Huaimo has written one draft
(https://datatracker.ietf.org/doc/draft-chen-ospf-abnormal-state-info/)
in 10 years ago(2010), and update it again in recent day. Will you rely
on it or design one new solution?
Will the solution procedures, protocol extension be different in OSPF
and IS-IS?
For PUAM solution, the procedures, and protocol usage(Both utilize only
the “prefix originator TLV”) is almost same, won’t it be easy to
implement, deploy and debug?
Best Regards
Aijun Wang
China Telecom
*From:*lsr-boun...@ietf.org <lsr-boun...@ietf.org> *On Behalf Of *Aijun Wang
*Sent:* Friday, October 15, 2021 3:16 PM
*To:* 'Les Ginsberg (ginsberg)' <ginsberg=40cisco....@dmarc.ietf.org>;
'Acee Lindem (acee)' <acee=40cisco....@dmarc.ietf.org>; 'Peter Psenak'
<ppsenak=40cisco....@dmarc.ietf.org>; lsr@ietf.org
*Subject:* Re: [Lsr] 【Technical Discussion】"Prefix Unreachable
Announcement" and "IS-IS and OSPF Extension for Event Notification"
Hi, Les and Acee:
The answer to your previous concerns are the followings.
For discussion convenience, I will use PUAM to represent “Prefix
Unreachable Announcement Mechanism”later.
==================================================================================================================
1. From Les:
https://mailarchive.ietf.org/arch/msg/lsr/IjiWOvYiXtcplVeQukbVRnmlEFY/
/For me, the solution has two major drawbacks:/
/1)It tries to repurpose an existing (and fundamental) Reachability
Advertisement into an UnReachability advertisement under certain conditions/
//
/The interoperability risks associated with this make me very reluctant
to go down this path./
/And the use of the same advertisement to indicate Reachability and
Unreachability is IMO highly undesirable./
/【WAJ//】：It is easy to make sure all of the routers within one domain
to upgrade to support the PUAM feature. The similar requirements apply
also to your introduced IS-IS Pulse PDU./
//
//
/2)The withdrawal of the "Unreachability Advertisement" after some delay
(which is necessary) remains problematic despite the authors attempts
to address thus/
/【WAJ//】Would you like to elaborate more accurate? /
2. From Acee:
https://mailarchive.ietf.org/arch/msg/lsr/SRmhsUCLphTqKRkMA_8BNNe9L54/
/1.//Usage of the prefix-originator for unreachability notification
requires that every router in the domain support the extension before it
can be used. If a router don't support it and ignores the
prefix-originator sub-TLV, it will actually prefer the advertising ABR
(due to LPM) and blackhole the data. /
/【WAJ//】The updates of every routers within the domain can be done in
deployment. We can add some capabilities bit in the //“Router
Information//”LSA. The ABR should only announces the PUAM message when
all of internal router supports this features./
/2.//The non-deterministic nature of the notification. Unreachability is
advertised for any route that is subsumed by a range and become
unreachable./
/【WAJ//】No. As described in
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-7,
the ABR has the ability to control when and for which prefix to send out
the PUAM./
//
/Is this advertised forever if the route in question is taken out of
service? /
/【WAJ//】No. Please see also the description in last paragraph of
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-7/
//
/What about a route that is mistakenly put into service - will we
advertise unreachability forever?/
/【WAJ//】Should the question be //“what about a route that is
mistakenly put out of service?//”, if so, the PUAM will be triggered.
But it will not be advertised forever./
//
/What if the PE is already unreachable when the ABR comes up - no
reachability information will be advertised. /
/【WAJ//】The PUAM will not be triggered. Please see the description in
last sentence of
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-7/
/For discussion convenience, I copy the section 7 of PUAM draft here:/
*7
<https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-7>.
Deployment Considerations*
To support the PUA advertisement, the ABRs should be upgraded
according to the procedures described in Section 4
<https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-4>.
The PEs that
want to accomplish the BGP switchover that described in Section 3.1
<https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-3.1>
and Section 5
<https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-5>
should also be upgraded to act upon the receive of the
PUA message. Other nodes within the network should ignore such PUA
message if they don't care or don't support it. The routers within
the IGP domain should not install erroneously the route to the
prefixes when they receives PUA message.
As described in Section 4
<https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-07#section-4>,
the ABR will advertise the PUA message
once it detects there is link or node down within the summary
address. In order to reduce the unnecessary advertisements of PUA
messages on ABRs, the ABRs should support the configuration of the
protected prefixes. Based on such information, the ABR will only
advertise the PUA message when the protected prefixes(for example,
the loopback addresses of PEs that run BGP) that within the summary
address is missing.
The advertisement of PUA message should only last one configurable
period to allow the services that run on the failure prefixes are
converged or switchover. If one prefix is missed before the PUA
mechanism takes effect, the ABR will not declare its absence via the
PUA mechanism.
//
/3.//Like the event notification draft, the unreachability notification
will trigger BGP reconvergence. /
/【WAJ//】Exactly, the above sentence should be //“Event notification
draft takes the similar procedure described in PUAM draft, that is the
PUAM will trigger BGP reconvergence.//”/
//
/Additionally, an ABR that has the route is supposed to advertise a more
specific route. However, by the time this happens, BGP reconvergence
should have already taken place. /
/【WAJ//】Without the aid of BFD, the convergence time of BGP should be
in second scale. The process of IGP flooding is event driven, then will
be quicker than BGP hello mechanism./
//
/4.//The interaction of MAA and reachable prefixes could cause quite a
bit of churn when there are oscillations. However, given 1-3, I don't
think we'll have to worry about this./
/【WAJ//】Please gives some examples in detail, or we can discuss this
later when the 1-3 concerns has been solved./
===================================================================================================================//
-----Original Message-----
From: Aijun Wang <wangai...@tsinghua.org.cn
<mailto:wangai...@tsinghua.org.cn>>
Sent: Thursday, October 14, 2021 3:36 PM
To: 'Les Ginsberg (ginsberg)' <ginsberg=40cisco....@dmarc.ietf.org
<mailto:ginsberg=40cisco....@dmarc.ietf.org>>; 'Acee Lindem (acee)'
<acee=40cisco....@dmarc.ietf.org
<mailto:acee=40cisco....@dmarc.ietf.org>>; 'Peter Psenak'
<ppsenak=40cisco....@dmarc.ietf.org
<mailto:ppsenak=40cisco....@dmarc.ietf.org>>; 'lsr@ietf.org'
<lsr@ietf.org <mailto:lsr@ietf.org>>
Subject: RE: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and OSPF
Extension for Event Notification"
Hi, Les:
I know you are the main person that guards the improvement of IS-IS
protocol, but the liveness of this protocol should be from various
contributions.
I admire your opinions, but think you should be more flexible to
hear/adopt other options.
What I worry is that do we need the seemed generalized solution to the
one mentioned use case in current stage? I think the basis to approach
this direction is not mature until now.
Let's give you one example that you have developed(please do not angry):
https://datatracker.ietf.org/doc/html/rfc6823 (December 2010) describe
the "GENINFO TLV" to transfer the application information within the
ISIS, but until now, only one application ID(1 for TRILL) is defined out
of the reserved 65535 values.
I will not expand the history and future of RFC6823. What I want to do
is that we do not repeat its experiences.
One additional comments, the PUA draft has been updated based on the
comments/suggestions from the LSR experts, it has passed several rounds
reviews of the LSR WG members.
We can focus to solve your remaining concerns later.
Let's first hear more opinions from other experts on the direction to
solve this problem. We all agree it can and should be solved via IGP
protocol.
Best Regards
Aijun Wang
China Telecom
-----Original Message-----
From: lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>
<lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>> On Behalf Of Les
Ginsberg (ginsberg)
Sent: Thursday, October 14, 2021 1:25 PM
To: Aijun Wang <wangai...@tsinghua.org.cn
<mailto:wangai...@tsinghua.org.cn>>; 'Les Ginsberg (ginsberg)'
<ginsberg=40cisco....@dmarc.ietf.org
<mailto:ginsberg=40cisco....@dmarc.ietf.org>>; 'Acee Lindem (acee)'
<acee=40cisco....@dmarc.ietf.org
<mailto:acee=40cisco....@dmarc.ietf.org>>; 'Peter Psenak'
<ppsenak=40cisco....@dmarc.ietf.org
<mailto:ppsenak=40cisco....@dmarc.ietf.org>>; lsr@ietf.org
<mailto:lsr@ietf.org>
Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and OSPF
Extension for Event Notification"
Aijun -
I appreciate the continued dialogue.
You no doubt remember that Peter and I discussed PUA with you and
co-authors several times over the years (at your kind invitation) -
even before you had submitted the draft.
We raised the same concerns with you then that I have mentioned earlier
in this thread.
None of the changes you have made have altered the basic mechanism that
you use - so my objections remain the same. And that isn’t going to
change...I don’t think PUA is a good solution.
The rest of your argument seems to be that we should move forward w the
PUA solution just because the draft has been around for a long time.
Sorry, that isn’t a valid argument.
Either the WG thinks PUA is good solution or it doesn't - that is the
only basis on which a decision to adopt/not adopt should be made. The
fact that you keep refreshing/updating the draft carries no weight.
Les
-----Original Message-----
From: Lsr <lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>> On Behalf Of
Aijun Wang
Sent: Wednesday, October 13, 2021 7:50 PM
To: 'Les Ginsberg (ginsberg)' <ginsberg=40cisco....@dmarc.ietf.org
<mailto:ginsberg=40cisco....@dmarc.ietf.org>>;
'Acee Lindem (acee)' <acee=40cisco....@dmarc.ietf.org
<mailto:acee=40cisco....@dmarc.ietf.org>>; 'Peter Psenak'
<ppsenak=40cisco....@dmarc.ietf.org
<mailto:ppsenak=40cisco....@dmarc.ietf.org>>; lsr@ietf.org
<mailto:lsr@ietf.org>
Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and
OSPF Extension for Event Notification"
Hi, Les:
Thanks for your invitation. We are considering how to merge our
directions to the same aim.
The reason that we want to finalize the PUA solution is due to it has
been discussed intensely on the previous IETF meetings and on the mail
list.(we start the discussion on October 2019, two years passed, now
in version 07) We have changed and updated the draft a lot to reflect
the comments from the LSR experts, including the comments from you.
The use cases, solution procedures are almost finished, then we think
it is time to start the adoption call for PUA draft.
For the remaining questions, we think we have plenty of time to solve
it after the adopt
But for "IS-IS and OSPF Extension for Event Notification" draft, it
just began the travel for the standardization activities.
I think it is one alternative solution to the PUA draft, but as we
have seen the comments on the list, whether to open the gate for the
event notification mechanism within IGP is needed to further intense discussion.
There may be some hidden problems has not been investigated for this
direction.
And, there is no any restriction within IETF that we should rely on
one solution to solve the same problem. Think about how many solutions
exist for the Traffic Engineering requirements?
Even within LSR WG, we have flooding reduction, flooding reflection
and TTZ solutions for the similar problems.
We have never mixed them for discussion and compare. There is seldom
solutions can satisfy all our preferences.
So, in conclusion, I recommend to standardize firstly the PUA draft,
and then to discuss whether to open the gate for the event
notification mechanism within IGP.
Anyway, for the general solution, currently we have only the same use
case in mind as that in PUA draft.
We are also kind to invite you, Peter, Acee to participate the PUA
solution, to solve the problems that you are worrying. Other LSR
experts(Tony Li, Greg, Robert, Jeff etc.) are also welcome The design,
implementation, deployment experiences of PUA mechanism can certainly
give the guides for the more general solution for further notification
event.
And, I still think PUA solution is the easiest way to solve the
problem, I think all of your concerning points will emerge later in
"IS-IS and OSPF Extension for Event Notification" draft.
Best Regards
Aijun Wang
China Telecom
-----Original Message-----
From: lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org> <lsr-boun...@ietf.org
<mailto:lsr-boun...@ietf.org>> On Behalf Of Les
Ginsberg (ginsberg)
Sent: Thursday, October 14, 2021 2:44 AM
To: Acee Lindem (acee) <acee=40cisco....@dmarc.ietf.org
<mailto:acee=40cisco....@dmarc.ietf.org>>; Peter Psenak
<ppsenak=40cisco....@dmarc.ietf.org
<mailto:ppsenak=40cisco....@dmarc.ietf.org>>; lsr@ietf.org
<mailto:lsr@ietf.org>
Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and
OSPF Extension for Event Notification"
This thread is becoming "diverse".
We are trying to talk about many different solutions (IGP, BGP, BFD) -
all of which may be useful and certainly are not mutually exclusive.
If we can agree that an IGP solution is useful, then we can use this
thread to set a direction for the IGP solution - which seems to me to
be something we should do independent of whether the other solutions are also
pursued.
With that in mind, here is my input on the IGP solutions:
PUA
-------
For me, the solution has two major drawbacks:
1)It tries to repurpose an existing (and fundamental) Reachability
Advertisement into an UnReachability advertisement under certain
conditions
The interoperability risks associated with this make me very reluctant
to go down this path.
And the use of the same advertisement to indicate Reachability and
Unreachability is IMO highly undesirable.
2)The withdrawal of the "Unreachability Advertisement" after some
delay (which is necessary) remains problematic despite the authors
attempts to address thus
Event Notification
------------------------
This avoids the drawbacks of PUA and is flexible enough to handle
future and unforeseen types of notifications.
