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    SubjectRe: IP defrag (was RE: ipchains blocking port 65535)
    On Wed, Jan 17, 2001 at 05:15:54PM -0000, Tony Gale wrote:
    >
    > On 17-Jan-2001 Jussi Hamalainen wrote:
    > > On Wed, 17 Jan 2001, Tony Gale wrote:
    > >
    > >> It looks like this is due to the odd way in which ipchains handles
    > >> fragments. Try:
    > >>
    > >> echo 1 > /proc/sys/net/ipv4/ip_always_defrag
    > >
    > > Thanks, this seems to do the trick. Does this oddity still exist
    > > in 2.4?
    > >
    >
    > Well, I haven't found it, but there is
    > /proc/sys/net/ipv4/ipfrag_high_thresh
    > /proc/sys/net/ipv4/ipfrag_low_thresh
    > /proc/sys/net/ipv4/ipfrag_time
    >
    > Perhaps 2.4 always defrags packets by default. Anyone confirm? This
    > is pretty much needed for any kind of firewall/masquerading system.

    Connection tracking always defrags as needed. masquerading/NAT/iptables
    with connection tracking uses that.

    This means that if any of these are enabled and your machine acts as a
    router lots of CPU could get burned in defragmentation, and packets
    will not forwarded until all fragments arrived.

    All very nasty, but unfortunately there is no alternative.


    -Andi
    -
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