SetLoopBack is an abstract virtual method that specifies the interface used to change the LoopBack socket option for the socket handle specified in AHandle to the value specified in AValue. 

Loopback is the ability to send data on a virtual circuit between two datastream sockets, or two datagram sockets in the same or different processes. One common use is for development and testing network applications, without a network (on a standalone computer). Another is to allow one application to access the services of another, even if it's located on the same machine. 

While these expectations are perfectly reasonable, not all protocol stack implementations guarantee the availability of these capabilities (including 127.0.0.1, the de facto standard loopback address on TCP/IP hosts). In addition, IPv6 and IP multicast usage may vary based on the protocol stack implementation. 

SetLoopBack must be overridden and implemented in a descendant class to provides access to the capabilities of the protocol stack for the platform or operating system hosting the Indy library.