BGP Load Balancing Mechanism

Learn the multiple use cases of BGP Load-Balancing Mechanism in live network

So By default BGP Protocol does not support load balancing, whenever BGP Protocol gets multiple path for a same prefix it just choose a single best path and install in Routing Table

We can perform load-balancing for both IBGP and EBGP neighborship.

we can force a router to have multipath for a same prefix using Load-Balancing feature that is Maximum-path feature, so if we talk about EBGP load-balancing works with only same ISP, if we are getting same prefix with different ISP or Different BGP-AS then this Maximum-path will not work to perform load-balancing, Maximum path works when we have 2 different path but have same ISP connected to customer EDGE router.

  1. So in this first case we have same ISP with same BGP-AS number 

 

So initially we can see Router R3 is getting prefix from both routers but only one path via 13.0.0.01 is best, now let’s configure Maximum-path Feature to make 2 path as best path

  • R3(config)#router bgp 300

  • R3(config-router)#maximum-paths 2

Now here we see *m  that indicates this is counted as Multi-path and if we see the routing table we can see both routes there as best path

So this is how we can perform load-balancing if we have same ISP.

  1. Lets us do with Different ISP/Different BGP-AS number and will see what will be the output after using Maximum-path feature.

Now let’s run the same feature here and will see what will be effect

  • R3(config)#router bgp 300

  • R3(config-router)#maximum-paths 2

And here we have the same output even after running Maximum-path feature for Different BGP-AS number.

Command set for IOS and IOS-XR

OS has a limit of 32 Multipath and IOS-XR can suppIort upto 64 Multipath

EBGP-IOS

EBGP-IOS-XR

  • Router BGP 300

  • maximum-paths 2

  • router bgp 300

  • address-family ipv4 unicast 

  • maximum-paths ebgp 2

IBGP-IOS

IBGP-IOS-XR

  • Router BGP 300

  • maximum-paths ibgp 2

  • router bgp 300

  • address-family ipv4 unicast 

  • maximum-paths ibgp 2

 

But even after getting installing 2 Multipath as best path in BGP and Routing table , a BGP router can only send a single best path to next neighbor, so in next topic Additional path we will see how we can propagate Multi-best path to other router. 

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