MPLS Label Stack
MPLS Label Structure
A label is a short, four-byte, fixed-length, locally-significant identifier 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
．TTL—Time to Live, 8 bits
A label is a short, four-byte, fixed-length, locally-significant identifier 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
．TTL—Time to Live, 8 bits
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