Wazz is right, it may be a gateway..... on the other hand it can be a network address translator from your cable provider. I've a set-up that is somehow a similar, all out-bound traffic are translated to a single IP address and all incoming are directed to the machines respective public addresses. I hope this helps.

Wazz may be correct, it can be your hosts gateway. Or it can be a network address translator. some practices a method of translating outgoing and incoming traffic to a single IP adress.