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New Member

bgp load sharing between iBGP and eBGP routes

I would like to do load sharing between one iBGP path and one EBGP path :

---------R3--------

(EBGP) (EBGP)

/ \

R1------(iBGP)-------R2

/ \

R3 will advertise only one LAN to R1 and R2.

I would like to achieve load balancing from R1 and from R2 to go to R3 LAN

So R1 directly to R3 and R1 to R3 through R2

As the EBGP route is prefered I can't do this load balancing.

I can see the following solutions :

1- To configure an EBGP multihop session between R1 and R3, then to apply in the BGP session "maximum-paths 2"

2- Or to configure maximum-paths eibgp 2 but it requires the 12.2(4)T

Is that right ? Is there another solution ?

Thanks for any help

  • Other Network Infrastructure Subjects
3 REPLIES
New Member

Re: bgp load sharing between iBGP and eBGP routes

For a better comprehension :

R3 is connected both to R1 and to R2

Bronze

Re: bgp load sharing between iBGP and eBGP routes

Other than breaking up the LAN prefix that R3 advertises, I can't think of a practical way to do this offhand. Load sharing between IBGP and EBGP isn't possible to my knowledge, though someone else may be able to correct me. Load sharing among EBGP paths has been available for a while, and load sharing among IBGP paths was introduced recently, but I don't recall ever seeing anything about load sharing between IBGP and EBGP paths.

What I mean by breaking up the prefix is this. Assume the LAN prefix is 10.1.1.0/24. You could have R3 advertise 10.1.1.0/25 to R1 and 10.1.1.128/25 to R2, which R2 would also advertise to R1. R1 would then send traffic destined to 10.1.1.0/25 directly to R3 and traffic destined to 10.1.1.128/25 would be routed via R2.

You'd want R3 to continue announcing the entire prefix (10.1.1.0/24) to both R1 and R2 (like it is currently) for redundancy purposes. So if the R1 <-> R2 link fails, traffic for 10.1.1.128/25 will follow the 10.1.1.0/24 route directly to R3.

Whether or not this type of load sharing is possible in your environment depends on the traffic patterns. The LAN prefix can be broken up any way you want, even into /32's if necessary. But if all or most traffic is sourced from or destined to a single host on the LAN, this won't do you any good.

Gold

Re: bgp load sharing between iBGP and eBGP routes

eiBGP load sharing really only works withing vpn environments:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080087c21.html#1027184

So, I wouldn't count on it helping you out here.... Configuring the multihop eBGP session seems to be your best bet, if that will work. You have to know about the next hop through both R2 and the connected link, and the igp path has to have the same cost.

Russ.W

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