Date: Wed, 28 Jan 2009 03:01:44 +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: <20090128024956.X86094@sola.nimnet.asn.au> In-Reply-To: <27cb3ada0901261803h301c8cd4xbf5dafcde1f6ff7c@mail.gmail.com> References: <27cb3ada0901251009x7a96019am672f8bd42380df90@mail.gmail.com> <20090126164357.F90458@sola.nimnet.asn.au> <27cb3ada0901261803h301c8cd4xbf5dafcde1f6ff7c@mail.gmail.com>
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On Mon, 26 Jan 2009, Len Gross wrote: > Ian, > > Thanks so much for taking the time to look at this problem. More like a parting shot over the shoulder before bedtime :) > I do not have any firewall running on any of the machines, unless > something "auto enables." The only rc.conf entries are ifconfig and > routing. > > The thing that is most puzzling to me is that everything is fine on > FreeBSD #2 even though it is "behind" a link with 1450 MTU. This > sounds like it must be a "bug" on FreeBSD #2 (version 7.0) routing > from the 1450 route to the 1500 route to FreeBSD 3. But if that were > true, why would running a Web Proxy on FreeBSD #1 work? What if you also set FreeBSD #2's more inside interface to 1450, as on FreeBSD #1? Apart from that I can't say anything as useful as David DeSimone's more detailed coverage of the issues, except that tcpdump on FreeBSD #3 should show what is (and isn't) happening more clearly. cheers, Ian > Some other data. I get the same problem if I replace FreeBSD 3 with a > Windows box. > I'm pretty sure I had similar behaviour with FreeBSD 6.3 as machine > #2,, but it was ignored at the time. I've seen the problem with > connections to two different ISPs. > > I can live with having a Web Proxy on FreeBSD # 1, but I am concerned > that this issue will crop up someplace else. > > -- Len > > On Sun, Jan 25, 2009 at 9:51 PM, Ian Smith <smithi@nimnet.asn.au> wrote: > > 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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