How to release unused DHCP ip addresses on cisco router

Posted on 2008-10-21
Last Modified: 2009-12-16
Hi Guys,

I have a block of /25 ip addresses, and I have a dhcp configure on the router, now am receiving messages that says

Free addresses 0
Address in use : 109
Percentage addresses free : 0%

I know that I havent got as many users on that network as indicated, although there are some that comes in once in a while.

Please, how do I release the ip addresses that are not in use.

Question by:lawre1108
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Expert Comment

ID: 22765232
Seems that you havent defined your lease time.. so the router is holding addresses I think the default is 8 days.

please run the following.

Router(dhcp-config)#lease DAYS HOURS MINUTES

To define the lease time of the addresses given to the client. You can make it infinite by using this command instead; lease infinite

You can also use the

Router#clear ip dhcp binding *

If you want to clear a certain binding not all of them, replace the * in the previous command with the IP address to be cleared.



Author Comment

ID: 22765421
Thanks knightfox,

Apart from clearing the binding on the router does Router#clear ip dhcp binding * have any other effect on the performance of the router and network.


Accepted Solution

knightfox earned 500 total points
ID: 22765897
no.. to make sure you can clear just one entry first...

Router#clear ip dhcp binding x.x.x.x

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Expert Comment

ID: 22765908
if you run the full clear binding it will force all of you clients to re-negotioate their leases when half of the lease time is reached.  If in the mean time another station is given the address then you  could have some conflicting issues.. Personaly I would clear the ones that you know are not in use, and wait until service ends to clear them all.


Author Comment

ID: 22766213
Thanks agin knightfox

That will be big job, where we have over 100 pc and other devices connected to the network.

Is there any way of doing it without any conflict.


Expert Comment

ID: 22766294
wait until service ends, clear them out once your users go home to be on the safe side...


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