Bug#516078: Related to MTU size?

[Maarten ter Huurne <maarten@treewalker.org>]

Hi,

I had a very similar problem after upgrading my gateway machine from Etch to 
Lenny. The gateway itself could do any kind of transfers to the internet, 
but the PCs for which it masquerades the traffic could do very little.

ICMP worked (tested with ping), UDP worked (tested with DNS lookups) and 
some TCP worked. Eventually I noticed that small amounts of data under TCP 
worked, but large amounts did not. For example, logging in with SSH worked, 
but when viewing a man page over that SSH connection it hung.

Then I looked at the MTU size if the interface connected to the internet and 
that was 576. I increased it to 1200 and suddenly all connections worked 
again. I read that 576 is the minimum supported MTU size, but for some 
reason it worked for direct connections but not for masqueraded connections.

The MTU 576 was set via DHCP by my internet provider, so now I configured 
the DHCP client to not set the MTU value.

Note: For me, going back to kernel 2.6.18 did not solve the problem.

Bye,
		Maarten