RFC 2858 and includes extensions to the original BGP standard that allows support for other protocols – one of which is IPv6! The command address-family was added to specify which new protocol functionality is being configured and is used when applying IPv6 addressing. Like EIGRP and OSPFv3, an IPv4 address must be configured as a router ID. The BGP configuration is not done at the interface level, it still is done in router configuration mode. The major difference is that neighbors must be first defined under router BGP configuration mode and then “activated” under IPv6 address-family mode submode. Networks and other parameters are also configured under IPv6 address-family mode submode.

To Configure MP-BGP: R3(config)# ipv6 unicast-routing ! R3(config)# router bgp 600 R3(config-rtr)# router-id 10.10.10.10 R3(config-rtr)# neighbor 2003:76:1:1::10 remote-as 700 R3(config-rtr)# address-family ipv6 unicast R3(config-rtr-af)# neighbor 2003:76:1:1::10 activate R3(config-rtr-af)# network 2003:2:2::/48 R3(config-rtr-af)# exit R3(config-rtr)# exit

Migrating to IPv6 Three options exist for transitioning from IPv4 to IPv6: dual stack, tunneling, or NAT: •

Dual Stack - this involves running IPv4 alongside IPv6 on the same system.

•

Tunneling - this option allows you to encapsulate IPv6 traffic within an IPv4 header.

•

NAT - a new network translation extension, NAT-PT allows IPv6-to4 translation.

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Dual Stack Using a dual-stack transition allows servers, clients, and applications to be slowly moved to IPv6. Both protocols can run concurrently, neither communicating with the other. If both IPv4 and IPv6 are running on a server for example, IPv6 will be used.

Configuration Example: R1# config t R1(config)# ipv6 unicast-routing R1(config)# ipv6 cef ! R1(config)# interface serial1/0/1 R1(config-if)# ip address 192.168.1.1 255.255.255.0 R1(config-if)# ipv6 address 2001:1:3:1:1/64

Dual-stacking IPv4 alongside IPv6 on systems works well, but it requires most of your infrastructure to support IPv6. In many cases, the network core does not support IPv6 or it has not been implemented. IPv6 tunnels solve this problem by allowing IPv6 islands to exist and bridging them over IPv4 systems. Because IPv6 tunnels provide virtual IPv6 connectivity through an IPv4 transport, it does not matter what specific IPv4 transport is used. The only requirement is that there is end-to-end IPv4 connectivity between both ends.

Manual Tunnels The tunnels discussed here are from one router to another. The source router (RouterA) encapsulates the IPv6 traffic in IPv4 headers, and then forwards it to the other end of the tunnel (Router B). Router B then decapsulates the packets and forwards them on to their destination using native IPv6. Manual IPv6 tunnels are easy to configure using the tunnel mode ipv6ip command. Using the Router A/B example above, the configuration on Router A would look something like this:

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RouterA(config)# interface tunnel0 RouterA(config-if)# ipv6 address 2001:2:0:7::/64 RouterA(config-if)# tunnel source 10.1.1.1 RouterA(config-if)# tunnel destination 10.3.3.1 RouterA(config-if)# tunnel mode ipv6ip RouterA(config-if)# exit

GRE Tunnels First, GRE tunnels are the default tunnel method on Cisco routers. GRE tunnels are very flexible and work over most protocols. The configuration is exactly the same as the manual configuration example above, but you do not have to specify the tunnel mode. Also, routing protocols can be enabled on GRE tunnel interfaces just as if they were physical interfaces.

6to4 Tunnels •

6to4 tunnels are similar to the manual tunnel, but set up the tunnel dynamically.

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6to4 tunnels use 2002::/16 IPv6 addresses in front of the 32 bit IPv4 address of the edge router – creating a 48 bit prefix. Each router on both sides of the tunnel needs a route to its peer. They only support static and BGP routes, so be careful.

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Configure the tunnel as if it was a manual tunnel, using the IPv4 address as the source, but don’t enter a destination. The tunnel requires an IPv6 address using the method just described. Finally, use the command tunnel mode ipv6ip 6to4.

NAT Translation is a unique solution because it allows IPv4 devices to communicate with IPv6 devices without the dual stack requirement. NAT-PT allows bidirectional translation services.

