Re: [Lsr] Using L1 for Transit Traffic in IS-IS

[Gyan Mishra <[e-mail]>]

Les

As co-author of the Area Proxy solution I support progressing Area Proxy
and can give some of my un-biased  reasons why Area Proxy would be more
beneficial over Flood Reflection from an operators POV.

Area proxy does provide a very elegant and simple easily deployable
solution to scale the backbone by providing a complete abstraction of the
Level 1 area topology within the Level 2 topology.

Flood Reflection tunneling hints at RFC 9012 BGP Tunnel encapsulation
attribute but is agnostic to tunnel type for the control plane flooding or
no tunneling with flood scoping to cut down on the flood adjacencies in the
backbone.

>From an Operators POV, in general are not fond of tunneling as being part
of the solution unless its a a bandaid patch to solve a problem, having to
account now for MTU packet transport  overhead. Another caveat with tunnels
is sub optimal routing and possible 1 hop short cuts that may not be
desirable which is described in the draft that could result in routing
loops.  Costing up the flood Reflection path is a workaround.

BGP Free MPLS / SR core where the RR sits in control plane outside of the
E2E data plane forwarding plane is a BGP free core design requirement and
as well for BGP MVPN, EVPN procedures which the control plane is separate
from the data plane, so is a inherent requirement for BGP.  Separation of
the IGP flooding function from the forwarding plane is quite a change to
normal IGP operation where the control plane and forwarding plane paths are
the same.

The flood reflectors can sit in the control plane so not in the forwarding
plane or can be in the forwarding plane with L1 or L2 shortcut.  So all
paths including the flood Reflector path can be used for forwarding,
however do to 1 hop L1 and L2 shortcut the flood reflector path can be
bumped up in coast so not preferred to prevent choking the flood reflectors
similar to issue where we exclude the BGP RR from forwarding plane so we
don’t choke the RR. My worry is the sub optimal routing from the 1 hop
tunnels could lead to routing loops of which as mentioned the workaround is
to cost high  the flood reflector path so it’s only used for control plane
flooding.


Responses in-line

Kind Regards

Gyan


On Sat, Dec 11, 2021 at 10:43 AM Les Ginsberg (ginsberg) <[e-mail]>
wrote:

> Gyan –
>
>
>
> Both drafts have been adopted as WG documents and been provided with early
> allocation of codepoints.
>
    Gyan> As co-author I am aware

> So there is nothing preventing implementations/deployments from proceeding
> and doing so without fear that if/when the documents proceed to become RFCs
> that there will be backwards compatibility issues because of codepoint
> changes.
>
> My concern is that there is no effort underway since WG adoption to use
> implementation experience to compare/contrast the solutions and determine
> whether one is better and/or if there really is a need for multiple
> solutions. That seemed to me to be the point of adopting both.
>
   Gyan>  In my response here I tried to  provide an unbiased compare and
contrast of the two solutions.

> I do not see the need to progress either document to RFC at this time –
and I am concerned that in doing so we make it even less likely that such a
comparison will ever be made.

 Gyan> I did the comparison above and I can further elaborate

I had hoped – as you are a representative of one of the potential users of
this technology and you had suggested that there might be reasons why you
were interested in both – that you could provide some input into when one
solution was more desirable than another.

 Gyan> Just to clarify that as an operator this is scalability issue is a
real world problem that needs to be solved.  As I am Co-Author of the Area
Proxy draft I truly believe that is a better solution, however this is a
solution that definitely needs solved..

The value add provided by a standards organization is that it allows the
industry to converge on an interoperable solution. If we simply become a
means of allocating codepoints in support of multiple non-interoperable
solutions then I think we as an organization have failed.
    Gyan> Agreed.  Interoperability is critical for all operators and is
what makes SDOs so valuable

> This does not mean that we should not support experimentation – and in
this case I think we are doing so.

 Gyan> Agreed.  And be able to progress both experimental to RFC and let
the industry decide on the best solution and then progress that solution as
standards track

>    Les
>
>
>
> *From:* Gyan Mishra <[e-mail]>
> *Sent:* Friday, December 10, 2021 10:56 PM
> *To:* Les Ginsberg (ginsberg) <[e-mail]>
> *Cc:* Acee Lindem (acee) <[e-mail]>; Muthu Arul Mozhi Perumal <
> [e-mail]>; Tony Li <[e-mail]>; Tony Przygienda <
> [e-mail]>; [e-mail]
> *Subject:* Re: [Lsr] Using L1 for Transit Traffic in IS-IS
>
>
>
>
>
> Hi Les
>
>
>
> My thoughts are that as both of these drafts are experimental, if both get
> published we can let the industry decide which is to be the preferred
> solution which can then progress as standards track to address
> interoperability issues with a single solution implemented by vendors.
>
>
>
> I think by picking one now over the other we are not letting the cards
> fall on the table and prematurely making a decision and not letting things
> naturally play out.
>
>
>
> I agree the implementation of each is non trivial however the router
> configuration could boil down to a simple knob similar to fast flooding.
> As an example there maybe use cases that for a DC CLOS topology where area
> proxy with n-way ECMP paths leaf to scale out spine maybe better suited,
> however in a core or aggregation domain maybe flood reflection maybe
> preferred from a topological perspective  during the study phase.
>
>
>
> I don’t have a crystal ball but it’s possible just as winning the lottery
> is possible that both drafts garnish industry support and from a sales and
> marketing perspective vendors can still have their cake and eat it too by
> solving a major backbone scalability issue win win for all and so
> developing both solutions that become standards track and implemented by
> all vendors.  No interoperability issues.
>
>
>
> I am in agreement on implementation that in the end having a single
> solution is most desirable to avoid interoperability.
>
>
>
> Kind Regards
>
>
>
> Gyan
>
>
>
> On Sat, Dec 11, 2021 at 12:24 AM Les Ginsberg (ginsberg) <
> [e-mail]> wrote:
>
> Gyan –
>
>
>
> I am interested in your perspective – but could you provide more details?
>
> What deployment scenarios do you have in mind where one solution is
> advantageous over the other? And why are both scenarios likely to be seen
> in the real world?
>
>
>
> I think you can appreciate that implementation of either solution is
> non-trivial – as is insuring interoperability – as is the actual deployment.
>
> What justifies doubling that effort?
>
>
>
> Thanx.
>
>
>
>     Les
>
>
>
> *From:* Gyan Mishra <[e-mail]>
> *Sent:* Friday, December 10, 2021 5:46 PM
> *To:* Muthu Arul Mozhi Perumal <[e-mail]>
> *Cc:* Acee Lindem (acee) <[e-mail]>; Les Ginsberg (ginsberg) <
> [e-mail]>; Tony Li <[e-mail]>; Tony Przygienda <
> [e-mail]>; [e-mail]
> *Subject:* Re: [Lsr] Using L1 for Transit Traffic in IS-IS
>
>
>
> All
>
>
>
> As Acee mentioned per the subject of this thread “Using L1 for transit
> traffic in IS-IS” is supported today and is deployed by operators with
> large backbones as well today, and both solutions,  area proxy and flood
> reflection now allows the L1 transit solution  to scale.
>
>
>
> Speaking from an operators perspective we are in favor of multiple
> solutions as their maybe use cases where one applies better then the other
> and vice versa.  Flexibility is a good thing.
>
>
>
> Kind Regards
>
>
>
> Gyan
>
>
>
> On Fri, Dec 10, 2021 at 1:54 AM Muthu Arul Mozhi Perumal <
> [e-mail]> wrote:
>
> Hi,
>
>
>
> It is possible to designate experimental RFCs as historic if there is no
> evidence of widespread use over a period of time, as is currently being
> done for HTTP-related experimental RFCs:
>
>
> https://datatracker.ietf.org/doc/status-change-http-experiments-to-historic/
>
>
>
> Hence, I think having multiple experimental publications for a problem is
> ok..
>
>
>
> Regards,
>
> Muthu
>
>
>
> On Fri, Dec 10, 2021 at 6:08 AM Les Ginsberg (ginsberg) <ginsberg=
> [e-mail]> wrote:
>
> Acee –
>
>
>
> Thanx for responding while you are on vacation.
>
>
>
> While it is true I am not enthusiastic about any of the solutions, my
> point of emphasis is that it’s a failure of WG process to simply move
> forward with all solutions – which it seems to me is what is about to
> happen.
>
>
>
> Note that this is completely consistent with what I said back when WG
> adoption for the drafts was being discussed (thanx to Tony P for pointing
> me back to that time (June 21, 2020)):
>
>
>
> *<snip>*
>
> *I support the WG adoption of
> https://datatracker.ietf.org/doc/draft-li-lsr-isis-area-proxy/
> <https://datatracker.ietf.org/doc/draft-li-lsr-isis-area-proxy/> .*
>
>
>
> *(I also support WG adoption of
> https://datatracker.ietf.org/doc/draft-przygienda-lsr-flood-reflection
> <https://datatracker.ietf.org/doc/draft-przygienda-lsr-flood-reflection> )*
>
>
>
> *I believe the problem space addressed by these two drafts warrants
