The user interface outlined in sections 2.7 and 3.8 of RFC- 793 needs to be extended for multihoming. The OPEN call MUST have an optional parameter:
OPEN( ... [local IP address,] ... )
to allow the specification of the local IP address.
Some TCP-based applications need to specify the local IP address to be used to open a particular connection; FTP is an example.
A passive OPEN call with a specified "local IP address" parameter will await an incoming connection request to that address. If the parameter is unspecified, a passive OPEN will await an incoming connection request to any local IP address, and then bind the local IP address of the connection to the particular address that is used.
For an active OPEN call, a specified "local IP address" parameter will be used for opening the connection. If the parameter is unspecified, the networking software will choose an appropriate local IP address (see Section 188.8.131.52) for the connection