RE: [tcpm] SYN in SYN_RCVD state

"Agarwal, Anil" <Anil.Agarwal@viasat.com> Sun, 21 October 2007 19:17 UTC

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Subject: RE: [tcpm] SYN in SYN_RCVD state
Date: Sun, 21 Oct 2007 15:17:32 -0400
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Thread-Topic: [tcpm] SYN in SYN_RCVD state
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From: "Agarwal, Anil" <Anil.Agarwal@viasat.com>
To: "Vishal Study" <vishal.study@gmail.com>, "Marco Mellia" <mellia@tlc.polito.it>
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On October 21, 2007, Vishal wrote -

> But RFC 793, pg 71 seem to say that the server should send out a RST
> if SYN is rx in SYN-RCVD state (assuming SYN seq number is within the
> window, which is true in the example I had mentioned).
>

Your example is covered by the rules on page 68 of RFC 793. The
retransmitted SYN segment is a duplicate segment and is outside
the receive window (SEG.SEQ is < RCV.NXT). 
Hence, the receiver sends an Acknowledgement and discards the segment.

Anil

Anil Agarwal
ViaSat Inc.
Germantown, MD 20876
USA


On 10/20/07, Marco Mellia <mellia@tlc.polito.it> wrote:
> Vishal Study ha scritto:
> > Consider the following scenario:
> >
> > 1. TCP client sends SYN to server; server goes to SYN_SENT state
> >
> > 2. server responds with SYN+ACK;  server goes to SYN_RCVD state
> > but SYN+ACK sent to client is lost somewhere in the network.
> >
> > 3. client re-sends SYN on its timeout (couple of seconds later) to
server
> >
> > What should be the server behavior? Should it retransmit SYN+ACK or
> > should it send a RST?
> >
> >
> Clearly the first case!
> Marco
>


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