Linux Networking Cookbook

6.1. Calculating Subnets with ipcalc

Problem

You often see documentation with instructions like "you must use different subnets for this to work," or "be sure your hosts are all on the same network." But, you're a bit hazy on what this means, and how to make the address calculations—is there a tool to help you?

Solution

There is indeed: ipcalc. This is a standard program available for any Linux. This command shows you everything you need to know for a single network:

	$ ipcalc 192.168.10.0/24
	Address:   192.168.10.0         11000000.10101000.00001010. 00000000
	Netmask:   255.255.255.0 = 24   11111111.11111111.11111111. 00000000
	Wildcard:  0.0.0.255            00000000.00000000.00000000. 11111111
	=>
	Network:   192.168.10.0/24      11000000.10101000.00001010. 00000000
	HostMin:   192.168.10.1         11000000.10101000.00001010. 00000001
	HostMax:   192.168.10.254       11000000.10101000.00001010. 11111110
	Broadcast: 192.168.10.255       11000000.10101000.00001010. 11111111
	Hosts/Net: 254                  Class C, Private Internet

So, here you see the old-fashioned dotted-quad notation, the newfangled CIDR notation, the available host address range, the number of hosts you can have on this network, and the binary addresses. ipcalc shows the network portion of the address, which is 192.168.10, and the host portion, which is 1–254. And it's a nice visual aid for understanding netmasks.

Warning

On Fedora, ipcalc is very different, and not nearly as helpful as the real ipcalc. You can install the real ipcalc from source, which you can download from http://freshmeat.net/projects/ipcalc/ ...