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jasonww04
Beginner

Auto clear ip dhcp conflict *?

Is there a command or config that will make a router automatically clear ip dhcp conflict * on a regular basis? I have a site that constantly has a problem with DHCP due to conflicts which is fixed simply by clearing the conflict table. If we could automate this, it would be great.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Joe Clarke
Hall of Fame Cisco Employee

You can use EEM for this.  This EEM applet will run the "clear ip dhcp conflict *" command every night at midnight.

event manager applet clear-dhcp-conflict

event timer cron cron-entry "0 0 * * *"

action 1.0 cli command "enable"

action 2.0 cli command "clear ip dhcp conflict *"

This assumes you have a release of IOS that supports EEM 2.1 or higher (which covers the majority of recent IOS releases).

View solution in original post

Joe Clarke
Hall of Fame Cisco Employee

No, it won't write a log message, but you could add one:

action 3.0 syslog msg "Cleared IP DHCP conflict records"

You can read more about EEM from http://www.cisco.com/go/eem .

View solution in original post

9 REPLIES 9
Jon Marshall
VIP Community Legend

jasonww04 wrote:

Is there a command or config that will make a router automatically clear ip dhcp conflict * on a regular basis? I have a site that constantly has a problem with DHCP due to conflicts which is fixed simply by clearing the conflict table. If we could automate this, it would be great.

Jason

I suspect this could be done with EEM. The expert for this sort of thing usually answers questions in the Network Mangement forum so you should move this post there.

Jon

Thank you. I moved it to Network Management, per your suggestion.

Joe Clarke
Hall of Fame Cisco Employee

You can use EEM for this.  This EEM applet will run the "clear ip dhcp conflict *" command every night at midnight.

event manager applet clear-dhcp-conflict

event timer cron cron-entry "0 0 * * *"

action 1.0 cli command "enable"

action 2.0 cli command "clear ip dhcp conflict *"

This assumes you have a release of IOS that supports EEM 2.1 or higher (which covers the majority of recent IOS releases).

View solution in original post

I put the command in exactly as you wrote it. When it runs, will it leave an entry in the log?

Also, can you point me to beginner documentation on the event manager? It seems like it could be really useful.

Joe Clarke
Hall of Fame Cisco Employee

No, it won't write a log message, but you could add one:

action 3.0 syslog msg "Cleared IP DHCP conflict records"

You can read more about EEM from http://www.cisco.com/go/eem .

View solution in original post

It works perfectly. Thanks for the help.

I modified your example to solve similar issue. I wanted it run every hour though. Here's how to modify Cron format:

https://en.wikipedia.org/wiki/Cron#Predefined_scheduling_definitions

My EEM simple script:

DV-CORE(config)#event manager applet ClearDHCP

DV-CORE(config-applet)#event timer cron cron-entry "0 * * * *"

DV-CORE(config-applet)#action 1.0 cli command "enable"

DV-CORE(config-applet)#action 2.0 cli command "clear ip dhcp conflict *"

DV-CORE(config-applet)#action 3.0 cli command "clear ip dhcp binding *"

Hi, what is the meaning of this below line

event timer cron cron-entry "0 0 * * *"

 

can u plz give some example of "time" instead of zero 0 0  and * * starts.

this can help me to understand what actually this command do.

 

Valery Kuznetsov
Enthusiast

Hello

You can use  ip dhcp conflict resolution