Secureit-net International Pte Ltd
27 Foch Road #02-09
Hoa Nam Building
Singapore 209264
Tel: (65) 6294 6244 / (65) 3151 6887
Fax: (65) 6294 6744

Classless Inter Domain Routing, Slash Network

CIDR stands for, Classless Inter Domain Routing. CIDR is a way to allocate and specify the Internet addresses used in inter-domain router more flexibly than with the original system of Internet Protocol address classes. As a result, the number of available Internet addresses has been greatly increased. CIDR is now the routing system used by virtually all gateway hosts on the Internet's backbone network. Many small companies also benefit from CIDR in that 4 Class C's can be grouped into one subnet to provide over 1000 IP Addresses.


Network Type Subnet Mask No of Ips
Slash 0 0.0.0.0 4 billion
Slash 1 128.0.0.0 2 billion
Slash 2 192.0.0.0 1billion
Slash 3 224.0.0.0 500 million
Slash 4 240.0.0.0 250 million
Slash 5 248.0.0.0 128 million
Slash 6 252.0.0.0 64 million
Slash 7 254.0.0.0 32 million
Slash 8 255.0.0.0 16 million
Slash 9 255.128.0.0 8 million
Slash 10 255.192.0.0 4 million
Slash 11 255.224.0.0 2 million
Slash 12 255.240.0.0 1 million
Slash 13 255.248.0.0 524288
Slash 14 255.252.0.0 262144
Slash 15 255.254.0.0 131072
Slash 16 255.255.0.0 65536
Slash 17 255.255.128.0 32768
Slash 18 255.255.192.0 16384
Slash 19 255.255.224.0 8192
Slash 20 255.255.240.0 4096
Slash 21 255.255.248.0 2048
Slash 22 255.255.252.0 1024
Slash 23 255.255.254.0 512
Slash 24 255.255.255.0 256
Slash 25 255.255.255.128 128
Slash 26 255.255.255.192 64
Slash 27 255.255.255.224 32
Slash 28 255.255.255.240 16
Slash 29 255.255.255.248 8
Slash 30 255.255.255.252 4
Slash 31 255.255.255.254 2
Slash 32 255.255.255.255 1


The first few on the list would be very difficult to manage network and the last two meaningless subnet mask that would serve no purpose since the only two ip addresses available are taken by the either the network number and broadcast address or are lacking in either.