Systems and methods for ip reachability in a communications network

A gateway comprising:

• an interface configured to provide communication with a requestor, wherein a DNS query requesting an IP address of a mobile device is received over the interface;
• a memory configured to maintain an address translation table that includes an network address translation (NAT) binding entry, the NAT binding entry associating an Internet protocol (IP) address of the mobile device with a public IP address;
• and
• at least one module that is configured to determine whether the IP address of the mobile device is available and whether the IP address is a local address that is not reachable from a public communications network without network address translation, and configured to create a network address translation (NAT) binding that associates the IP address of the mobile device with a public IP address and to create a response to the requestor that includes the public IP address associated with the IP address of the mobile device to allow communication between the requestor and the mobile device.

Logic encoded on one or more tangible, non-transient media for execution and when executed operable to:

• receive, at a gateway, a domain name system (DNS) query from a requestor to obtain an Internet Protocol (IP) address of a mobile device to enable communication with the mobile device over a public communications network;
• determine whether the IP address of the mobile device is available at the gateway;
• redirect the DNS query if the IP address of the mobile device is unavailable at the gateway;
• if the IP address of the mobile device is available at the gateway, determine whether the IP address of the mobile device is a local address, wherein the local address is an address to which the requestor cannot send data over the public communications network without network address translation;
• and
• if the IP address of the mobile device is a local address,
• create a network address translation (NAT) binding that associates the IP address of the mobile device with a public IP address wherein the public IP address provides an address recognized by the gateway as an address to which the requestor can send data to establish communication with the mobile device over the public communications network, and
• send, to the requestor, a response that includes the public IP address associated with the IP address of the mobile device to allow communication with the mobile device over the public communications network.