From owner-freebsd-net Fri Apr 5 13:20:40 2002 Delivered-To: freebsd-net@freebsd.org Received: from rwcrmhc51.attbi.com (rwcrmhc51.attbi.com [204.127.198.38]) by hub.freebsd.org (Postfix) with ESMTP id D19C037B419; Fri, 5 Apr 2002 13:20:33 -0800 (PST) Received: from bmah.dyndns.org ([12.233.149.189]) by rwcrmhc51.attbi.com (InterMail vM.4.01.03.27 201-229-121-127-20010626) with ESMTP id <20020405212033.GBLD18078.rwcrmhc51.attbi.com@bmah.dyndns.org>; Fri, 5 Apr 2002 21:20:33 +0000 Received: from intruder.bmah.org (localhost [IPv6:::1]) by bmah.dyndns.org (8.12.2/8.12.2) with ESMTP id g35LKXt2034175; Fri, 5 Apr 2002 13:20:33 -0800 (PST) (envelope-from bmah@intruder.bmah.org) Received: (from bmah@localhost) by intruder.bmah.org (8.12.2/8.12.2/Submit) id g35LKW00034174; Fri, 5 Apr 2002 13:20:32 -0800 (PST) Message-Id: <200204052120.g35LKW00034174@intruder.bmah.org> X-Mailer: exmh version 2.5+ 20020404 with nmh-1.0.4 To: Andrew Gallatin Cc: Terry Lambert , bmah@FreeBSD.ORG, net@FreeBSD.ORG Subject: IP fragmentation (was Re: Fatal trap 12: page fault while in kernel mode) In-reply-to: <15533.57961.725030.692387@grasshopper.cs.duke.edu> References: <20020403181854.I42720-100000@angui.sh> <15532.29114.310072.957330@grasshopper.cs.duke.edu> <200204050504.g355493C001200@intruder.bmah.org> <15533.46222.49598.958821@grasshopper.cs.duke.edu> <3CADE0E7.ED472650@mindspring.com> <15533.57961.725030.692387@grasshopper.cs.duke.edu> Comments: In-reply-to Andrew Gallatin message dated "Fri, 05 Apr 2002 12:44:09 -0500." From: bmah@FreeBSD.ORG (Bruce A. Mah) Reply-To: bmah@FreeBSD.ORG X-Face: g~c`.{#4q0"(V*b#g[i~rXgm*w;:nMfz%_RZLma)UgGN&=j`5vXoU^@n5v4:OO)c["!w)nD/!!~e4Sj7LiT'6*wZ83454H""lb{CC%T37O!!'S$S&D}sem7I[A 2V%N&+ X-Image-Url: http://www.employees.org/~bmah/Images/bmah-cisco-small.gif X-Url: http://www.employees.org/~bmah/ Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Fri, 05 Apr 2002 13:20:32 -0800 Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org [Moving to -net] If memory serves me right, Andrew Gallatin wrote: > > Alternately, it would be a good idea to have a "ip_maxpacketfrags" > > instead of an "ip_maxfragpackets", to put a hard limit on the > > number of mbufs that can be consumed by the fragment reassembly > > process. > > I think this is the best solution. Just for the heck of it, I started reading through ip_input.c to see how hard this would be to do. Haven't got there yet, I saw something odd: the variables ip_nfragpackets and nipq look *awfully* similar. It looks like they both track the number of reassembly queues, because they're initialized to zero, and incremented and decremented at the same time. Their limits (ip_maxfragpackets and maxnipq respectively) are even initialized on consecutive lines. The only difference I can see is that in ip_input(), if nipq > maxnipq, all of the fragments for some other packet in the current hash bucket get dropped (with the wonderfully descriptive comment "gak"). The check for ip_nfragpackets comes in ip_reass(), where if ip_nfragpackets >= ip_maxfragpackets, then we drop the current fragment. (Is it possible that the second check masks the effects of the first?) I couldn't find any obvious explanation in the CVS log for ip_input.c. Am I missing something, or are these two variables basically doing the same thing? Thanks, Bruce. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message