SSH connection hangs on shell commands when used through tinc

[Guus Sliepen]

On Thu, Oct 02, 2008 at 06:00:42PM +0300, Viktors Žilinskis wrote:

> [...] The connection
> establishes well, I can ping FreeBSD and Ubuntu virtual IPs in both
> directions, no problems so far. But when I use any shell commands which have
> significant text output, the ssh connection just hangs. For example, if I
> list files in a small direcotry (5-10) it lists them, If i list a bigger
> directory it hangs. It also hangs on other commands, like top. Interestingly
> enough, I tried to do that in the opposite direction - connected via ssh to
> FreeBSD box virtual IP from Ubuntu box, and I could not find a command which
> could hang the connection.
> 
> I've tried to use different ssh clients, but this does not help. Though I am
> not sure, I think there  should be something wrong with my tinc setup.

It sounds like a MTU problem. Either a router is silently dropping packets that
are too large, or it is correctly sending back ICMP Fragmentation Needed
packets and a firewall somewhere is blocking them. Some options to work around
the problem:

- Add "PMTUDiscovery = yes" to your host config files.
- Add "PMTU = 1400" to your host config files, or add "ifconfig $INTERFACE mtu 1400" to the tinc-up scripts.
- Add "TCPOnly = yes" to your host config files.

Of course, the best solution is to fix the offending router/firewall. Let me
know if everything fails.

-- 
Met vriendelijke groet / with kind regards,
     Guus Sliepen <guus at tinc-vpn.org>
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