SACK out of window segments?

[Jozsef Kadlecsik]

Hi Dave,

There had been a long thread on netfilter-devel recently with the subject
[PATCH] TCP window tracking patch backported from the 2.6 tree:

https://lists.netfilter.org/pipermail/netfilter-devel/2005-June/020281.html
https://lists.netfilter.org/pipermail/netfilter-devel/2005-June/020279.html
https://lists.netfilter.org/pipermail/netfilter-devel/2005-June/020317.html
https://lists.netfilter.org/pipermail/netfilter-devel/2005-July/020292.html
https://lists.netfilter.org/pipermail/netfilter-devel/2005-July/020349.html
https://lists.netfilter.org/pipermail/netfilter-devel/2005-July/020350.html

It seems that at least Linux 2.4.25 accepts and (S)ACKs segments which
otherwise looks to be out of window ones. In order to cope with that I had
to add code to the TCP connection tracking part of netfilter.

The question is wether that was a SACK bug in 2.4.25? Or there's something
in the RFCs we overlook and what looks like a violation is actually an RFC
conformant feature?

Thank you your help,
Jozsef
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