Thanks for the clarifications to Peter and Ketan. (I now understand
what I missed about the control for END.DT2M.)
It seems that as currently laid out, the document appears to define the
encoding for END.T, but does not provide enough information to use it?
Which suggests that we should either improve it or remove it.
The inclusion of END.T in the network programming draft means that
removing it will leave a gap with us standardizing the meaning of END.T
but not the control to communicate it. That seems better than a partial
definition of how to communicate it.
Yours,
Joel
On 9/29/2020 4:39 AM, Peter Psenak wrote:
Joel, Ketan,
On 28/09/2020 15:25, Ketan Talaulikar (ketant) wrote:
Hi Joel,
Please check inline below.
-----Original Message-----
From: Lsr <lsr-boun...@ietf.org> On Behalf Of Joel M. Halpern
Sent: 25 September 2020 19:08
To: Ketan Talaulikar (ketant) <ketant=40cisco....@dmarc.ietf.org>;
lsr@ietf.org
Subject: Re: [Lsr] I-D Action: draft-ietf-lsr-isis-srv6-extensions-10.txt
Thanks Ketan. Let me paraphrase to confirm I understand, with some
suggestions. And repeat the last question which seems to have gotten
lost.
It seems that you are saying that the arg field is defined for now so
the format is consistent, but is not used by any behavior defined in
this draft.
[KT] The ISIS draft does not actually define any behavior - it only
specifies signaling of a subset of behaviors defined in net-pgm. You
are right that the behaviors that are listed as being signalled by
ISIS in the current document do not support an ARG.
ARG is part of the SID. The fact that it is not used currently by any
SID that is defined for ISIS, does not mean the ARG part of the SID does
not exists. We advertise the SID as 128 bits in ISIS, so we ARG is part
of it.
If so, should we say explicitly that ARG is (or MUST be) 0 for all the
behaviors defined in this draft?
[KT] I am not sure it is necessary. A future ISIS extension may
introduce support for signaling of a behavior that supports ARG.
draft-ietf-spring-srv6-network-programming only defines ARG for END.DT2M.
We can certainly say in ISIS draft that for the SIDs defined in it,
there are no ARGs.
Then separately the folks working on the END.DT2M behavior can write
their own draft one how to advertise that in is-is? Presumably with
an additional sub-TLV dealing with k and x?
[KT] End.DT2M is signaled in BGP and specified in BGP extensions. If a
future ISIS extension was to advertise a SID with a behavior
supporting ARG, then it would need to clarify its handling of the ARG.
Also, can you tell me how the association of an END.T behavior with a
table is understood from the advertisement as described in the draft?
[KT] Indeed, the End.T signaling does not carry the table context with
it.
I would tend to remove the END.T from the ISIS draft. If we need it, we
could define it in a separate document.
thanks,
Peter
Thanks,
Ketan
Thank you,
Joel
On 9/25/2020 1:39 AM, Ketan Talaulikar (ketant) wrote:
Hi Joel,
Please check inline below.
-----Original Message-----
From: Lsr <lsr-boun...@ietf.org> On Behalf Of Joel M. Halpern
Sent: 25 September 2020 03:18
To: Acee Lindem (acee) <a...@cisco.com>; lsr@ietf.org
Subject: Re: [Lsr] I-D Action:
draft-ietf-lsr-isis-srv6-extensions-10.txt
First, there is a slight confusion in the way I formed the quesiton,
but I think it still applies.
The piece of this draft is section 9, which advertises the length of
the arg portion of the SID. But does not provide specific meanings
for specific values.
[KT] This is quite appropriate for this draft since it is only
specifying a generic SID structure and not associated with any
specific behavior.
The example of an ARG in the network programming draft does provide
part of the explicit interpretation of the ARG. It says that it is a
list of k items, each of x bits, where each x bit blob identifies an
OIF.
[KT] The net-pgm draft in sec 4.12 introduces a specific End.DT2M
behavior which includes support for ARG. That said, I am not quite
sure about that text in that section which talks about how the ARG
bits are formed and what they signify. I believe the ARG in this case
is a locally assigned identifier that maps to an ESI so that it can
be used for ESI filtering - much the same as an ESI label for
split-horizon filtering. I see a comment from one of the ADs on this
and I expect that the authors will clarify.
This leaves two gaps, and a more general question.
1) How does the receiver know the meanings of the OIF indices so that
he can correctly fill them in?
2) The NP draft says that k and x are defined on a per SID basis.
But I do not see anywhere in the isis draft to advertise the values
of k and x, only arg (which is k*x).
[KT] I hope the previous comment explains.
The more general question is, is there a requirement we can write
down about how receivers will be able to understand ARG fields in
general?
One can argue that it would belong in the network programming draft;
I would prefer not to delay that with a significant technical addition.
[KT] I don't believe the handling of ARG is something that can be
generalized. It has to be something specific to the behavior that it
is associated with. Therefore, each behavior that supports an ARG
needs to specify its handling. The net-pgm draft is doing it for
End.DT2M and future documents that introduce other behaviors
requiring ARG would be expected to the same.
Thanks,
Ketan
There is a related question that I came across while trying to
explain this question.
END.T must be associated with a forwarding table. I presume this is
done by where one puts the END.T (however-many-subs) TLV. But I can
not find anything in this draft that says this. There is precisely
one reference to End.T in the draft.
Thank you,
Joel
On 9/24/2020 5:25 PM, Acee Lindem (acee) wrote:
H Joel,
Can you reference the specific section in the IS-IS SRv6 draft you
are commenting on? I seem to remember this discussion but it was at
least a month back, if not more.
Thanks,
Acee
On 9/23/20, 6:31 PM, "Lsr on behalf of Joel Halpern"
<lsr-boun...@ietf.org on behalf of j...@joelhalpern.com> wrote:
The announcement prompted me to look again and think about an
interaction between this and the network programming draft.
To be
clear, I am NOT objecting to either this or the network
programming
draft. I am just wondering what I am missing.
The NP draft, and the advertisement mechanism allows a router to
advertise the number of bits for the ARG portion of a SID.
Q1: The point presumably is to avoid needing to advertise
each of the
individual values?
An example of this is, I think, and ARG for the table
selection where
the ARG is the table number for the packet to be looked up in?
Q2: If so, how does the head end know what table number
corresponds to
what meaning? If this requires a separate advertisement
there seems
to be no savings. if this requires out-of-band knowledge
then we seem
to have lost the benefit of advertising all of this in the
routing protocol.
I suspect I am simply missing a piece. can someone explain
please?
Thank you,
Joel
On 9/23/2020 4:40 PM, internet-dra...@ietf.org wrote:
>
> A New Internet-Draft is available from the on-line
Internet-Drafts directories.
> This draft is a work item of the Link State Routing WG of
the IETF.
>
> Title : IS-IS Extension to Support
Segment Routing over IPv6 Dataplane
> Authors : Peter Psenak
> Clarence Filsfils
> Ahmed Bashandy
> Bruno Decraene
> Zhibo Hu
> Filename :
draft-ietf-lsr-isis-srv6-extensions-10.txt
> Pages : 25
> Date : 2020-09-23
>
> Abstract:
> Segment Routing (SR) allows for a flexible definition
of end-to-end
> paths by encoding paths as sequences of topological
sub-paths, called
> "segments". Segment routing architecture can be
implemented over an
> MPLS data plane as well as an IPv6 data plane. This
draft describes
> the IS-IS extensions required to support Segment
Routing over an IPv6
> data plane.
>
>
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