Usable IP addresses are separated in 3 classes: class A, B and C. As we previously discussed, class A addresses are the ones from 0.0.0.0 to 127.255.255.0, class B are from 128.0.0.0 to 191.255.255.255 and class C are those IP addresses in the range of 192.0.0.0 to 223.255.255.255. To help you easily understand this topic, we will use an example IP address from each class.
Finding the network, broadcast and host address on a class A IP address.
A class A IP address is an IP within the range of 0.0.0.0 to 127.255.255.255. We will use the IP 10.0.0.1 in this example. This IP address, not only it belongs to class A, but it also belongs to the private IP space, used for internal networks. The default subnet mask for a class A address is 255.0.0.0. This means, our network is from 10.0.0.0 to 10.255.255.255.
Previously, we told you that the first IP address on a network is the network address. In the networking world we use this address to refer to whole network. The network address in our case is 10.0.0.0.
We also told you that the broadcast address, the address used for a host to send packets in the whole network, is the last address. Yes, that’s correct, the broadcast address in our case is 10.255.255.255.
Any address between the network and the broadcast address is an usable address for your network hosts, meaning that you can have up to 16,777,214 hosts in your network (2^24 – 2).
Finding the network, broadcast and host address on a class B IP address.
This time, we will use the 180.250.0.1 IP address. As you can see, this is a valid class B address, and it’s a public one. The default subnet mask for a class B address is 255.255.0.0. We get the range from 180.250.0.0 to 180.250.255.255 for our network. As you may already guessed, the network address is 180.250.0.0 and the broadcast address is 180.250.255.255. The remaining addresses are used by the hosts of the network, but the network can have no more than 65,534 (2^16 – 2) hosts.
Finding the network, broadcast and host address on a class C IP address.
Similar to the other examples, we take a class C address: 193.10.0.1. The default netmask in class C is 255.255.255.0 meaning that we’ll get the network within the range of 193.10.0.0 to 193.10.0.255. The network address is 193.10.0.0 and the broadcast address is 193.10.0.255. We can have up to 254 hosts in our network.
The subnet mask is the component in IP addressing that separates networks. When you assign an IP address to a device, you must assign a network mask too. If you’re not assigning the correct subnet mask, you will end up with no connectivity between that host and the others. The bits set to 1 in the subnet mask denotes that those bits in the IP address cannot change. Comparing these bits allows devices in the network to know which network they belong to.
Routers are making an ANDing operation to find out the network address. ANDing is a basic binary operation. In this process, they compare the IP address bits with the subnet mask bits. If the bits are set to 1, the result of the ANDing operation will be 1. If they are both 0 or any combination of 1 with 0, the result is 0. Let’s use an example to better describe this. We will use the IP address 192.0.0.1 with the netmask 255.255.0.0 to determine the network address.
IP address: 192 . 0 . 0 . 1
11000000 00000000 00000000 00000001
Netmask: 255 . 255 . 0 . 0
11111111 11111111 00000000 00000000
Network: 11000000 00000000 00000000 00000000
192 . 0 . 0 . 0
We hope you found this topic about IP addresses helpful in your preparation for the CCNA exam. In the our next topic we will study the subneting process. This will help you work with Variable Length Subnet Masking (VLSM) and Classless Inter-Domain Routing (CIDR) and it’s a very important topic in your preparation for Cisco’s CCNA exam.