The location of the host servers is known to the redirectors, which are specially equipped routers. They maintain information about host servers and the services currently installed on them. Each redirector maintains a redirector table, which lists the transport-level service access points (in our case pairs of IP addresses and port numbers) for which packets must be redirected, and the host server to which the packets must go.
When a redirector receives an IP packet, it checks the destination IP
address and port in the header against the entries in the redirector
table. If it finds a match, it forwards the packet to the appropriate
server host. If there is no match, the packet is simply forwarded
to the origin host.
A packet is redirected to the appropriate host server by
tunnelling it using IP-in-IP encapsulation. The host server is
equipped to detect tunnelled packets and to forward them internally to
the service 
.