Number of used ip addresses

[yasserTL]

Hello 

I have a question that I am curious about and was wondering if you could help me out.

I currently have a Cisco router, specifically the NCS540 model. I have assigned an IP address of /21 to it, and then further divided this subnet into sub-interfaces. Each sub-interface has been assigned with IP addresses of /28 and /27.

My question is: Is there any command that can assist me in finding only the unused IP addresses within /16 or calculate the total number of used IP addresses? I am eager to know if there is a solution to this.

thanks'

[ammahend]

Install an IP scanner tool like advanced-Ip-scanner or namp or something else, and scan a subnet you need to find used/unused IP, time to scan will depend on how big of a subnet you scan. Follow this tutorial if you like

[Richard Pidcock]

I suppose you could issue a "show ip arp" command and that would show you all the IP's that have populated in the ARP table (i.e. used addresses that have answered arp requests).  It would be a little cumbersome to sort out, but should give you what you need.  Alternatively you could issue the same command for each subinterface (i.e. "show ip arp Gi0/0/x.x" where Gi0/0/x.x is your specific subinterface).  That would at least have it sorted for each specific subinterface.

Hope that helps.