What is a Netmask?

A subnet mask is also called a network mask, address mask, or subnet mask. It is a type used to indicate which bits of an IP address identify the subnet where the host is located, and which bits identify Is the host's bit mask. The subnet mask cannot exist alone; it must be used in conjunction with an IP address. The subnet mask has only one function, which is to divide an IP address into two parts: a network address and a host address. ^[1]

Subnet mask is in

A subnet mask is a 32-bit address and is a technique used in conjunction with an IP address. It has two main functions, one is to shield part of the IP address to distinguish

Since the number of subnet masks depends on the number of possible subnets and the number of

There are two types of subnet masks. One is the default (auto-generated) subnet mask, and the other is a custom subnet mask. ^[6]

The variable length subnet mask VLSM is a subnet mask with a different length for each segment of the IP address. The subnet can be hierarchically addressed in order to make the most efficient use of the existing address space. The emergence of Variable-Length Subnet Masks (VLSM) is to break the traditional address division method based on the class (class) as a standard to reduce the shortage of IP addresses. Its role is to save IP address space; reduce the size of the routing table. Note that when using VLSM, the routing protocols used must be able to support it. These routing protocols include

If it is all IPv6, there is no concept of subnet mask. IPV6 is end-to-end connection communication, no subnet is required. However, at present, it seems that more of them use IPV6 in the way of tunneling on IPV4. It will take quite a long time to completely eliminate IPV4, and the subnet mask is still required.

In IPv6, there is no concept of a subnet mask, nor is there a concept of a network number or a host number. In IPv6, the prefix length can be understood as the subnet mask. The interface ID can be understood as the host number. In Windows XP, the prefix length of IPv6 addresses defaults to 64 bits. The IPv6 address space is too large, and the subnet of a subnet may be much larger than the entire IPv4 world, so the concept of a subnet has been diluted in the IPv6 world. However, if hosts at the same site want to communicate directly (without going through a router), they still need the same prefix.