定长子网划分和可变长度子网划分的英文

Sure, I can explain both fixed-length subnetting and variable-length subnet masking (VLSM) in English.

**Fixed-Length Subnetting:**
In fixed-length subnetting, each network is divided into a specific number of bits for the network identifier (prefix) and a fixed number of bits for the host identifier. The prefix length remains constant across all subnets within a given network. This method is simpler to manage but can lead to inefficient use of IP space if the network size does not require the full allocated address range.

**Variable-Length Subnet Masking (VLSM):**
On the other hand, VLSM is a more advanced technique where different subnets can have varying lengths of prefixes. This allows for greater addressing efficiency by allocating larger prefixes to smaller networks and smaller prefixes to larger networks, which need more hosts. With VLSM, there is no fixed number of host bits; instead, the mask is used dynamically to determine the number of hosts per subnet. It optimizes IP usage but requires more complex calculations and configuration.

**Related questions:**
1. How does VLSM overcome the limitations of fixed-length subnetting?
2. What are the benefits of using VLSM in terms of network design?
3. Can you give an example of when to use fixed-length subnetting versus VLSM?