Re: [lisp] [Last-Call] Tsvart last call review of draft-ietf-lisp-pubsub-10

[[e-mail]]

Re-,

Thanks Magnus for clarifying.

I suggest to add the following in Section 6:

NEW:
   As a reminder, the initial transmission and retransmission of Map-
   Notify messages by a Map-Server follow the procedure specified in
   Section 5.7 of [RFC9301].  Some state changes may trigger an overload
   that would impact, e.g., the outbound capacity of a Map-Server.  A
   similar problem may be experienced when a large number of state were
   simultaneously updated.  To prevent such phenomena, Map-Servers
   SHOULD be configured with policies to control the maximum number of
   subscriptions and also the pace of Map-Notify messages.  The exact
   details to characterize such policies are deployment and
   implementation specific.  Likewise, this document does not specify
   which notifications take precedence when these policies are enforced.

Do we need to say more without going too much into implementation territory?

Cheers,
Med

De : Magnus Westerlund <[e-mail]>
Envoyé : vendredi 27 janvier 2023 11:39
À : BOUCADAIR Mohamed INNOV/NET <[e-mail]>; [e-mail]
Cc : [e-mail]; [e-mail]; [e-mail]
Objet : Re: [Last-Call] Tsvart last call review of draft-ietf-lisp-pubsub-10

Hi Med,

Overall, the spec leverages the mechanisms in both RFC9301 and RFC9303. I don't know if you checked those when performing your review.

MW: Yes, I looked at those, and as you cite some of it I can explain why I think this isn't sufficient for this specification.

> -----Message d'origine-----
> De : last-call <[e-mail]<mailto:[e-mail]>> De la part de Magnus
> Westerlund via Datatracker
> Envoyé : mardi 24 janvier 2023 14:20
> À : [e-mail]<mailto:[e-mail]>
> Cc : [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>;
> [e-mail]<mailto:[e-mail]>
> Objet : [Last-Call] Tsvart last call review of draft-ietf-lisp-
> pubsub-10
>
> Reviewer: Magnus Westerlund
> Review result: Not Ready
>
> This document has been reviewed as part of the transport area
> review team's ongoing effort to review key IETF documents. These
> comments were written primarily for the transport area directors,
> but are copied to the document's authors and WG to allow them to
> address any issues raised and also to the IETF discussion list for
> information.
>
> When done at the time of IETF Last Call, the authors should
> consider this review as part of the last-call comments they
> receive. Please always CC [e-mail]<mailto:[e-mail]> if you reply to or
> forward this review.
>
> My review comments are:
>
>
> C.      When a Map-Notify is to be sent there are no discussion in
> regards to
> congestion control of the transmission of the Map-Notify.

[Med] CC is already covered in 9301. We are not repeating what is already specified in Section 5.7 of 9301:

   A Map-Server sends an unsolicited Map-Notify message (one that is not
   used as an acknowledgment to a Map-Register message) only in
   conformance with Section 3.1 ("Congestion Control Guidelines") of
   [RFC8085] and Section 3.3 ("Reliability Guidelines") of [RFC8085].  A
   Map-Notify is retransmitted until a Map-Notify-Ack is received by the
   Map-Server with the same nonce used in the Map-Notify message.  An
   implementation SHOULD retransmit up to 3 times at 3-second
   retransmission intervals, after which time the retransmission
   interval is exponentially backed off (base of 2, that is, the next
   backoff timeout interval is doubled) for another 3 retransmission
   attempts.  Map-Notify-Ack messages are only transmitted upon the
   reception of an unsolicited Map-Notify; Map-Notify-Ack messages are
   not retransmitted.
MW: Yes, the issue is that in the context of subscriber service, I think it is relevant to discuss how to ensure that the server does not try to overload its own outgoing paths as N subscribers to a particular mapping will result in N outgoing message when that mapping is updated. That N messages can't in general be sent all immediately as it will result in a large spike, for large enough values of N overloading. That needs some discussion. And as I discussed in my review the retransmission timer being fixed at 3 seconds will need to be taken into account. Because if one pace so that the pacing of the N Map-Notify so that it will take more than 3 seconds then the retansmissions will also start result in additional load when they occur.


"unsolicited Map-Notify" is what draft-ietf-lisp-pubsub is about. Section 5.7 of 9301:

   The fields of the Map-Notify are copied from the corresponding Map-
   Register to acknowledge its correct processing.  In the Map-Notify,
   the 'Authentication Data' field is recomputed using the corresponding
   per-message key and according to the procedure defined in the
   previous section.  The Map-Notify message can also be used in an
   unsolicited manner.  This topic is out of scope for this document.
   See [LISP-PUBSUB] for details.

 As the
> Map-Notify appear to be unicast IP/UDP packets being sent one per
> subscriber at the time an updated mapping is registered with the
> map-server all these messages will be generated. There need to be
> some rate limiting for this transmission to prevent congestion
> near the map-server. If sufficient number of subs are in place
> also the retransmission will have to be rate limited as not all
> Map-Notify messages will have been sent when its time to start to
> perform retransmissions.

Yes, I understood that this is what is referenced.
My point is that the pubsub mechanism creates new issues as it both build up states and when the Map-Notify messages are triggered the whole state needs to be considered in doing reasonable things.
Cheers
Magnus

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