Re: [mpls] Review of draft-mirsky-mpls-bfd-directed-03

Nobo Akiya <nobo.akiya.dev@gmail.com> Mon, 17 August 2015 00:08 UTC

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Date: Mon, 17 Aug 2015 09:08:19 +0900
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From: Nobo Akiya <nobo.akiya.dev@gmail.com>
To: Gregory Mirsky <gregory.mirsky@ericsson.com>
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Cc: Ross Callon <rcallon@juniper.net>, mpls <mpls@ietf.org>, "draft-mirsky-mpls-bfd-directed@tools.ietf.org" <draft-mirsky-mpls-bfd-directed@tools.ietf.org>
Subject: Re: [mpls] Review of draft-mirsky-mpls-bfd-directed-03
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Hello Greg, Mach,

As I indicated in a separate email, one remaining comment is minor and I do
not believe it is a blocker before this document becoming adopted as a WG
document. If you can address it in the next revision after it becoming a WG
document, I'm happy.

Regards,
Nobo

On Sun, Aug 16, 2015 at 12:26 PM, Nobo Akiya <nobo.akiya.dev@gmail.com>
wrote:

> Hi March, Greg,
>
> My apologies for very delayed response.
>
> Please see in-line with [NOBO].
>
> Note I've snipped out sections that I accept your response.
>
>
>> > Section 2
>> >
>> > o if reverse direction is in Down state, the head-end node would not
>> >    receive indication of forward direction failure from its egress
>> >    peer.
>> >
>> > [NOBO] I found above to be slightly unclear in 2 aspects.
>> >
>> > Since this section is describing the limitations of using BFD on an
>> > unidirectional explicitly routed path, what does "if reverse direction
>> is in Down state" mean?
>> >
>> > Additionally, "would not receive indication of forward direction
>> > failure from its egress peer" is a bit cryptic. If the egress peer
>> > detected that forward direction failed (e.g., BFD session timed out),
>> > then the egress peer will send few BFD control packets with DOWN
>> > state, IP routed. Thus the ingress peer will notice the problem of the
>> forward direction.
>> >
>> > Readers can likely benefit from having this bullet point better
>> clarified.
>> >
>>
>> GIM≫ Would the following wording be more deterministic:
>>    o  failure detection on the reverse path cannot reliably be
>>       interpreted as bi-directional failure and thus trigger, for
>>       example, protection switchover of the forward direction;
>>
>>    o  if a failure of the reverse path being ignored, the ingress node
>>       would not receive indication of forward direction failure from its
>>       egress peer.
>>
>>
>
> [NOBO] The second bullet may create more confusion. Can we keep just the
> first bullet and add a bit of clarifications as below?
>
> * a failure detection on the reverse path cannot reliably be
>   interpreted as bi-directional failure and thus trigger, for
>   example, protection switchover of the forward direction.
>   When the BFD session on the egress node declares a failure
>   (i.e., forward direction failure), the failure may or may not
>   reach the ingress node. Therefore, the BFD session on the
>   ingress node declaring failure may be a result of just the
>   reverse path failure or both forward and reverse paths
>   failures.
>
> Regards,
> Nobo
>