BGP Load Balancing Question Single ISP redundant links

[AlexD2030]

Question with BGP load balancing.  

Unless I missed something, is it possible to use BGP load balancing for redudnant links to single ISP?  I have read > https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html and the document has load balancing to a single ISP, using and IGP (EIGRP in doc) / (Load Sharing with the Loopback Address as a BGP Neighbor).  Looking for some explanation as to why BGP will not load balance when using BGP, when I lab this. I found information stating that the Router ID of the next hop should be different.  If I use the neighbor command and set the next hop as the other side of the interface, NOT the loopback, would this not suffice for load balancing?BGP, 

 

[ngkin2010 · Accepted solution]

Hi,

Did you try to configure "maximum-paths 2" under "router bgp <AS>"?

[AlexD2030]

Welp that was fairly simple. Now working properly.  I thought maximum paths effect iBGP not eBGP, I was wrong. I only had bgp bestpath as-path multipath-relax, which I am now re-reading about. Seems that was the wrong command too.

Thanks.

[ngkin2010]

Hi,

The command "bgp bestpath as-path multipath-relax" is used to load balance between the routes from different AS (e.g. 0.0.0.0/0 from AS1 and 0.0.0.0/0 from AS2). By default, Cisco IOS does not allow load balance between AS.

So if you have multi-home with multiple ISP, you will need to issue both commands.


Ref: https://community.cisco.com/t5/routing/bgp-bestpath-as-path-multipath-relax/td-p/3709661

By default, IOS does not allow you to load balance between multiple paths received from different AS numbers. This commands changes this default behavior. I have seen some customers using it to load balance between two default routes (0/0) received from two upstream ISPs.

[Joseph W. Doherty]

Yes, unlike IGP, where Cisco generally default to a ECMP value of four (or six?), BGP defaults to only one.

[omz]

Hi 

bgp needs the routes in the routing table first before it will put in the bgp table

instead of igp you could use static routes to put in the routing so bgp will have them in bgp table

from that doc - 

By default, Border Gateway Protocol (BGP) selects only a single best path and does not perform load balancing. This document shows how to perform load sharing in different scenarios with the use of BGP. For additional information about load balancing, refer to How Does Load Balancing Work?.

load balancing vs load sharing 

https://ipwithease.com/load-balancing-vs-load-sharing/