BGP Max AS Limit


Scenario:

AsianFish inc. is expanding their business towards Europe so they need to expand their network as well. BGP has been configured for inter-AS connectivity but you want to make sure you don’t receive just any prefix on the Internet. Business has been fishy lately so there’s no budget for routers with enough memory to carry all the BGP prefixes. To make sure your routers keep running you only want to accept prefixes from a number of autonomous systems.

Goal:

  • All IP addresses have been preconfigured for you.
  • Configure EBGP between AS 1 – 2, AS 2 – 3 and AS 3 – 4.
  • Advertise the loopback0 interfaces of all routers in BGP.
  • Configure router Tilburg so it only allows prefixes from directly connected autonomous systems.
  • You are not allowed to use as path filtering or any regular expressions.

IOS:

c3640-jk9s-mz.124-16.bin

Topology:

BGP Max AS Limit

Video Solution:

Configuration Files

You need to register to download the GNS3 topology file. (Registration is free!)

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

Opt In Image
Do you want your CCNA or CCNP Certificate?

The How to Master series helps you to understand complex topics like spanning-tree, VLANs, trunks, OSPF, EIGRP, BGP and more.

Written by René Molenaar - CCIE #41726

You May Also Like

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

6 Comments

  1. Debug ip bgp update ….Always good to capture debug outputs

    Mar 1 00:23:33.835: BGP(0): 192.168.23.2 rcv UPDATE about 1.1.1.0/24DENIED due to: AS-PATH length over 4072;

    Tilburg

    bgp maxas-limit 1

    Thanks for the awesome lab Rene. U made the life easier to practice BGP labs 🙂

    1. Using a debug like this is excellent to verify your work…your welcome 🙂

  2. man, none of the BGP debugs i did generated a message like the one Farhan showed 🙁

    all i got is the following:

    %BGP-6-MSGDUMP_LIMIT: unsupported or mal-formatted message received from 192.168.23.2:
    FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 0033 0200 0000 1840 0101 0040 020A 0202
    0000 0002 0000 0001 4003 04C0 A817 0218 0101 01

    %BGP-6-ASPATH: Long AS path 2 1 received from 192.168.23.2: BGP(0) Prefixes: 1.1.1.0/24

    good lab.

    1. Try this.
      debug ip bgp
      debug ip bgp update

      and later:
      clear ip bgp *

      you should see this.
      *Mar 1 00:14:41.707: BGP(0): 192.168.23.2 rcv UPDATE about 1.1.1.0/24 — DENIED due to: AS-PATH length over 4072;

Comments are closed.