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BGP Multipath Load Balancing

Written by Nick on . Posted in BGP

Scenario

You've got a single multi-homed BGP connection to two ISPs. You want to load balance traffic to a specific destination but you have no control over what the ISPs are doing with that route as it traverses the network! You helped the ISP build their network ... but then they fired you and left you scratching your head trying to enable load balancing.

Goal:

  • Nothing has been preconfigured for you!
  • Make the required physical connections as depicted in the diagram.
  • Configure the IP addresses as depicted in the diagram (begin with 192.168).
  • Configure eBGP as follows using the connected physical interfaces as update sources:
    * R1 to R3
    * R1 to R2
    * R3 to R4
    * R4 to R5
    * R2 to R5
  • Add a loopback on R1 and R5 with addresses 1.1.1.1/32 and 5.5.5.5/32 respectively.
  • Pull these loopbacks into BGP using the network command, and no other networks afterwards.
  • Configure an outbound route-map on R5 to set the origin to "?" for all routes it sends to R2.
  • Configure an outbound route-map on R5 to set the origin to "e" for all routes it sends to R4.
  • Configure an outbound route-map on R2 to set the MED to 2 for all routes it sends to R1.
  • Configure an outbound route-map on R3 to set the MED to 3 for all routes it sends to R1.
  • Ensure R1's BGP table reflects these updates, and ensure you have connectivity from 1.1.1.1 to 5.5.5.5.
  • *** From this point forward, you cannot configure any other router except R1. You used to work at the ISP and configured their network for them, but they just fired you. ***
  • Enable load balancing for the 5.5.5.5 network within BGP. You will know when you are successful when R1's routing table has two entries for 5.5.5.5/32 (one next hop is R2, the other is R3).

IOS:

c3725-adventerprisek9-mz.124-7.image

Topology:

bgp load balance