hello!
My computer is a host of the lan,throgh which i can access the Internet.
by ipconfig(XP),i know my ip address is 10.139.35.55,mask is 255.255.255.0,default gate is 10.139.35.1.
Now i change the mask(my computer) to 255.255.0.0 or 255.0.0.0 i won't be able to access some sites.however,when i change to 255.255.255.128, 255.255.255.192, 255.255.255.224,etc,it seems work well.
so,can anybody explain why this happens with an example ?For instance,i want to talk with a host in the Internet,what does my computer do(involving ip and mask)?,the router(gate) ?That is,if the mask changes,what happens to them?
the more specific,the better!
Simple question?maybe.looking forward to your accurate and confident explanation!i don't want to be mislead! thanks.

If you're really interested, you can start here, but briefly:

The subnet mask tells the computer what its subnet is, that is, what addresses will it be able to reach without having to go through a router. The ip address contains the network number and the host number. The subnet mask is used to retrieve both from the ip address. When you change the subnet mask to 255.255.0.0 or 255.0.0.0, you are telling the computer that more hosts are reachable without going through a router which is why some of them stop working. Changing the subnet mask to 255.255.255.128 tells is fewer hosts are available without going through a router, so your computer sends the messages through the router first. It will still work, but is not as efficient and you will lose communication unnecessarily with some hosts on your subnet if the router should go down.

thanks very much! that is exactly what i wanted,it cleared my biggest confusion,thanks!