Re: [Lsr] New Version Notification for draft-wang-lsr-prefix-unreachable-annoucement-03.txt

Hi Acee:

In fact, we have meet some scenarios where redundant paths cannot be deployed within a area. Especially when the access area uses the nearby access principle, ABRs form disordered combinations, which makes it difficult to deploy physical or tunnel connections. In addition, advertising unreachable prefixes can prevent traffic detours. Of course, This draft also has some other attempts to use Segment Routing to automatically establish connections between ABRs.

Thanks

Zhibo Hu

-----Original Message-----
From: Acee Lindem (acee) [mailto:acee@cisco.com] 
Sent: Tuesday, July 28, 2020 1:51 AM
To: Aijun Wang <wangaj3@chinatelecom.cn>; lsr@ietf.org
Cc: Huzhibo <huzhibo@huawei.com>; Xiaoyaqun <xiaoyaqun@huawei.com>
Subject: Re: [Lsr] New Version Notification for draft-wang-lsr-prefix-unreachable-annoucement-03.txt

Speaking as an LSR Working Group member:

Asking the WG precisely how to advertise prefix unreachability is the wrong question - it is analogous to asking whether to use a car or truck to drive off the edge of a cliff. Rather than messing up OSPF and IS-IS with these complex and unnecessary mechanisms, it would be better to address the requirement in your network design. Note that the unreachability of a given summarized prefix is only relevant if it is reachable through another ABR. In this case, the network design should provide adequate intra-area redundancy to provide communications between the ABRs. If this cannot be accomplished, an intra-area adjacency should be established over a tunnel between the ABRs in the backbone. Contrary to section 6.1, Looping is normally not a problem as ABRs should add back hole routes for their advertised summaries. 

Acee

On 7/26/20, 9:34 PM, "Lsr on behalf of Aijun Wang" <lsr-bounces@ietf.org on behalf of wangaj3@chinatelecom.cn> 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-drafts@ietf.org [mailto:internet-drafts@ietf.org] 
    Sent: Monday, July 27, 2020 9:16 AM
    To: Zhibo Hu <huzhibo@huawei.com>; Aijun Wang <wangaj3@chinatelecom.cn>; Yaqun Xiao <xiaoyaqun@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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