Check Available IP

[hs08]

Hello,

Currently my core switch (using 9300 series) as internal dhcp server, how we can know how much ip available in the dhcp pool for particular subnet?

[Kasun Bandara · Accepted solution]

@hs08 hi

use below command.

#show ip dhcp pool

this will show all the pools in your switch. if you need to see only specific pool use below.

#show ip dhcp POOL_NAME

[hs08]

Hi @Kasun Bandara 

Here result of my pool, in this pic are my pool is full?

[matthew2587]

Your dhcp pool is full. You are currently leasing 246 address and excluding 8. This makes 254 addresses in total which is equal to the size of your pool.

[hs08]

If we decrease the lease time, will the ip used will decrease at the time or should wait? Also in the previous picture there are 8 address excluded, how we can know which ip address is excluded?

Here my pool config

[matthew2587]

If you decrease the lease time, I assume that the new lease time would only apply to clients requesting or renewing their IP address. This means that the used IPs would not necessarily decrease right away.

If you do "sh run", in the configuration you will see excluded addresses right next to dhcp pool config. Or you can do "sh ip dhcp binding" and find the addresses that are not being leased.

[hs08]

I do clear ip dhcp binding, and found the excluded address is increased.

When the leased address is 37,the excluded address is 12

When the leased address is 70,the excluded address is 17

On the router i only have 5 IP excluded

So my question is, when there are any client with static IP this will counted as excluded address?

[MHM Cisco World]

https://www.firewall.cx/cisco/cisco-switches/cisco-switch-router-dhcp-server-conflicts.html

Wifi' so client associations get IP and then leave and the IP will there until leased time end.

The solution I think in wlc' do you config idle timeout?

[Gopinath_Pigili]

Hi hs08,

we can have Look at the subnet mask. For example  255.255. 255.0. That means your DHCP server has 254 IP addresses in that subnet...You can use Router# show ip dhcp binding

The show ip dhcp binding command to display the IP addresses that have already been assigned. Verify that the address pool has not been exhausted. If necessary, re-create the pool to create a larger pool of addresses.

Best regards
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[hs08]

can we make an alert if there any dhcp pool which reach 90% utilization by SNMP maybe?

[matthew2587]

In your dhcp pool configuration, you can configure "utilization mark high percentage log". This will create a system log whenever the utilization percentage specified is exceeded.

[MHM Cisco World]

Hmm'

Utilization mark high can use to generate log (for SNMP i will check OID of dhcp pool)' this log can used then with EEM to automatically clear ip dhcp binding.

But to be honest' I dont like this solution I will check how can prevent guest exhaust the pool.

MHM

[hs08]

Do the utilization mark  (high/low) : 100/0 mean we can change the utilization mark to some values?

[MHM Cisco World]

Yes you can 

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/12-2sx/dhcp-12-2sx-book/config-dhcp-server.html

This guide how you config utilize mark.

But using it with eem or not it depends on your choice.

MHM