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1. To enable NAT-PT IPv4 to IPv6 translation on a router, the first step is to use the ipv6 nat command on each interface participating in the translation. 2. The second step is to define at least one NAT-PT prefix. Only traffic matching the prefix will be translated. To apply it globally on the router, enter ipv6 nat prefix/prefix_length in global configuration mode. To apply it to traffic on a specific interface, enter ipv6 nat prefix/prefix_length in interface configuration submode. 3. Define the address mappings (either static or dynamic) using the options discussed below.

Static NAT-PT For an IPv6 to IPv4 static mapping: R1(config)# ipv6 nat v6v4 source ipv6_address ipv4_address

For an IPv4 to IPv6 static mapping: R1(config)# ipv6 nat v4v6 source ipv4_address ipv6_address

Dynamic NAT-PT There are many ways to implement dynamic NAT using IPv6, but at its most basic level a pool of addresses is created and the router temporarily assigns them to hosts as needed.

For an IPv4 to IPv6 dynamic mapping: R1(config)# ipv6 nat v4v6 pool name begining_ipv6 ending_ipv6 prefix-length prefix-length R1(config)# ipv6 nat v4v6 source list (access-list_number | name) pool name

For an IPv6 to IPv4 dynamic mapping:

R1(config)# ipv6 nat v6v4 pool name begining_ipv4 ending_ipv4 prefix-length prefix-length R1(config)# ipv6 nat v6v4 source list (access-list_number | name) pool name

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Cisco Chapter 8:

642 Simulation 902 Scenarios 88 | P a g e

EIGRP/OSPF Redistribution Simulation Example: PROBLEM •

In this scenario, routers R2 and R3 need to be configured for redistribution between their respective EIGRP and OSPF Autonomous Systems.

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Only R2 and R3 can be configured and the traffic path from R1 to the 10.1.1.0 network should use the links with the greatest bandwidth.

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When completed, router R1 should be able to ping a host in the 10.1.1.0/24 network.

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SOLUTION First we need to find out 5 parameters (Bandwidth, Delay, Reliability, Load, MTU) of the s1/1 interface (the interface of R2 connected to R4) for redistribution:

R2# show interface s1/1

Now write down these 5 parameters, notice that we have to divide the Delay by 10 because its metric unit is in tens of microseconds. For example, if we get: Bandwidth=1544 Kbit Delay=20000 us Reliability=255 Load=1 MTU=1500 bytes …then we would redistribute as follows:

R2#config terminal R2(config)# router R2(config-router)# R2(config-router)# R2(config-router)# R2(config-router)# R2(config-router)#

ospf 1 redistribute eigrp 200 metric-type 1 subnets exit router eigrp 200 distance eigrp 90 109 redistribute ospf 1 metric 1544 2000 255 1 1500

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Notice in the configuration above the "distance eigrp 90 109" command on R2. This drops the external EIGRP administrative distance from 170 to 109 (one less than OSPF’s AD value of 110) coming in from R3 so that it will be more trustworthy than the OSPF link between R2 and R4.

R3# show interface fa1/1

For R3 we use the show interface fa1/1 to get the same 5 parameters. For example we get Bandwidth=10000 Kbit, Delay=1000 us, Reliability=255, Load=1, MTU=1500 bytes. Now let’s configure it the same way we did R2:

R3#config terminal R3(config)#router ospf 1 R3(config-router)#redistribute eigrp 200 metric-type 1 subnets R3(config)#exit R3(config-router)#router eigrp 200 R3(config-router)#redistribute ospf 1 metric 10000 100 255 1 1500

Verification Perform a “show ip route” on R1 to see the 10.1.1.0/24 network (the network behind R4) in the routing table. Next, ping from R1 to the network to validate the connectivity. Finally perform a traceroute on R1 to the fa1/1 interface of R1 to make sure the traffic is going form R1-R2-R3-R4. This fulfills the “highest bandwidth” requirement – using the Fast Ethernet links instead of the Serial connection.

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IPv6 OSPF Virtual Link Simulation Example: PROBLEM •

In this scenario, two organizations have merged and need to connect their core routed networks. Luckily, both have already implemented IPv6 routing using OSPF, but their area numbers do not fit together well.

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You have been tasked with getting their core OSPF routers up and running using their current area configuration until a full redesign can be performed.

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Currently, R4’s loopback address cannot be seen in R1’s routing table (and vice-versa).

