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Sendmail & IpTable Rules

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linux-howto

http://serverfault.com – I need to setup IpTable Rules for a server with nginx, ssh and sendmail. Now, the problem is, with my rules I can not send emails to other hosts anymore. Emails to localhost do work, but sending to different servers does not, when the firewall is up. I tried opening both Incoming and Outgoing Port 25 and DNS lookup ports, but nothing worked. Any ideas? Update: Here are my rules: #! /bin/sh # firewall iptable rules interface="eth0" # first, deny all iptables -P INPUT DROP iptables -P OUTPUT DROP iptables -P FORWARD DROP # open loopback device completely iptables -A INPUT -i lo -j ACCEPT (HowTos)

grtyyu's picture
Submitted by grtyyu on 08/30/2012

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I want to add whitelist in my system using iptables. So I searched the web and find this:

iptables -I INPUT -s 10.0.0.0/8 -j ACCEPT iptables -I INPUT -s 127.0.0.1/8 -j ACCEPT iptables -I INPUT -s 192.168.0.0/16 -j ACCEPT iptables -P INPUT DROP

and it really works. So I fire iptable -F to delete all rules, then I cannot connect to this server anymore.

I want to setup a VPN server for personal use, so I follow the blog article [1], and it work like a charm.

The only thing I am wondering is if the iptable's rule secure, e.g.

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

And I have only one public interface eth0, are there any risk in using the rule above?

From other place, I see other alternatives of iptable rules, e.g.

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