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Cell Relay Retreat>MPLS WG Archive>month:2003-Mar> msg00354



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[PWE3] MPLS PID

  • From: Eric Rosen <erosen@cisco.com>
  • Date: Thu, 27 Mar 2003 13:26:02 -0500
  • cc: "'curtis@fictitious.org'" <curtis@fictitious.org>, "'Thomas D. Nadeau'" <tnadeau@lucidvision.com>, "'George Swallow'" <swallow@cisco.com>, "W. Mark Townsley" <townsley@cisco.com>, "Andrew G. Malis" <Andy.Malis@vivacenetworks.com>, "'mpls@uu.net'" <mpls@UU.NET>, tnadeau@cisco.com
  • User-Agent: EMH/1.14.1 SEMI/1.14.3 (Ushinoya) FLIM/1.14.3(Unebigoryōmae) APEL/10.3 Emacs/21.2(sparc-sun-solaris2.8) MULE/5.0 (SAKAKI)


Shahram> First  of all  I meant  computing  CRC over  the first  20 byte  of
Shahram> payload header and  comparing it to the suspected  IP CRC in octets
Shahram> 11 and 12 of the payload. If  they match then it is IPv4, if not it
Shahram> is something else (similar procedure for IPv6)

Shahram> Secondly  I am  proposing it  now. Is  there a  problem? I  feel my
Shahram> procedure is far superior to just checking 4 bits to decide whether
Shahram> the payload is IP or not. 

Certainly it's  not superior in  terms of the  amount of computation  or the
number of memory accesses required ;-)

Architecturally,  it doesn't  seem  superior  either.  It  is  based on  the
assumption that the one's complement sum of the first 20 bytes of a non-IPv4
payload will not be zero.  And it doesn't seem to handle IPv6.

  • References: