Comment 13 for bug 1501588

Christian Rank (c-rank) wrote :

The logs submitted by the bug reporter contain lines like
Sep 30 23:31:07 castiana wpa_supplicant[25653]: l2_packet_send - sendto: Message too long

I had exactly the same problem, so I checked the MTU of my wireless interface and noticed that it was set to 1280.

After issuing
   ifconfig <wlan-interface> mtu 1500
the wpa connection works again.

But, after being connected some time, the MTU decreases again to 1280. The reason in my setup seems to be some strange behaviour of NetworkManager and IPv6:
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> address xxx.xxx.xxx.160
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> plen 23 (255.255.254.0)
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> gateway xxx.xxx.xxx.252
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> server identifier xxx.xxx.xxx.252
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> lease time 1200
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> nameserver 'xxx.xxx.xxx.253'
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> domain name 'xxx.de'
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <info> (wlp2s0): DHCPv4 state changed bound -> bound
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <warn> (wlp2s0): Lowering IPv6 MTU (1500) to match device MTU (0)
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <warn> (wlp2s0): IPv6 MTU (0) smaller than 1280, adjusting
Dec 7 13:46:31 rank-Latitude-E4310 NetworkManager[731]: <warn> (wlp2s0): Raising device MTU (0) to match IPv6 MTU (1280)

Since we have no IPv6 in our WLAN, I disabled IPv6 for the connection in NetworkManager. Unfortunately, this does not change anything - after the first DHCP renewal, the MTU is set to 1280 again ...

This calls for further investigation ...