pMTU discovery

[Bernhard Schmidt]

On 08.06.2012 19:05, Bernhard Schmidt wrote:
> On 08.06.2012 18:47, Bernhard Schmidt wrote:
>
>> PEBKAC, I was just being stupid. Compiled fine, will test right away.
>
> It basically works, but I think you are using the wrong MTU value. I'm
> currently in an IPv4-only non-MTU-challenged location. Cisco Anyconnect
> client connects with 1418 bytes MTU, openconnect with 1315. I'm not
> exactly sure what the difference between X-DTLS-MTU and D-CSTP-MTU is
> supposed to be, but the tunnel should be able to transport the larger
> value.
>
> TCP_INFO rcv mss 1348, snd mss 1348, adv mss 1448, pmtu 1500
> [...]
> X-CSTP-MTU: 1315
> X-DTLS-MTU: 1418
> DTLS option X-DTLS-MTU : 1418
>
> I'll try MTU challenged (DSL) and native IPv6 transport either tonight
> or during the weekend.

IPv6 with MTU 1492:

TCP_INFO rcv mss 1368, snd mss 1368, adv mss 1428, pmtu 1500
X-CSTP-MTU: 1335
X-DTLS-MTU: 1386

IPv4 with MTU 1492:

TCP_INFO rcv mss 1368, snd mss 1368, adv mss 1448, pmtu 1500
X-CSTP-MTU: 1335
X-DTLS-MTU: 1418

Can openconnect output the _sent_ HTTP headers somehow?

Best Regards,
Bernhard