RPC over HTTP version 1 (Windows NT 4.0, Windows 2000) and version 2 (Windows Server 2003) introduce support for a new remote procedure call (RPC) transport protocol that allows RPC to operate over Transmission Control Protocol (TCP) port 80. Version 2 also allows RPC to operate over TCP port 443. Operating over TCP ports 80 and 443 allows a client and a server to communicate in the presence of most proxy servers and firewalls. COM Internet Services allows DCOM to use RPC over HTTP (referred to as the Tunneling TCP/IP Protocol in the DCOM Configuration utility [Dcomcnfg.exe]) to communicate between DCOM clients and DCOM servers.
For additional information about COM Internet Services and RPC over HTTP, see the "References" section later in this article.