Re: [Idr] TCP & BGP: Some don't send terminate BGP when holdtimer expired, because TCP recv window is 0

Christoph Loibl <c@tix.at> Tue, 15 December 2020 20:58 UTC

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From: Christoph Loibl <c@tix.at>
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Date: Tue, 15 Dec 2020 21:57:47 +0100
Cc: "Jakob Heitz (jheitz)" <jheitz@cisco.com>, "idr@ietf.org" <idr@ietf.org>, Robert Raszuk <robert@raszuk.net>
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To: John Scudder <jgs@juniper.net>
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Subject: Re: [Idr] TCP & BGP: Some don't send terminate BGP when holdtimer expired, because TCP recv window is 0
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John,

Thanks for answering my question in more detail. Maybe I was unclear (but reading your email I think we are talking about the same).

> On 15.12.2020, at 21:00, John Scudder <jgs@juniper.net> wrote:
> 
> I think you are talking about this scenario. I’ll copy the example from Rob’s message cited above:
> 
>   rtr-A                   rtr-B
>   (congested c-p)         (uncongested c-p)
>   send window: >0         send window: 0
>   recv window: 0          recv window: >0	
> 
> In this case we expect:
>  a) rtr-B does not send any BGP packet (KEEPALIVE/UPDATE/NOTIFICATION)
> to rtr-A in normal operating circumstances.
>  b) rtr-A does not expect any KEEPALIVE/UPDATE packets from rtr-B. The
> session remains established even if no packet is received in the
> holdtime.
>  c) rtr-A continues to send KEEPALIVE packets to rtr-B.
> 

The part I have a problem to understand is b). It is clear that rtr-A will not receive any packets from rtr-B because rtr-B cannot send them (send window: 0). But does "rtr-A does not expect any KEEPALIVE/UPDATE packets from rtr-B” mean that rtr-A has essentially suspended its hold-timer until it is ready to receive new messages and opens up its recv window? If yes, why? I would expect timers to run independently of the transport protocol.

Cheers Christoph

-- 
Christoph Loibl
c@tix.at | CL8-RIPE | PGP-Key-ID: 0x4B2C0055 | http://www.nextlayer.at