Ok to use both EGP & BGP from same AS on T3 Backbone

Thu Jun 25 23:02:30 UTC 1992

Hi.  A few weeks back this list was notified to cease peering with 
the NSFNET using both EGP and BGP from peers within the same AS. 
The T3 routing software now allows this configuration with no adverse 
side effects. 

However, please continue to avoid using both EGP and BGP to peer with 
the T1 NSFNET (from the same AS).  Thanks.

  --Steve Widmayer
    Merit/NSFNET

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 >Date: Tue, 2 Jun 92 10:19:22 EDT
 >From: skw
 >To: regional-techs
 >Subject: Please avoid EGP & BGP backbone peering from the same AS...
 >
 >Hi.  Some NSFNET sites are configured to run both EGP and BGP sessions with
 >the NSFNET from the same AS at the same time.  Please avoid this practice
 >and run only one or the other until further notice.  We have discovered
 >lost routes and black holing of traffic on the T3 backbone under such a
 >configuration.
 >
 >An excerpt from Curtis Villamizar <curtis at ans.net>:
 >
 > >Subject: mixing BGP and EGP at the same metric
 > >
 > >The problem arises when there is an EGP route and one or more
 > >alternate routes with equal policy metric (either EGP or BGP) and the
 > >EGP route is favored.  If the favored EGP route is lost and an
 > >alternate BGP route with the same metric exists, the alternate BGP
 > >route will always be advertised to the IBGP neighbors.  If an
 > >alternate EGP route exists, it will not be advertised and will not be
 > >installed.  Depending on which route is found first (hash table
 > >position dependent), the alternate route may not be installed.  The
 > >more alternate routes at the same metric, the more likely you are to
 > >have this problem.
 > >
 > >
 >
 >  --Steve Widmayer
 >    Merit/NSFNET
 >