Date: Thu, 31 Aug 2006 09:08:35 -0700 From: Sam Leffler <sam@errno.com> To: Hans Nieser <h.nieser@xs4all.nl> Cc: freebsd-net@freebsd.org Subject: Re: iwi discarding oversized packets while mtu=1500 for src/dst Message-ID: <44F70983.40705@errno.com> In-Reply-To: <44F4CF17.8060203@xs4all.nl> References: <44F4CF17.8060203@xs4all.nl>
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Hans Nieser wrote: > 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 I see none of the basic info needed to help. OS version? description of how the device is setup (e.g. ifconfig cmds) and current state--ifconfig iwi0. Sam
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