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Loopback addresses and BGP

Posted on 2009-05-08
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Last Modified: 2012-05-06
I need a clarification to make is it correct to say that use of loopback interfaces as BGP source address is recommended since the loopback interface  unlike a physical Interface / subinterface does not go down . As such this reduces the flapping on the BGP tables in the network
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Question by:sgknoc
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by:JFrederick29
ID: 24335961
Yes, assuming the router has multiple physical interfaces or paths to which the loopback can be reached.  If the router only has one physical interface or one path to it's neighbor(s), using a loopback doesn't provide any further stability.
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by:lanboyo
ID: 24335981
Well, certainly true on iBGP connections. eBGP requires connectivity to your peer, and usually this is on a single interface anyway.
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donnlee earned 500 total points
ID: 24342918
The following are best practices for BGP and addressing:
Case1: When configuring an iBGP session, use/configure the other router's loopback address.
Case2: When configuring an eBGP session, and there is only one link to the other router, use the other router's physical interface address (usually the address on the other side of the /30 or /31 link).
Case3: When configuring an eBGP session, and there are multiple links to the other router, use eBGP multihop and the other router's loopback address.

Because a router can have both iBGP and eBGP sessions, the above rules use the "other router" terminology.

All routers should be configured with a loopback address because IGPs (OSPF, IS-IS) will use that address for the router-id, and you almost always run BGP with an IGP.

I have been doing BGP for 14 years at Cisco and later at large Internet companies.
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