I would like to extend the offer already made by Peter to the authors
of PUA to join us and work on the Event Notification draft.
The authors of PUA certainly deserve credit for raising awareness of
the problem space and it would be good to have them working with us on
a single IGP solution.
But PUA is not an alternative that I can support.
Les
> -----Original Message-----
> From: Lsr <lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>> On Behalf Of Acee
Lindem (acee)
> Sent: Wednesday, October 13, 2021 9:49 AM
> To: Peter Psenak <ppsenak=40cisco....@dmarc.ietf.org
<mailto:ppsenak=40cisco....@dmarc.ietf.org>>; lsr@ietf.org
<mailto:lsr@ietf.org>
> Subject: Re: [Lsr] "Prefix Unreachable Announcement" and "IS-IS and
> OSPF Extension for Event Notification"
>
> Hi Peter,
>
> See inline.
>
> On 10/13/21, 4:42 AM, "Peter Psenak"
> <ppsenak=40cisco....@dmarc.ietf.org
<mailto:ppsenak=40cisco....@dmarc.ietf.org>> wrote:
>
> Hi Acee,
>
> On 12/10/2021 21:05, Acee Lindem (acee) wrote:
> > Speaking as WG Chairs:
> >
> > The authors of “Prefix Unreachable Announcement”have
> requested
an
> > adoption. The crux of the draft is to signal unreachability of a prefix
> > across OSPF or IS-IS areas when area summarization is employed and
> > prefix is summarised. We also have “IS-IS and OSPF Extension for Event
> > Notification”which can be used to address the same use case.
> The
drafts
> > take radically different approaches to the problem and the authors of
> > both drafts do not wish to converge on the other draft’s method so it is
> > understandable that merging the drafts really isn’t an option.
>
> just for the record, I offered authors of "Prefix Unreachable
> Announcement" co-authorship on "Event notification" draft, arguing the
> the event base solution addresses their use case in a more elegant and
> scalable way. They decided to push their idea regardless.
>
> One solution to this problem would have definitely been better.
>
> > Before an adoption call for either draft, I’d like to ask the WG:
> >
> > 1. Is this a problem that needs to be solved in the IGPs? The use case
> > offered in both drafts is signaling unreachability of a BGP peer.
> > Could this better solved with a different mechanism (e.g., BFD)
> > rather than flooding this negative reachability information across
> > the entire IGP domain?
>
> we have looked at the various options. None of the existing ones would
> fit the large scale deployment with summarization in place. Using BFD
> end to end to track reachability between PEs simply does not scale.
>
> It seems to me that scaling of BFD should be "roughly" proportional
> to BGP session scaling but I seem to be in the minority. My opinion
> is based on SDWAN tunnel scaling, where BFD is used implicitly in
> our solution. How many other PEs does a BGP edge PE maximally peer with?
> Thanks,
> Acee
>
>
> Some people believe this should be solved by BGP, but it is important to
> realize that while the problem statement at the moment is primarily
> targeted for egress PE reachability loss detection for BGP, the
> mechanism proposed is generic enough and can be used to track
> the
peer
> reachablity loss for other cases (e.g GRE endpoint, etc) that do not
> involve BGP.
>
> We went even further and explored the option to use completely out of
> band mechanism that do not involve any existing protocols.
>
> Simply, the advantage of using IGP is that it follows the existing MPLS
> model, where the endpoint reachability is provided by IGPs. Operators
> are familiar with IGPs and know how to operate them.
>
> On top of the above, IGP event notification can find other use cases in
> the future, the mechanism defined in draft is generic enough.
>
>
> > 2. Assuming we do want to take on negative advertisement in the IGP,
> > what are the technical merits and/or detriments of the two
> approaches?
>
> we have listed some requirements at:
>
>
> https://datatracker.ietf.org/doc/html/draft-ppsenak-lsr-igp-event-
> notification-00#section-3
>
> From my perspective the solution should be optimal in terms of amount
> of data and state that needs to be maintained, ideally separated from
> the traditional LS data. I also believe that having a generic mechanism
> to distribute events has it own merits.
>
> thanks,
> Peter
>
> >
> > We’ll reserve any further discussion to “WG member”comments
> on the two
> > approaches.
> >
> > Thanks,
> > Acee and Chris
> >
>
>
> _______________________________________________
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> Lsr@ietf.org <mailto:Lsr@ietf.org>
> https://www.ietf.org/mailman/listinfo/lsr
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