Hi, Peter:
Currently, we have the following consideration:
1. If not all of the ABRs announce the unreachability of the specified 
prefix(the specified prefix is still up), such PUA information will continue 
advertising by the unreachable ABRs.
2. If all of the ABRs announce the PUA of the specified prefix, such 
information will be announced for a configurable duration, to make sure other 
protocol(for example BGP) that based on the specified prefix has converged.
How about the above consideration and 
Do you have other thoughts ?

Aijun Wang
China Telecom

> On Jul 30, 2020, at 17:21, Peter Psenak <ppsenak=40cisco....@dmarc.ietf.org> 
> wrote:
> 
> ´╗┐Hi Ajun,
> 
> one additional problem on top of others that have been mentioned is how are 
> you going to get rid of "old" un-reachability announcements/
> 
> Let's imagine you have the following prefixes in your area 1:
> 
> - 10.10.0.1/32 - 10.0.0.255/32 - used for loopback adresses
> - 10.10.1.0/30 - 10.10.10.252/32 - used for transit links
> 
> For simplicity your summary for area 1 is 10.0.0.0/16
> 
> 1. Everything is up, you generate 10.0.0.0/16 on the ABR that connects to 
> area 1 to all remaining connected areas
> 
> 2. A router in area 1 with loopback 10.10.0.25/32 goes down.
> 
> 3. ABR in area 1 generates un-reachable announcement for 10.0.0.25/32 to all 
> other connected areas
> 
> 4. When does ABR stop generating the un-reachable announcement for 
> 10.0.0.25/32? In section 6 you mention that "The receiver router should keep 
> the black hole routes for PUA as one configurable time(MAX_T_PUA)", but the 
> draft does not say anything about when the un-reachability announcements 
> should be removed by ABR. We can not rely on 10.10.0.25/32 ever coming back, 
> as the user may have simply removed it for good. Keeping the "stale" 
> un-reachability announcements may result in the LSDB growth over the period 
> of time.
> 
> 
> thanks,
> Peter
> 
> 
> 
> 
>> On 27/07/2020 03:32, Aijun Wang wrote:
>> Hi, LSR experts:
>> We have uploaded the new version of this PUA(Prefix Unreachable 
>> Announcement) draft. The main updates are the followings:
>> 1) Describes the solution that using tunnel to redirect traffic among ABRs, 
>> when all ABRs reaches the PUA limit.
>> 2) Describe fast rerouting to avoid routing black hole.
>> 3) Defining PUA capabilities announcements for OSPFv2/OSPFv3 and ISIS.
>> There are also some arguments about the current solution for PUA, for 
>> example:
>> 1) Is it suitable to set the "Prefix Originator" sub-TLV to NULL to indicate 
>> the prefix is unreachable?
>> 2) if not, what's the consideration? What's the other convincible solution?
>> Wish to hear comments and suggestions on the above issues. We will also have 
>> the presentation on the coming IETF LSR meeting.
>> Best Regards
>> Aijun Wang
>> China Telecom
>> -----Original Message-----
>> From: internet-dra...@ietf.org [mailto:internet-dra...@ietf.org]
>> Sent: Monday, July 27, 2020 9:16 AM
>> To: Zhibo Hu <huzh...@huawei.com>; Aijun Wang <wang...@chinatelecom.cn>; 
>> Yaqun Xiao <xiaoya...@huawei.com>
>> Subject: New Version Notification for 
>> draft-wang-lsr-prefix-unreachable-annoucement-03.txt
>> A new version of I-D, draft-wang-lsr-prefix-unreachable-annoucement-03.txt
>> has been successfully submitted by Aijun Wang and posted to the IETF 
>> repository.
>> Name:        draft-wang-lsr-prefix-unreachable-annoucement
>> Revision:    03
>> Title:        Prefix Unreachable Announcement
>> Document date:    2020-07-27
>> Group:        Individual Submission
>> Pages:        11
>> URL:            
>> https://www.ietf.org/internet-drafts/draft-wang-lsr-prefix-unreachable-annoucement-03.txt
>> Status:         
>> https://datatracker.ietf.org/doc/draft-wang-lsr-prefix-unreachable-annoucement/
>> Htmlized:       
>> https://tools.ietf.org/html/draft-wang-lsr-prefix-unreachable-annoucement-03
>> Htmlized:       
>> https://datatracker.ietf.org/doc/html/draft-wang-lsr-prefix-unreachable-annoucement
>> Diff:           
>> https://www.ietf.org/rfcdiff?url2=draft-wang-lsr-prefix-unreachable-annoucement-03
>> Abstract:
>>    This document describes the mechanism that can be used to announce
>>    the unreachable prefixes for service fast convergence.
>>                                                                              
>>      Please note that it may take a couple of minutes from the time of 
>> submission until the htmlized version and diff are available at 
>> tools.ietf.org.
>> The IETF Secretariat
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