DHCP Help

[ryancdavis]

Current configuration on a cisco 2921 (Verson 15.0(1r)M9 Release (fc1)):

ip dhcp pool Voice

network 10.21.179.0 255.255.255.128

default-router 10.21.179.1

option 150 ip 10.21.179.196 10.21.179.200

Issue is when a device looks to renew their lease no IP's are available.  Debug ip dhcp events tells me the dhcp pool is exhausted.  It appears that when the devices, Cisco phones in this case,  goes to renew their lease, they do not renew with the current IP they already have.  This causes the pool to become exhausted of ip addresses.  For some reason, the router holds the IP's in reserved status and will not reassign them back out for a specific amout of time.

Anyone have any ideas?

[ankugarg]

Can you post the full running config ?

[cadet alain]

Hi,

If you haven't got thousands of phones  then assign them static bindings for their specific  mac-addresses

ip dhcp pool PHONE1

  host x.x.x.x 

hardware-address xxxx.xxxx.xxxx

and so on for each phone keeping the parent pool with all the settings then each child pool will inherit these: default-router, tftp server,...

Regards.

Alain.

[johnlloyd_13]

In addition to what others have suggested, why not shorten the DHCP lease time?

Sent from Cisco Technical Support iPhone App

[Ven Taylor]

You really have two choices:

Decrease your dhcp timer.

Increase your dhcp scope.

If you have more devices than your scope allows, you're going to see this problem over and over.

If you don't, then just decreasing the time the router keeps the mac address assigned to the ip will do the trick.

Ven

[ryancdavis]

What's the command for decreasing the dhcp timer.

Tac suggested I use the command "no ip dhcp conflict logging."

[johnlloyd_13]

hi ryan,

thanks for the rating! kindly use the DHCP command below. default is 24 hours or 1 day.

Router(dhcp-config)#lease