/30 Subnet Mask

A /30 subnet mask is a prefix length commonly used in a point-to-point connection between two network devices. A /30 network divides a large network into a very smaller network containing just 4 ranges of IP addresses. The first IP address in this range is the network ID, and the last IP address in this range is the broadcast IP. Hence, there are 2 usable IP addresses in a /30 subnet mask.

For example, if we want to subnet 192.168.2.0/24 with a /30 subnet mask, the first subnet will have 192.168.2.0 as the network ID, a usable IP address of 192.168.2.1 to 192.168.2.2, and a broadcast IP address of 192.168.2.3. The second subnet will have a network ID of 192.168.2.4, a usable IP range of 192.168.2.5 to 192.168.2.6, a broadcast IP address of 192.168.2.7, and so on.

Here is the table of networks obtained by subnetting with a /30 subnet mask.

Network AddressUsable IP addressBroadcast IP address
.0.1-.2.3
.4.5-.6.7
.8.9-.10.11
.12.13-.14.15
.16.17-.18.19
.20.21-.22.23
.24.25-.26.27
.28.29-.30.31
.32.33-.34.35
.36.37-.38.39
.40.41-.42.43
.44.45-.46.47
.48.49-.50.51
.52.53-.54.55
.56.57-.58.59
.60.61-.62.63
.64.65-.66.67
.68.69-.70.71
.72.73-.74.75
.76.77-.78.79
.80.81-.82.83
.84.85-.86.87
.88.89-.90.91
.92.93-.94.95
.96.97-.98.99
.100.101-.102.103
.104.105-.106.107
.108.109-.110.111
.112.113-.114.115
.116.117-.118.119
.120.121-.122.123
.124.125-.126.127
.128.129-.130.131
.132.133-.134.135
.136.137-.138.139
.140.141-.142.143
.144.145-.146.147
.148.149-.150.151
.152.153-.154.155
.156.157-.158.159
.160.161-.162.163
.164.165-.166.167
.168.169-.170.171
.172.173-.174.175
.176.177-.178.179
.180.181-.182.183
.184.185-.186.187
.188.189-.190.191
.192.193-.194.195
.196.197-.198.199
.200.201-.202.203
.204.205-.206.207
.208.209-.210.211
.212.213-.214.215
.216.217-.218.219
.220.221-.222.223
.224.225-.226.227
.228.229-.230.231
.232.233-.234.235
.236.237-.238.239
.240.241-.242.243
.244.245-.246.247
.248.249-.250.251
.252.253-.254.255

/30 Subnet Mask Usable IP Address

In the /30 subnet mask, there are 4 ranges of IP addresses; the first one in the range is the network address, and the last IP address in this range is the broadcast IP address. Hence, there are 2 usable IP addresses in the /30 subnet mask.

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/30 Subnet Mask Dotted Decimal Notation

The dotted decimal notation for a /30 subnet mask is 255.255.255.252.. This representation is gotten by setting the first 30 bits of the 32-bit IPv4 address to ‘1s’, setting the remaining 2 bits to ‘0s’, and converting from binary to decimals.

dotted decimal notation for /30 subnet mask

/30 Wildcard Mask

The wildcard mask for /30 prefix length is 0.0.0.3. This is gotten by subtracting each octet of the subnet mask from 255.

Subnetting Class C Network with /30 Subnet Mask

To subnet a Class C network with a /30 prefix length, 6 bits are borrowed from the host bits and added to the network bits, leaving 2 bits for the host bits.

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subnetting class network with /30 subnet mask

Therefore, when a class C network is subnetted with a /30 subnet mask, we will obtain the following number of subnetworks:

2^6 = 64

Hence, a /30 subnet mask will divide a class C network into 64 subnetworks, with each subnetwork having 4 ranges of IP addresses.

Subnetting Class B Network with /30 Subnet Mask

To subnet a Class B network with /30 subnet mask, 14 bits are borrowed from the host bits and added to the network bits.

subnetting a class B network with /30 subnet mask

Hence, the number of subnets obtainable when we subnet a class B network with a /30 prefix length is obtained as follows:

2^14 = 16384.

Therefore, a /30 prefix length will divide a class B network into 16384 subnetworks, with each subnetwork having 4 ranges of IP addresses.

Subnetting Class A Network with /30 Subnet Mask

To subnet a class A network with a /30 prefix length, 22 bits need to be borrowed from the host bits and added to the network bits.

Subnetting class A network with /30 subnet mask

So, the number of subnetworks obtainable when we subnet a Class A network with a /30 subnet mask is given by:

2^22 = 4194304

Therefore, a /30 subnet mask will divide a Class A network into 4194304 subnetworks, with each subnetwork having 4 ranges of IP addresses.

How Many host in /30

There are a total of 4 ranges of IP addresses in a /30 prefix length. The first IP address in this range is the network address, and the last IP address in this range is the broadcast IP address. Therefore, there are 2 IP addresses that can be assigned to a host in a /30 subnet mask.

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How Many Subnets in /30

The number of subnetworks obtainable when we subnet with a /30 subnet mask depends on the class of the network. Class C networks yield 64 subnetworks; class B networks yields 16384 subnetworks; and class A networks yield 4194304 subnetworks when subnetted with the /30 prefix length.

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