The /31 subnet mask, just like the /30 subnet mask, is a prefix length used in point-to-point connections between two network devices. A /31 subnet mask divides a large network into subnetworks with just 2 ranges of IP addresses.
Unlike other subnet masks, /31 does not have a network address or a broadcast IP address. It is only used in a point-to-point connection that does not need a network address or a broadcast IP address. The two end-point network devices in a point-to-point connection communicate using unicasts messages; there is no need for a broadcast IP address or network ID.
Therefore, if we subnet 192.168.2.0/24 with a /31 subnet mask, the first subnet will comprise an IP range of 192.168.2.0 to 192.168.2.1; there is no network ID or broadcast IP address. The second subnet will comprise two IP addresses: 192.168.2.2 and 192.168.2.3, both for the two interfaces of the point-to-point connection, and so on.
/31 Subnet Mask Usable IP Address
In the /31 subnet mask, there are two ranges of IP addresses, and these two addresses can be configured on the network devices. A /31 subnet mask is useful in a point-to-point connection between two network devices where there is no need for a network ID and a broadcast IP address.
/31 Wildcard Mask
The wildcard mask for /31 prefix length is 0.0.0.1. his is gotten by subtracting each octet of the subnet mask from 255.
/31 Subnet Mask Dotted Decimal Notation
The dotted decimal notation for a /31 subnet mask is 255.255.255.254. This representation is gotten by setting the first 31 bits of the 32-bit IPv4 address to ‘1s’, setting the remaining 1 bits to ‘0s’, and converting from binary to decimals.
Subnetting Class C Network with /31 Subnet Mask
To subnet a Class C network with a /31 subnet mask, 7 bits are borrowed from the host bits and added to the network bits.
Therefore, when a class C network is subnetted with a /31 subnet mask, we will obtain the following number of subnetworks:
2^7 = 128.
Hence, a /31 subnet mask will divide a /31 subnet mask into 128 subnetworks, each having 2 ranges of IP addresses.
Subnetting Class B Network with /31 Subnet Mask
To subnet a class B network with a /31 subnet mask, we need to borrow 15 host bits and add them to the network bits.
Hence, the number of subnets obtainable when we subnet a class B network with a /31 prefix length is obtained as follows:
2^15 = 32,768.
Therefore, a /31 prefix length will divide a class B network into 32,768 subnetworks, with each subnetwork having 2 ranges of IP addresses.
Subnetting Class A Network with /31 Subnet Mask
To subnet a Class A network with a /31 prefix length, we need to borrow 23 bits from the host bits and add them to the network bits.
So, the number of subnetworks obtainable when we subnet a Class A network with a /31 subnet mask is given by:
2^23 = 8388608
Therefore, a /31 subnet mask will divide a Class A network into 8388608 subnetworks, with each subnetwork having 2 ranges of IP addresses.
How Many host in /31
There are 2 ranges of IP addresses in a /31 subnet mask, and these 2 IP addresses can be used to assign a host. A /31 subnet mask is used in a point-to-point connection between two network devices and therefore does not need a network ID or a broadcast IP address.
How Many Subnets in /31
The number of subnetworks obtainable when we subnet with a /31 subnet mask depends on the class of the network. Class C networks yield 128 subnetworks; class B networks yields 32,768 subnetworks; and class A networks yield 8,388,608 subnetworks when subnetted with the /31 prefix length.
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