Date: Sun, 17 Dec 2000 12:20:01 -0500 From: "Ryan Masse" <rmasse@max-info.net> To: "Julian Elischer" <julian@elischer.org> Cc: "FreeBSD-Questions" <freebsd-questions@freebsd.org> Subject: Re: PPPoE and MTU problem Message-ID: <009201c0684d$97b89200$0600a8c0@Home> References: <20001217113357.A3485@atlas.internal.bermuda.de> <3A3CA2DE.28AB4780@elischer.org>
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From: "Julian Elischer" <julian@elischer.org> > Nils Bokermann wrote: > > > > Hi! > > > > The following problem: I have a DSL-Connection to the internet, and a > > few client behind the BSD-Box (see picture). I can do connections to the > > internet, nearly everything works. But I DO have 2 systems (which I > > desperatly need), which do NOT fragment the packets. When using a Linux > > Router (don't blame me for that) everything just works fine. Is there a > > problem with my configuration, or is that a BSD-specific-Problem. > > > > client <-- ethernet (MTU=1500) --> FreeBSD-Box <-- DSL > > (MTU=1492)-->Provider(german Telekom) > > > > unakruemel# uname -a > > FreeBSD kruemel.monster.sensibelchen.org 4.2-BETA FreeBSD 4.2-BETA #4: > > Fri Dec 8 15:27:31 CET 2000 root@kruemel.monster.sensibelchen.org:/usr/src/sys/compile/KRUEMEL > > i386 > > > > kruemel# ipfw list > > 00100 allow ip from any to any via lo0 > > 00200 allow ip from any to any via rl0 > > 00300 allow tcp from any to any out xmit tun0 setup > > 00400 allow tcp from any to any via tun0 established > > 00500 allow udp from any to any via tun0 > > 00600 allow log logamount 100 tcp from any to any 80 setup > > 00700 allow log logamount 100 tcp from any to any 22 setup > > 00800 allow log logamount 100 tcp from any to any 20 setup > > 00900 allow log logamount 100 tcp from any to any 25 setup > > 01000 reset log logamount 100 tcp from any to any 113 in recv tun0 > > 01100 allow udp from any to any 53 out xmit tun0 > > 01200 allow udp from any 53 to any in recv tun0 > > 65435 allow icmp from any to any > > 65435 deny log logamount 100 ip from any to any > > 65535 deny ip from any to any > >ng thatyou are using ipfw to filter rather than the > > it's intersting thatyou are using ipfw to filter rather than the > filtering in ppp. but no matter it should still work. > The maximum frame size that can be passed through a dsl router is 1492 because the modem adds an 8 frame header and trailer which then adds up to 1500 the max mtu value... I have had the same problem when i first setup my dsl over my lan... Even though the max mtu value for a dsl connection is 1492 it dosen't mean that your system can process that size packet to the internet.. On my lan the magical mtu value was 1464 bfore packets were fragmented. So you may have to ajust accordingly. If you have a windows box on ur network you can do the following do determine the max mtu size for your network. PING -f -l <MTU size> <IP address of default gateway> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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