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Re: Penultimate Hop Popping

  • From: Eric Osborne <eosborne@cisco.com>
  • Date: Mon, 1 Sep 2003 18:36:52 -0400
  • Cc: mpls-ops@mplsrc.com
  • Resent-Date: Mon, 1 Sep 2003 19:42:54 -0400
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On Fri, Aug 29, 2003 at 10:24:22PM +0530, Bhavesh Modi wrote:
> 
> Hi all
> 
> As RFC 3031 says ( Section 3.16 ), If we do not use Penultimate Hop 
> Popping , the egress router will have to do two table lookups even in 
> case of only single label in label stack - one for determinig that it 
> has to pop the label & second traditional IP lookup. But instead of 
> only telling to pop the label can't we have one more field which gives 
> it next hop? If we have such thing, there is no need of penultimate hop 
> popping in case of stack of sigle label atleast. Has any vendor 
> implemented such technique?

What you're talking about is replacing explicit-null with a real label
value.  This is an implementation-specific thing at the tail; simply
advertise a non-null, real label for a given prefix or next-hop or
whatever.  One of the problems with this approach is dealing with the
payload of whatever's underneath this bottom label without looking at
the payload.




eric

> 
> -Bhavesh Modi
> MTech-ICT
> DA-IICT.
> Gandhinagar
> 
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