The Common INET support allows an installation to connect up to 32 different instances of TCP/IP or other AF_INET physical file systems. Application programs that use sockets do not need to change any code to take advantage of the multiple AF_INET file systems.

Supporting multiple AF_INET physical file systems and providing a single file system image to the user means that the Common INET must perform a set of management and distribution functions that govern how a socket behaves with multiple file systems. A fundamental requirement for distributing work across multiple file systems is an understanding of the IP configurations of each file system. The IP configurations are needed to determine which file system should handle a bind() to a particular home IP address, a connect(), a sendto(), and so forth.

When the Common INET processes a socket request that requires it to select only a particular file system based on an input IP address from a user, the Common INET uses its copy of each file system's IP configuration to select the correct file system to process the user's request. Copies of the IP configurations are maintained by the Common INET internally, and are only used for "prerouting" a socket call to the correct file system. The file system that was selected performs all of the official file system functions, such as routing, once the socket request reaches the file system from the Common INET.

Each file system that is connected to the Common INET must provide a copy of its internal IP routing table. An ioctl is issued to each transport provider (TP) as part of the PFS initialization. This allows the Common INET function to query the routing tables for that file system. Once the Common INET prerouter function has successfully retrieved and stored routing information from a particular file system, message BPXF206I is issued to the hardcopy log. Message BPXF206I is also issued whenever a file system refreshes its routing table. For example, IBM's TCP/IP may refresh its routing tables as part of the OBEYFILE command. Message BPXF207I is issued to the hardcopy log whenever the Common INET deletes internal routing information for a file system. When the connection with a specific file system is severed, the Common INET routing information for that file system is deleted.