Load balancing is not possible in a multihomed environment with two ISPs

[Ibrahim Jamil]

Hi all

as per cisco config example :

Load Sharing When Multihomed to Two ISPs Through Multiple Local Routers

Load balancing is not possible in a multihomed environment with two ISPs. BGP selects only the single best path to a destination among the BGP paths that are learned from different ASs, which makes load balancing impossible. But, load sharing is possible in such multihomed BGP networks. On the basis of predetermined policies, traffic flow is controlled with different BGP attributes.

Does the "maximum-path" solve the above statements 

thanks 

[Carlos Villagran]

Hi!

This is more about a design preference. Some hosts could use router A as gateway while router A prefer certain ISP as output and other traffic goes B, etc. Other tools such as PBR can be of help too. 

However, if we are talking about load-balancing per packet trough both ISPs then I do not think that is a recommended behavior since you will have many packets reaching destination out of order.

Hope it helps, best regards!

JC

[Ibrahim Jamil]

Hi carlos

Does the "maximum-path" solve the above statements 

[Carlos Villagran]

Hi!

Yes, it will allow you to have more than 1 route to the same destination installed in your routing table. Please refer to the following cisco documentation for the BGP load-sharing:

http://www.cisco.com/c/en/us/td/docs/ios/12_2sx/feature/guide/fsxeibmp.html

maximum-paths eibgp

To configure multipath load sharing for external BGP (eBGP) and internal (iBGP) routes, use themaximum-paths eibgp command in address family configuration mode. To disable multipath load sharing for eBGP and iBGP routes, use the no form of this command.

maximum-paths eibgp number [import number]

no maximum-paths eibgp number [import number]

Hope it helps, best regards!

JC

[Joseph W. Doherty]

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Posting

You need it, but it alone will not use distribute traffic to different AS BGP peers connecting to the same router.  You'll also need "bgp bestpath as-path multipath-relax".

More info: https://supportforums.cisco.com/discussion/10144976/where-i-can-find-info-bgp-bestpath-path-multipath-relax