dhcp conflicts on my router

Brent Rockburn · ‎05-14-2010

I am having an issue at one of my sites with DHCP. It seems that random machines will fall off the map and their phones as well until they are rebooted and get a new address.

Has anyone seen this before?

Thanks,

May 14 14:15:58.330 PDT: DHCPD: Seeing if there is an internally specified pool class:

May 14 14:15:58.330 PDT: DHCPD: htype 1 chaddr 001e.3748.fd5e

May 14 14:15:58.330 PDT: DHCPD: remote id 020a00000a4223fe2000000a

May 14 14:15:58.330 PDT: DHCPD: circuit id 00000000

May 14 14:16:00.670 PDT: DHCPD: Seeing if there is an internally specified pool class:

May 14 14:16:00.670 PDT: DHCPD: htype 1 chaddr 0009.6ba7.aea7

May 14 14:16:00.670 PDT: DHCPD: remote id 020a00000a4223fe2000000a

May 14 14:16:00.670 PDT: DHCPD: circuit id 00000000

May 14 14:16:07.671 PDT: DHCPD: Seeing if there is an internally specified pool class:

May 14 14:16:07.671 PDT: DHCPD: htype 1 chaddr 0009.6ba7.aea7

May 14 14:16:07.671 PDT: DHCPD: remote id 020a00000a4223fe2000000a

May 14 14:16:07.671 PDT: DHCPD: circuit id 00000000

ip dhcp excluded-address 10.xx.35.250 10.xx.35.254
ip dhcp excluded-address 10.xx.35.120 10.xx.35.126
ip dhcp ping packets 0
!
ip dhcp pool Voice
   network 10.xx.35.0 255.255.255.128
   option 150 ip 10.xx.1.10 10.xx.1.15
   default-router 10.xx.35.126
   dns-server 10.xx.4.206 10.xx.4.208 139.142.2.3 66.244.223.130
!
ip dhcp pool Workstations
   network 10.xx.35.128 255.255.255.128
   default-router 10.xx.35.254
   dns-server 10.xx.4.206 10.xx.4.208 139.142.2.3 66.244.223.130
   domain-name chgfe.biz
!

rt-3825-1#sh ip dhcp conflict
IP address        Detection method   Detection time          VRF
10.xxxx.3        Gratuitous ARP     May 14 2010 12:15 AM
10.xx.35.51       Gratuitous ARP     May 14 2010 12:16 AM
10.xx.35.131      Gratuitous ARP     May 14 2010 08:45 AM
10.xx.35.132      Gratuitous ARP     May 14 2010 08:47 AM
10.xx.35.134      Gratuitous ARP     May 14 2010 09:12 AM
10.xx.35.137      Gratuitous ARP     May 14 2010 10:25 AM
10.xx.35.138      Gratuitous ARP     May 14 2010 12:07 PM
10.xx.35.139      Gratuitous ARP     May 14 2010 12:07 PM
10.xx.35.140      Gratuitous ARP     May 14 2010 12:07 PM
10.xx.35.141      Gratuitous ARP     May 14 2010 12:07 PM
10.xx.35.144      Gratuitous ARP     May 14 2010 12:08 PM
10.x.35.146      Gratuitous ARP     May 14 2010 02:03 PM

Calin C. · ‎05-18-2010

If you do:

clear ip dhcp conflict

does it solve the problem?

I think the issue is with the gratuitous arp. Look what I have found:

A Cisco router will send out a gratuitous ARP message out of all interfaces when a client connects and negotiates an address over a PPP connection. However, by default, gratuitous ARP messages are not sent out when the client receives the address from the local address pool. The ip gratuitous-arps non-local command option is the default form and is not saved in the running configuration.

http://www.cisco.com/en/US/docs/ios/12_3/ipaddr/command/reference/ip1_s1g.html#wp1080936

Let me know if this helps you somehow!