Networking question

Never thought about it before and now I am dealing with a real issue
that may have a root cause in networking.

When I have the typical internet app it is simple: client sends htttp
msg, it goes to the network adapter, through the wire to another
network adapter, to the web server.

Now, what is the routing scheme when both client and server are on the
same box, so my http msg goes to localhostort_number. How are the
network facilities on the box involved?

I am running the second scenario and I see the failure of system
components caused by machine running out of memory when individually,
there is absolutely no reason to any of the system components to cause
that (no memory leaks in individual tasks).