From owner-freebsd-net@FreeBSD.ORG Tue Aug 29 23:36:56 2006 Return-Path: X-Original-To: freebsd-net@freebsd.org Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1474D16A500 for ; Tue, 29 Aug 2006 23:36:56 +0000 (UTC) (envelope-from h.nieser@xs4all.nl) Received: from smtp-vbr9.xs4all.nl (smtp-vbr9.xs4all.nl [194.109.24.29]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9BFEC43D45 for ; Tue, 29 Aug 2006 23:36:55 +0000 (GMT) (envelope-from h.nieser@xs4all.nl) Received: from [192.168.1.64] (aphax.nl [82.92.29.227]) by smtp-vbr9.xs4all.nl (8.13.6/8.13.6) with ESMTP id k7TNarWa091715 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Wed, 30 Aug 2006 01:36:54 +0200 (CEST) (envelope-from h.nieser@xs4all.nl) Message-ID: <44F4CF17.8060203@xs4all.nl> Date: Wed, 30 Aug 2006 01:34:47 +0200 From: Hans Nieser User-Agent: Thunderbird 1.5.0.5 (X11/20060805) MIME-Version: 1.0 To: freebsd-net@freebsd.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Virus-Scanned: by XS4ALL Virus Scanner Subject: iwi discarding oversized packets while mtu=1500 for src/dst X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 29 Aug 2006 23:36:56 -0000 Hi, Today I wanted to go back to using FreeBSD on my laptop, which is still installed but hasn't been used for several months because I am still waiting for a stable Intel HDA driver. So I performed a full upgrade of my installed ports. However I ran into an issue that prevented me from logging in to my FreeBSD server over ssh. When I tried to login to the server I got the usual "Password: " prompt, but as soon as I typed my password and hit enter, nothing happened. At first I thought it was a DNS issue, but after disabling UseDNS in sshd_config I still ran into it. Also, other computers on my LAN were able to ssh to the server without problems and I could ssh from the server to the laptop and any other computer on my LAN without problems. Upon closer inspection I found that logging into my FreeBSD sshd server from my FreeBSD laptop triggered a bunch of iwi0 errors in dmesg (on the laptop): iwi0: discard oversize frame (ether type 800 flags 3 len 1518 > max 1514) iwi0: discard oversize frame (ether type 800 flags 3 len 1518 > max 1514) iwi0: discard oversize frame (ether type 800 flags 3 len 1518 > max 1514) iwi0: discard oversize frame (ether type 800 flags 3 len 1518 > max 1514) (and many more, probably aggregated from several login attempts). Note that I have not touched any MTU settings at all and that all computers on my LAN have the default MTU (1500) set (according to ifconfig). To check that my server's NIC was in fact sending packets of 1518 bytes I sniffed a SSH login from my Gentoo desktop computer to the server with wireshark which did capture a packet of 1518 bytes: No. Time Source Destination Protocol Info 36 1.678370 192.168.1.1 192.168.1.64 SSHv2 Encrypted response packet len=1448 Frame 36 (1518 bytes on wire, 1518 bytes captured) Ethernet II, Src: Albatron_0f:40:c7 (00:0a:48:0f:40:c7), Dst: SitecomE_1b:35:d9 (00:0c:f6:1b:35:d9) Internet Protocol, Src: 192.168.1.1 (192.168.1.1), Dst: 192.168.1.64 (192.168.1.64) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 47797 (47797), Seq: 1896, Ack: 1733, Len: 1448 SSH Protocol So it would seem that my desktop's NIC (or WNIC actually) can handle these "oversized" packets (if they are in fact oversized, I don't really know at what layer the MTU setting is applied), while my Laptop's WNIC (iwi) doesn't. Can anyone shed some light on who or what is to blame for my problems and what the best way to solve it is? I can at least get things working by lowering my server's MTU, but I really don't understand why this is a problem now because I'm pretty sure I've succesfully been able ssh to my server in the past from my laptop and I never ever had to touch any MTU settings. I should mention that I am actually not sure if the problem was present before I updated all my ports since it was the first thing I did. But I guess if it was caused by an update it would have to be something with the iwi-firmware port, unfortunately I don't know if it was updated. My server's NIC: xl0@pci2:0:0: class=0x020000 card=0x10001458 chip=0x920010b7 rev=0x78 hdr=0x00 vendor = '3COM Corp, Networking Division' device = '3C905C-TX Fast EtherLink for PC Management NIC' class = network subclass = ethernet Laptop's NIC: iwi0@pci1:3:0: class=0x028000 card=0x27018086 chip=0x42208086 rev=0x05 hdr=0x00 vendor = 'Intel Corporation' device = 'PRO/Wireless 2200BG Network Connection' class = network