IP Readdressing

The IP Readdressing feature enables redirecting unknown gateway traffic based on the destination IP address of the packets to known/trusted gateways.

IP Readdressing is configured in the flow action defined in a charging action. IP readdressing works for traffic that matches a particular ruledef, and hence the charging action. IP readdressing is applicable to both uplink and downlink traffic. In the Enhanced Charging Subsystem, uplink packets are modified after packet inspection, rule matching, and so on, where the destination IP or port is determined, and replaced with the readdress IP or port just before they are sent out. Downlink packets (containing the readdressed IP or port) are modified when they are received, before the packet inspection, where the source IP or port is replaced with the original server IP or port number.

For one flow from an MS, if one packet is re-addressed, then all the packets in that flow is re-addressed to the same server. Features like DPI and rule-matching remain unaffected. Each IP address and port combination are defined as a ruledef.

In case of IP fragmentation, packets with successful IP reassembly are readdressed. However, IP fragmentation failure packets are not readdressed.

There are two different approaches for the readdress server selection, in case, server-list is configured under charging-action.

  • round-robin: In round-robin approach, server selection happens in round-robin manner for every new flow. In round-robin, only active servers in the list are considered for selection.

  • hierarchy-based approach: In hierarchy-based approach, servers are tagged as primary, secondary, tertiary, and so on, depending on the order they are defined in the readdress server-list. All flows are readdressed to the primary server until it is up and running. If Primary server goes down, then flows are readdressed to secondary server and the same logic goes on. Once primary server is active then flows switch back to primary server for readdressing.

An extra CLI is provided that enables user to select from hierarchy or round-robin approach for server selection. Both round-robin and hierarchy-based server selection approaches are applicable for both IPv4 and IPv6 based servers.