[Lsr] 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 <[e-mail]>]

Hi, Acee:

Until now, I haven't found any reasonable explanation that " prefixes with an infinite metric are unreachable by design " in the existing documents(for example, https://datatracker.ietf.org/doc/draft-ietf-lsr-ospf-ls-link-infinity/ gives the reason to introduce the value of LSLinkInfinity). 
There are many possible scenarios that the 'total cost' of one prefix reach the infinite metric.

Actually, such design can lead the network traffic be broken unintentionally(I have given you the example, with or without summary LSA). 

The proposal within the current UPA will activate such dormant, should be abandoned feature, and bring more network outages accidently.

The WG should seek other solution to achieve the same aim of UPA proposal.

Best Regards

Aijun Wang
China Telecom

-----邮件原件-----
发件人: Acee Lindem [mailto:[e-mail]] 
发送时间: 2025年5月12日 19:12
收件人: Aijun Wang <[e-mail]>
抄送: Peter Psenak <[e-mail]>; lsr <[e-mail]>
主题: Re: [Lsr] [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

Speaking as WG member:

Aijun, 

> On May 11, 2025, at 9:33 PM, Aijun Wang <[e-mail]> wrote:
> 
> Hi, Acee:
> 
> The "area range" is not always be configured at the ABR, or the "area range" may not cover all of the prefixes within the area.
> In such situation, if there is no summary LSA advertised for these prefixes( with which their total cost exceed LSInifinity), the routers within other area can't reach these prefixes.
> The network traffic will be discarded wrongly.

The UPA is specifically targeted toward prefixes that are subsumed by a shorter prefix corresponding to a summary. 


> 
> And, we can image even another scenario, even the routers within the same area can't reach these prefixes, if they treat the prefixes that the 'total cost' equal LSinifity as unreachable.

> 
> This is one remain bug of RFC 2328. The situation is same for 
> RFC5305/RFC5308 UPA solution shouldn't depend on such bug base.

There is no bug in RFC 2328/RFC 5305/RFC 5308, prefixes with an infinite metric are unreachable by design. 
I'm not going to debate this. 

Acee



> 
> 
> Best Regards
> 
> Aijun Wang
> China Telecom
> 
> -----邮件原件-----
> 发件人: [e-mail] 
> [mailto:[e-mail]] 代表 Acee Lindem
> 发送时间: 2025年5月9日 22:18
> 收件人: Aijun Wang <[e-mail]>
> 抄送: Peter Psenak <[e-mail]>; lsr <[e-mail]>
> 主题: [Lsr] Re: [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
> 
> 
> 
>> On May 9, 2025, at 10:08 AM, Aijun Wang <[e-mail]> wrote:
>> 
>> Hi, Acee:
>> 
>> If no summary LSA  for these prefixes, then, there will be no LSA for these prefixes, it leads the same WRONG results—-such prefixes are unreachable in another area.
> 
> As long as there is at least 1 reachable route subsumed by the area range, there will be a summary-LSA.
> 
> Acee
> 
> 
> 
>> 
>> Aijun Wang
>> China Telecom
>> 
>>> On May 9, 2025, at 21:58, Acee Lindem <[e-mail]> wrote:
>>> 
>>> Speaking as WG member,
>>> 
>>> 
>>>> On May 9, 2025, at 9:28 AM, Peter Psenak <ppsenak=[e-mail]> wrote:
>>>> 
>>>> Aijun,
>>>> 
>>>>> On 09/05/2025 15:22, Aijun Wang wrote:
>>>>> 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.
>>>> no UPA does not affect prefixes that are advertised with valid metric.
>>>>> 
>>>>> 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.
>>>> If the prefix metric is LSInfinity, the prefix is unreachable. UPA does not change any of that.
>>>>> 
>>>>> It’s time to fix RFC2328/RFC5305/RFC5308.
>>>> I don't think so.
>>> 
>>> I agree. There is nothing in the UPA draft, that says the unreachable prefix will be included in the summary cost calculation. I don't know how one would come to that conclusion.
>>> 
>>> Also, for OSFP, in section 12.4.3 of RFC 2328, routes with a metric of LSInfinity or higher are explicitly disqualified from the summary computation.
>>> 
>>>   o Else, if the routing table cost equals or exceeds the
>>>      value LSInfinity, a summary-LSA cannot be generated for
>>>      this route.
>>> 
>>> 
>>> Thanks,
>>> Acee
>>> 
>>> 
>>> 
>>> 
>>> 
>>>>> 
>>>>> Let’s do this together before forwarding the UPA draft?
>>>> no, we are not going to modify the LSInfinity in any way inside or outside of the UPA.
>>>> I'm done with this discussion now.
>>>> Regards,
>>>> Peter
>>>>> 
>>>>> Aijun Wang
>>>>> China Telecom
>>>>> 
>>>>>> On May 9, 2025, at 18:04, Peter Psenak <[e-mail]> 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: [e-mail] 
>>>>>>> [mailto:[e-mail]] 代表 
>>>>>>> [e-mail]
>>>>>>> 发送时间: 2025年5月9日 2:21
>>>>>>> 收件人: [e-mail]
>>>>>>> 抄送: [e-mail]
>>>>>>> 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-prefi
>>>>>>> x
>>>>>>> -announce/
>>>>>>> 
>>>>>>> There is also an HTMLized version available at:
>>>>>>> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-igp-ureach-
>>>>>>> p
>>>>>>> refix-announce-05
>>>>>>> 
>>>>>>> A diff from the previous version is available at:
>>>>>>> https://author-tools.ietf.org/iddiff?url2=draft-ietf-lsr-igp-ure
>>>>>>> a
>>>>>>> ch-prefix-announce-05
>>>>>>> 
>>>>>>> Internet-Drafts are also available by rsync at:
>>>>>>> rsync.ietf.org::internet-drafts
>>>>>>> 
>>>>>>> 
>>>>>>> _______________________________________________
>>>>>>> Lsr mailing list -- [e-mail] To unsubscribe send an email to 
>>>>>>> [e-mail]
>>>>>>> 
>>>>>>> _______________________________________________
>>>>>>> Lsr mailing list -- [e-mail] To unsubscribe send an email to 
>>>>>>> [e-mail]
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> Lsr mailing list -- [e-mail]
>>>>>> To unsubscribe send an email to [e-mail]
>>>> 
>>>> _______________________________________________
>>>> Lsr mailing list -- [e-mail]
>>>> To unsubscribe send an email to [e-mail]
>>> 
>>> _______________________________________________
>>> Lsr mailing list -- [e-mail]
>>> To unsubscribe send an email to [e-mail]
>> 
> 
> _______________________________________________
> Lsr mailing list -- [e-mail]
> To unsubscribe send an email to [e-mail]
>