Re: [Lsr] Working Group Adoption of "IGP Unreachable Prefix Announcement" - draft-ppsenak-lsr-igp-unreach-prefix-announce-04

[Peter Psenak <[e-mail]>]

Robert,

On 31/08/2023 02:36, Robert Raszuk wrote:
>>  it would be helpful to summarize the common parts of the two solutions,
> 
> Actually IMO it would be much more helpful to summarise differences of 
> both solutions not common parts.

please read both drafts and you would easily get the difference. If you 
are not in favor of doing that, please read Les's response to Zhibo, it 
has the most important parts.

thanks,
Peter

> 
> Thx,
> r.
> 
> 
> 
> On Thu, Aug 31, 2023 at 11:23 AM Dongjie (Jimmy) <[e-mail] 
> <mailto:[e-mail]>> wrote:
> 
>     Hi Les and Robert,____
> 
>     __ __
> 
>     Please see some comments inline:____
> 
>     __ __
> 
>     *From:*Lsr [mailto:[e-mail]
>     <mailto:[e-mail]>] *On Behalf Of *Robert Raszuk
>     *Sent:* Thursday, August 31, 2023 4:19 PM
>     *To:* Les Ginsberg (ginsberg) <ginsberg=[e-mail]
>     <mailto:[e-mail]>>
>     *Cc:* Huzhibo <huzhibo=[e-mail]
>     <mailto:[e-mail]>>; Peter Psenak (ppsenak)
>     <[e-mail] <mailto:[e-mail]>>; linchangwang
>     <[e-mail] <mailto:[e-mail]>>;
>     Acee Lindem <[e-mail] <mailto:[e-mail]>>; lsr
>     <[e-mail] <mailto:[e-mail]>>;
>     [e-mail]
>     <mailto:[e-mail]>
>     *Subject:* Re: [Lsr] Working Group Adoption of "IGP Unreachable
>     Prefix Announcement" -
>     draft-ppsenak-lsr-igp-unreach-prefix-announce-04____
> 
>     __ __
> 
>     *Hi Les,*____
> 
>     __ __
> 
>     > But existing implementations will NOT ignore a prefix reachability advertisement just because ____
> 
>     > it has a source Router ID set to 0 as draft-wang-lsr-prefix-unreachable-annoucement defines.____
> 
>     __ __
> 
>     True, but let's do not forget the bigger picture here. The dst is
>     already covered by summary so for the ____
> 
>     app it really does not matter ... It is reachable anyway. ____
> 
>     __ __
> 
>     Bottom line is that both solutions need to have upgraded code to use
>     the new trigger. ____
> 
>     __ __
> 
>     [Jie] Agreed. Consider the existence of the summary route,
>     advertising Max_Metric for a prefix covered by the summary route
>     will not make it unreachable. A router needs to either understand
>     the new flags as defined in draft-ppsenak, or understand the
>     semantic of the NULL originator as specified in draft-wang to behave
>     accordingly. This make me wonder whether it is still necessary to
>     set the metric of that prefix to Max?____
> 
>     __ __
> 
>     After several rounds of update, to me the two solutions becomes
>     similar in principle , just choose different ways to encode the
>     trigger information. ____
> 
>     __ __
> 
>     __ __
> 
>     *Dear LSR chairs,*____
> 
>     __ __
> 
>     I am not sure what harm would it make to start WG adoption call on
>     both drafts and see the results. ____
> 
>     __ __
> 
>     [Jie] This sounds like a reasonable suggestion. ____
> 
>     __ __
> 
>     And since the WG has been discussing this problem and the two
>     solution drafts for a while, it would be helpful to summarize the
>     common parts of the two solutions, and highlight their difference,
>     so that people can understand the current state and make their
>     decision. ____
> 
>     __ __
> 
>     Best regards,____
> 
>     Jie____
> 
>     ____
> 
>     So far I am not seeing strong and uniform adoption support for
>     either one :) ____
> 
>     __ __
> 
>     Not sure why some authors feel like their work was rejected. ____
> 
>     __ __
> 
>     Cheers,____
> 
>     R.____
> 
>     __ __
> 
>     __ __
> 
>     On Thu, Aug 31, 2023 at 4:57 AM Les Ginsberg (ginsberg)
>     <ginsberg=[e-mail]
>     <mailto:[e-mail]>> wrote:____
> 
>         Zhibo -____
> 
>         ____
> 
>         Please see inline.____
> 
>         ____
> 
>         > -----Original Message-----____
> 
>         > From: Huzhibo <huzhibo=[e-mail]
>         <mailto:[e-mail]>>____
> 
>         > Sent: Wednesday, August 30, 2023 6:33 PM____
> 
>         > To: Les Ginsberg (ginsberg) <[e-mail] <mailto:[e-mail]>>; Peter Psenak
>         (ppsenak)____
> 
>         > <[e-mail] <mailto:[e-mail]>>; linchangwang
>         <[e-mail]
