BGP Load Sharing using loopback or maximum path

[vishaw jasrotia]

Hi,

My concern is regarding BGP load-sharing using loop-back and maximum path. In single homed (two link between two routers in different AS)  environment if I am doing load-sharing using loopback or maximum path, What exact difference is in between these two approaches ( loopback or maximum path). 

Thanks 

[paul driver]

Hello

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@vishaw jasrotia wrote:

Hi,

My concern is regarding BGP load-sharing using loop-back and maximum path. In single homed (two link between two routers in different AS)  environment if I am doing load-sharing using loopback or maximum path, What exact difference is in between these two approaches ( loopback or maximum path). 

Thanks 

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@vishaw jasrotia wrote:

My concern is regarding BGP load-sharing using loop-back and maximum path. In single homed (two link between two routers in different AS)  environment if I am doing load-sharing using loopback or maximum path, What exact difference is in between these two approaches ( loopback or maximum path). 

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Well TBH both require that the bgp peering adjacency are from the same ASN

Load sharing with loopbacks will have two physical interfaces from a rtr that will peer with two physical interfaces of its adjacent rtr over just a single bgp peering address (loopback) , This bgp peering that will be between each loopback of these rtrs would be reachable by either an IGP or static routes via their physical interfaces, so in the event of either of these physical interfaces failing the bgp peering doesn't drop and reachability isn't lost

Maximum paths is performed when you have dual bgp peerings to the same ASN over two physical interfaces, Now by default a setting of one maximum path is applied meaning ONLY the best route in the bgp rib from these two peerings will be entered into the route table however when this value is changed (maximum-paths x) and if all is equal in the bgp path selection multipaths to the same prefix can be populated into the route table

The decision to which interface to forward traffic for either of these features above would probably be based on either the lowest bgp id of each peering or maybe even the lowest neighbor id.

[vishaw jasrotia]

Thanks Paul.

Please correct me  what I understand from your explanation in term of load sharing using loopback and multipath. I have  a scenario  Router A and Router B. Both are connected using two links and in different AS.

1) If I go with BGP peering using loobpack. And I have a reachability  between two loopback using static routes. I can see in my routing table two path for loopback address. This way I can achieve load sharing.

2) If I go with maximum path. Then if the routes learned through BGP peers are matching attributes pattern then I able to see the more path in my routing table. This way I can also achieve load sharing.

The difference what I found between these two is, in loopback case I am installing two routes statically regardless of matching the BGP attribute pattern.  But in case of maximum path if two routes are matching in term of attributes, then only we are able to see the two routes in our routing table.

Thanks