CIDR, short for Classless Inter-Domain Routing, is a replacement for the older Classful network addressing architecture that was in use since 1981. CIDR was introduced in 1993 to address the issue of IP address shortage.
The CIDR method divides the address space for Internet Protocol Version 4 (IPv4) into five address classes. Each class, coded in the first four bits of the address, defines either a different network size, i.e. number of hosts for unicast addresses (classes A, B, C), or a multicast network (class D). The fifth class (E) address range is reserved for future or experimental purposes. Now, IPv6 is fast replacing IPv4 allowing huge expansion for more users and devices on the internet.
Maskbit:
Maskbits in CIDR allow you to discover specific IP ranges within the network.
Example: /24 is the Maskbit for the Subnet 255.255.255.0, i.e. 192.168.0.1/24 = Range of IPs from 192.168.0.1 to 192.168.0.255.
Subnet |
CIDR Maskbit |
Total IPs in Range |
Number of Class C networks |
255.255.255.255 |
/32 |
1 |
1/256th |
255.255.255.240 |
/28 |
16 |
1/16th |
255.255.255.0 |
/24 |
256 |
1 |
255.255.0.0 |
/16 |
65,536 |
256 |
For OpManager versions 125174 and above:
For OpManager versions below 125174:
Note: OpManager supports discovery of Hyper-V hosts and VMs using CIDR.