Re: [RTG-DIR] Rtgdir last call review of draft-ietf-mpls-p2mp-bfd-06

[Joel Halpern <[e-mail]>]

What you say makes sense.  I think we need to acknowledge the inbound 
congestion risk, even if we choose not to try to ameliorate it.  Your 
approaches seems to address the outbound congestion risk from the root.

YOurs,

Joel

On 2/24/2024 6:25 PM, Greg Mirsky wrote:
> Hi Joel,
> thank you for the clarification. My idea is to use a rate limiter at 
> the root of the p2mp LSP that may receive notifications from the 
> leaves affected by the failure. I imagine that the threshold of the 
> rate limiter might be exceeded and the notifications will be 
> discarded. As a result, some notifications will be processed by the 
> headend of the p2mp BFD session later, as the tails transmit 
> notifications periodically until the receive the BFD Control message 
> with the Final flag set.  Thus, we cannot avoid the congestion but 
> mitigate the negative effect it might cause by extending the 
> convergence. Does that make sense?
>
> Regards,
> Greg
>
> On Sat, Feb 24, 2024 at 2:39 PM Joel Halpern <[e-mail]> wrote:
>
>     That covers part of my concern.  But....  A failure near the root
>     means that a lot of leaves will see failure, and they will all
>     send notifications converging on the root. Those notifications
>     themselves, not just the final messages, seem able to cause
>     congestion.  I am not sure what can be done about it, but we
>     aren't allowed to ignore it.
>
>     Yours,
>
>     Joel
>
>     On 2/24/2024 3:34 PM, Greg Mirsky wrote:
>>     Hi Joel,
>>     thank you for your support of this work and the suggestion. Would
>>     the following update of the last paragraph of Section 5 help:
>>     OLD TEXT:
>>        An ingress LSR that has received the BFD Control packet, as
>>     described
>>        above, sends the unicast IP/UDP encapsulated BFD Control
>>     packet with
>>        the Final (F) bit set to the egress LSR.
>>     NEW TEXT:
>>        As described above, an ingress LSR that has received the BFD
>>     Control
>>        packet sends the unicast IP/UDP encapsulated BFD Control
>>     packet with
>>        the Final (F) bit set to the egress LSR. In some scenarios, e.g.,
>>        when a p2mp LSP is broken close to its root, and the number of
>>     egress
>>        LSRs is significantly large, the control plane of the ingress LSR
>>        might be congested by the BFD Control packets transmitted by
>>     egress
>>        LSRs and the process of generating unicast BFD Control packets, as
>>        noted above.  To mitigate that, a BFD implementation that supports
>>        this specification is RECOMMENDED to use a rate limiter of
>>     received
>>        BFD Control packets passed to processing in the control plane
>>     of the
>>        ingress LSR.
>>
>>     Regards,
>>     Greg
>>
>>     On Thu, Feb 22, 2024 at 4:10 PM Joel Halpern via Datatracker
>>     <[e-mail]> wrote:
>>
>>         Reviewer: Joel Halpern
>>         Review result: Ready
>>
>>         Hello,
>>
>>         I have been selected as the Routing Directorate reviewer for
>>         this draft. The
>>         Routing Directorate seeks to review all routing or
>>         routing-related drafts as
>>         they pass through IETF last call and IESG review, and
>>         sometimes on special
>>         request. The purpose of the review is to provide assistance
>>         to the Routing ADs.
>>         For more information about the Routing Directorate, please see
>>         https://wiki.ietf.org/en/group/rtg/RtgDir
>>
>>         Although these comments are primarily for the use of the
>>         Routing ADs, it would
>>         be helpful if you could consider them along with any other
>>         IETF Last Call
>>         comments that you receive, and strive to resolve them through
>>         discussion or by
>>         updating the draft.
>>
>>         Document: draft-name-version
>>         Reviewer: your-name
>>         Review Date: date
>>         IETF LC End Date: date-if-known
>>         Intended Status: copy-from-I-D
>>
>>         Summary:  This document is ready for publication as a
>>         Proposed Standard.
>>             I do have one question that I would appreciate being
>>         considered.
>>
>>         Comments:
>>             The document is clear and readable, with careful
>>         references for those
>>             needing additional details.
>>
>>         Major Issues: None
>>
>>         Minor Issues:
>>             I note that the security considerations (section 6) does
>>         refer to
>>             congestion issues caused by excessive transmission of BFD
>>         requests.   I
>>             wonder if section 5 ("Operation of Multipoint BFD with
>>         Active Tail over
>>             P2MP MPLS LSP") should include a discussion of the
>>         congestion implications
>>             of multiple tails sending notifications at the rate of 1
>>         per second to the
>>             head end, particularly if the failure is near the head
>>         end.  While I
>>             suspect that the 1 / second rate is low enough for this
>>         to be safe,
>>             discussion in the document would be helpful.
>>
>>