> attention.*
>
> *…*
>
> *The easy road for the WG to take would be to simply allow both drafts to
> proceed to Experimental RFCs, but I hope we are able to do more than this.
> Multiple solutions place undesirable burdens on vendors and providers
> alike.*
>
>
>
> *To the extent they feel comfortable, I encourage folks who wish to deploy
> such solutions to share their requirements and discuss how each of the
> solutions*
>
> *address their requirements/fall short of addressing their requirements. I
> think this would help the WG discover better ways forward.*
>
>
>
> *<end snip>*
>
>
>
> Don’t think we have made progress in that regard…
>
>
>
>    Les
>
>
>
>
>
> *From:* Acee Lindem (acee) <[e-mail]>
> *Sent:* Thursday, December 9, 2021 1:59 PM
> *To:* Les Ginsberg (ginsberg) <[e-mail]>; Tony Przygienda <
> [e-mail]>
> *Cc:* Tony Li <[e-mail]>; [e-mail]
> *Subject:* Re: [Lsr] Using L1 for Transit Traffic in IS-IS
>
>
>
> Hi Les,
>
>
>
> I know you don’t feel that the IGP should solve this problem but there was
> lots of interest in the three solutions to reduce the overhead when using
> IS-IS L1 as transit for IS- IS L2. Let’s not rehash that.
>
>
>
> What do feel needs to be done? Note that I’m on vacation and unlikely to
> engage again until next week…
>
>
>
> Thanks,
> Acee
>
>
>
> *From: *"Les Ginsberg (ginsberg)" <[e-mail]>
> *Date: *Thursday, December 9, 2021 at 2:05 PM
> *To: *Tony Przygienda <[e-mail]>
> *Cc: *Tony Li <[e-mail]>, "[e-mail]" <[e-mail]>, Acee
> Lindem <[e-mail]>
> *Subject: *RE: [Lsr] Using L1 for Transit Traffic in IS-IS
>
>
>
> Let me try to clarify my position…
>
>
>
> Two disjoint sets of authors looked at the same problem space and
> independently came up with two different (and incompatible) protocol
> extensions to provide a solution.
>
>
>
> (Aside: I believe fully that both sets of authors have done their best to
> define what they think is a good solution. If anything I have said suggests
> otherwise,  that was not my intent and I apologize to both sets of authors
> for any misunderstanding.)
>
>
>
> Both solutions have been published as WG documents and assigned protocol
> codepoints.
>
> We are now being asked to publish both drafts as RFCs (I am assuming based
> on Tony Li’s response that the LC request for Area Proxy is soon to happen.)
>
>
>
> I don’t believe the WG has reached consensus that the IGPs should be
> extended to address the problem.
>
> I don’t believe the WG has reached consensus as to which solution is
> “better”.
>
> I don’t believe the WG has even discussed whether a single solution or
> multiple solutions are required.
>
> If multiple solutions are required, there has been no discussion as to
> when each of the solutions should be used. Are there some deployment
> scenarios where flood-reflection is a better fit and some where area proxy
> is a better fit?
>
> Is there a need for additional solutions i.e., deployments where neither
> of the current candidates are suitable?
>
>
>
> It seems to me that by entertaining a LC request at this point we are
> simply functioning as a pass through to allow multiple individual solutions
> to be published as RFCs. And while there are currently two solutions to the
> same problem space asking to progress, I think we can expect others and we
> have no basis on which to reject other proposals.
>
>
>
> This is very different from how any other work brought before the
> LSR/OSPF/IS-IS WGs has been done in the 20+ years during which I have been
> an active participant.
>
> In all other cases, the WG has strived to come up with a single
> interoperable solution.
>
> Sometimes only one solution is proposed and it is refined based on
> discussion and then progressed.
>
> Sometimes multiple solutions are proposed and there is discussion of both
> which results in choosing one over the other or some sort of merge of the
> solutions.
>
> But I do not recall a case where the WG simply allowed multiple
> non-interoperable solutions to the same problem to be published as RFCs
> largely w/o comment.
>
>
>
> I do not think this is an appropriate use of the Standards process and I
> do not think this serves the industry.
>
> This does not mean that either solution is w/o merit – but I do think the
> requests for Last Call are premature.
>
> But, this is just my opinion.
>
> If the WG (members, chairs, and ADs) think otherwise then the WG should
> act appropriately.
>
>
>
> Thanx for listening.
>
>
>
>    Les
>
>
>
>
>
> *From:* Tony Przygienda <[e-mail]>
> *Sent:* Wednesday, December 8, 2021 5:27 AM
> *To:* Les Ginsberg (ginsberg) <[e-mail]>
> *Cc:* Tony Li <[e-mail]>; [e-mail]; Acee Lindem (acee) <
> [e-mail]>
> *Subject:* Re: [Lsr] Using L1 for Transit Traffic in IS-IS
>
>
>
> Les, all sounds to me unfortunately like a gripe (and a late one @ that
