iwi discarding oversized packets while mtu=1500 for src/dst

[Sam Leffler]

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 at 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 at 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