Question on IP address for IP Chains

I writing my ipchains and want to distinguish between my IP address and those of others. I'm using a modem connection and my IP address is dynamicaly allocated by my Internet provider. How do I specify a constant IP address in the IP chains when the provider is changing the IP address everytime I log in? Is there a way to associate the provider assigned IP address with a constant IP address my one user system can recognize? Would the IP address that I specify in the IP chains be 127.0.0.1 or would that be a security problem? I noticed in rc.config there is a SETUPDUMMYDEV. Also there is a IP_DYNIP as well. Might these be used to somehow associate the IP providors address with a constant value that can be put in my IP chains.