> This is executed from rc.local on the old machine (IP > addresses altered to > protect the innocent): > > echo "Turning on IP Forwarding" > /bin/echo "1" > /proc/sys/net/ipv4/ip_forward > > echo "Setting IPMasq Rules" > /usr/sbin/ipmasqadm mfw -A -m 3 -r 10.0.0.1 > > echo "PortForwarding" > /usr/sbin/ipmasqadm portfw -a -P tcp -L 192.168.1.1 25 -R 10.0.0.1 25 > > The new machine that I'm running this on is a CentOS 4.2 > x86-64 running > kernel 2.6.9-22.0.1.EL. Some of the research that I've done > indicates that > I should have something like this going on: > > iptables -t nat -A PREROUTING -p tcp -i eth1 -d 192.168.1.1 --dport > 25 -j DNAT --to 10.0.0.1:25 > iptables -A FORWARD -p tcp -i eth0 -d 10.0.0.1 --dport 25 -j ACCEPT > > But that doesn't work. Then I ran across a site that added a couple > of statements to the mix: > > echo 1 > /proc/sys/net/ipv4/ip_forward > > iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE > > The additional lines don't help my cause either and I am a > bit lost here. > If anyone has any helpful information I would greatly > appreciate it. Thanks. As I understand it, you want to forward smtp traffic from the internet to your smtp server. Replace the variables I inserted with the actual values. # No forwarding until the rules have been setup echo 0 > /proc/sys/net/ipv4/ip_forward # FORWARD policy DROP # This drops everything that doesn't match in the following rules $ipt -P FORWARD DROP # ACCEPT packets that have been matched by a state NEW rule $ipt -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT # Allow NAT for your LAN $ipt -A FORWARD -m state --state NEW -i <if_lan> -o <if_inet> \ -s <net_lan> -j ACCEPT # Perform NAT for your LAN $ipt -t nat -A POSTROUTING -o <if_inet> -s <net_lan> \ -j SNAT --to <ip_inet> # Allow portforwarding for smtp server $ipt -A FORWARD -m state --state NEW -i <if_inet> -o <if_lan> \ -d <ip_smtp_svr> -p tcp --dport 25 -j ACCEPT # Perform portforwarding for smtp server $ipt -t nat -A PREROUTING -i eth1 [-d <ip_inet>] \ -p tcp --dport 25 -j DNAT --to <ip_smtp_svr>:25 # Rules have been setup ; turn on forwarding echo 1 > /proc/sys/net/ipv4/ip_forward You can find a tutorial on iptables here : http://iptables-tutorial.frozentux.net/iptables-tutorial.html Gr, Rob
