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From: cam@md.interlink.com (Chris Markle)
Newsgroups: comp.protocols.tcp-ip
Subject: Routers, IP networks, and wide-area networks
Message-ID: <9103211614.AA22207@leo.md.interlink.com>
Date: 21 Mar 91 16:14:51 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 30

Folks,

(Please respond directly to me and I will summarize for the net.)

When IP routers are connected to each other via X.25 networks, is the X.25
network treated as a single IP network/subnetwork, or is each "point-to
point" link (ie. X.25 virtual circuit) treated as a separate network/sub-
network? (Or are the "links" not treated as networks at all?)

For example, assume that I have an X.25 network with three routers connected
to it, R-a, R-b, and R-c; each router knows about the other two. Each router 
is attached to a single Ethernet; for simplicity, each Ethernet is a separate 
IP network - R-a is attached to 192.1.1, R-b to 192.1.2, and R-c to 192.1.3 
(class C networks all).

Would the X.25 network be assigned a single network number, say 192.1.4, and
each router would have an X.25-side IP address of 192.1.4.x? Or would each
"link" (VC) between each router have network numbers assigned to it (eg.
R-a <-> R-b is 192.1.4, R-a <-> R-c is 192.1.5, and R-b <-> R-c is 192.1.6)?

I'm sure that there's no "cut and dried" answer to this, but I was just
wondering how this is "usually" or "commonly" handled with current IP routers.

(If each link gets an IP network/subnetwork address, it seems like in a big 
X.25 or other wide-area network many addresses will be chewed up just on these
point-to-point links. Even subnetting results in many subnets addresses being
consumed. Like Arsenio says, "hmm...")

Chris Markle
Interlink Computer Sciences