Subnetting on the AR

When many hosts are distributed on an internal network, the internal host IDs can be divided into multiple subnet IDs to facilitate management. A network can be divided into multiple subnets to conserve IP address space and support flexible IP addressing.
Subnetting is implemented within the internal network. The internal network has only one network ID for the external network. When packets are transmitted from the external network to the internal network, the router on the internal network selects a route for the packets based on the subnet ID and finds the destination host.
Subnet division of an IP address in Class B is used as an example. The subnet mask consists of a string of continuous 1s and 0s. The value 1 corresponds to the network ID and subnet ID, and the value 0 corresponds to the host ID.
The first 5 bits of the host ID is used as the subnet ID. The subnet ID ranges from 00000 to 11111, allowing a maximum of 32 (25) subnets. Each subnet ID has a subnet mask. For example, the subnet mask of the subnet ID 11111 is After performing an AND operation on the IP address and the subnet mask, you can obtain the network address.
Subnetting reduces the available IP addresses.For example, a Class B IP address contains 65534 (216-2) host IDs. After 5 bits in the host ID are used as the subnet ID, there can be a maximum of 32 subnets, each having an 11-bit host ID. Each subnet has a maximum of 2046 host IDs (211- 2, excluding the host IDs with all 1s and all 0s). Therefore, the IP address has a maximum of 65472 (32 x 2046) host IDs, 62 less than the maximum number of host IDs before subnetting.

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