IANA Registry and Processing Recommendations for the First Nibble Following a Label Stack
RFC 9790, “IANA Registry and Processing Recommendations for the First Nibble Following a Label Stack”, is a Proposed Standard document published in July 2025 by K. Kompella, S. Bryant, M. Bocci, G. Mirsky, L. Andersson, J. Dong. It updates RFC 4928. The canonical text is published by the RFC Editor.
Abstract
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.
What “Proposed Standard” means
An entry-level standards-track specification: stable, peer-reviewed and a solid basis for implementation, though it may still evolve before becoming an Internet Standard.
The canonical text of RFC 9790 is hosted at rfc-editor.org. Available in HTML,TXT,PDF,XML.
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