IBGP and IGP interaction

Radha Gowda <rxg@proteon.com> Fri, 26 May 1995 16:47 UTC

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From: Radha Gowda <rxg@proteon.com>
Subject: IBGP and IGP interaction
To: bgp@ans.net
Date: Fri, 26 May 1995 12:23:03 -0400 (EDT)
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I am a bit confused with IBGP and IGP interaction.  I'd appreciate
any clarifications.

          AS 1             AS 2
         -----            -----
         | 1 | -----/---- | 2 |
         -----            -----
           \                /
 -----------\--------------/-----------
             /            \      AS 3
              \          /
             -----     -----
             | 4 |--/--| 3 |  (the connection between 3 and 4 could be
             -----     -----   direct or many hops inbetween)

                  IBGP and OSPF/RIP


IBGP is used only for exchanging routing information across an AS, and 
the updates should not be used to install routes in the forwarding table.
This makes sense, if the AS is a transit AS and with automatic tag 
generation, the OSPF external routes will not even be considered while 
sending updates to external neighbors.

Suppose there is already a BGP readvertisable route (learnt from EBGP)
in the forwarding table,  and we learn an alternate path from IBGP 
that we consider as well although not the best path.  What is the correct 
behaviour when the external path goes away?

Or suppose the path learnt from IBGP is a better path.  So should the 
BGP route be deleted from the forwarding table?  Or should it be deleted
only if an internal path exists to the route?

Thanks,
Radha

IBGP and IGP interaction Radha Gowda
Re: IBGP and IGP interaction kannan
Re: IBGP and IGP interaction Radha Gowda