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bgp multipath vs peering using loopback

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Mar 6th, 2014
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What is the benefit of using bgp multipath versus using loopback while peering to the same ebgp neighbor with multiple path?



In my lab scenario, I have 2 routers (R1 and R2) connected to each other using fa0/0 and fa0/1.  I have the choice of peering using loopback with update source lo and ebgp multihop  or peering using the the physical interface (fa0/0 and fa0/1) with the command maximum-path (multpath) to achieve load balancing.


What is the main advantage of using multpath command versus using the loopback method?

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cadet alain Thu, 03/06/2014 - 10:18
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Hi,

-peering with loopbacks will only install one path in the RIB and the BGP session will not be torn if one link fails

-using multipath will install 2 paths for the prefix in the RIB and so CEF will do the load-sharing on both paths


Regards


Alain



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Jon Marshall Thu, 03/06/2014 - 10:25
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Hi Alain


Just for your info.


There will only be one routing entry in the IP routing table but it will be a recursive route ie. the next hop will be the loopback which is reachable via both physical interfaces.


So the routing table will have one entry but CEF will resolve the recursive route and install two entries into the forwarding table one via each physical interface.


So it will actually use both links


Jon

cadet alain Thu, 03/06/2014 - 11:15
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Hi Jon,


Thanks for the info.


Regards


Alain




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