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SOLUTION You should know by now that in OSPF, all areas must connect back to the backbone area (area 0). In this case, that isn’t an option because the directions specifically ask us not to change the current area assignments. The solution? A virtual link! We can configure area 1 as a transit area for area 2 using the area virtual-link command.

R2> enable R2# configure terminal R2(config)# ipv6 router ospf 1 R2(config-rtr)# area 1 virtual-link 3.3.3.3

(Notice that we have to use neighbor router-id 3.3.3.3, not R2′s router-id 2.2.2.2) Now onto R3:

R3> enable R3# configure terminal R3(config)# ipv6 router ospf 1 R3(config-rtr)# area 1 virtual-link 2.2.2.2

That’s all there is to it!

Verification:

To verify that R1 has a route to R4’s loopback interface, use the show ipv6 route command on R1.

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OSPF Simulation Example: PROBLEM •

Sharky’s Surf ‘n Turf is a fast-growing corporate seafood establishment and needs your help. A new HQ office was recently constructed with connectivity provided by router R1. Your task is to configure and verify connectivity between the current HQ head-end router (R2) and the new location (R1).

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The physical cabling between R1 and R2 has been completed, but the configuration of OSPF Area 1 needs to be completed to include ONLY R1 s1/0 and R2 s1/1. The mask should be configured to allow only the two interfaces to participate in the OSPF area.

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Also, Area 1 should be configured in a way so that it does not receive any inter-area or external routes (except default routes). The interfaces have already been configured with the IP addresses shown in the diagram.

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SOLUTION 1. Let’s start with R1. There are two primary considerations in this scenario. First, Area 1 must be configured to include only R1 and R2’s interfaces. The network that the circuit is using is /30, meaning we need to use a wildcard mask for the OSPF area that reflects that /30 address range. 0.0.0.3 will do just that. R1#config terminal R1(config)# router ospf 1 R1(config-router)# network 192.168.4.40

0.0.0.3 area 1

The second major consideration for this scenario is that Area 1 should be configured in a way so that it does not receive any inter-area or external routes (except default routes). That’s code for a totally stubby area. In this case, R1 needs to have the stub command applied.

R1(config-router)# area 1 stub R1(config-router)# exit

2. Moving on to R2. The same network wildcard must be applied to R2: R1#config terminal R1(config)# router R1(config-router)# R1(config-router)# R1(config-router)#

ospf 1 network 192.168.4.40 0.0.0.3 area 1 area 1 stub no-summary exit

Notice the area 1 stub no-summary command. R2 is the ABR, so if we want Area 1 to be a totally stubby area then we need to use the no –summary command here. That’s it! Fairly simple, but VERY important practice for the exam.

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Policy-Based Routing Simulation Example: PROBLEM •

You’ve been tasked with providing a routing policy solution to a new web-startup company. They have heavy outbound HTTP traffic loads and want to use a dedicated frame relay circuit to carry it.

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Configure router PBR in such a way that all HTTP traffic traverses the frame relay link to ISP A if the link is up. All other traffic can go through either link. Only router PBR can be configured and due to network policies, static routes and default routes are not allowed.

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SOLUTION 1. First we need to create an access list that defines the web traffic. PBR(config)# access-list 101 permit tcp any any eq www A source of “any” is used to capture all EIGRP network sources.

2. Now we create a route map that sets the next-hop for the web traffic.

PBR(config)# route-map PBR(config-route-map)# PBR(config-route-map)# PBR(config-route-map)# PBR(config)# route-map PBR(config-route-map)#

PBR permit 10 match ip address 101 set ip next-hop 10.1.1.1 exit PBR permit 20 exit

Notice that the first statement sets the next-hop address for the HTTP traffic and the following route map line (20) allows any other traffic through unmodified. If line 20 wasn’t used, the implicit deny would drop any non-web traffic.

3. Last step is to apply the route map to the internal-facing interface on router PBR. PBR(config)# int fa0/1 PBR(config-if)# ip policy route-map PBR PBR(config-if)# exit PBR(config)# exit

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4. Verification On a host in the internal EIGRP network, generate HTTP traffic destined for the internet. Next, use the show route-map command to verify that packets are being matched against the new filter. PBR# show route-map

You should see something like “Policy routing matches: 12 packets…” in the output if your configuration is correct.

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