DHCP SERVER AT ROUTER WITH HIGH LEVEL OF IP CONFLICT

ROGER FERNANDO MAJO ZACARIAS · ‎09-22-2012

Hello,

I am having problems with our DHCP Server configured at cisco router 2610:

Constantly we receive a message at log of ip conflict:

Sep 10 10:21:15.520 GMT: %DHCPD-4-DECLINE_CONFLICT: DHCP address conflict: client 0100.2713.b839.67 declined 10.100.101.228.

Sep 11 10:46:04.679 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.102.199.

Sep 17 08:55:00.115 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.80.

Sep 17 09:13:08.628 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.88.

Sep 17 09:23:45.940 GMT: %DHCPD-4-DECLINE_CONFLICT: DHCP address conflict: client 019c.b70d.6e82.73 declined 10.100.101.97.

Sep 17 11:11:07.780 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.109.

Sep 17 11:32:07.101 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.112.

Sep 17 11:34:16.481 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.114.

Sep 18 15:30:39.472 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.143.

Sep 19 09:14:46.796 GMT: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.100.101.155.

Sep 22 12:47:14.309 GMT: %SYS-5-CONFIG_I: Configured from console by cisco on vty0 (172.17.10.213)

DHCP_SITEL#

The configuration of DHCP at router is:

ip dhcp excluded-address 10.100.101.240 10.100.101.254

ip dhcp excluded-address 10.100.101.0 10.100.101.50

ip dhcp excluded-address 10.100.0.0 10.100.100.255

ip dhcp excluded-address 10.100.103.0 10.100.255.255

!

ip dhcp pool SITEL

network 10.100.0.0 255.255.0.0

default-router 10.100.106.1

dns-server 10.100.104.1

lease 2

!

Also we have a MERAKI acccess-point connected to a switch abd it connect and disconnect many times a day.

Can someone tell us how to avoid this problem?

Thaking you in advance.

Roger

Giuseppe Larosa · ‎09-22-2012

Hello Roger,

the router has probably assigned almost all the IP addresses in the DHCP pool.

You can check DHCP pool level of use with

show ip dhcp pool

If the leased addresses is near to the total addresses you have the DHCP pool all used.

Because you have a /16 subnet ( quite uncommon) you can easily add space to the DHCP pool changing the set of excluded IP addresses.

For specific devices like the Meraki access-point you can configure a dedicated DHCP address pool to implement a sort of reservation

You have to use the client-id or hardware-address command to specify for what client device the individual pool is dedicated

ip dhcp pool MERAKI

network ...

hardware-address

Hope to help

Giuseppe

ROGER FERNANDO MAJO ZACARIAS · ‎09-22-2012

Hi Guiseppe,

The command: show ip dhcp pool, does not exists.

the only options are:

DHCP_SITEL#sh ip dhcp ?

binding DHCP address bindings

conflict DHCP address conflicts

database DHCP database agents

import Show Imported Parameters

server Miscellaneous DHCP server information

The show ip dhcp binding shows:

DHCP_SITEL#sh ip dhcp binding
IP address Hardware address Lease expiration Type
10.100.101.202 0180.6007.6f39.fc Sep 29 2012 02:00 PM Automatic
DHCP_SITEL#

We have configured DHCP snooping at switch connected directly to DHCP SERVER and the command:

show ip dhcp snooping binding, shows:

SW_2960_RADIO_CCCR#sh ip dhcp snooping binding

MacAddress IpAddress Lease(sec) Type VLAN Interface

------------------ --------------- ---------- ------------- ---- ----------

----------

14:5A:05:86:07:F0 10.100.101.79 88429 dhcp-snooping 1 FastEther

net0/15

00:24:D6:A4:F0:AA 10.100.101.187 68295 dhcp-snooping 1 FastEther

net0/15

34:51:C9:92:49:02 10.100.101.180 106986 dhcp-snooping 1 FastEther

net0/15

14:8F:C6:44:A0:29 10.100.101.193 79597 dhcp-snooping 1 FastEther

net0/23

00:21:CC:B9:40:63 10.100.101.181 105631 dhcp-snooping 1 FastEther

net0/20

80:60:07:6F:39:FC 10.100.101.202 602255 dhcp-snooping 1 FastEther

9C:B7:0D:47:22:78   10.100.101.171   66884       dhcp-snooping   1     FastEther
net0/15
74:E5:0B:4D:AA:86   10.100.101.189   76878       dhcp-snooping   1     FastEther
net0/15
74:E5:0B:4D:79:92   10.100.101.188   69640       dhcp-snooping   1     FastEther
net0/15
Total number of bindings: 46

SW_2960_RADIO_CCCR#

As you can see there is only 46 assigned ip addreess and we have enable 02 pools: 10.100.101.x and 10.100.102.x

Do you recommend to implement hardware-addreess for each access-point implented?

What advantage offers the command. harware-addreess? This option can avoid more frequently conflict issues?

Thanking you in advance.

Roger