Re: A question about RFC5884

"Carlos Pignataro (cpignata)" <> Tue, 18 July 2017 10:25 UTC

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From: "Carlos Pignataro (cpignata)" <>
To: Mach Chen <>
CC: "Reshad Rahman (rrahman)" <>, "" <>
Subject: Re: A question about RFC5884
Thread-Topic: A question about RFC5884
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Date: Tue, 18 Jul 2017 10:25:38 +0000
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Hi Mach,

I had not suggested it, but I think that idea has merit. If there are enough updates needed to the spec based on additional running-code learning, or ambiguities that are causing interoperable confusion, the net of a -biz can be positive.

When that same idea crossed my mind, I thought that the question should be part of a larger consideration from the chairs of maturity, pipeline, and advancement of BFD specs, and not taken in isolation. 5884 seems to require localized fixes only.


Sent from my iPad

On Jul 18, 2017, at 9:14 AM, Mach Chen <<>> wrote:

Hi Carlos,

Do you suggest to do a 5884-bis?

Best regards,

From: Carlos Pignataro (cpignata) []
Sent: Monday, July 17, 2017 10:56 PM
To: Mach Chen
Cc: Reshad Rahman (rrahman); Ashesh Mishra;<>
Subject: Re: A question about RFC5884

Hi Mach,

On Jul 17, 2017, at 10:42 AM, Mach Chen <<>> wrote:
Hi Carlos,

Thanks for sharing your thoughts.

IMHO, it may not be necessary to consider this LSP Ping based bootstrapping as normal LSP ping.

Would it be considered an abnormal LSP Ping? :-)

If RFC 5884 references RFC 4379, I'd expect it means an LSP Ping as specified in 4379, or those processes for LSP Ping be updated.

Sent from my iPad

And since both the ingress and egress LSR process the echo messages in the context of BFD session establishment, it should be no problem to process as described in RFC5884.

BTW, RFC5884 does not specify which reply mode will be used :)

Best regards,

From: Carlos Pignataro (cpignata) []
Sent: Monday, July 17, 2017 6:58 AM
To: Reshad Rahman (rrahman)
Cc: Mach Chen; Ashesh Mishra;<>
Subject: Re: A question about RFC5884


I also agree with the conclusion of this thread in regards to what RFC 5884 says. However, can that be in conflict with RFC 8029's procedures, in which the reply might be expected?

There is certainly no need to carry any information in an MPLS LSP Ping reply, since at that point the discriminatory are already carried in BFD. The reply might be important only if FEC validation fails.

I wonder though if the text of "The egress LSR MAY respond with an LSP Ping Echo" intended to convey that whether to reply or not depends on the value of the Reply Mode field in the Echo request.

Sent from my iPad

On Jul 16, 2017, at 6:22 PM, Reshad Rahman (rrahman) <<>> wrote:

My take too is that the RFC is pretty clear that Echo reply from egress
LSR is not mandatory.


On 2017-07-16, 4:29 PM, "Rtg-bfd on behalf of Mach Chen"
<<> on behalf of<>> wrote:

Hi Ashesh,

Thanks for your prompt response, we're on the same page!

Best regards,

???: Ashesh Mishra []
????: 2017?7?16? 22:26
???: Mach Chen
??: Re: A question about RFC5884

That's how I read it ... assuming that proper handling of the LSR echo
gracefully dropping it on rx.


On Jul 16, 2017, at 3:58 PM, Mach Chen <<>> wrote:

Hi BFDers,

We met a multi-vendor interoperate issue recently, it's about whether
an Echo
reply is necessary.

In Section 6 of RFC5884, 2nd paragraph

"... The egress LSR MAY respond with an LSP Ping Echo
 reply message that carries the local discriminator assigned by it for
 the BFD session."

>From the above text, my understanding is that an Echo reply is
optional, the
egress LSR can freely to return or not return an Echo reply, and the
Ingress LSR
should not expect there MUST be an Echo reply, but if there is one, it
handle it properly.

Is my understanding correct?