BGP Communities


Scenario:

You are working on a small network of a ISP located in Germany. One of your colleagues is sending you prefixes tagged with communities. He’s telling you to match on those communities and change your routing policy based on them. You have no idea what he’s talking about but you are sure you can fix it!

Goal:

  • All IP addresses have been preconfigured for you.
  • Configure EBGP between router NewYork and Amsterdam.
  • Configure EBGP between router NewYork and Hamburg.
  • Advertise the loopback0 interface on router Amsterdam and Hamburg.
  • Configure router Hamburg to send the community value 100:100 for network 23.23.23.0 /24.
  • Configure router NewYork to match on the community value and send traffic for 23.23.23.0 /24 to router Hamburg.

IOS:

c3640-jk9s-mz.124-16.bin

Topology:

BGP Communities

Video Solution:

Configuration Files

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Written by René Molenaar - CCIE #41726

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About the Author: Rene Molenaar

René - CCIE #41726 is the creator of GNS3Vault.com where he shares CCNA, CCNP and CCIE R&S labs. He also blogs about networking on http://networklessons.com

4 Comments

    1. i do not think so.
      i believe the intent of this lab is to show how you can manipulate path selection using the BGP Community value.

      this lab says have Hamburg set community for 23.23.23.0/24 to 100:100, and send that community to New York.

      next, the lab says for New York to match on community value 100:100 and set New York to send [all] traffic for 23.23.23.0/24 to Hamburg (prefer Hamburg over Amsterdam).

      if New York does not match on and prefer community 100:100, there should be 2 destinations for network 23.23.23.0/24 – Amsterdam and Hamburg.

      if the lab is done successfully, i believe the intent is to only have a route to Hamburg for network 23.23.23.0/24.

      Example:

      BEFORE:
      see in my output before BGP community is set that there are 2 paths to 23.23.23.0/24.
      the best path in my lab was set to Amsterdam.

      NewYork#sh ip bgp | i Net|\*
      Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
      Network Next Hop Metric LocPrf Weight Path
      * 23.23.23.0/24 192.168.13.3 0 0 2 i
      *> 192.168.12.2 0 0 2 i

      AFTER:
      after i applied my solution to this lab, there is only 1 entry for network 23.23.23.0/24.

      NewYork#sh ip bgp | i Net|\*
      Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
      Network Next Hop Metric LocPrf Weight Path
      *> 23.23.23.0/24 192.168.13.3 0 0 2 i

      don’t know if i’m correct… just my 2 cents 🙂

      1. oops… gotta correct myself b/c i had 2 mistakes in my lab.

        1) forgot to add a “permit any” to my route-map, and it was filtering out 23.23.23.0/24 from Amsterdam.

        2) also forgot to create my BGP community list ACL and wasn’t actually acting upon the 100:100 community.

        nonetheless, i still think both Amsterdam and Hamburg are supposed to be advertising 23.23.23.0/24 for this 🙂

        MY CORRECTED *AFTER* OUTPUT:

        NewYork#sh ip bgp | i Net|\*
        Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
        Network Next Hop Metric LocPrf Weight Path
        *> 23.23.23.0/24 192.168.13.3 0 100 2 i
        * 192.168.12.2 0 0 2 i

        my bad

Comments are closed.