>         <mailto:[e-mail]>>;____
> 
>         > Acee Lindem <[e-mail] <mailto:[e-mail]>>; lsr
>         <[e-mail] <mailto:[e-mail]>>____
> 
>         > Cc: [e-mail]
>         <mailto:[e-mail]>____
> 
>         > Subject: RE: [Lsr] Working Group Adoption of "IGP Unreachable Prefix____
> 
>         > Announcement" - draft-ppsenak-lsr-igp-unreach-prefix-announce-04____
> 
>         > ____
> 
>         > Hi Les:____
> 
>         > ____
> 
>         >     I think you may have connected something. Existing routers, on receiving a____
> 
>         > prefix reachability advertisement with a____
> 
>         > U-Flag described in https://datatracker.ietf.org/doc/draft-ppsenak-lsr-igp-
>         <https://datatracker.ietf.org/doc/draft-ppsenak-lsr-igp-ureach-prefix-announce/>____
> 
>         > ureach-prefix-announce/
>         <https://datatracker.ietf.org/doc/draft-ppsenak-lsr-igp-ureach-prefix-announce/> also will interpret that prefix as being reachable.____
> 
>         ____
> 
>         [LES:] This statement is incorrect.____
> 
>         RFC 5305 states:____
> 
>         ____
> 
>         <snip>____
> 
>         If a prefix is advertised with a metric larger then
>         MAX_PATH_METRIC____
> 
>             (0xFE000000, see paragraph 3.0), this prefix MUST NOT be
>         considered____
> 
>             during the normal SPF computation.  This allows
>         advertisement of a____
> 
>             prefix for purposes other than building the normal IP
>         routing table.____
> 
>         <end snip>____
> 
>         ____
> 
>         (Equivalent statement in RFC 5308 for IPv6)____
> 
>         ____
> 
>         Existing implementations will ignore the advertisement purely on
>         the basis of the metric value - this does not depend upon
>         understanding the U bit.____
> 
>         ____
> 
>         But existing implementations will NOT ignore a prefix
>         reachability advertisement just because it has a source Router
>         ID set to 0 as draft-wang-lsr-prefix-unreachable-annoucement
>         defines.____
> 
>         ____
> 
>         It is worth noting that AFTER the publication of
>         draft-ppsenak-lsr-igp-pfx-reach-loss-00 in March 2022
>         (subsequently renamed as
>         draft-ppsenak-lsr-igp-ureach-prefix-announce), the authors of
>         draft-wang-lsr-prefix-unreachable-annoucement apparently
>         realized they had  an interoperability problem with existing
>         routers (something many of us had been highlighting for years)
>         and in V10 (published in Jul 2022) an option was added to
>         advertise using maximum metric (the solution already proposed by
>         draft-ppsenak). But because the authors apparently didn’t want
>         to abandon the use of "Router ID = 0", the new version of the
>         draft proposed a dependency on how the unreachable prefix should
>         be advertised. If all routers in the network indicated support
>         for the new extension (indicated by yet another protocol
>         extension - a new Router Capability sub-TLV for IS-IS) then the
>         use of Router ID = 0 could be used, but if any router in the
>         network did not advertise the new capability, then the use of
>         max-metric is required. Which means the solution requires
>         routers advertising unreachability to potentially regenerate the
>         advertisement in a different form whenever the state of support
>         by all routers in the network for the extension changes.____
> 
>         ____
> 
>         > Both two draft used The 0xFE000000 metric indicates that the prefix is not____
> 
>         > reachable. Doesn't make a difference at this point.____
> 
>         ____
> 
>         [LES:] The solution defined in
>         draft-ppsenak-lsr-igp-unreach-prefix-announce does not introduce
>         any interoperability issues with existing routers, does not
>         require multiple encoding formats, and does not require a router
>         to regenerate advertisements in a different form based on the
>         state of support by all routers in the network.____
> 
>         I think this makes a big difference. 😊____
> 
>         ____
> 
>             Les____
> 
>         ____
> 
>         > ____
> 
>         > Thanks____
> 
>         > ____
