Hi Padma,
Thanks again for the feedback! You’re making some good points. Please see below
for some comments inline with [AR].
From: lisp <lisp-boun...@ietf.org> on behalf of Padma Pillay-Esnault
<padma.i...@gmail.com>
Date: Thursday, January 5, 2023 at 8:29 AM
To: Alberto Rodriguez-Natal (natal) <natal=40cisco....@dmarc.ietf.org>
Cc: lisp@ietf.org <lisp@ietf.org>, Sharon Barkai
<sharon.barkai=40getnexar....@dmarc.ietf.org>, Jordi Paillissé
<jordi.pailli...@upc.edu>
Subject: Re: [lisp] LISP PubSub to Proposed Standard?
Dear Alberto and authors
Thank you for the good work on this doc. I fully support moving this document
as a proposed standard, however I have a few comments on the document. See PPE
below
1. Introduction
<...>
In general, when an ITR/RTR/PITR wants to be notified for mapping
changes for a given EID-prefix, the following steps occur:
(1) The ITR/RTR/PITR sends a Map-Request for that EID-prefix.
(2) The ITR/RTR/PITR sets the Notification-Requested bit (N-bit) on
the Map-Request and includes its xTR-ID and Site-ID.
(3) The Map-Request is forwarded to one of the Map-Servers that the
EID-prefix is registered to.
(4) The Map-Server creates subscription state for the ITR/RTR/PITR
on the EID-prefix.
(5) The Map-Server sends a Map-Notify to the ITR/RTR/PITR to
acknowledge the successful subscription.
(6) When there is a change in the mapping of the EID-Prefix, the
Map-Server sends a Map-Notify message to each ITR/RTR/PITR in
the subscription list.
(7) Each ITR/RTR/PITR sends a Map-Notify-Ack to acknowledge the
received Map-Notify.
This operation is repeated for all EID-prefixes for which ITR/RTR/
PITR want to be notified. The ITR/RTR/PITR can set the N-bit for
several EID-prefixes within a single Map-Request.
<...>
PPE - This section relies on section 6.1 of rfc 9301 and gives as an example
the simplest use case. The concluding paragraph also gives the impression that
this is the only processing pub sub needs to do. Both the section 6.1 and here
do not address all the use cases.
[AR] Yes, this is just a simple case to illustrate the idea and general flow.
The example certainly is not meant to be comprehensive. We can maybe add a note
to mention that this the simplest example and that the details for this and
other cases are found later in the document, what do you think?
I suggest removing this from the introduction and instead clearly define the
scope and then define all the use cases as in a real deployment scenario in
section 3. See more about this below.
[AR] I have no strong opinion about removing the simple example from the intro.
I’m leaning towards keeping it, as there seemed to be some consensus around
having an example (even if simple) in the intro. What others think?
<...>
3. Deployment Assumptions
The specification described in this document makes the following
deployment assumptions:
(1) A unique 128-bit xTR-ID (plus a 64-bit Site-ID) identifier is
assigned to each xTR.
(2) Map-Servers are configured in proxy-reply mode, i.e., they are
solicited to generate and send Map-Reply messages for the
mappings they are serving.
The distribution of xTR-IDs (and Site-IDs) are out of the scope of
this document.
<...>
PPE - The section 3 is sparse and could define use cases in this section. In a
real life deployment, there may be a variety of use cases such as
1. an ITR/PITR/RTR joins an existing LISP network and subscribes to specific
existing EID prefixes updates (this is addressed in the intro)
2. an ITR/PITR/RTR joins "early" a growing LISP network and subscribes to an
EID prefix NOT YET present in the database ( covered by 8.4 in rfc 9301? - more
below)
[AR] In this case PubSub follows the same logic defined in 9301. As in 9301,
“the least-specific prefix that both matches the original query and does not
match any EID-Prefix known” is computed and a subscription created for this
prefix. The creation of this subscription is kind of implicit in the PubSub
spec, and I agree with you that maybe we want to make this more explicit.
Thanks for bringing this up! We’ll clarify on -11.
3. an ITR/PITR/RTR sends multiple requests where the range of prefix/len is
removed and readded are slightly different or overlapping, how do we cover the
use case of "holes"?
