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Community Member

IP DHCP Best Practices

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 (172.21.17.0/24). 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.

Regards,

Mujeeb

4 REPLIES
Bronze

Re: IP DHCP Best Practices

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

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

Hall of Fame Super Silver

Re: IP DHCP Best Practices

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

Giuseppe

Community Member

Re: IP DHCP Best Practices

Hi,

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 172.21.17.185

Thanks & Regards,

Mujeeb

Community Member

Re: IP DHCP Best Practices

Hi,

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

Regards,

Mujeeb

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