[Lsr] Re: 答复: [LSInfinity Features within OSPF is FLAWed, it should be Abandoned, not Enhanced instead] I-D Action: draft-ietf-lsr-igp-ureach-prefix-announce-05.txt

[Aijun Wang]

Hi, Peter: UPA doesn’t influence the results of the prefixes that are set to be the LSInfinity at its originator, but it influences the results of the prefixes whose metrics are lower than LSInfinity. I have show you the example in the previous mail—-For example, in https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47864-ospfdb5.html , when prefix 4.0.0.0/8 reaches to the ABR, it is reachable(prefix cost is 0xffffff-0x40, lower than LSInfinity). But after the ABR advertise the prefix in area 1 with the Summary LSA, its metric will be LSInfinity. According to the UPA rule, or RFC 2328, every router(includes the final receiver) within the area 1 will treat this prefix as unreachable, which is NOT right. It’s time to fix RFC2328/RFC5305/RFC5308. Let’s do this together before forwarding the UPA draft? Aijun Wang China Telecom On May 9, 2025, at 18:04, Peter Psenak <ppse...@cisco.com> wrote:  Aijun, the problem you have described below has no relevance to the UPA. In the UPA case we are deliberately originating the prefix with the unreachable metric, so adding anything to it at ABR is not going to make any difference, it will stay as unreachable. As I have replied to you many times the meaning of the LSInfinity was defined in the base protocol specification and we are not altering it in any way. We are using it the way it was defined. Regards, Peter On 09/05/2025 10:55, Aijun Wang wrote: Hi, Peter: I noticed the updated draft includes the new contributors to respect their previous efforts, this should be encouraged within IETF. But, I must point out that, the direction that Reusing the LSInfinity to advertise the unreachable information should be discarded. The LSInfinity feature that is defined in RFC 2328 is FLAWED, we should try to fix it, not exploit it again. Let's give you the simple example, that described in "OSPF Inter-Area Routing" [1] This is one 20 years ago article, it states clearly that when ABR do the summary action, it will add the cost of the prefix itself and the cost of the path between the prefix originator and the ABR together, as the newly cost of the summary LSA for the prefix: In the example, the original cost of 4.0.0.0/8 is 10, the link cost between Router 1.1.1.1 and Router 2.2.2.2 is 64, the ABR(router 2.2.2.2) will advertise the summary LSA for 4.0.0.0/8 to Area 1, with the cost set to 10+64=74 (please see the output of "r2.2.2.2#show ip ospf database summary 4.0.0.0") Then coming the question(let's take the same example): If the cost of prefix 4.0.0.0/8 is set to 0xffffff-0x40(64), on ABR(router 2.2.2.2), the cost of summary LSA for prefix 4.0.0.0/8 will reach 0xfffff. If the ABR(router 2.2.2.2) follow the guideline of RFC 2328, the prefix 4.0.0.0/8 will be unreachable, and will be not advertised to area 1, router in area 1 can't reach the 4.0.0.0/8. But actually, 4.0.0.0/8 is reachable via the ABR(router 2.2.2.2). If we consider there may be several hops between the prefix originator and the ABR, then the cost of the prefix can't exceed 【0xffffff-(several hops)*(possible link metric)】, which will be varied with different network topology, and can't be considered as one universal value, even a definite range. Then, such flaw in OSPF 2328, and also the similar mechanism in RFC 5305/RFC5308 for IS-IS should be fixed. The reason that there is no emerged network outrage in these years is that the operator configure seldom the cost of the prefix directly. But if we expand the LSInfinity feature as described in this WG document, more chaos, and network outrages will be emerged. Let's stop forwarding to this direction. [1]: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47864-ospfdb5.html Best Regards Aijun Wang China Telecom -----邮件原件----- 发件人: forwardingalgori...@ietf.org [mailto:forwardingalgori...@ietf.org] 代表 internet-dra...@ietf.org 发送时间: 2025年5月9日 2:21 收件人: i-d-annou...@ietf.org 抄送: lsr@ietf.org 主题: [Lsr] I-D Action: draft-ietf-lsr-igp-ureach-prefix-announce-05.txt Internet-Draft draft-ietf-lsr-igp-ureach-prefix-announce-05.txt is now available. It is a work item of the Link State Routing (LSR) WG of the IETF. Title: IGP Unreachable Prefix Announcement Authors: Peter Psenak Clarence Filsfils Daniel Voyer Shraddha Hegde Gyan Mishra Name: draft-ietf-lsr-igp-ureach-prefix-announce-05.txt Pages: 15 Dates: 2025-05-08 Abstract: In the presence of summarization, there is a need to signal loss of reachability to an individual prefix covered by the summary. This enables fast convergence by steering traffic away from the node which owns the prefix and is no longer reachable. This document describes how to use the existing protocol mechanisms in IS-IS and OSPF, together with the two new flags, to advertise such prefix reachability loss. The IETF datatracker status page for this Internet-Draft is: https://datatracker.ietf.org/doc/draft-ietf-lsr-igp-ureach-prefix-announce/ There is also an HTMLized version available at: https://datatracker.ietf.org/doc/html/draft-ietf-lsr-igp-ureach-prefix-announce-05 A diff from the previous version is available at: https://author-tools.ietf.org/iddiff?url2=draft-ietf-lsr-igp-ureach-prefix-announce-05 Internet-Drafts are also available by rsync at: rsync.ietf.org::internet-drafts _______________________________________________ Lsr mailing list -- lsr@ietf.org To unsubscribe send an email to lsr-le...@ietf.org _______________________________________________ Lsr mailing list -- lsr@ietf.org To unsubscribe send an email to lsr-le...@ietf.org _______________________________________________ Lsr mailing list -- lsr@ietf.org To unsubscribe send an email to lsr-le...@ietf.org

_______________________________________________
Lsr mailing list -- lsr@ietf.org
To unsubscribe send an email to lsr-le...@ietf.org