[Wylug-discuss] Using vi over SSH over VPN over 3G connection.

[David Morris]

Hi,

Thanks all for the very helpful suggestions - I can't get to try them
until lunch time but I'll work through the different suggestions and
see if I can figure it out.

Many thanks again!

David


On 10 March 2011 17:22, John Hodrien <J.H.Hodrien at leeds.ac.uk> wrote:
> On Thu, 10 Mar 2011, Paul Brook wrote:
>
>> My guess is this is an MTU issue.  Typical symptoms are that initially
>> tings
>> work fine, but TCP connections block once large blocks of data are
>> transferred.  Ethernet usually has an MTU of 1500 bytes. The average
>> terminal
>> displays about 2000 characters, so vim "instantly" printing a screenful of
>> data on startup is probably sufficient to trigger this.
>>
>> In theory the TCP connection should automatically accommodate network
>> segments
>> (e.g. VPN tunnels) with a lower MTU[1]. However it's common for firewalls
>> to
>> interfere with this process by blocking ICMP messages.
>>
>> Try manually reducing the MTU on the 3G and/or VPN interfaces. If this
>> confirms the above diagnosis then you have a few options: Beat the
>> router/firewall with a clue stick until PMTU discovery works, have linux
>> hack
>> round the problem for you by enabling TCP MSS clamping, or live with the
>> manual MTU hacks.
>
> That was exactly my suspicion too, hence why I asked about scp.  You often
> see
> a typical ssh connection work fine, but when you scp a big file you're
> guaranteed to use big packets that cause it to stall.  I've seen this with
> Talk Talk who run with a lower than normal MTU.
>
> So despite not saying that with my initialy post, my thinking tallies
> exactly
> with this.
>
> jh
>
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