wpa_supplicant fails to connect with EAP

Jouni Malinen j
Mon Aug 17 16:39:46 PDT 2015

On Mon, Aug 17, 2015 at 11:35:48AM -0500, Kenny Pearce wrote:
> Aug 17 11:15:24 parmenides wpa_supplicant[1312]: wlan21: CTRL-EVENT-EAP-METHOD EAP vendor 0 method 13 (TLS) selected
> Aug 17 11:15:24 parmenides wpa_supplicant[1312]: l2_packet_send - sendto: Message too long

What MTU do you have configured on wlan21? E.g., check what "ifconfig
wlan0" returns.

> The only thing that looks like a significant error to me in this output
> is "l2_packet_send - sendto: Message too long" but Googling that message did not lead to any useful hits. Does anyone know what might cause this kind of problem, or how to fix it?

I have not seen this before, but my first guess would be that something
has reduced the MTU on the netdev so much that the default EAP-TLS
fragmentation limit gets hit. wpa_supplicant does not currently check
the MTU and update the fragmentation limit automatically, but now that I
learned about this, I'll probably make it do so. As a workaround, you
can try to reduce EAP fragment size with fragment_size=<bytes> parameter
(though, I do not know how to do that with NetworkManager). Setting
fragment_size to something like 100 bytes less than netdev MTU would
hopefully get rid of this issue (or alternatively, increase the MTU
back to more common 1500 if there is no real need to make it smaller).
Jouni Malinen                                            PGP id EFC895FA

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