RFC 5880, "Bidirectional Forwarding Detection (BFD)", June 2010

Errata ID: 7082
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: Glebs Ivanovskis
Date Reported: 2022-08-12
Verifier Name: John Scudder
Date Verified: 2022-09-06

Section 6.7.3 says:

Otherwise (bfd.AuthSeqKnown is 0), bfd.AuthSeqKnown MUST be set to
1, and bfd.RcvAuthSeq MUST be set to the value of the received
Sequence Number field.

Replace the contents of the Auth Key/Digest field with the
authentication key selected by the received Auth Key ID field.  If
the MD5 digest of the entire BFD Control packet is equal to the
received value of the Auth Key/Digest field, the received packet
MUST be accepted.  Otherwise (the digest does not match the Auth
Key/Digest field), the received packet MUST be discarded.

It should say:

Replace the contents of the Auth Key/Digest field with the
authentication key selected by the received Auth Key ID field.  If
the MD5 digest of the entire BFD Control packet is not equal to the
received value of the Auth Key/Digest field, the received packet
MUST be discarded.

Otherwise, the packet MUST be accepted, bfd.AuthSeqKnown MUST be set to
1, and bfd.RcvAuthSeq MUST be set to the value of the received
Sequence Number field.

Notes:

1. Don't manipulate bfd.AuthSeqKnown and bfd.RcvAuthSeq before Auth Key/Digest check.
2. Explicitly mention what bfd.AuthSeqKnown and bfd.RcvAuthSeq must be set to in both cases (bfd.AuthSeqKnown is 0 and bfd.AuthSeqKnown is 1).

Based on email exchange: https://mailarchive.ietf.org/arch/msg/rtg-bfd/lDxFfNpqo4kwuNEUY0AbjMBb8JU/

(See also https://mailarchive.ietf.org/arch/msg/rtg-bfd/Ngf3Chmpy_EqNPlmuMZOslayy2E/)

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