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Date:	Mon, 17 Dec 2012 14:03:54 -0800
From:	Eric Dumazet <>
To:	Rick Jones <>
Subject: Re: Whence a description of how to enable TCP FASTOPEN in a
 net-next kernel?

On Mon, 2012-12-17 at 13:56 -0800, Eric Dumazet wrote:

> I guess you need to enable fastopen both for client and server :
> echo 3 >/proc/sys//net/ipv4/tcp_fastopen

vi +475 Documentation/networking/ip-sysctl.txt

tcp_fastopen - INTEGER
        Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
        in the opening SYN packet. To use this feature, the client application
        must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
        connect() to perform a TCP handshake automatically.

        The values (bitmap) are
        1: Enables sending data in the opening SYN on the client.
        2: Enables TCP Fast Open on the server side, i.e., allowing data in
           a SYN packet to be accepted and passed to the application before
           3-way hand shake finishes.
        4: Send data in the opening SYN regardless of cookie availability and
           without a cookie option.
        0x100: Accept SYN data w/o validating the cookie.
        0x200: Accept data-in-SYN w/o any cookie option present.
        0x400/0x800: Enable Fast Open on all listeners regardless of the
           TCP_FASTOPEN socket option. The two different flags designate two
           different ways of setting max_qlen without the TCP_FASTOPEN socket

        Default: 0

        Note that the client & server side Fast Open flags (1 and 2
        respectively) must be also enabled before the rest of flags can take

        See include/net/tcp.h and the code for more details.

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