BGP Attribute AS Path

Posted by August 31, 2011 in BGP

Scenario:

A local steelmill has asked you to help them with their BGP network. The steelmill has two sites and routing information is used by using BGP. Everything is working fine except the backup link is being used for all traffic at this moment. Can you influence BGP so the traffic path is changed? Are you as tough as steel?

Goal:

  • All IP addresses have been preconfigured for you as specified in the topology picture.
  • Configure EBGP between router Copper and Zinc.
  • Configure EBGP between router Steel and Zinc.
  • Configure IBGP in AS 1.
  • Advertise the 4.4.4.0 /24 network on router Zinc.
  • Make sure router Aluminium sends traffic to 4.4.4.0 /24 to router Steel, you are only allowed to use the AS Path attribute.

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IOS:

c3640-jk9o3s-mz.124-16.bin

Topology:

BGP Attribute AS Path

Video Solution:

Configuration Files

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Once you are logged in you will find the configuration files right here.

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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

14 Comments

  1. Make sure router Colorado sends traffic to 3.3.3.0 /24 to router Claiborne, you are only allowed to use the AS Path attribute.

  4. Hello Rene, in the video you tell about a loopbacks in AS 1 and OSPF but in scenario and goal do not show. Thanks for the info is so much useful for certification.

    1. Hi Emilio,

      Whenever we configure IBGP it has to be a "full mesh". It’s best practice to configure IBGP between loopbacks but this means we need to use static routes or an IGP to advertise the networks on the loopback interfaces. I didn’t add these tasks in this scenario because they are "best practices".

      Rene

      1. Rene thanks for you response, I understand what you saying. I Will take that in count for another BGP Labs.

  5. One thing driving me a bit crazy on this lab is that there is no access list 1. I looked this up in my cisco book and they show an example excluding the match statement and it worked as well. Curious why it works with match ip address 1? Also tried match as-path 1 which did NOT work. Also tried creating the acl 1 with ip address of the neighbor which also did not work.

    Thank you

    1. hi Psy4HA i think if you match an access list in route map and you did not define any access list it will permit every thing ,in this lab RENE maybe forget that you can check another site of Rene Molenaar it explane there also

  6. Hey Rene , a network administrator can use a filter list to control the AS-PATH PREPANDING .Although i applied the filter list on router copper ,still it showing the network with as path 2 2 2 2 2 i .

  7. such a simple and great lab. it tested my knowledge. i rushed in by configuring an AS-path routemap on router aluminium without realising that it wont stop the route going through via copper!

  8. i did the same thing as Haz – i initially configured an as-path prepend route-map inbound on Aluminium, and it did NOT work.

    i followed up by doing an inbound route-map on Copper to prepend the as-path attribute instead of Zinc, which worked… 6 of one and half dozen of the other i suppose 🙂

    i found a blurb on “http://routerjockey.com/2011/02/28/bgp-essentials-the-art-of-path-manipulation/” saying that as-path prepend cannot be used in iBGP.

    i haven’t found any Cisco documentation mentioning this yet… but i continue to look.

    very good lab !

  9. Hi René
    After the “set as path prepend” has been executed on Zinc, why don’t Steel receive the route for 4.4.4.0/24 from Copper (with AS-Path 2 3) and put it in the “bgp table” along with the route it receives directly from Zinc with AS Path 2 ?

    Thanks in advance

  10. Hello Rene,

    You are awesome….All your labs are perfect and anyone can be a master in fews days with some dedications..

    Thanks for providing such stufs….

    Namit Joshi

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