> now that things were worked on in WG for years & are ready to RFC being
> customer deployed, @ least flood reflection is).
>
>
>
> Plus,  unless you have a dramatically better idea than the drafts extended
> I fail to understand what your point is except as Tony1 says "we should not
> scale IGP higher?" (AFAIS hierarchy is not an answer here unless you ask
> customers for a flag day with lots new static configuration everywhere and
> possibly restructuring of their network to a hard-coded "hierarchy" and
> albeit such effort may work in some totalitarian countries on in pretty
> small networks, the majority of large ISIS customers will end such
> discussions in timeframe of single minutes clock count ;-)
>
>
>
> -- tony
>
>
>
> On Wed, Dec 8, 2021 at 4:23 AM Les Ginsberg (ginsberg) <ginsberg=
> [e-mail]> wrote:
>
> (Subject was:  RE: [Lsr] WG Last Call for "IS-IS Flood Reflection"
> -draft-ietf-lsr-isis-flood-reflection-05)
>
>
>
> (Changing the subject as Acee has suggested that discussion of the problem
> space is inappropriate for the WG LC thread)
>
>
>
> Tony (and everyone) –
>
>
>
> This isn’t the first contentious issue the WG has considered. By way of
> comparison (hopefully a useful one), a number of folks (including you and
> I) are participating in another contentious issue – fast-flooding.
>
> But for fast-flooding there is broad WG consensus that fast-flooding is
> something that IS-IS should do. The contentious part is regarding what is
> the best way to do it. And we are proceeding in a manner where different
> algorithms are being tested while still in the WG document stage. And there
> is hope (still TBD) that multiple algorithms may be able to interoperate.
>
>
>
> Here, I am not convinced that there is broad WG consensus that this is a
> problem that the IGPs should solve. (If I am wrong on that I presume the WG
> members will let me know.)
>
> And, we have multiple proposals, none of which have any hope of
> interoperating with each other.
>
> And we have had very little discussion about the problem space. (not your
> fault – certainly you have been willing as have the authors of the
> competing draft)
>
>
>
> So, at best, I think WG LC is premature. I would like to see more
> discussion as to whether this is a problem that IGPs should solve as well
> as a general look at how this might be done with and/or without the IGPs.
>
> And since all of the proposed solutions have been allocated code points,
> they can continue to gain implementation/deployment experience in the
> meantime. Therefore, I do not see that we need to make this choice now.
>
>
>
> I realize that you are not the one asking for WG LC and I don’t know when
> you plan to do so and I am not trying to influence you in that regard.
>
> But for me, WG LC is at best premature.
>
>
>
> As regards you trying to solve a real world customer ask, I was aware of
> that. And I believe the authors of flood-reflection can make the same claim.
>
>
>
> Thanx for listening,
>
>
>
>     Les
>
>
>
>
>
>
>
>
>
> *From:* Tony Li <[e-mail]> *On Behalf Of *Tony Li
> *Sent:* Tuesday, December 7, 2021 2:53 PM
> *To:* Les Ginsberg (ginsberg) <[e-mail]>
> *Cc:* Acee Lindem (acee) <[e-mail]>; Acee Lindem (acee) <
> [e-mail]>; [e-mail]
> *Subject:* Re: [Lsr] WG Last Call fo "IS-IS Flood Reflection"
> -draft-ietf-lsr-isis-flood-reflection-05
>
>
>
>
>
> Les,
>
>
>
> And in response to Tony Li’s statement:  “…the IETF is at its best when it
> is documenting de facto standards”
>
>
>
> 1) I fully believe that our customers understand their requirements(sic)
> better than we (vendors) do. But that does not mean that they understand
> what is the best solution better than we do.
>
> When a customer comes to me and says “Can you do this?” my first response
> is usually “Please fully describe your requirements independent of the
> solution.”
>
>
>
>
>
> If it matters at all, Area Proxy is the result of a customer explaining
> his issues and my attempt to address them.  I’m sorry you don’t like my
> proposal.
>
>
>
>
>
> 2)Not clear to me that there is an existing “de facto standard” here –
> which is reinforced by the fact that we have so many different solutions
> proposed.
>
>
>
>
>
> There isn’t. Yet. Thus, it’s not time to pick one vs. the other.
>
>
>
> Tony
>
>
>
>
>
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>
> --
>
> [image: Image removed by sender.] <http://www.verizon.com/>
>
> *Gyan Mishra*
>
> *Network Solutions Architect *
>
> *Email [e-mail] <[e-mail]>*
>
> *M 301 502-1347*
>
>
>
> --
>
> [image: Image removed by sender.] <http://www.verizon.com/>
>
> *Gyan Mishra*
>
> *Network Solutions Architect *
>
> *Email [e-mail] <[e-mail]>*
>
> *M 301 502-1347*
>
>
>
-- 

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *

*Email [e-mail] <[e-mail]>*



*M 301 502-1347*