RFC 5340, "OSPF for IPv6", July 2008

Note: This RFC has been updated by RFC 6845, RFC 6860, RFC 7503, RFC 8362, RFC 9454

Errata ID: 7649
Status: Rejected
Type: Technical
Publication Format(s) : TEXT
Reported By: Owen DeLong
Date Reported: 2023-09-19
Rejected by: John Scudder
Date Rejected: 2024-01-11

Section A.3.3 (in part) says:

Interface MTU
      The size in bytes of the largest IPv6 datagram that can be sent
      out the associated interface without fragmentation.  The MTUs of
      common Internet link types can be found in Table 7-1 of [MTUDISC].
      Interface MTU should be set to 0 in Database Description packets
      sent over virtual links.

It should say:

Interface MTU
      The size in bytes of the largest IPv6 datagram that can be sent
      out the associated interface without fragmentation.  The MTUs of
      common Internet link types can be found in Table 7-1 of [MTUDISC].
      Interface MTU should be set to 0 in Database Description packets
      sent over OSPF virtual links. This rule should not be applied to tunnel
      or other software interfaces.

Notes:

OSPF Virtual links carry only OSPF packets so MTU negotiation is not needed and this provision makes sense. For interfaces that have an actual MTU, even though they may be "virtual" interfaces, they are not "virtual links" in the intended meaning of this paragraph. As such, this change will provide clarification and remove ambiguity from the current standard. At least one popular router vendor implements this RFC as MTU = 0 sent on all GRE interfaces which results in incompatibilities with most other router platforms which expect an actual value. The router vendor points to this provision in the RFCs as justification for their implementation. It is (arguably) a legitimate, if nonsensical interpretation of the existing text.
--VERIFIER NOTES--
See discussion at https://mailarchive.ietf.org/arch/msg/lsr/mrmkQt9ETTYemukBzl6K_FmgHps/

It seems as though there is not clear consensus for the proposed change or even to make a similar change; as such the normal WG process (internet draft, WG consensus) is a better way to pursue the goal.

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