From owner-freebsd-questions Wed Nov 1 21:21: 0 2000 Delivered-To: freebsd-questions@freebsd.org Received: from blount.mail.mindspring.net (blount.mail.mindspring.net [207.69.200.226]) by hub.freebsd.org (Postfix) with ESMTP id 073EB37B479 for ; Wed, 1 Nov 2000 21:20:57 -0800 (PST) Received: from sloth (user-2ivfiia.dialup.mindspring.com [165.247.202.74]) by blount.mail.mindspring.net (8.9.3/8.8.5) with SMTP id AAA24452 for ; Thu, 2 Nov 2000 00:20:55 -0500 (EST) From: "Timothy L. Robertson" To: Subject: Flaky IP Connection Date: Wed, 1 Nov 2000 21:20:53 -0800 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Everyone, I've been having problems with my PPPoE connection. It works fine most of the time, but sometimes connections hang. On repeatable time seems to be when I cvsup, but it also seems to hang when sendmail exchanges certain messages with my ISP's SMTP server. I've found that this icmp packet seems to suggest the problem: tcpdump -vvv -X -i tun0 -s 2000 icmp tcpdump: listening on tun0 20:06:30.673201 165.247.202.104 > 165.247.202.104: icmp: 165.247.202.104 unreachable - need to frag (mtu 1480) for 165.247.202.104.iad2 > 165.247.202.104.cvsup: [|tcp] (DF) (ttl 64, id 1920, bad cksum 0!) (ttl 255, id 1921) 0x0000 4500 0038 0781 0000 ff01 d383 a5f7 ca68 E..8...........h 0x0010 a5f7 ca68 0304 7dc7 0000 05c8 4500 05dc ...h..}.....E... 0x0020 0780 4000 4006 0000 a5f7 ca68 a5f7 ca68 ..@.@......h...h 0x0030 0407 176f 150c 95c6 This confuses me a little, because my MTUs are set to 1492, not 1480: bash-2.03$ ifconfig fxp0: flags=8843 mtu 1492 inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255 inet6 fe80::202:b3ff:fe03:aae1%fxp0 prefixlen 64 scopeid 0x1 ether 00:02:b3:03:aa:e1 media: autoselect (100baseTX) status: active supported media: autoselect 100baseTX 100baseTX 10baseT/UTP 10baseT/UTP xl0: flags=8843 mtu 1492 inet 10.0.0.2 netmask 0xffffff00 broadcast 10.0.0.255 inet6 fe80::201:2ff:fe48:ad91%xl0 prefixlen 64 scopeid 0x2 ether 00:01:02:48:ad:91 media: 10baseT/UTP (10baseT/UTP ) supported media: 10baseT/UTP 10baseT/UTP 10baseT/UTP lp0: flags=8810 mtu 1500 ppp0: flags=8010 mtu 1500 sl0: flags=c010 mtu 552 faith0: flags=8000 mtu 1500 gif0: flags=8010 mtu 1280 gif1: flags=8010 mtu 1280 gif2: flags=8010 mtu 1280 gif3: flags=8010 mtu 1280 lo0: flags=8049 mtu 16384 inet6 fe80::1%lo0 prefixlen 64 scopeid 0xb inet6 ::1 prefixlen 128 inet 127.0.0.1 netmask 0xff000000 tun0: flags=8151 mtu 1492 inet6 fe80::202:b3ff:fe03:aae1%tun0 --> :: prefixlen 64 scopeid 0xc inet 165.247.202.104 --> 165.247.202.1 netmask 0xffffffff Opened by PID 107 My best guess about what's happening is that sometimes a packet of length > 1480 bytes gets sent out, somehow gets diverted back to my own interface (by NAT or ipfw?) and then gets stuck by this 1480 MTU. Is this a bug or do I have something misconfigured? Why does tcpdump report a different MTU than ifconfig? Any help appreciated. Thanks, - - -Tim timothyr@timothyr.com -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 6.5.8 for non-commercial use iQA/AwUBOgD5sBJDu7xQsK72EQJrGACffELEe042gbQ3uk4X2BcAosSo02cAoKiR C7nwHRCxQgYKVls0j2AQ+as8 =97+C -----END PGP SIGNATURE----- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message