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FW: Next Hop Attribute

  • From: Charles Smith
  • Date: Thu Mar 29 09:40:04 2001

re-posted for broader audience:

My apologies if this has been discussed recently...

Is there a collective wisdom as to why the BGP RFC makes the statements that
it does about the BGP next hop attribute? Specifically:

(From RFC 1771): "A BGP speaker must never advertise an address of a peer to
that peer
  as a NEXT_HOP, for a route that the speaker is originating.  A BGP
  speaker must never install a route with itself as the next hop.

  When a BGP speaker advertises the route to a BGP speaker located in
  its own autonomous system, the advertising speaker shall not modify
  the NEXT_HOP attribute associated with the route.  When a BGP speaker
  receives the route via an internal link, it may forward packets to
  the NEXT_HOP address if the address contained in the attribute is on
  a common subnet with the local and remote BGP speakers."

At routers that have EBGP session injecting routes into its own AS on Cisco
routers we set the next-hop-self attribute to eliminate synchronization
issues, but I'm curious as to why the RFC made these requirements in the
first place?

Thank you for any brain cycles spent on this.

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