> 
>         > Zhibo Hu____
> 
>         > ____
> 
>         > > -----Original Message-----____
> 
>         > > From: Lsr [mailto:[e-mail] <mailto:[e-mail]>] On
>         Behalf Of Les Ginsberg____
> 
>         > > (ginsberg)____
> 
>         > > Sent: Thursday, August 31, 2023 12:31 AM____
> 
>         > > To: Peter Psenak <ppsenak=[e-mail]
>         <mailto:ppsenak=[e-mail]>>; linchangwang____
> 
>         > > <[e-mail] <mailto:[e-mail]>>;
>         Acee Lindem <[e-mail] <mailto:[e-mail]>>;____
> 
>         > > lsr <[e-mail] <mailto:[e-mail]>>____
> 
>         > > Cc: [e-mail]
>         <mailto:[e-mail]>____
> 
>         > > Subject: Re: [Lsr] Working Group Adoption of "IGP Unreachable Prefix____
> 
>         > > Announcement" - draft-ppsenak-lsr-igp-unreach-prefix-announce-04____
> 
>         > >____
> 
>         > > Changwang -____
> 
>         > >____
> 
>         > > It is very important to note ...____
> 
>         > >____
> 
>         > > <snip>____
> 
>         > > > > 2. The Draft #1 utilizes the existing mechanisms [RFC7794] and____
> 
>         > > > > [RFC9084] to____
> 
>         > > > indicate reachability by checking whether the originator information____
> 
>         > > > is____
> 
>         > > > >    NULL.____
> 
>         > > <end snip>____
> 
>         > >____
> 
>         > > This statement is incorrect. There is no existing mechanism defined in the____
> 
>         > > protocol that states that a prefix reachability advertisement sent with a____
> 
>         > > source router ID == 0 implies unreachability.____
> 
>         > > Please see https://www.rfc-editor.org/rfc/rfc7794.html#section-2.2
>         <https://www.rfc-editor.org/rfc/rfc7794.html#section-2.2>____
> 
>         > >____
> 
>         > > Existing routers, on receiving a prefix reachability advertisement with a____
> 
>         > > Source Router ID == 0 will interpret that prefix as being reachable - which____
> 
>         > > is exactly the opposite of the intent defined in____
> 
>         > > https://www.ietf.org/archive/id/draft-wang-lsr-prefix-unreachable-annouc <https://www.ietf.org/archive/id/draft-wang-lsr-prefix-unreachable-annouc>____
> 
>         > > ement-12.txt____
> 
>         > > This is one of the things which is broken in this draft.____
> 
>         > > This fact has been pointed out to the authors many times over the years -____
> 
>         > > but they have consistently ignored it.____
> 
>         > >____
> 
>         > > On the other hand,____
> 
>         > > https://www.ietf.org/archive/id/draft-ppsenak-lsr-igp-ureach-prefix-annou <https://www.ietf.org/archive/id/draft-ppsenak-lsr-igp-ureach-prefix-annou>____
> 
>         > > nce-04.txt uses an existing mechanism defined in RFC 5305 to insure that____
> 
>         > > legacy routers who do not understand the new use case or the new flags____
> 
>         > > will ignore the prefix reachability advertisement. This has been verified by____
> 
>         > > testing against multiple implementations.____
> 
>         > >____
> 
>         > > Please be accurate in the statements that you make.____
> 
>         > >____
> 
>         > >    Les____
> 
>         > >____
> 
>         > >____
> 
>         > > > -----Original Message-----____
> 
>         > > > From: Lsr <[e-mail] <mailto:[e-mail]>> On Behalf Of
>         Peter Psenak____
> 
>         > > > Sent: Wednesday, August 30, 2023 8:43 AM____
> 
>         > > > To: linchangwang <[e-mail] <mailto:[e-mail]>>;
>         Acee Lindem____
> 
>         > > > <[e-mail] <mailto:[e-mail]>>; lsr
>         <[e-mail] <mailto:[e-mail]>>____
> 
>         > > > Cc: [e-mail]
>         <mailto:[e-mail]>____
> 
>         > > > Subject: Re: [Lsr] Working Group Adoption of "IGP Unreachable Prefix____
> 
>         > > > Announcement" - draft-ppsenak-lsr-igp-unreach-prefix-announce-04____
> 
>         > > >____
> 
>         > > > Changwang,____
> 
>         > > >____
> 
>         > > > On 30/08/2023 08:15, linchangwang wrote:____
> 
>         > > > > Hi WG,____
> 
>         > > > >____
> 
>         > > > > When considering adoption, it's important to take into account the____
> 
>         > > > > following____
> 
>         > > > drafts as well.____
> 
>         > > > >____
> 
>         > > > > Draft #1 link：https://www.ietf.org/archive/id/draft-wang-lsr-prefix-
