Date: Sat, 03 Jul 2004 09:38:58 +0200 From: Andre Oppermann <andre@freebsd.org> To: Mike Silbersack <silby@silby.com> Cc: freebsd-net@freebsd.org Subject: Re: RANDOM_IP_ID sysctl? Message-ID: <40E66292.95598473@freebsd.org> References: <200406291413.ab33924@salmon.maths.tcd.ie> <20040702190516.Q65076@odysseus.silby.com>
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Mike Silbersack wrote: > > On Tue, 29 Jun 2004, 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? > > > > David. > > I'd rather see a sysctl that switched between incremental frag IDs and > arc4random() based IDs, followed by the removal of RANDOM_IP_ID. > > For more info, see: > > http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/netinet/ip_id.c > > (I think we're still using the old code that's collision prone.) > > Given that we're in a 16-bit space anyway, it's simpler to just use > arc4random and stop pretending that we can avoid collisions. > > Remember: An IP ID collision is equivalent to a packet being lost; this > is not a big deal. An ip_id collision is only a problem (packet loss) if it is being fragmented along the way and the delivery of the fragments happens out-of-order, so that a fragment from a different packet gets re- assembled with part of an earlier one. Having many concurrent connections to the same remote end-point with fragmentation in between is of course making the chances bigger to hit this. -- Andre
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