[AR] Something to note is that in PubSub you get notifications for updates on
more-specific prefixes covered by the ones you’re subscribed to. This is
analogous to how in 9301 you would get more-specific records in a Map-Reply.
PubSub also sends notifications when a prefix is removed (and subsequently,
when a more-specific is removed). It’s true that the the logic for handling
more-specifics in PubSub was implicit in -09 but we added some text in -10 to
make it more explicit (Sec 6). Your question is very valid, let us know if you
feel the clarifications added in -10 help or more clarifications are needed.
4. scale - what if we have a large number of subscriptions - do we intend them
to be aggregated or rely on 5.5 in rfc 9301?
[AR] As you point out, Section 5.5 of 9301 expects EID prefixes to be
aggregable to some extent. Since PubSub builds on top of 9301, the assumptions
should be not much different.
The document would be much clearer if the processing expected for each of these
use cases were described explicitly.
Consider, the pub sub mechanism is used to minimize the number of messages
exchanged and timing issues by using a triggered event solution. However, it is
unclear how it works for use case 2 when there is no existing EID entry yet.
Upon receiving a negative map reply should there be periodic resend of SMR from
the RTR/ITR/PITR? Or is the first SMR stored somewhere on the Mapping System on
a temporary entry and when the EID is added later does it trigger the response?
If the entry is temporary must the SMR requestors renew their request- if so
what periodicity? Can the two behaviors coexist?
[AR] Since PubSub follows 9301 logic, the current behavior would create this
“temporary entry” (as discussed above). Now, a periodic retry would be very
similar to what standard 9301 does without PubSub. If we want to enable a retry
model, we can introduce an optional configuration that specifies that if a
subscription request hits an EID prefix not registered in the mapping-system,
no PubSub operation takes place and a regular NMR is returned from the MS (so
we fall back to 9301 and thus retry behavior). How does this sound?
If there is periodic resend until the EID entry is present then the pub sub is
still polling for an event rather than being event driven for the first part of
the process then the MS and requestors should have a configuration that
accounts for the polling or timing out of an entry.
[AR] Yes, if we are to introduce this optional behavior where PubSub falls back
to standard 9301 on non-registered prefixes, we can specify that the TTL to
return in the negative map-reply could be configurable, which will effectively
control the polling/timeout intervals.
As different implementations may have specific behaviors (e.g retry when it
receives a negative map reply or assumption a subscription is preprovisioned)
there is an implicit assumption both endpoints are acting in a cooperative
manner. Perhaps there is another deployment assumption that the mapping system
and the RTR/ITR/PITR have a collaborative behavior (periodicity, polling
mechanism, event trigger) by config or default config.
[AR] One implicit deployment assumption is that all devices involved support
rfc9301. By enabling the option of falling back to standard 9301 we could
achieve the behavior you suggest without additional machinery or configuration,
what do you think?
Thanks again for the review Padma, very good comments, hope the replies help.
Thanks!
Alberto
Thanks
Padma
[Image removed by sender.]
On Fri, Dec 9, 2022 at 3:48 AM Jordi Paillissé
<jordi.pailli...@upc.edu<mailto:jordi.pailli...@upc.edu>> wrote:
+1
Jordi
El 8/12/22 a les 22:18, Prakash Jain (prakjain) ha escrit:
> +1
> - Prakash
>
> On 12/8/22, 8:09 AM, "lisp on behalf of Sharon Barkai"
> <lisp-boun...@ietf.org<mailto:lisp-boun...@ietf.org> on behalf of
> sharon.barkai=40getnexar....@dmarc.ietf.org<mailto:40getnexar....@dmarc.ietf.org>>
> wrote:
>
> ++
>
> --szb
> Cell: +972.53.2470068
> WhatsApp: +1.650.492.0794
>
> > On Dec 8, 2022, at 18:02, Dino Farinacci
> <farina...@gmail.com<mailto:farina...@gmail.com>> wrote:
> >
> >
> >>
> >> Hi Luigi, all,
> >>
> >> I also think that it is reasonable to publish this spec as a proposed
> standard.
> >
> > +1.
> >
> > Dino
> > _______________________________________________
> > lisp mailing list
> > lisp@ietf.org<mailto:lisp@ietf.org>
> > https://www.ietf.org/mailman/listinfo/lisp
>
> _______________________________________________
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