IP DHCP Best Practices

Unanswered Question
Nov 17th, 2008

Hi Group,

I have a query regarding DHCP conflicts. One of our customer is using Cisco 4500 switches in Core/Distribution and these switches are running DHCP service as well. There is one DHCP Pool configured for IP Phones ( Yesterday we got compalint from cutomer that IP Phones are not able to get IP address so I checked the primary 4500 switch and found 'DHCP conflict' log messages so I used ' claer ip dhcp conflict *' command and after that all IP Phones started getting ip addresses.

What could be the possible cause of this problem ? Should we disable logging of DHCP conflicts ?

Can we avoid such incident by using 'ip dhcp ping' command ? Kindly guide me in this reagrd.

Thanks in Advance.



I have this problem too.
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gnijs Tue, 11/18/2008 - 05:44

1) Have you configured the same pool range on two switches ?

2) Are you sure there is no "rogue" dhcp server in the subnet ?

Giuseppe Larosa Tue, 11/18/2008 - 06:23

Hello Mujeeb,

>>Should we disable logging of DHCP conflicts ?

No, this allowed you to detect the problem it isn't the problem cause it is handy to detect the problems.

Are both C4500 serving the same address pool ?

Hope to help


rmujeeb81 Tue, 11/18/2008 - 08:11


Yes, DHCP pool on both primary and secondary switches is same. Primary switch is the root switch for all Vlans. Below is the log message for your reference,

%DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged

Thanks & Regards,


rmujeeb81 Tue, 11/18/2008 - 08:19


Here is a CORRECTION that secondary switch is the root switch for few VLANs.




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