From owner-freebsd-net@FreeBSD.ORG Tue Apr 22 22:52:26 2003 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 839C537B401 for ; Tue, 22 Apr 2003 22:52:26 -0700 (PDT) Received: from gw.catspoiler.org (217-ip-163.nccn.net [209.79.217.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id D5D0B43F75 for ; Tue, 22 Apr 2003 22:52:25 -0700 (PDT) (envelope-from truckman@FreeBSD.org) Received: from FreeBSD.org (scratch.catspoiler.org [192.168.101.3]) by gw.catspoiler.org (8.12.6/8.12.6) with ESMTP id h3N5qHXB028433; Tue, 22 Apr 2003 22:52:21 -0700 (PDT) (envelope-from truckman@FreeBSD.org) Message-Id: <200304230552.h3N5qHXB028433@gw.catspoiler.org> Date: Tue, 22 Apr 2003 22:52:17 -0700 (PDT) From: Don Lewis To: silby@silby.com In-Reply-To: <20030422004104.Q523@odysseus.silby.com> MIME-Version: 1.0 Content-Type: TEXT/plain; charset=us-ascii cc: freebsd-net@FreeBSD.org Subject: Re: IP fragmentation disagreement between current and stable X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Apr 2003 05:52:26 -0000 On 22 Apr, Mike Silbersack wrote: > > On Tue, 22 Apr 2003, Don Lewis wrote: > >> will contain 222 bytes of data. With a 14 byte Ethernet header and a 20 >> byte IP header, that just fits into one 256 byte mbuf. I wonder if >> there is a divide by 4 to calculate the number of words, and the >> >> Could this be a driver problem instead of a problem in the stack itself? >> Both ends are fxp cards. > > A similar problem was found with Via Rhine chips, where having multiple > packets exactly fill up the internal FIFO seemed to cause those packets to > be dropped. Naturally, this only cropped up with fragmented ping packets > of certain lengths. We never bothered patching it because, well, no clear > solution presented itself, and it wouldn't occur in normal usage. > (Actually, changing from store and forward back to smaller DMA sizes might > have fixed it, I'm not sure.) > > So, I would not rule out the possibility of a driver / chipset bug. It's starting to smell like a bug in the -current fxp driver. The de card I tried works ok. The other fxp card I tried with the same part number fails. I'd forgotten that I had a Red Hat 7.3 partition on this box, so I reinstalled the fxp card and booted Red Hat and I was able to ping the box, but that isn't quite as interesting as I had hoped because Linux sends out the fragments in the reverse order. I also moved the fxp card to a 4.8-stable box and it worked fine there too. The only things I haven't tried are the D-Link card I stumbled across, and I haven't tried booting current on one of my older machines that has an fxp port on the motherboard. The fact that tcpdump on the -current box doesn't show the problem also makes me think that the problem isn't in the IP stack.