Ip dhcp conflict resolution not available in the cisco 4500

[marwa.jeljli1]

Hi all,

I have a problem of dhcp conflict on my core switch cisco 4500 E.

I found in some other discussion that i can resolve this issue automatically by activating the dhcp resolution by executing the following command "ip dhcp conflict resolution [interval in munite].

Thus, i dont need to do it manually by execution the cisco command "clear ip dhcp conflict *".

Now, my problem is that i couldn't find the parameter "resolution" but i found the "logging" one when i tried to execute the desired command.

The IOS version is "Cisco IOS Software, Catalyst 4500 L3 Switch Software (cat4500e-ENTSERVICES-M), Version 12.2(54)SG1, RELEASE SOFTWARE (fc1)"

Thank your for help

Marwa 

[Mark Malone]

Hi

you should be able to trace the conflict can you provide the log that you seen in the switch that shows the conflict it should have the mac address , then you can trace it and change the ip address of the device , usually confliction comes from an address not being excluded from pool given out dynamically but then somewhere down the line it gets set as static on same network

[marwa.jeljli1]

Hi mark,

We dont have this problem. Our issue is that we have two core switch with HSRP  and they act both as dhcp servers with same configuration of pools. Thus, when the first core switch isnot available, the second one will respond to dhcp clients requests.

We have put the described configuration since 2011 and it works fine and no conflicts were reported. one year ago, the problem started occuring and now it becomes very frequent and we dont know exactly what is the cause.

Some others forums says that we should devide the pool into two ranges and specify each switch with a different range. But in this case, we dont have the backup if the primary switch is down. also, if it was a missconfiguration, how it does work for years?

Thanks for your help

Marwa 

[Mark Malone · Accepted solution]

Hi

Short answer not sure how it worked without giving you a conflict , its bad practice to have same pool on multiple devices it should have generated conflict before that , not recommended at all and expected to get a conflict.Think about it dhcp is broadcast at first so you have same pool on 2 different devcies giving out same info it was only matter of time before it happened and something clashed as it all same broadcast domain

you should split the pool really between both devices as you seen or else use a real MS dhcp servers that can have backup/primary dhcp of same pools in cluster  environment , cisco ios is really just if you don't have a dhcp server it can act as one but it doesn't have same ability's as a specifically built dhcp server