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Re: Cisco - ip verify unicast reverse-path

  • From: Mark Prior
  • Date: Sun Feb 13 08:28:49 2000

     And then there is http://www.cisco.com/warp/public/707/newsflash.html.  It
     says that the RPF check is based on CEF.  I'm not familiar with CEF and
     want to clarify something about unicast RPF.  If the source address of a
     packet arrived on an interface that would not be the preferred route for
     that address but is one of the less-preferred routes would the packet get
     dropped?

Nope it has to be the preferred route.

     If, as I hope, it would not, I don't understand the argument that it
     doesn't work for multi-homed connections.  Such systems should be
     advertising their routes over all connections - thus the routes should
     appear on all paths outbound from the multi-homed systems (less any long
     prefix filtering being done by the upstreams).

I agree it would be more helpful if the test was "a route exists"
instead of "the best route" as I have seen it cause havoc with
customers who have multiple links to us and get the MEDs wrong.

Mark.





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