Ketan –
I am very happy to be wrong in this case. 😊
We are in full agreement.
Les
From: Lsr <[email protected]> On Behalf Of Ketan Talaulikar
Sent: Monday, November 6, 2023 11:52 PM
To: Les Ginsberg (ginsberg) <[email protected]>
Cc: John Drake <[email protected]>; Peter Psenak (ppsenak)
<[email protected]>; Aijun Wang <[email protected]>; [email protected]
Subject: Re: [Lsr] Technical questions for draft about unreachable prefixes
announcement
Hi Les,
I disagree with your reading of RFC9084 (OSPF Prefix Originator).
Sec 1
This document proposes extensions to the OSPF protocol for the inclusion of
information associated with the router originating the prefix along with the
prefix advertisement. These extensions do not change the core OSPF route
computation functionality.
Sec 2.1
For intra-area prefix advertisements, the Prefix Source OSPF Router-ID Sub-TLV
MUST be considered invalid and ignored if the OSPF Router ID field is not the
same as the Advertising Router field in the containing LSA. Similar validation
cannot be reliably performed for inter-area and external prefix
advertisements.¶<https://www.rfc-editor.org/rfc/rfc9084.html#section-2.1-6>
A received Prefix Source OSPF Router-ID Sub-TLV with the OSPF Router ID field
set to 0 MUST be considered invalid and ignored. Additionally, reception of
such sub-TLVs SHOULD be logged as an error (subject to rate limiting).
As editor of this document, it is absolutely clear to me that we are referring
to the sub-TLV and not the prefix advertisement. So, when the value is set to
0, the sub-TLV is invalid and ignored - the prefix reachability is not at all
affected.
This is the reason why I am firmly opposed to using Prefix Originator value 0
for UPA or any other indication.
I hope I am able to convince you :-)
Thanks,
Ketan
On Tue, Nov 7, 2023 at 12:44 AM Les Ginsberg (ginsberg)
<[email protected]<mailto:[email protected]>> wrote:
To add to what Ketan has stated…
draft-wang-lsr-prefix-unreachable-annoucement defines the same mechanism for
both OSPF and IS-IS i.e., it proposes to use a prefix-originator sub-TLV with
address set to 0.0.0.0 to indicate unreachability.
For OSPF, this might be considered compatible with RFC 9084 where it is stated
that advertisements with “Router ID field set to 0 MUST be considered invalid
and ignored” - though Ketan has indicated this usage is undesirable.
However, no equivalent statement was ever made for IS-IS in RFC 7794 – so this
simply does not work in the case of IS-IS.
I (among others) pointed this out to the authors of draft-wang multiple times
over the years, but my feedback was ignored.
Which is an example of why I would like to echo Ketan’s sentiments – let’s
please put an end to this non-constructive discussion.
The authors of draft-wang have had many opportunities over the years to respond
in a more constructive way to feedback. They were also – as Peter has indicated
– given an opportunity to co-author draft-ietf-lsr-igp-ureach-prefix-announce
out of respect for them bringing the problem space to the attention of the WG.
They declined – which of course is their right. But they do not have the right
to endlessly oppose the consensus of the WG.
Let’s please move on.
Les
From: Lsr <[email protected]<mailto:[email protected]>> On Behalf Of
Ketan Talaulikar
Sent: Monday, November 6, 2023 3:01 PM
To: John Drake
<[email protected]<mailto:[email protected]>>
Cc: Peter Psenak (ppsenak) <[email protected]<mailto:[email protected]>>; Aijun
Wang <[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>
Subject: Re: [Lsr] Technical questions for draft about unreachable prefixes
announcement
Hi Aijun,
As your co-author on the OSPF Prefix Originator RFC, I have stated many times
(e.g. [1]) that overloading semantics of Prefix Originator is not a good or
clean protocol encoding. Semantically, it is wrong and a very bad protocol
design in my opinion. Going by this logic, tomorrow, someone would want to
encode some different meaning for all 1's value in the originator address. We
cannot be doing such (IMHO) HACKS in the protocol encodings.
It is better to signal the semantics/meaning explicitly using specific flags
that are meaningful.
The authors of draft-ppsenak (now a WG document) agreed to this feedback from
WG members and incorporated the U/UP flags in their draft. However, the authors
of draft-wang seem to continue to refuse to accept feedback. It is perhaps one
of the reasons why the WG adopted the draft-ppsenak and not draft-wang.
