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    SubjectRe: Maximum sockets & a SYN question
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    mjz207@is9.nyu.edu (Matthew J Zito) writes:
    >
    > Hmmmm....we did some testing by syn-flooding my workstation with and
    > without syn-cookies, and while the number of incoming syn_recv was much
    > higher without syn_cookies enabled, we still saw (using netstat -na) a
    > steadily higher number of incoming syn_recvs. Is this normal? We assumed
    > that because of that, the syn_cookies were not completely working (or
    > aren't a panacea for syn flooding). Based on your description, it would
    > seem that it would stop flooding in its tracks. Perhaps there was a
    > problem in our admittedly un-scientific test.

    Syncookies only kick in when the SYN-RECV queue overflows. A connection established
    by a syncookie basically "skips" the syn-recv state, it goes directly to ESTABLISHED
    from nothing after the cookie is verified. This does not affect the still full
    syn-recv queue.

    You can increase the per socket backlog queue using the
    tcp_max_syn_backlog sysctl. This makes sense if you want to use
    timestamps/sack/window scaling even on a heavily loaded server.


    -Andi

    --
    This is like TV. I don't like TV.

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