bgp load balancing just between 1 bgp group

[from88]

Hello,

I got a connectivity to ISP containing 3 eBGP neighbours. Two of them are in the same BGP group - same ISP, same AS. And other one is other ISP with different AS.

My goal is to load balance just between the neighbors in the BGP group - because they're from the same ISP. For that i need to make a as-path relax, because even two neighbours in the same ISP, the BGP AS'es the route traverses are different, but the count is the same.

So for that i explicitly set multipath parameter under BGP group, then under the bgp process address-family ipv4 unicast i set these line:

maximum-paths ebgp 2 selective

and

bgp bestpath as-path multipath-relax 

And seems the routers doesnt respect the selective keyword. It start to balane even between the third neigbour which doesnt have multipath tag enabled.

Any other ways to ensure the load balancing just between two particular neighbours ?

[balaji.bandi]

Are they peering with same router on your side or differrent routers ?

how about with the command  maximum-path 2  towards same ISP config (with 2 different Links and peers) ?  or post the config to understand.

[Giuseppe Larosa]

Hello @from88 ,

use

neighbor x.x.x.x local-preference 200 for the two eBGP peers in  same AS that you want to prefer

by the way the check is only on the peering AS (the leftmost in AS path string )  so you should be fine with

maximum-paths 2

with no other additional knobs

Hope to help

Giuseppe

[from88]

hello,

Thanks, but if i would set local pref two that two neighbours, the third one - other ISP would be excluded from sending the traffic, because local pref would win on the other 2 neighbours. My goal is to share the traffic between that three neighbours, where two resides in the same ISP but in different availability zones, and the other one is just a separate ISP with one link.

I see that this could be impossible to reach in my case. So the only thing left is to create a separate inbound policies for neighbours in the same ISP to prefer different subnets, but my first goal is to have the same policies just to improve bgp process configuration to create load balancing per bgp isp group.

@balaji.bandi  Just maximum-paths 2 doesnt really work - because some routes from that two neighbours comes via different AS'es. So it doesnt not load balance ALL routes, just small portions. So i thought that bgp as path relax command would help. But after this, i see that router takes into load balancing that other one separate ISP also, because it has same count of ASes too.. 

And it's a bug or no - i dont know - that selective load balancing starts to doesnt work - when bgp as path relax command is entered.