How to use 30 subnet mask or /30 subnet IP addressing with example
/30 subnet mask is the most common and widely used while assigning the IP address to the network. Although it is not used that much in practice labs, however, it is commonly used in the real network it is used more than any other subnet mask.
/30 mask have 30 network bit and only 2 host bits
11111111.11111111.11111111.11111100
/30 subnet only provides 4 IPs per network so we only have 2 usable IPs per network. This mask is rarely used in the local area network however this is the most efficient way of assigning the IP address to two connected endpoints of the routers.
In a connection between two routers, we only need two IPs so we should always use a /30 subnet mask to the router interface.
In the image below, you can check two routers that are configured using this subnet mask.
If we want to create /30 subnets from one /24 subnet then we will be able to create 64 subnets.
Let us practice the /30 subnetting example below
Subnetting 205.1.1.0/24 into /30
As we discussed earlier that each /30 will have 4 IP addresses so the following IP address ranges will be available to us after subnetting.
205.1.1.0 – 205.1.1.3
205.1.1.4 – 205.1.1.7
205.1.1.8 – 205.1.1.11
205.1.1.12 – 205.1.1.15
205.1.1.16- 205.1.1.19
And, this will continue until we have the IP address available
In the following image
Assign IP addresses.
Find out the missing IP addresses and Fix the IP addressing.
In this network diagram, we have assigned IP addresses from the available subnets created while subnetting /24 subnet range.
- The IP address assigned to the connected router is from subnet 205.1.1.16/30 so another available IP address from this range is 205.1.1.17 that we can assign to the interface.
- IP address 205.1.1.20 is the subnet ID which is the wrong configuration; we should assign IP address 205.1.1.22 on the interface.
- 205.1.1.27 is the broadcast address of the subnet 205.1.1.24 so to correct the configuration; we can assign the IP address 205.1.1.26.
- The IP address which is assigned to the router is 205.1.1.29 which is from the 205.1.1.28 subnet now both PC should also be on the same subnet however we do not have two extra IPs so we can only configure one PC with an IP address 205.1.1.30. We cannot add more than one PC on this network.
