On Apr 24, 2025, at 16:29, Peter Psenak <[email protected]> wrote:
On 23/04/2025 11:18, Aijun Wang wrote:
Hi, All:
I read carefully again the WGLC draft, and OBJECT strongly for its forwarding.
The reasons are the followings:
Section I: Decent IETF Behaviors
1) The scenario, initial solution and intense discussions are described,
initiated, organized by the authors of
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-00
(From October 2019), there is no any mentions in this document for these
experts’ efforts. This is not the decent behavior within IETF.
2) The idea of
https://datatracker.ietf.org/doc/html/draft-ietf-lsr-igp-ureach-prefix-announce-04#section-4
is first describe in
https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement-06#section-7
(March, 2021), ONE YEAR Earlier than the initial draft of the WGLC document.(
https://datatracker.ietf.org/doc/html/draft-ppsenak-lsr-igp-ureach-prefix-announce-00)
(March, 2022). This is another non-decent behavior within IETF.
I find above claims to be false and rather aggressive.
As a response to the accusations above I'm sending the historical summary of
how things evolved over time the time. Thanks to Les for remembering and
collecting some of these facts.
I'm not planing to participate in any further discussion on this matter.
The Prefix Unreachable Advertisement Draft(PUA)
https://datatracker.ietf.org/doc/draft-wang-lsr-prefix-unreachable-annoucement/
was first published in October of 2019.Significant discussion of the merits of
the draft continued over the next few years - both on and off the WG list.
It was pointed out to the authors that the proposed solution was problematic -
not least because it depended on a non-backwards compatible advertisement
(using a source router-id of 0.0.0.0 in prefix reachability advertisements).
Although various modifications were made to the draft over the years, the core
mechanism of the solution was never changed.
Over the years, customer interest in a solution to this problem increased. In
March of 2022 an alternative solution to the problem - the Unreachable Prefix
Advertisement Draft (UPA)
https://datatracker.ietf.org/doc/draft-ietf-lsr-igp-ureach-prefix-announce/ was
published.
It uses a fully backwards compatible advertisement - sending prefix reachability with a
metric value already defined in existing RFCs are meaning "do not consider this
prefix in SPFs".
The authors of the PUA draft, who rightfully deserve credit for first bringing
this problem to the attention of the WG, were invited to join as co-authors on
the UPA draft, but they declined and continued to promote the PUA solution.
WG presentations for both drafts were made at IETF 114:
https://datatracker.ietf.org/meeting/114/materials/slides-114-lsr-08-
prefix-unreachable-announcement-00
https://datatracker.ietf.org/meeting/114/materials/slides-114-lsr-07-
upa-00 In September of 2023 the UPA draft was adopted as a WG
document - indicating that the consensus of the WG favored the UPA solution
(backwards compatible) over the PUA solution (not-backwards compatible).
Since then, implementations of the UPA draft have been written and successfully
deployed.
In April of 2025 WG Last Call has been initiated on the UPA draft.
thanks,
Peter
Section II: Technical Analysis
1) The WGLC provide two methods to label the unreachable prefixes, one
depends on LSInifinity setting of the advertised prefix, the other depends on
the newly defined flag.
They are redundancy and confusion. The meaning of LSinifinity is already
defined in the existing documents, and there is no necessary to rephrase them.
The solution needs only depend on one method.
2) For the usage of LSInifinity, although RFC 2328 and RFC 5305 defines
its possible usage, if they are used in such way(I have not heard any operator
deploy such mechanics), their deployment should be gradually disappearing, not
enhance instead. There are three reasons for such considerations:
a) The maximum metric value is often treated as the last resort of
reachability, not the unreachability. It will lead more confusions for the
setting of such metric in the network.
b) It states clearly in the RFC 2328 section 14.1, that “Premature aging can
also be used when, for example, one of the router's previously advertised external
routes is no longer reachable. In this circumstance, the router can flush its AS-
external-LSA from the routing domain via premature aging. This procedure is
preferable to the alternative, which is to originate a new LSA for the destination
specifying a metric of LSInfinity."
c) During the SPF calculation, the final cost is the summary of every
segment cost. It is possible that the final cost exceed also the LSinfinity,
but the prefix is reachable.
3) For the Signaling Method, it defines the additional flags based one
newly defined sub-TLV for OSPF, and existing sub-TLV for IS-IS.
Far complex than the usage of “Prefix Originator” directly. The document just
want to make some differences, not the efficiency.
4) The WGLC document doesn’t solve the area/domain partition scenaro,
which may appear in the network, and is already covered by
https://datatracker.ietf.org/doc/draft-wang-lsr-prefix-unreachable-annoucement/
(let’s call it Founder Document). It states, “UPA does not make the problem of
an area partition any worse. ”-----Actually, it does worse----If one ABR can’t
reach the egress router(PE1), but another ABR can reach, there should be no
switchover of the egress router(PE2), which may be reachable, or may be
unreachable.-----There should be some coordinate mechanism among the ABRs, as
that described in the above Founder Document.
5) There is no any consideration for the balance of reachable information
and unreachable information announcements. It will be disaster in some critical
condition.
Best Regards
Aijun Wang
China Telecom
发件人: [email protected]
[mailto:[email protected]] 代表 Aijun Wang
发送时间: 2025年4月22日 0:12
收件人: Yingzhen Qu <[email protected]>
抄送: lsr <[email protected]>; lsr-chairs <[email protected]>
主题: [Lsr] Re: WG Last Call for
draft-ietf-lsr-igp-ureach-prefix-announce (4/17/2025 - 5/2/2025) I object its
forwarding, from the beginning of its WG adoption.
Aijun Wang
China Telecom
On Apr 18, 2025, at 02:13, Yingzhen Qu <[email protected]> wrote:
Hi,
This email begins a 2 week WG Last Call for the following draft:
IGP Unreachable Prefix Announcement
https://datatracker.ietf.org/doc/draft-ietf-lsr-igp-ureach-prefix-an
nounce/
Please review the document and indicate your support or objections by May 2nd, 2025.
Authors and contributors,
Please indicate to the list your knowledge of any IPR related to this work.
Thanks,
Yingzhen
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