North American Network Operators Group
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Re: Who does source address validation? (was Re: what's that smell?)

  • From: Jeff Aitken
  • Date: Tue Oct 08 12:12:12 2002 
On Tue, Oct 08, 2002 at 11:49:41AM -0400, Jared Mauch wrote:
> > Of course, this is the IP RIB and may not include all the 
> > potential paths in the BGP Adj-RIBs-In, right?  As such, 
> > you've still got the potential for asymmetric routing to 
> > break things.
> 
> 	No, this is "if i have a path in fib" back to this source,
> transmit else drop;

Unless I'm missing something, that's what he said; fib == loc-rib
for the purposes of this discussion, and loc-rib is built from the
various adj-ribs-in.

That said, I'm curious to know how asymmetric routing can break
this.  As long as someone is sending (and you are installing) a
prefix that includes the source address this check will pass. 
If you don't have a route back to the source at all, that isn't
asymmetric routing, it's network partitioning, assuming the source
is legitimate.


--Jeff