How to find unused ip address/subnets from the network

[KM2018]

Hi All,

simple query but i have doubts...

we have Cisco 3850 - core switch, I need to pick a unused ip address from the network range. 

In core switch i could see there are multiple network ranges ( /8,/16/24 )and few subnetted subnets.

how could do i differentiate used & unused subnets ? based on number of subnets in the range ? 

Or is there any command to list out the subnets ?

No access to DHCP scope :(

Thanks

KM

[marce1000]

 - By doing proper network management and have knowledge on the used subnets (and or allocated ip-addresses, although the latter can be automated by using DHCP services/products).

 M.

[balaji.bandi]

Adding to other post.

1.Either you need to have automated scanning all the IP address, that take ages and IP changes you would not have track.

2. other options snmpwalk, request admin to have read only snmp access for the DHCP Server and running snmp query to get the data (this what i did for one of client, since different department manages DHCP Server)

[KM2018]

@balaji.bandi  Thanks for your reply , Even we have different team for DHCP, will reach out to them.

BR

KM

[paul driver · Accepted solution]

Hello

If you don't have any good IPAM documentation and no access to the dhcp scopes then at best ping is your only option and this isnt by far trustworthy.

The ip address you ping may not respond as the host may not be active, icmp is being denied etc.. so no response doesn't necessary indicate the ip address if available to use.

So determining a free ip address under your circumstances will be difficult to prove i assume.

[KM2018]

Thank you so much for your reply !!!

KM