From: Cosmin Ratiu <cratiu@ixiacom•com>
To: netdev@vger•kernel.org
Subject: TCP TSecr question
Date: Fri, 10 Apr 2009 19:24:56 +0300 [thread overview]
Message-ID: <49DF72D8.2020002@ixiacom.com> (raw)
Hello,
There is an issue with this field in SYN packets when tw reuse/recycle
is on.
Quoting from RFC 1323, section 3.2:
The Timestamp Echo Reply field (TSecr) is only valid if the ACK
bit is set in the TCP header; if it is valid, it echos a times-
tamp value that was sent by the remote TCP in the TSval field
of a Timestamps option. When TSecr is not valid, its value
must be zero. The TSecr value will generally be from the most
recent Timestamp option that was received; however, there are
exceptions that are explained below.
On Linux, when the sysctl_tcp_tw_reuse or recycle is on, the most recent
timestamp from a previous connection is sent instead of 0. From what I've
seen in the source, this has to do with PAWS against delayed/duplicate SYN
packets.
My questions:
1) Is this violation of RFC 1323 useful in PAWS or did I misunderstand
the whole situation?
2) Is there any other RFC that amends 1323 to specify this behavior or is it
a Linux-specific enhancement?
Thank you,
Cosmin.
reply other threads:[~2009-04-10 16:40 UTC|newest]
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