I have added this since a friend of mine told me something I have totally forgotten. Certain stupid Internet Service Providers use IP addresses assigned by IANA for their local networks on which you connect to. For example, the Swedish Internet Service Provider and phone monopoly Telia uses this approach for example on their DNS servers, which uses the 10.x.x.x IP address range. A common problem that you may run into when writing your scripts, is that you do not allow connections from any IP addresses in the 10.x.x.x range to yourself, because of spoofing possibilities. Well, here is unfortunately an example where you actually might have to lift a bit on those rules. You might just insert an ACCEPT rule above the spoof section to allow traffic from those DNS servers, or you could just comment out that part of the script. This is how it might look:
/usr/local/sbin/iptables -t nat -I PREROUTING -i eth1 -s \
10.0.0.1/32 -j ACCEPT
I would like to take my moment to bitch at these Internet Service Providers. These IP address ranges are not assigned for you to use for dumb stuff like this, at least not to my knowledge. For large corporate sites it is more than o.k., or your own home network, but you are not supposed to force us to open up ourselves just because of some whim of yours. You are large Internet providers, and if you can't afford buying some 3-4 IP addresses for your DNS servers, I have a very hard time trusting you.