Date: Mon, 26 Jan 2009 16:51:42 +1100 (EST) From: Ian Smith <smithi@nimnet.asn.au> To: Len Gross <sandiegobiker@gmail.com> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: MTU or Fragmentation Problems on 7.0? Message-ID: <20090126164357.F90458@sola.nimnet.asn.au> In-Reply-To: <27cb3ada0901251009x7a96019am672f8bd42380df90@mail.gmail.com> References: <27cb3ada0901251009x7a96019am672f8bd42380df90@mail.gmail.com>
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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
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