WG chairs, is there a way to put an end to this debate such that it does not
continue endlessly?
Thanks,
Ketan
[1] thread
https://mailarchive.ietf.org/arch/msg/lsr/FNbqHPhphY3GOfw-NWkLjmoRDVs/
On Mon, Nov 6, 2023 at 7:31 PM John Drake
<[email protected]<mailto:[email protected]>> wrote:
Aijun,
You castigated Peter for his lack of rigor in his reply to your email, however,
I think that was completely unfounded. Further, your reply to Peter seems to
be argument by emphatic assertion, rather than "technical analysis/comparison".
Thanks,
John
On Monday, November 6, 2023 at 08:41:38 AM PST, Aijun Wang
<[email protected]<mailto:[email protected]>> wrote:
Hi, Peter:
Let’s focus on the technical analysis/comparison for the mentioned issues, and
don’t repeat the subjective comments that without any solid analysis.
Detail replies inline below.
Aijun Wang
China Telecom
On Nov 6, 2023, at 14:53, Peter Psenak
<[email protected]<mailto:[email protected]>> wrote:
Aijun,
please see inline:
On 06/11/2023 13:23, Aijun Wang wrote:
Hi, all:
Here are some technical questions for the hurry adopted draft about unreachable
prefixes announcement:
1) There exists already “prefix originator” sub-TLV to indicate the associated
prefix is unreachable, what’s the advantage of using other undefined,
to-be-standardized, to-be-implemented sub-TLV?
many people have already commented on why overloading the “prefix originator”
sub-TLV to signal unreachability is a bad idea. Please accept that feedback.
[WAJ] No one gives the technical analysis. Can you explain technically in
detail?
You can set the prefix metric to LS-infinity to indicate the unreachability,
why can’t we the prefix originator to NULL to indicate the
unreachability?———The key idea for using “prefix originator” is here: if there
is no router originate the associated prefix, then it is certainly unreachable.
It is more straightforward than the LS_Infinity, and is also more easily
implemented, deployed than the to-be-defined, to-be-standardized sub-TLV.
2) It is unnecessary to define the “UP” flag——if the operator know the
unreachable event in advance, they can also schedule the switchover of the
related services in advance. Why bother IGP to transfer such information?
looks like there are folks that see the value in it. I let them to comment
more, but I don't necessarily see a problem in an extra bit. If you don't like
it, don't use it.
3) There is very limited usage of LS_Infinity in current network. From the
operator’s viewpoint, we will decrease its usage also in future. Then the
solution should try their best to avoid their usages——Current solutions instead
enhance its usage——It is unacceptable. Let’s keep the network simple.
the reasons for using the LSInfinity for unreachability has been discussed at
great length a;ready. It's the backward compatibility for routers not
supporting the new signalling - we need to avoid them interpreting the
unreachability as reachability.
[WAJ] My emphasis is that we shouldn’t enhance the usage of LS-Infinity(you
propose that the LS-Infinity metric must be carried) Instead, we should try to
fade them out:
1) If all routers within one area/domain all support the new capabilities, we
need not require the summary LSA to carry LS-infinity metric.
2) The Maxage of LSA can also be used to achieve the similar effects of legacy
node bypassing.
4) We can’t ignore the partitions scenarios or let’s it go.
if you feel like the partition is the problem, you can write a separate draft
and address it there. We are NOT trying to solve it with UPA draft. And for a
reason.
[WAJ] They are coupled. If you don’t consider it now, you need to update your
proposal later.
5) There should be some mechanisms to control the volume of advertised
unreachable information, when compared with reachable information, as done in
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-12#section-6.
please look at the section 6 of the UPA draft.
[WAJ] I am referring to the balance advertisement of reachable information, as
did in the above link, not the simple statement as the following: “It is also
recommended that implementations limit the number of UPA advertisements which
can be originated at a given time. “
Actually, even for your above statement,
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-12#name-deployment-considerations-4
gives more guidelines, I think you can refer to it again.
thanks,
Peter
Please consider the above technical issues carefully before evaluating and
adopted any proposal.
If the above issues can’t be solved, we request the WG to adopt also the
https://datatracker.ietf.org/doc/draft-wang-lsr-prefix-unreachable-annoucement/,which
cover and solve all of the above issues.
Aijun Wang
China Telecom
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