doubt on CIDR

hey..

CIDR means classless interdomain routing rite...so is it possible to have something like 192.168.0.0/20... and then have 16 subnets each with 2^12 hosts or do we only borrow bits from the host ID that is in the case of a 192.168.0.0 we can only borrow from the Host ID - last octet..?m kinda confused on this one..

The classless term is important here! With CIDR you are no more limited by stuffs like class A, class B or class C. Therefore, with a subnet like 192.168.0.0/20 you can have 2^12 - 2 hosts. But, of course, you must use the appropriate netmask (/20) on every hosts...

hey thnks for d reply!..so dat means i can design Vlans hvin n/w ids as 192.168.10.0, 192.168.20.0 etc etc and den enable communication via em thru a layer 3 switch..?coz i tght CIDR-->means modifying the default subnet mask-->which is to borrow bits only frm host ID-->in which case our new subnet mask ll be minimum /24 in case of class C

CIDR means that you configure your network with what ever subnet mask. So your NOT bounded to using only /8 /16 or /24. But that does not always mean that you can borrow from the network bits. For example, A company buys the class C range 193.11.22.x. Here the company cannot borrow from network bits to assign a subnet mask of say /21 since this will include IP ranges that the company did not pay for. They will have to by a set of class C ranges to do that.

On the other hand, 192.168.x.x (although is a class C /24) is a PRIVATE ip range. So any one can use it internaly borrowing from network bits with masks like /17 or /20 as you said.

Hope I did not confuse you.

etc etc and den enable communication via em thru a layer 3 switch

This is one of my favorite concepts of networking. Also, I am not sure if you are familiar with iner-vlan routing but, I would look into Routing switch modules or do some research on the term "Router on a Stick."