What is CIDR?

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

 

To discover a complete network (CIDR/Subnet based discovery):

For OpManager versions 125174 and above:

    1. Go to Settings - > Network Discovery -> New Discovery.
    2. Select the Subnet tab.
    3. Network IP: Specify the Network IP to be discovered.
    4. Select the required Credentials
    5. Click on Discover and OpManager will direct you to the 'Discovered Devices' page.
    6. Approve or Ignore the discovered devices by clicking on the respective options. The approved devices will be added to the OpManager inventory and moniotored. The ignored devices will be removed from the queue of discovered devices and restricted from future addition.

 

For OpManager versions below 125174:

    1. Go to Settings - > Discovery -> Discovery Profile.
    2. Select the CIDR option.
    3. Network IP: Specify the Network IP to be discovered.
    4. Discovery Credentials: Select the configured Credentials required for the discovery process.
    5. Navigate to the next page and configure Discovery rules, associate and discover interfaces and schedule the discovery process if required. Click on Save and Execute at the end to initiate discovery.

 

Note: OpManager supports discovery of Hyper-V hosts and VMs using CIDR.


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