Another couple of examples

(a) X's DISPLAY environment variable, where the host and port are encoded in a single string (port = display+6000)

(b) CORBA, where an IOR contains hostname and port

Both of these have problems when it comes to firewalls, the best solution for X for instance is using Xnest to proxy the display on the far side of the firewall.

CORBA introduced bidirectional-IOP to help solve the firewall-traversal problem by attempting to reuse existing connections.