If you have two or more network interfaces 
When you install sl_proxy on a machine with two or more network interfaces it is not always possible for the machine to decide which is the appropriate interface or if the ip address is correct.
It is possible that an inappropriate IP address is selected by the operation of sl_proxy though the address of the interface can be selected automatically if addresses are reported accurately.
Example:
PC <-------------> Relay Server <---------> xDSL private IP private IP global IP
When Relay Server (sl_relay) selects global IP as Relay Server IP address, it is then not possible to communicate normally between the viewer PC and the Relay Server.
For security each component program of sl_proxy always observes the communication IP address of the other party. When the IP address changes in some way, the communication is interrupted.
When there are two or more network interfaces, the IP address automatically acquired are not necessarily the same IP address used when actually communicating.
So that connected IP address does not change, each program can have the interface to be used for communication fixed by using -i option.
