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Old 04-03-2008, 02:06 AM   #1
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[SOLVED SOLVED SOLVED] S L O W secure connections on debian router

Hi all,

I have just setup my Debian lenny router box (p4 cel, eth0 + eth1) and now, all the 'dows boxes behind it take forever to connect to certain secure connections, like msn and netbanking. I'm totally stumped by this, since none of my configuration has changed since two months ago, when everything worked perfect. It only started playing up when I changed m/b and cpu this week and updated the install.

The path goes like this--

---> DSL via bridged modem ---> Lenny box- eth1 (ppp0)--> iptables firewall with NAT enabled--> Lenny box- eth0 --> 8 port switch --> ms boxes

This configuration worked perfect until I upgraded hardware. Normal browsing works perfect, and secure connections from the router itself are fine, it's just the rest of the network that has a problem. I can't remember if I had ssl on it before... so I can't tell if it had anything to do with it.

Any hints???

Last edited by maerkis; 04-03-2008 at 11:31 AM. Reason: problem solved
Old 04-03-2008, 11:19 AM   #2
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ok.... mtu was too big

in /etc/networking/interfaces for eth0:

mtu 1452
and /etc/ppp/providers/provider:

mtu 1452
and thanks to mikey79 for this snippet of code for the iptables script:


iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
now everything works nicely again... still befuddles me why a hardware change would cause such a problem, though. With a lot of testing, I discovered that the mtu setting for ppp0 had to be equal to or greater than that of eth0... the basic troubleshooting routine seems to be to keep decreasing the values of both until things work again, though eth1 which has the ppp0 connection on it needs to be left at mtu of 1500.


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