Explain the concept of subnet masks and how they are used in IP addressing.

Subnet masks are used in IP addressing to divide an IP address into two parts: the network address and the host address. The subnet mask is a 32-bit value that consists of a series of ones followed by a series of zeros. The ones represent the network portion of the IP address, while the zeros represent the host portion.

When an IP packet is sent from one device to another, the subnet mask is used to determine whether the destination IP address is on the same network or a different network. The subnet mask is applied to both the source and destination IP addresses using a logical AND operation. This operation results in a network address, which is then used to determine the appropriate routing path for the packet.

For example, let's consider an IP address of 192.168.1.100 with a subnet mask of 255.255.255.0. Applying the subnet mask to this IP address using a logical AND operation, we get the network address of 192.168.1.0. This means that any device with an IP address starting with 192.168.1 is on the same network.

Subnet masks allow for efficient use of IP addresses by dividing them into smaller subnetworks. This is particularly useful in large networks where a single IP address range may not be sufficient. By using subnet masks, network administrators can create multiple smaller networks within a larger network, each with its own unique network address.

Subnet masks also play a crucial role in routing. Routers use subnet masks to determine the best path for forwarding packets between networks. When a router receives a packet, it compares the destination IP address with its routing table, which contains information about network addresses and corresponding interfaces. The router uses the subnet mask to determine which network the destination IP address belongs to and forwards the packet accordingly.

In summary, subnet masks are used in IP addressing to divide an IP address into a network address and a host address. They allow for efficient use of IP addresses and play a vital role in routing packets between networks.