Need help with configuring ebgp multipath

[jalalyounus]

Hi;

The situation is that a client of ours is dual homed to us. The interface details are as under:

Gi0/2/0/11         up          up          RN-WU-PRIMARY

Gi0/1/0/11         up          up          RN-WU-BACKUP

Our EBGP configurations with this client are:

neighbor 9.7.8.66

  remote-as 1200

  use neighbor-group OUR-MEMBER

  password encrypted 14303808155D7E1C7C3B21

  description UW-RN

  address-family ipv4 unicast

   route-policy UW in

   route-policy TIER-A-OUT out

  !

!

neighbor 9.7.8.70

  remote-as 1200

  use neighbor-group OUR-MEMBER

  password encrypted 01342C0742525238795F5C

  description UW- RN-BACKUP

  address-family ipv4 unicast

   route-policy UW in

   route-policy TIER-A-OUT out

  !

!

!

The issue is that they are advertizing their network block on the back up interface, but no traffic is coming in from our side.  The want us to enable max paths = 2 on our end for teh back up link to send traffic. 

My understanding is that by doing this they would have two paths in their forwarding table for every prefix learnt from us. Can some body point out how can this be achieved. I mean what commands are to be used to enable max path = 2 and under which bgp peering?

regards

[rsimoni]

Hi Jalal,

From what you describe the issue is that you would like to use both the eBGP links from your router to the customer one(s), as per customer request.

So, if you enable max path = 2 YOUR router will have 2 paths in the RIB/FIB for the customer prefix(es) and not the customer one.

The feature is called BGP Multipath and has to be configured in the BGP global or address-family context.

the command is

maximum-path n (where n is 2 if you want to import 2 paths)

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml#bgpmpath

As the document says the imported paths MUST have the same caracteristics for multipath to work.

Note that when you enable it your router will load-balance all the prefixes which are learned from multiple next hops - meaning that other customers dual-homed to this router will start see incoming traffic from the 2 links.

If your customer wants to load balance in the outgoing direction they have to configure the same feature under their BGP process (provided that the 2 eBGP links are terminated to the same router).

Riccardo

[Miroslav Berkov]

Hi Jalal,

just try http://ospfmon.com services to check up your router config

[Vasileios Bouloukos MSc, ITIL, CCIE]

Does your network use Route Reflector RR?

If you use RR then you can not achieve load balance with the configuration described by Riccardo.