The is intended to allow alternative services to detect loops, differentiate traffic for purposes of load balancing, and generally to ensure that it is possible to identify the intended destination of traffic, since introducing this information after a protocol is in use has proven to be problematic.
When a client uses an alternative service for a request, it can indicate this to the server using the
Alt-Used HTTP header.
the domain name of the server.
- <port> Optional
TCP port number on which the server is listening.