RFC 9790: IANA Registry and Processing Recommendations for the First Nibble Following a Label Stack
Recent RFCs 2025-07-11
Summary:
This document creates a new IANA registry (called the "Post-Stack
First Nibble" registry) for the first nibble (4-bit field)
immediately following an MPLS label stack. Furthermore, this document
presents some requirements for registering new values and making the
processing of MPLS packets easier and more robust.
The relationship between the IANA "Post-Stack First Nibble" registry
and the "IP Version Numbers" registry (RFC 2780) is described in this
document.
This document updates RFC 4928 by deprecating the heuristic method
for identifying the type of packet encapsulated in MPLS.