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Constant DHCP Conflicts on Router

I have been seeing consistent DHCP conflicts on my router now for the last 2-3 months. I know, because I personally have physically checked all active PC's on the network and are not having an issue with users statically assigning their PC's. I am 110% positive on this.

My question is, could there be an issue with the arp cache timeout being to long at the Cisco Default timeout of 4 hours? We currently have the DHCP timeout set to 15 minutes, because we don't want the users standing around not doing anything. Could this wide range of arp cache timeout vs. DHCP timeout cause conflicts to reoccur often?

Also, I have also come across a command to put in my router no ip dhcp conflict logging. We aren't logging these conflicts in an external log and typically just clear them when they occur. From what I understand about this command it basically does not exclude this IP address from the DHCP pool when a conflict is detected. Am i correct about this?



I have seen a similiar issue for the past year, a few conflicts a day, invalid mac addresses that are reporting the conflict. I clear the conflicts and can watch a few a days continue to increase - -this is in multiple locations running dhcp on local router, various models, various IOS above 12.4.15

000218: Feb 23 00:35:52: %DHCPD-4-DECLINE_CONFLICT: DHCP address conflict:  client 0190.4ce5.3b4c.fa declined

000219: Mar  2 00:38:57: %DHCPD-4-DECLINE_CONFLICT: DHCP address conflict:  client 0190.4ce5.3b4c.fa declined



Cisco recommends to configure no ip dhcp conflict logging when not saving the binding database  on flash or on an external machine so you should configure this indeed.

It won't impede the conflict detection feature.



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Thanks and this resolved the issue.


I have had a further look into my looks like my cisco even through it is giving green connection lights is not giving out ip's ........ Looking at my current connection setup ....... I have an Asus modem router (DSL AC68U) connected via ethernet to one of the ports on the cisco and netgear switches - I then am trying to distribute through the house. 


My thoughts are maybe the netgear and cisco switch on asus router is too much - and there is a bun fight going on over ip allocation creating issues.


So I thought I might - try disconnecting the netgear switch - and see what happens and test.

If that fails I could disable the Asus router dchp and allocate a static ip - then let the cisco do its own thing - hopefully in a happy way ;-)


Do you think I am looking at this the right way????