RFC 5036, "LDP Specification", October 2007Source of RFC: mpls (rtg)
Errata ID: 3416
Publication Format(s) : TEXT
Reported By: Jeff Wheeler
Date Reported: 2012-11-26
Rejected by: Adrian Farrel
Date Rejected: 2012-11-26
Section 3.1 says:
For a platform-wide label space, these SHOULD both be zero.
It should say:
For a platform-wide label space, these MUST both be zero.
See Section 2.2.2 text, "The last two octets of LDP Identifiers for platform-wide label spaces are always both zero."
The text in 2.2.2 is descriptive of the LDP identifiers, but not a requirement. The text in 3.1 describes how the LDP identifier is constructed.
The purpose of the "SHOULD" is to direct normal behavior, but not to absolutely require the use of zero in these two octets if a good reason can be found.
Furthermore, there is nothing that would actually prohibit the use of non-zero values. The identifier of a label space is a local matter and another node, seeing a label space identifier, should not make any assumptions about the label space (e.g., it being a global label space or not), nor should it really matter.