From owner-freebsd-net@FreeBSD.ORG Mon Jan 26 05:51:48 2009 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7ACD010656D6 for ; Mon, 26 Jan 2009 05:51:48 +0000 (UTC) (envelope-from smithi@nimnet.asn.au) Received: from sola.nimnet.asn.au (paqi.nimnet.asn.au [220.233.188.227]) by mx1.freebsd.org (Postfix) with ESMTP id 6FF818FC0A for ; Mon, 26 Jan 2009 05:51:46 +0000 (UTC) (envelope-from smithi@nimnet.asn.au) Received: from localhost (localhost [127.0.0.1]) by sola.nimnet.asn.au (8.14.2/8.14.2) with ESMTP id n0Q5pgLM071937; Mon, 26 Jan 2009 16:51:43 +1100 (EST) (envelope-from smithi@nimnet.asn.au) Date: Mon, 26 Jan 2009 16:51:42 +1100 (EST) From: Ian Smith To: Len Gross In-Reply-To: <27cb3ada0901251009x7a96019am672f8bd42380df90@mail.gmail.com> Message-ID: <20090126164357.F90458@sola.nimnet.asn.au> References: <27cb3ada0901251009x7a96019am672f8bd42380df90@mail.gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: "freebsd-net@freebsd.org" Subject: Re: MTU or Fragmentation Problems on 7.0? X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 26 Jan 2009 05:51:48 -0000 On Sun, 25 Jan 2009, Len Gross wrote: > The following configuration works fine _until_ I make a change in MTU > setting on the link between FreeBSD1 and FreeBSD2 > > Internet > | > Router x.x.x.x > 192.168.0.1/16 > | > FreeBSD #1 192.168.0.202 /16 > 6.3 192.168.1.1/ 24 > | > FreeBSD #2 192.168.1.2/24 > 7.0 192.168.1.5/24 > | > FreeBSD #3 192.168.5.2/24 > 7.0 > > All connections are Ethernet. > > If I change the MTU on 192.168.1.1 to 1450 and the corresponding MTU > on 192.168.1.2 to 1450, then Web Browsing on FreeBSD2 continues to > work, BUT browsing on FreeBSD3 "fails" (mostly.) > > On FreeBSD 3 > Ping and nslookup work fine from FreeBSD3 > I can get to Google but virtually no other web sites > Using tcpdump there is lots of unusual stuff, some relating to > fragmentation ICMP? Do any of these machines have a firewall rule blocking ICMP? You want to be sure at least icmptypes 3,11 are flowing freely to/from FreeBSD3, as well as pings (icmptypes 0,8) which are apparently permitted. cheers, Ian > If I put a Web Proxy on FreeBSD 1, everything works fine. > > I have tried putting mtu = 1450 using route change on all the routes, > but that didn't help. > When I did this I verified all routes had 1450 mtu via netstat ?arW > > So I am unsure if this is a FreeBSD bug, a "internet" fragmentation issue or ??? > Amongst the strangest things is that FreeBSD 2 is unaffected; Firefox > runs fine there > > (There was a thread in October about mtu issues in 7.0 but it didn't > seem to help my problem.) > (I run 1450 MTU to support testing of an experimental protocol., but > all the above is with straight out of the box FreeBSD.) > > -- Len