Date: Tue, 18 Jun 2002 15:09:42 -0700 (PDT) From: Tom Samplonius <tom@sdf.com> To: Mike Tancsa <mike@sentex.net> Cc: freebsd-net@FreeBSD.ORG Subject: Re: tracking down strange MTU issues with PPPoE) Message-ID: <Pine.BSF.4.05.10206181454460.23627-100000@misery.sdf.com> In-Reply-To: <5.1.0.14.0.20020618163928.05018cf0@marble.sentex.ca>
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Well, if you need to find the MTU, the ppp logs should tell you what the remote end is telling you to use. Usually, if you are having a MTU problem, it relates to fragmentation, MTU detection and ICMP filters. FreeBSD uses MTU detection by default. However, MTU detection requires that ICMP "can't fragment" messages be received, and some broken sites filter all ICMP. I know that the Redback has an "ignore don't fragment" feature. If this is enabled, it will fragment packets, it would normally throw away. This feature will break MTU detection too, but at least the end user won't notice, and packets will flow. Tom On Tue, 18 Jun 2002, Mike Tancsa wrote: > > The DSL whole supplier we use (Bell Canada) has been turfing their Redback > SMSes and moving to an ERX from unisphere networks. > > With the Redback, all was great... I had a FreeBSD box acting as a NAT > gateway for a number of Windows boxes and all was great. Then, the > customer got moved over to one of these ERXes and there is now some strange > MTU problem. Couple of things. Supposedly the default MTU on the ERX is > 1472 (or 1452) depending on who you talk to and not 1492. > > e.g. when doing a fetch to > >> lynx2.8.4rel.1.tar.bz2 doesn't seem to exist in /usr/ports/distfiles/. > >> Attempting to fetch from http://lynx.isc.org/current/. > Receiving lynx2.8.4rel.1.tar.bz2 (1940531 bytes): 0%^C > 16682 bytes transferred in 89.5 seconds (186.41 Bps) > fetch: transfer interrupted > > Notice the speed... Its totally brutal. yet, a transfer from just a few > hops away is fine. > > My question is, how can I track this problem down ? There seems to be some > strange interaction with FreeBSD because if I put a Windows box on the > other end, it does not suffer from this same problem. I can easily repeat > the problem, but the question is, how can I track down the issue and then > explain it to my telco. > > (Note, I have tried various MTU and MRU settings. > > Thanks for any pointers. > > 4.6-STABLE FreeBSD 4.6-STABLE #0: Tue Jun 18 > > > default: > set log Phase Chat LCP IPCP CCP tun command > ident user-ppp VERSION (built COMPILATIONDATE) > > # Ensure that "device" references the correct serial port > # for your modem. (cuaa0 = COM1, cuaa1 = COM2) > # > set device /dev/cuaa1 > > set speed 115200 > set dial "ABORT BUSY ABORT NO\\sCARRIER TIMEOUT 5 \ > \"\" AT OK-AT-OK ATE1Q0 OK \\dATDT\\T TIMEOUT 40 CONNECT" > set timeout 180 # 3 minute idle timer (the default) > enable dns # request DNS info (for resolv.conf) > > > pppoe: > set device PPPoE:fxp1 > #set mtu 1452 > #set mru 1452 > set speed sync > enable lqr > set lqrperiod 5 > set cd 5 > set dial > set login > set timeout 0 > disable deflate pred1 mppe > deny deflate pred1 mppe > set authname user@example.com > set authkey thepassword > set ifaddr 10.0.0.1/0 10.0.0.2/0 255.255.255.0 0.0.0.0 > add default HISADDR > > > > ---Mike > -------------------------------------------------------------------- > Mike Tancsa, tel +1 519 651 3400 > Sentex Communications, mike@sentex.net > Providing Internet since 1994 www.sentex.net > Cambridge, Ontario Canada www.sentex.net/mike > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-isp" in the body of the message > > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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