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Another way you can represent both the IP address and the subnet mask, at the same time is using a notation called classless inter-domain routing notation, or CIDR The way the CIDR works is to count the number of bits in the subnet masks and then just note the number of bits. Very simple notation and one certainly that you're going to see. Now you don't have to really understand to be able to configure a Server 2003 computer but you are going to see it as we work with DHCP and as we work with routing table entries. Its primary function by the way is to simplify some of these routing table entries, especially those in use on the Internet and reduce the number of hosts that are wasted in typical class B networks. Now here is an example of what we've learned so far. We have the IP address of 192.168.2.100 with a subnet mask of 255.255.255.0. Now without referring back to our binary notation, we probably understand by now that this is eight ones, that's eight ones and that's eight ones so, how many ones in total, how many bits are turned on, how many bits define the subnet mask, 24 of them. So another way we can represent this right here is in CIDR notation, 192.168.2.100/24 is this IP address and subnet mask. Where you might see this especially is where we start to subnet and super net and here's another example of using CIDR notation. What if you saw the CIDR notation of 192.168.100.35/20? This is an IP address in subnet mask CIDR notation. Well if we have 20 bits better set to on in the subnet mask, here's with that subnet mask would look like in binary. 8 ones, 8 ones, so 8, 16, 17, 18, 19, 20, ones and then the rest if we use our rules, and we have to, use our rules of subnet mask, contiguous ones followed by contiguous zeros, then we end up with a subnet mask that looks like this. In decimal what does this look like, if you were to type IPconfig, you would see a subnet mask that would look like this, 255.255.240.0. Can we use 240? Yes we can because that 240 decimal follows the rules. So this notation would look like this if we were to see it in decimal or if we use a utility like IPconfig. Again you might not use CIDR day to day but it's a very important to be able to recognize, exactly what that CIDR notation means because especially for test questions they might just give you an IP address in CIDR notation and it becomes essential for you to convert to either binary or to decimal in order to answer the question correctly.