contiguous and discontiguous

[vishalpatil86]

Hi,

Can anyone tell me what are contiguous and discontiguous networks?

I googled this, but didn't get any satisfactory explanation

[mbilgrav]

I think :

its like "connected" and "disconnected", like in wildcard bits are contiguous 1's

like "one cloud" and "two clouds"

so if you have just one cloud, its contiguous, but if you have two clouds connected is discontiguous

discontiguous is like you have several component make it together.

My 1st google hit:

http://en.wiktionary.org/wiki/discontiguous

[vishalpatil86]

sorry, but didn;t undaerstand what you trying to explain me..

[Vinod Arya]

A Contiguous network is a single Class A, B, or C network for which all routes to subnets of that network pass through only other subnets of that same single network.

A discontiguous network will have two or more subnetworks of a classful network connected together by different classful networks.

Discontiguous subnets are really a major issue when it comes to classful routing protocols or trying to achive intelligent summarization across your network.  Otherwise, most major routing protocols can adapt to them - it just results in a larger routing table.

Say you have 10.8.0.0/16, 10.9.0.0/16, 10.10.0.0/16, and 10.11.0.0/16.   If you own all of these networks, you could advertise them summarized as 10.8.0.0/14.

However, if you only owned the 10.8, 10.9, and 10.11 network spaces, you could not.  You would then only be able to summarize it down to two routes - 10.8.0.0/15, and 10.11.0.0/16.

The idea is that contiguous subnets can all be reach in the same direction.  So if you have 4 routers, and routers A, B and C all point packets destined to 10.8 through 10.11 to router D via a summary address, that works so long as the 10.8.0.0/14 network all resides off of router D.  However, as explained earlier, if 10.10.0.0/16 resides on router B, then traffic destined to that network would not reach it's destination. That is a case where you break up your summarization as the networks are no longer "contiguous".

You can search Cisco.com for the words contiguous and discontiguous and you will find some articles that provide graphics and slightly better explanations.

Check this one :

http://docstore.mik.ua/cisco/CCNP-CCDP/CID-CP2001/CID-184.html

-Thanks

[Richard Burts]

I like the explanation from Vinod. I would try to say it in a slightly different way.

A network is contiguous if you can get from every part of that network to every other part of that network without going outside of the network.

A network is discontiguous if going from one part of the network to some other part of the network you must go through some different network.

HTH

Rick

[vishalpatil86]

thank you vinod and richards