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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