BGP virtual next hop load balance

Latest reply: Sep 25, 2019 06:48:14 403 1 5 2


As well-known, BGP gets mass of attributes to help choosing the best route which will be advertised to the BGP peers, In which scenario, load balancing is disabled by default. But for some special reasons, load balancing is required in BGP network. In this post, we are going to introduce a way to implement the load balancing, BGP virtual next hop.

 

BGP virtual next hop is commonly used in the scenario when ASBR advertise the routes received from the EBGP neighbor.

When the ASBR received the routes, the next hop is modified to a virtual next hop which had been imported into the IGP protocol, and advertising the modified routes to the IBGP neighbor, the IBGP neighbor will iterate the IBGP route into the virtual next hop, when the load balancing is realized on the IGP protocol, the BGP load balancing is realized.

 

As the example below

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R3 imports direct network 100.1.1.0/32 into BGP protocol, we can check the BGP routing table on R4,

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The result displays only the route comes from the AR1 is elected as the best and loaded into the routing table.

 

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The routing table checking result verify the conclusion.

 

 

To implement the BGP virtual next hop load balancing, we need add a same static route on all the ASBR routers, and import this static route into the IGP protocol. Then modify the next hop of the BGP routes received from the EBGP neighobor to the IP address which the static route towards to. When the IGP load balancing is realized, the IBGP routes will iterate to the imported virtual next hop, and BGP load balancing is realized.

 

1.      Add a static route towards to a virtual IP address(NOT used on the local router also on the remote router) on the AR1 and AR2,

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2.      configure a route policy to match the routes received from the EBGP peer(those wanted to be load balancing) and modify the next hop to the virtual IP;

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3.      import the static route into the IGP on both ASBR routers;

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4.      apply the route-policy;

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After these steps, check the BGP routing table on R4,

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As seen, the nexthop for 100.1.1.1/32 is 33.3.3.3 which is the virtual IP.

Checking the routing table on R4,


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as the figure shows, the traffic to the 100.1.1.1/32 are load balancing on the two links(out interface g0/0/0 and g0/0/1).

 


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Sprout
Created Sep 25, 2019 06:48:14 Helpful(0) Helpful(0)

Thank you for sharing!
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