Subnetting on an S series switches

A network can be divided into multiple subnets to conserve IP address space and support flexible IP addressing.
When many hosts exist on an internal network, the internal host IDs can be divided into multiple subnets to facilitate management. Then the entire network contains multiple small networks.
Subnetting is implemented within an 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 routing device on the internal network selects a route for the packets based on the subnet ID and find the destination host.
Take subnet division of an IP address in Class B as an example. The subnet mask consists of a string of continuous 1s and 0s. 1s correspond to the network ID field and the subnet ID field while 0s correspond to the host ID field.
The first 5 bits of the host ID is used as the subnet ID. The subnet ID ranges from 00000 to 11111, allowing for a maximum of 32 (2 to the power of 5) subnets. Each subnet ID has a subnet mask. For example, the subnet mask of the subnet ID 11111 is 255.255.248.0. 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, normally an IP address of Class B can contain 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 with an 11-bit host ID. That is, 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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