The MPLS WG Archive

[David Charlap <David.Charlap@marconi.com>]

Lee Garth wrote:
> 
>    What if an LSR node receives a packet with a label, and the LFIB in 
> the LSR doesn't have a matching entry for the label? Eg. there is no 
> entry in LFIB whose incoming label is the same as the label from the 
> receiving packet.

If you receive a packet with an unknown label, you should drop the packet.

To do anything else would result in undefined behavior.

Some people have entertained the idea of popping the label in this
situation.  This is bad, because a transit switch does not know the
nature of the packet under the label.  It might not be an IP packet. The
transit switch may not have routing information to the destination
(assuming it is IP.)  If there are inner labels, the transit switch may
not be able to handle them either.  (For example, VPN-identifying labels
are usually unknown to all but the PE routers.)

-- David


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