Re: [Lsr] https://tools.ietf.org/html/draft-wang-lsr-prefix-unreachable-annoucement-05

Hi, Tony:

-----Original Message-----
From: lsr-bounces@ietf.org <lsr-bounces@ietf.org> On Behalf Of Tony Li
Sent: Tuesday, March 9, 2021 11:12 AM
To: Aijun Wang <wangaj3@chinatelecom.cn>
Cc: lsr <lsr@ietf.org>; draft-wang-lsr-prefix-unreachable-annoucement <draft-wang-lsr-prefix-unreachable-annoucement@ietf.org>; Acee Lindem (acee) <acee@cisco.com>; Aijun Wang <wangaijun@tsinghua.org.cn>; Gyan Mishra <hayabusagsm@gmail.com>
Subject: Re: [Lsr] https://tools.ietf.org/html/draft-wang-lsr-prefix-unreachable-annoucement-05

Hi Aijun,

> [WAJ] We just want to avoid such silent discard behavior, especially for the scenario that there is BGP session run on such failure prefix. 

Stuffing things in the IGP seems like a poor way of determining that there’s a BGP failure.  Wouldn’t BFD be a more appropriate way of determining the loss of connectivity?  Or aggressive BGP keepalive timers?
[WAJ] For BFD, you need to configure between each pair of them to track the connectivity.  For BGP keeplive times, the duration is too long.

> The other side of BGP peer can quickly remove the BGP session when it receives such PUA message which tell it the other peer is down now. Other BGP peer protection procedures can then take effects on.
> The immediate notification of the failure prefix can certainly accelerate the switchover of BGP control plane and also the service traffic that such BGP session carries.

The IGP is a very poor way of delivering service liveness information.
[WAJ] why? 

>>> For scenarios 2, because the specified prefixes can be accessed via another ABR, then we can let this ABR to advertise the details prefixes information for the specified address, which behavior is similar with RIFT, as also mentioned in the presentation materials.
>> 
>> 
>> Agreed.
> 
> [WAJ] Even for this scenario, the advertisement of the detail prefixes is trigger also via the PUA message from other ABR.

That seems 100% unnecessary as the longer prefix will attract the traffic in the way that you want.
[WAJ] If the ABR advertises such detail prefix, it will certainly attract the traffic. But here the PUA message is just to trigger the ABR to advertise such detail prefix, or else, such ABR will still advertise the summary address.

Tony

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