Posted by: paragon | October 11, 2009

Slash notation for subnet masks quick reference

One thing I can never remember quickly is slash notation, it is not difficult but I just can’t seem to remember it quickly!  So here is a quick reference guide.  In slash notation, a single number indicates how many bits of the IP address identify the network the host is on. A netmask of has a netmask of 8 + 8 + 8 = 24.

For example, writing is the same as specifying an IP address of with a corresponding netmask of Often you have to enter the netmask as slash notation, an easy task with the usual However if your network doesn’t have 255 hosts, for example only 8 hosts, then the netmask will be

The following table lists the variable length subnets from 1 to 32, the CIDR [3] representation form (/xx) and the Decmial equivalents. (M = Million, K=Thousand, A,B,C= traditional class values)

Conversion table here:

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