I have a lan with 2 computers. My gateway is running iptables (masquerading) and shares connection to the internet for another laptop. my Laptop can connect to the internet but cannot access wwwhotmailcom, wwwmappyfr and some others; though my gateway can connect to them. Any idea of this problem?

You must have conflicting iptables rules, more specifically rules applying to computers behind your firewall (your laptop). There is no masquerading involved for your firewall box, only for computers going through it.

The only thing I need for masqueraing is this:
iptables -t nat -A POSTROUTING -s $network_addr -j SNAT --to $external_ip

Also ensure your laptop isn't enforcing any filtering by shutting down iptables on it.

I have got only one rule for iptables.

I have ever tried
IPTABLES -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
or
IPTABLES -t nat -A POSTROUTING -j SNAT --to-source $IP

my gateway has not any problem to connect every site on internet.
my laptop (under WinXP) can connect all site on the internet EXCEPT hotmail, mappy.
I tried to sniff when it connects to hotmail for example, but hotmail does not
respond. google responds well. So my problem affects only particular web server.
So my question is:
why my laptop can connect google and cannot connect hotmail?

thank you for your responses...

What happens when you try to do a tracert from the laptop?

have you treid bypassing the router?

What about this?

check if u are blocking the said sites on ur xp machine..

I don't think my laptop is enforcing any filtering by shutting down iptables nor it blocks some sites because it is the same problem when my laptop is under XP or under linux.
How can I bypass my router? (my lalptop can go anywhere on internet when it is directly plugged my adsl modem in)
Thank you again for your help.

Am I correct, in that the XP laptop can connect to some websites but not others? If so, it sounds like an ECN issue.

ok I've read a post on this site (see below, thanks to nufish)) which has dealed with the same problem (problem about mtu between ppp and ethernet?).

I've fixed it by adding a rule to iptables:

$IPTABLES -I FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

Now everything is ok!
see you...

just have seen:
http://www.linuxquestions.org/questi...threadid=15009