>         <https://www.ietf.org/archive/id/draft-wang-lsr-prefix->____
> 
>         > > > unreachable-annoucement-12.txt____
> 
>         > > > > Draft #2 link：https://www.ietf.org/archive/id/draft-ppsenak-lsr-igp-
>         <https://www.ietf.org/archive/id/draft-ppsenak-lsr-igp->____
> 
>         > > > ureach-prefix-announce-04.txt____
> 
>         > > > >____
> 
>         > > > > Reasons are as follows:____
> 
>         > > > >____
> 
>         > > > > 1. The two drafts mentioned above are similar in nature.____
> 
>         > > > >    The draft #1 covers more scenarios than the draft #2 as mentioned____
> 
>         > > > > by____
> 
>         > > > Zhibo Hu mail.____
> 
>         > > > >    Therefore, a more in-depth discussion and technical comparison____
> 
>         > > > > should____
> 
>         > > > take place before any adoption decision is made.____
> 
>         > > > >____
> 
>         > > > > 2. The Draft #1 utilizes the existing mechanisms [RFC7794] and____
> 
>         > > > > [RFC9084] to____
> 
>         > > > indicate reachability by checking whether the originator information____
> 
>         > > > is____
> 
>         > > > >    NULL. On the other hand, the draft #2 introduces a new flag to____
> 
>         > > > > indicate____
> 
>         > > > reachability.____
> 
>         > > > >    From an implementation perspective, it would be easier to____
> 
>         > > develop____
> 
>         > > > > using____
> 
>         > > > the existing RFC mechanisms.____
> 
>         > > > >____
> 
>         > > > > 3. The Draft #1 covers more scenarios and can address the____
> 
>         > > > > aggregation issues____
> 
>         > > > of multiple ABRs.____
> 
>         > > > >    However, the Draft #2 explicitly states in Chapter 6 that it does____
> 
>         > > > > not support____
> 
>         > > > this scenario.____
> 
>         > > >____
> 
>         > > > to be more precise, draft #1 talks about more scenarios, it does not____
> 
>         > > > solves any of them, as these scenarios can not be solved by what the____
> 
>         > > > draft #1 introduces.____
> 
>         > > >____
> 
>         > > > draft#2 clearly states the fact that these scenarios are not addressed.____
> 
>         > > >____
> 
>         > > > thanks,____
> 
>         > > > Peter____
> 
>         > > >____
> 
>         > > > >____
> 
>         > > > > 4. If we remove the additional scenarios covered in Draft #1 and____
> 
>         > > > > compare the____
> 
>         > > > two drafts, the only remaining difference is the method of indicating____
> 
>         > > > unreachable prefixes -____
> 
>         > > > >    either through a UPA flag or using the originator TLV.____
> 
>         > > > >____
> 
>         > > > >____
> 
>         > > > > Thanks,____
> 
>         > > > > Changwang____
> 
>         > > > >____
> 
>         > > > >____
> 
>         > > > > -----Original Message-----____
> 
>         > > > > From: Lsr [mailto:[e-mail] <mailto:[e-mail]>] On
>         Behalf Of Acee Lindem____
> 
>         > > > > Sent: Thursday, August 24, 2023 3:58 AM____
> 
>         > > > > To: lsr____
> 
>         > > > > Cc: [e-mail]
>         <mailto:[e-mail]>____
> 
>         > > > > Subject: [Lsr] Working Group Adoption of "IGP Unreachable Prefix____
> 
>         > > > Announcement" - draft-ppsenak-lsr-igp-unreach-prefix-announce-04____
> 
>         > > > >____
> 
>         > > > > LSR Working Group,____
> 
>         > > > >____
> 
>         > > > > This begins the working group adoption call for “IGP Unreachable____
> 
>         > > > > Prefix____
> 
>         > > > Announcement” - draft-ppsenak-lsr-igp-unreach-prefix-announce-04.____
> 
>         > > > > Please indicate your support or objection on this list prior to____
> 
>         > > > > September 7th,____
> 
>         > > > 2023.____
> 
>         > > > >____
> 
>         > > > > Thanks,____
> 
>         > > > > Acee____
> 
>         > > > > ___________________________________________________
> 
>         > > > > Lsr mailing list____
> 
>         > > > > [e-mail] <mailto:[e-mail]>____
> 
>         > > > > https://www.ietf.org/mailman/listinfo/lsr
>         <https://www.ietf.org/mailman/listinfo/lsr>____
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