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Date:	Tue, 14 Oct 2014 11:40:44 -0400
From:	John Heffner <>
To:	Eric Dumazet <>
Cc:	"Yurij M. Plotnikov" <>,
	Netdev <>,
	"Alexandra N. Kossovsky" <>
Subject: Re: TCP socket receives strange packet

On Tue, Oct 14, 2014 at 11:00 AM, Eric Dumazet <> wrote:
> On Tue, 2014-10-14 at 18:09 +0400, Yurij M. Plotnikov wrote:
>> Connected TCP socket receives packet without timestamps option which
>> exists in SYN, SYNACK and ACK. It is packet 4 in attached tcpdump output.
>> tcpdump output description: The host has address (server)
>> and the peer host has address (client).
>> Establishing connection: Timestamps option exists in SYN, SYNACK and ACK
>> (packets 1, 2 and 3 in attached file), so accepted socket should receive
>> packets only with timestamps option.
> Can you point the RFC paragraph stating so ?
> I have wondering if this behavior was correct some time ago, and could
> not find a definitive answer.
> RFC 1323 4.2.1 seems to suggest it is valid to accept a segment without
> TS.
> R1) If there is a Timestamps option in the arriving segment...
>  There is no : Else drop the segment.

I can't think of a good reason to drop unless you're trying to use the
timestamp fields as extra security against off-path injection attacks.
  (It doesn't currently help much for that.)

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