1841 and DHCP issue

[rkovelman]

Hello,

I am not sure if this is by design or not but I have dhcp running on my 1841 basically with a 192.168.1.1 - 192.168.1.255 pool.  While I do have set excluded ranges I find that the system does not look for any open IP's once it reaches that last IP.  For instance while the pool is that large it does end at .180.  I would think the system would go back to .1 and look for any IP's that might not be addressed.  For instance 192.168.1.2, 192.168.1.3 are not show in the binding table as being used and to me they seem available.  Any reason why the system does not use them?

Thank you

[cadet alain]

Hi,

could you do sh ip dhcp conflict

Regards.

Alain

[rkovelman]

At the time of the issue I recieved this and still this:

192.168.1.2      Ping               Nov 08 2011 10:45 PM                                   

192.168.1.3      Ping               Nov 08 2011 10:45 PM                                   

192.168.1.6      Ping               Nov 08 2011 10:45 PM                                   

192.168.1.7      Ping               Nov 08 2011 10:45 PM                                   

192.168.1.9      Ping               Nov 08 2011 10:45 PM                                   

192.168.1.11     Ping               Nov 08 2011 10:45 PM                                   

192.168.1.14     Ping               Nov 08 2011 10:45 PM                                   

192.168.1.16     Ping               Nov 08 2011 10:45 PM                                   

192.168.1.17     Ping               Nov 08 2011 10:45 PM                                   

192.168.1.19     Ping               Nov 08 2011 10:45 PM                                   

192.168.1.21     Ping               Nov 08 2011 10:45 PM                                   

192.168.1.41     Ping               Nov 08 2011 10:46 PM                                   

192.168.1.48     Ping               Nov 08 2011 11:11 PM                                   

192.168.1.49     Ping               Nov 08 2011 11:11 PM                                   

192.168.1.50     Ping               Nov 08 2011 11:11 PM                                   

192.168.1.57     Ping               Nov 09 2011 05:35 AM                                   

192.168.1.64     Ping               Nov 09 2011 07:20 AM                                   

192.168.1.80     Ping               Nov 09 2011 09:37 AM                                   

192.168.1.108    Ping               Nov 09 2011 10:28 AM                                   

192.168.1.111    Ping               Nov 09 2011 10:28 AM                                   

192.168.1.120    Ping               Nov 09 2011 10:39 AM                                   

192.168.1.151    Ping               Nov 10 2011 09:48 AM                                   

192.168.1.161    Ping               Nov 10 2011 10:03 AM                                   

192.168.1.94     Ping               Nov 16 2011 10:05 AM                                   

192.168.1.130    Ping               Nov 21 2011 09:44 AM                                   

192.168.1.169    Ping               Nov 21 2011 10:49 AM                                   

192.168.1.137    Ping               Nov 29 2011 10:46 AM                                   

192.168.1.178    Ping               Dec 08 2011 10:36 AM                                   

192.168.1.103    Ping               Dec 19 2011 09:52 AM                                   

192.168.1.109    Ping               Dec 19 2011 10:10 AM                                   

192.168.1.110    Ping               Dec 19 2011 10:10 AM                                   

192.168.1.125    Ping               Dec 20 2011 10:43 AM                                   

192.168.1.147    Ping               Dec 20 2011 11:00 AM                                   

192.168.1.122    Gratuitous ARP     Dec 20 2011 10:15 PM                                   

192.168.1.54     Gratuitous ARP     Dec 21 2011 12:10 AM

Take into account the issue or what I feel the issue is was on January 13 2012.  I am not sure why there is a gratuitous ARP on those last two IP's though.

[cadet alain]

Hi,

you can clear the IP addresses you are sure are not assigned anymore with the  clear ip dhcp conflict

command.

I know clients are using GARP to detect conflicts but apparently the IOS does so in some cases as is stated here:

"

A Cisco router will send out a gratuitous ARP  message when a client connects and negotiates an address over a PPP  connection. This transmission occurs even when the client receives the  address from a local address pool. "

Regards.

Alain

[rkovelman]

Great thanks!  I was able to get 30 more IP's back into the pool with that command.  Is there anyways to make this automated?  I would hate to waste time in checking to see if the IP is active and if not then clearing it out.

[cadet alain · Accepted solution]

Hi,

if you ain't got no dhcp database configured anyway Cisco recommends disabling conflict logging with the no ip dhcp conflict logging command.

All modern OSes should use GARP requests anyway before accepting a DHCP leased address.

Regards.

Alain