Loopback issue on ASBR

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Oct 1st, 2007
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Dear All,

Can anyone help in understanding the impact of using public IP on loopback interface. Is it possible to use the same loopback IP for eBGP peering and OSPF router-id. What would be the impact on routing decisions? Shall we use OSPF neighbour IP address as router-id in OSPF config (Forced way)?

Please share your observations and comments.

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paul.matthews Mon, 10/01/2007 - 02:25
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You can use the same address for OSPF router ID and for BGP Peering, The use of the address should have no effect upon routing decisions.

Bear in mind with BGP that if you are using a loopback for peering, you and the neighbouting AS need to have multihop configured, and you need routes to get to and from each other's loopback addresses (assuming they are doing the same)

The real issue I can see is that you have a loopback interface that may be reachable externally, and your firewalls etc should help with that. You have to have *something* that is routable somewhere!

Kevin Dorrell Mon, 10/01/2007 - 02:52
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Just an additional comment. If you have synchronization, then be aware that BGP has a funny idea of what constitutes synchronization where the underlying IGP is link-state like OSPF. For each route, you must have the same BGP rid as the OSPF rid originating the route, otherwise the route will get dropped.

Kevin Dorrell



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