Tuesday, May 10, 2011

MPLS Label Structure

A label is a short, four-byte, fixed-length, locally significant identifier, the which is Used to identify a Forwarding Equivalence Class (FEC). The label which is put on a particular packet represents the FEC to which that packet is assigned.



Label —Label Value (Unstructured), 20 bits . Carries the actual value of the label
0/2:IPv4/IPv6 Explicit NULL Label - must be sole label stack entry (forward based on IPv4/v6) .
1:Router Alert Label ;(need software process) .
3:Implicit NULL Label .

Exp —Experimental Use, 3 bits; currently used as a Class of Service (CoS) field.

S —Bottom of Stack, 1 bit . S-Bottom of Stack, 1 bit

TTL —Time to Live, 8 bits . TTL-Time to Live, 8 bits

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