These terms are used when looking at a group of networks or subnets.
Let's say you're looking at a group of networks / sub-nets. A contiguous group would all be together. Take the following example:
Discontiguous networks would have a "break" so that when viewed from "start to finish" they do not form a continuous range of IP addresses... Borrowing from the example above, this list would be discontiguous:
...because it is "missing" the range 10.2.0.0/16.
Think of it from the view of summarization. Contiguous networks are easier to summarize in one (or few) summary ranges. Discontiguous networks require more summary statements because the range is not continuous.
Hope this helps,
I think long back we had similar conversation under this thread :
Hope its still helpful.
I appreciate the link by Vinod to a thread in which we both were participants and believe that it does have good information to respond to this question.
I would like to make a comment about the response from Ed. While his interpretation of the semantics of discontiguous is technically correct I believe that it is slightly misleading in terms of how that term is usually used in discussions of networking. I believe that a better example would be to think about an example with two routers. Think about router A with LAN subnet of 172.16.1.0/24 and router B with LAN subnet of 172.16.2.0/24. And think about them connected by a link whose subnet is 10.10.10.0/24. These are discontiguous because both LAN are in the same network but are connected by a link in a different network.
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You are quite welcome. The concepts of contiguous and discontiguous are a bit subtle, and are things that we do not think about as much now as we used to. Back when classful routing protocols like RIP and IGRP were common it was a much bigger deal if your network was discontiguous. The classless routing protocols like OSPF and EIGRP that are commonly deployed now are much more tolerant of discontiguous networks. So we tend not to think about that aspect nearly as much.