EIGRP Configured on a Frame Relay Network

I spent a little time this afternoon going over the next EIGRP lab in the CCNP Lab Portfolio. I learned some useful types regarding EIGRP and how it works over Frame. For the most part you can configure EIGRP as normal but EIGRP works off of split-horizon rules. Split horizon pretty much tells a router not advertise a route out of the same interface that it learned the route from to begin with. There for in the diagram router West and East didn't know about each other due to not being able to advertise the same route back to HQ. To get past this, I had to turn of split horizon on the HQ router with the following command:

no ip split-horizon eigrp 1

Once I entered this command under the EIGRP configuration, sure enough all routes came right up!

EIGRP Configuration, Bandwidth, and Adjacencies

I was able to tackle the second lab in the BSCI Lab Portfolio and I can already say with confidence that this book will help me greatly with my studies. I learned a few things between this lab and he first lab that I wouldn't of ever known or thought about. Last week was a very simple two router lab with basic static route configuration. However I learned something that I didn't even know these Cisco routers could do, and that's programming scripts. The Lab Portfolio goes over a neat little script that allows you to test ping configurations without having to go through and ping every interface over and over on each router to verify connectivity. Check out a preview of the script I used for the first lab below, it's called TCL Script and you can access it by typing the tclsh command when you are in enabled mode:

foreach address { 10.1.1.1 10.1.2.1 10.1.3.1 10.1.4.1 10.100.12.1 10.2.1.1 10.2.2.1 10.2.3.1 10.2.4.1 10.100.12.2 } { ping $address }

It pretty much says for each IP address listed, ping it, as simple as that!


I finished my first EIGRP lab today and picked up some cool new commands such as the ping ip address repeat number of times command. Which you can ping an IP address as many times as needed, an example would be ping 10.1.1.1 repeat 1000. This tells the router to ping 10.1.1.1 1000 times, great for testing experiments with routing protocols while packets are being sent across the network!.

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Route Reflectors For BGP

BGP specifies that routes learned using Interior BGP should never be learned by other IBGP peers. Because of this rule, BGP requires that all IBGP networks to be complety fully meshed as shown in the picture above. Therefore if you had just 13 routers in your AS running IBGP, you would need 78 total connections in order for all 13 routers to connect to every other router! This causes a big problem with bandwidth due to sending redundant data across all of the routers at the same time.

To over come this, the creation of Route Reflectors (RR) were created. Route Reflectors allows an AS that's running IBGP to not have to use a complete full-mesh topology. Instead you can creat whats called clusters which can group sets of routers together. You can think of a cluster as a mini network that sits inside of your AS. But instead of a full-meshed topology, the cluster is designed in a hub and spoke fashion with one router being designated the Route Reflector (Hub) and the other routers being the spokes that connect to the RR. The Route Reflector then passes its updates to the AS, other clusters, or even other AS's depending on the configuration. This saves on the number of BGP TCP sessions that must be maintained and and also reduces the BGP routing traffic!

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BGP Communities

If we used just prefix-lists and distribute lists to filter BGP updates it would be a very manual intensive job due to the size of most BGP networks and the fact that you would have to configure each router one at a time! Today I learned that you can group routers running BGP into groups that can share the same filtering information. Therefore you would only need to configure one of the routers in the group for all of the other routers to know what updates should be filtered and what shouldn't.

"BGP communities function allows routers to tag routes with an indicator (the community) and allows other routers to make decisions (filter) based on that tag. BGP communities are used for destinations (routes) that share some common properties and that, therefore, share common policies; routers, therefore, act on the community, rather than on individual routes. Communities are not restricted to one network or autonomous system, and they have no physical boundaries."

the community attribute is considered an optional transitive attribute. If a router receives an update with community attribute information but doesn't use that attribute, it will ignore it but pass it along to other BGP neighbor peers. The community attribute consists of 32-bits, 16 for the Autonomous System number (AS) and the other 16 identifies the community number.

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Creating Prefix-Lists for BGP Routing 2

I spent this early afternoon finishing up the BSCI BGP Appendix section on prefix-lists for BGP, I mainly created a lab that specifies that that the network 172.30.0.0 /24 in the AS 65500 only shows as the supernet 172.0.0.0/8 in the AS 65000 BGP table as shown above. Tomorrow I will learn a little bit about BGP communities and go over what I've learned!

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Creating Prefix-Lists for BGP Routing

I spent a good bit of my morning learning and configuring BGP prefix-lists which I will wrap up tomorrow most likely. Prefix-lists provide greater flexibility over access-lists due to the fact you're allowed more granular control of where you want input your statements inside the prefix list. This differs from the standard access-list where one no command on the ACL requires you to recreate the access-list completely! I'm still not entierly sure how prefix-lists differ from ip access-list commands which allows you to enter sequence number states like prefix-lists. I do know that you can control exactly how you want a neighbor BGP autonomous sysstem (AS) to know about external routes by using the le and ge commands.

The le and ge values are used in a prefix-list statement to create a range of the prefix length to be matched more specifically compared to the network/length commands used in the prefix-list statements. Prefix lists do provide the advantage of being less performance intensive due to not requiring the amount of route lookup processing sometimes required by large access-list tables.

As you can see in the above lab I worked earlier, the prefix list tells AS_65000 to only let AS_65002 know about the 172.16.0.0 /16 external network instead of the more specific 172.16.10.0 /24 and 172.16.11.0 /24 routes.

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