Date: Mon, 25 Apr 2005 07:56:16 +1000 From: Matthew Sullivan <matthew@uq.edu.au> To: Andre Oppermann <andre@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: DF (Don't frag) issues Message-ID: <426C1600.106@uq.edu.au> In-Reply-To: <426BC78A.3E56D99B@freebsd.org> References: <426426AE.2060406@uq.edu.au> <20050420084413.GA27304@walton.maths.tcd.ie> <42663EA1.3020409@uq.edu.au> <426A3F49.6090203@uq.edu.au> <20050424150211.GA87520@walton.maths.tcd.ie> <426BC78A.3E56D99B@freebsd.org>
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[-- Attachment #1 --] Andre Oppermann wrote: >David Malone wrote: > > >>On Sat, Apr 23, 2005 at 10:27:53PM +1000, Matthew Sullivan wrote: >> >> >>>Ok well thanks to Andrew @ Supernews and a lot of debugging it appears >>>there is a bug.... >>> >>>sys/netinet/ip_icmp.c: line 440 >>> if (!mtu) >>> mtu = ip_next_mtu(mtu, 1); >>>Problem is ip_next_mtu will always return 0 when called with (0, 1) ... >>> >>> >>I think this might be a bug, but Andre would know better. Andre - >>it looks to me as if the first argument to ip_next_mtu here should >>be the current MTU for the path, but it is being set to the mtu >>from the ICMP message, which (in this case) is zero. >> >> > >This is a bug indeed. Let me think how to fix this most efficiently... > > > >>(This is in the code that has just been moved to tcp_ctlinput.) >> >> >> >>>Apparently the gateway should be suggesting a MTU value for use.... the >>>gateway is also FreeBSD 5.3 so something needs fixing .. :-/ >>> >>> >>Are you using ip fast forwarding on the gateway? It calculates the >>size that is put into the ICMP message in a slightly different way >>to the other forwrd path. >> >> > >The quoted code above is used only for incoming ICMP packets. It >does not generate them? What is the problem being observed exactly? > > > As David suggested my config is shown here: http://lists.freebsd.org/pipermail/freebsd-current/2005-April/048980.html After talking with people I see 2 issues..... 1/ The bug is being triggered when the incoming 'need frag' ICMP message doesn't have a suggested value. This ICMP message is being generated by 'stealth.sorbs.net' which is a FreeBSD 5.3 p9 server running FAST_IPSEC (no crypto card yet - waiting for delivery), and otherwise pretty standard kernel. As for fast forwarding: net.inet.ip.fastforwarding: 0 2/ The bug itself is also a problem, as it cannot be guarenteed that the host returning the ICMP 'need frag' will fill in a suggested mtu, so that also needs to be looked at (but I guess you know that already ;-)) Regards, Mat -- Matthew Sullivan Specialist Systems Programmer Information Technology Services The University of Queensland [-- Attachment #2 --] 0 *H 01 0 + 0 *H 0r0Z*0 *H 01 0 UAU10U Queensland10UBrisbane1%0#U The University of Queensland1(0&U Information Technology Services10UCertificate Server0 040121233621Z 060121233621Z01 0 UAU1%0#U The University of Queensland1'0%U Information Tecnology Services10 &,dccmatt10UMatthew Sullivan1 0 *H matthew@uq.edu.au0\0 *H K 0HA ~?AJ#0z^TY%L ~3:ܠDŽoӄ'Zբ,pK h0f0U 0 `HB0 U #0&2MA{7XT0 U 0matthew@its.uq.edu.au0 *H ]f*fe 7>Că3$K:C%˜pr0( ;wP@H$U ҷs;#B dYMz9 Z ȥ-Z=53Fl .jٍ \]W)R+,!6Ampz:3 JFwH2LRD"ױTb^#)/xgBRr{(1&fcv@Jpc4fc y{SaU0r0Z*0 *H 01 0 UAU10U Queensland10UBrisbane1%0#U The University of Queensland1(0&U Information Technology Services10UCertificate Server0 040121233621Z 060121233621Z01 0 UAU1%0#U The University of Queensland1'0%U Information Tecnology Services10 &,dccmatt10UMatthew Sullivan1 0 *H matthew@uq.edu.au0\0 *H K 0HA ~?AJ#0z^TY%L ~3:ܠDŽoӄ'Zբ,pK h0f0U 0 `HB0 U #0&2MA{7XT0 U 0matthew@its.uq.edu.au0 *H ]f*fe 7>Că3$K:C%˜pr0( ;wP@H$U ҷs;#B dYMz9 Z ȥ-Z=53Fl .jٍ \]W)R+,!6Ampz:3 JFwH2LRD"ױTb^#)/xgBRr{(1&fcv@Jpc4fc y{SaU1@0<001 0 UAU10U Queensland10UBrisbane1%0#U The University of Queensland1(0&U Information Technology Services10UCertificate Server*0 + -0 *H 1 *H 0 *H 1 050424215616Z0# *H 12 " 6jx\w0R *H 1E0C0 *H 0*H 0 *H @0+0 *H (0 +71001 0 UAU10U Queensland10UBrisbane1%0#U The University of Queensland1(0&U Information Technology Services10UCertificate Server*0 *H 101 0 UAU10U Queensland10UBrisbane1%0#U The University of Queensland1(0&U Information Technology Services10UCertificate Server*0 *H @k 'tp:,A ߆-Py[ȶA |7T~W$fP>TyD %n
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