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From: Tom Herbert <tom@herbertland.com>
To: Linux Kernel Network Developers <netdev@vger.kernel.org>
Subject: Flow label persistence
Date: Thu, 19 Nov 2020 08:49:21 -0700	[thread overview]
Message-ID: <CALx6S353fPF=x4=yr4=a4zYCKVLfCRbFhEKr14A1mBRug7AfaA@mail.gmail.com> (raw)

HI,

A potential issue came up on v6ops list in IETF that Linux stack
changes the flow label for a connection at every RTO, this is the
feature where we change the txhash on a failing connection to try to
find a route (the flow label is derived from the txhash). The problem
with changing the flow label for a connection is that it may cause
problems when stateful middleboxes are in the path, for instance if a
flow label change causes packets for a connection to take a different
route they might be forwarded to a different stateful firewall that
didn't see the 3WHS so don't have any flow state and hence drop the
packets.

I was under the assumption that we had a sysctl that would enable
changing the txhash for a connection and the default was off so that
flow labels would be persistent for the life of the connection.
Looking at the code now, I don't see that safety net, it looks like
the defauly behavior allows changing the hash. Am I missing something?

Thanks,
Tom

             reply	other threads:[~2020-11-19 15:49 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-19 15:49 Tom Herbert [this message]
2020-11-19 17:56 ` Flow label persistence Eric Dumazet
2020-11-19 19:18   ` Willem de Bruijn

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