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

"Jakob Heitz (jheitz)" <jheitz@cisco.com> Sat, 12 December 2020 07:15 UTC

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From: "Jakob Heitz (jheitz)" <jheitz@cisco.com>
To: Enke Chen <enchen@paloaltonetworks.com>, "idr@ietf.org" <idr@ietf.org>
Thread-Topic: [Idr] TCP & BGP: Some don't send terminate BGP when holdtimer expired, because TCP recv window is 0
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Archived-At: <https://mailarchive.ietf.org/arch/msg/idr/WXQLJeErpvDJuNR4gJBhSQQIQ-E>
Subject: Re: [Idr] TCP & BGP: Some don't send terminate BGP when holdtimer expired, because TCP recv window is 0
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Kill and restart all from scratch with BGP is a scary prospect,
especially if it's just going to repeat.

How about we graceful restart it.
Require GR to be in effect on the session.
Then either RST or silently drop the session and start a new one.
The receiver should accept the new session and do GR.
And, yeah, use a long timer. Don't restart again until at least the EOR
is both sent and received and only then start the boom timer again.

Regards,
Jakob.

From: Idr <idr-bounces@ietf.org> On Behalf Of Enke Chen
Sent: Friday, December 11, 2020 10:15 PM
To: idr@ietf.org
Cc: Enke Chen <enchen@paloaltonetworks.com>
Subject: Re: [Idr] TCP & BGP: Some don't send terminate BGP when holdtimer expired, because TCP recv window is 0

Hi, Folks:

There is an interesting article titled "When TCP Sockets Refuse to Die":

      https://blog.cloudflare.com/when-tcp-sockets-refuse-to-die/

which recommends using the TCP keepalive option and the TCP_USER_TIMEOUT option together to deal with several TCP "stuck" scenarios.

To strike a balance between maintaining routing stability and working around these corner cases, how about we recommend using these two TCP options with a timeout value larger than the BGP per-session holdtimer (e.g.,  2 * bgp_holdtimer) ?

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

"Jakob Heitz (jheitz)" <jheitz@cisco.com<mailto:jheitz@cisco.com>> Sat, 12 December 2020 03:29 UTCShow header<https://mailarchive.ietf.org/arch/browse/idr/>

Good point Keyur.

A receiver may be overwhelmed for a long time and not open its TCP window to avoid

silly window syndrome or some other reason. The receiver may still be functional

and able to clear its backlog, albeit in a long time. Resetting such a session

will only make the situation worse. Telling the difference between this case

and a receiver stuck in a bug is difficult.



Regards,

Jakob.

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