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RFC 5884, "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)", June 2010

Source of RFC: bfd (rtg)

Errata ID: 5085
Status: Verified
Type: Technical

Reported By: Balaji Rajagopalan
Date Reported: 2017-08-11
Verifier Name: Deborah Brungard
Date Verified: 2017-12-15

Section 6 says:

   On receipt of the LSP Ping Echo request message, the egress LSR MUST
   send a BFD Control packet to the ingress LSR, if the validation of
   the FEC in the LSP Ping Echo request message succeeds.  This BFD
   Control packet MUST set the Your Discriminator field to the
   discriminator received from the ingress LSR in the LSP Ping Echo
   request message.  The egress LSR MAY respond with an LSP Ping Echo
   reply message that carries the local discriminator assigned by it for
   the BFD session.  The local discriminator assigned by the egress LSR
   MUST be used as the My Discriminator field in the BFD session packets
   sent by the egress LSR.

   The ingress LSR follows the procedures in [BFD] to send BFD Control
   packets to the egress LSR in response to the BFD Control packets
   received from the egress LSR.  The BFD Control packets from the
   ingress to the egress LSR MUST set the local discriminator of the
   egress LSR, in the Your Discriminator field.  The egress LSR
   demultiplexes the BFD session based on the received Your
   Discriminator field.  As mentioned above, the egress LSR MUST send
   Control packets to the ingress LSR with the Your Discriminator field
   set to the local discriminator of the ingress LSR.  The ingress LSR
   uses this to demultiplex the BFD session.

It should say:

On receipt of the LSP Ping Echo request message, the egress LSR
MUST send a BFD Control packet to the ingress LSR, if the
validation of the FEC in the LSP Ping Echo request message
succeeds.  This BFD Control packet MUST set the Your Discriminator
field to the discriminator received from the ingress LSR in the LSP
Ping Echo request message. The local discriminator assigned by the
egress LSR MUST be used as the My Discriminator field in the BFD
session packets sent by the egress LSR.

The ingress LSR follows the procedures in [BFD] to send BFD Control
packets to the egress LSR in response to the BFD Control packets
received from the egress LSR.  The BFD Control packets from the
ingress to the egress LSR MUST set the local discriminator of the
egress LSR in the Your Discriminator field. The egress LSR
demultiplexes the BFD session based on the received Your
Discriminator field. As mentioned above, the egress LSR MUST send
Control packets to the ingress LSR with the Your Discriminator field
set to the local discriminator of the ingress LSR.The ingress LSR
uses this to demultiplex the BFD session.

The egress LSR processes the LSP Ping Echo request message in
accordance with the procedures defined in [RFC 8029]. The LSP Ping
Echo reply message generated by the egress LSR MAY carry the local
discriminator assigned by it for the BFD session, as specified in
section 6.1.

Notes:

Submitter:
It is not clear from the original text which of the following is optional:
- The egress MUST send a reply, but the discriminator in the reply is optional
- The reply itself is optional

Technically, the reply cannot be optional, because the egress needs to report LSP-Ping verification status to the ingress.

The proposed text recommends to include BFD discriminator in the reply. This was the intent of the original text.

Verifier:
The original Errata proposed correcting the last sentences of the second paragraph of Section 6. After discussion in the working group, it was agreed both the second and third paragraphs shown above of Section 6 needed to be revised to the three paragraphs of the corrected text shown above.

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