Re: RANDOM_IP_ID sysctl?

From: David Malone (dwmalone_at_maths.tcd.ie)
Date: 06/29/04

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    To: Max Laier <max@love2party.net>
Date: Tue, 29 Jun 2004 16:44:13 +0100

    > > On Tue, Jun 29, 2004 at 02:13:38PM +0100, David Malone wrote:
    > > > It seems to me that RANDOM_IP_ID might be better as a sysctl rather
    > > > than a kernel option. Would anyone mind if I changed this?

    > I personally think that RANDOM_IP_ID is something that should be tweakable on
    > a per-interface basis (at least). I usually want randomized IDs on my uplink
    > interface while it could harm my GigE internal network due to faster ID reuse
    > cycles.

    Though, on your GigE internal network, you can probably use jumbograms
    to avoid fragmentation and avoid having to pay any attention to IP
    IDs ;-) There was code to only bother setting the IP ID for packets
    with DF set, but that caused certain odd pieces of network kit that
    ignored DF to be sick...

    > FYI, pf(4) can set randomized IDs on a per interface (and even on a per
    > connection) basis.

    pf is probably the best place for this sort of more flexable IP ID
    setting.

    > David, I'd appreciate to review your patches in order to avoid breakage of pf,
    > thanks.

    Certainly.

    > One would clearly transform the now present "#ifdef" with "if (sysctlvar)"
    > and hence this will not incur overhead (one compare is nothing to worry
    > about).

    Yes - this is exactly what I had in mind. I'm certain that the
    overhead of the extra "if ()" will be lost in the cost of the IP
    stack.

    Currently RANDOM_IP_ID also controls other things, such as flow id
    generation for IPv6. Making it a sysctl would also give us independent
    control over these things.

            David.
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