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Cell Relay Retreat>MPLS WG Archive>month:2002-Apr> msg00203



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PHP

  • From: Eric Rosen <erosen@cisco.com>
  • Date: Tue, 23 Apr 2002 13:00:44 -0400
  • cc: Markus Jork <mjork@avici.com>, mpls@UU.NET
  • User-Agent: EMH/1.14.1 SEMI/1.14.3 (Ushinoya) FLIM/1.14.3(Unebigoryōmae) APEL/10.3 Emacs/21.2(sparc-sun-solaris2.6) MULE/5.0 (SAKAKI)

Eric> the problem with option 2  is that MPLS forwarding likes to obtain the
Eric> data link header as a result of the label lookup

Alia> But when you remove the last label, it is then necessary to do some IP 
Alia> header  processing  such  as   TTL  decrementing  or,  at  the  least,
Alia> inheriting. 

You are correct, but that does not contradict my statement. 

It's clear  that performing  the TTL  processing when you  pop off  the last
label requires manipulating  the IP header.  But the  MPLS specs say nothing
about using the contents of the header to help choose the outgoing data link
header, except  in the case  where the label  lookup indicates that  the LSR
itself is the packet's next hop.

So  an implementation  that is  compliant with  the  existing specifications
cannot necessarily  be relied  upon to  perform option 2  when a  single LSP
carries both IPv4 and IPv6, and PHP is used.

  • Follow-Ups:
    • PHP
      • From: Markus Jork <mjork@avici.com>
  • References:
    • PHP
      • From: Alia Atlas <aatlas@avici.com>