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Dhcp conflict with a new Cisco 3560cx 12pd-s.

CiscoKid74
Level 1
Level 1

Hi everyone, I have a new but configured basically Cisco 3560cx 12pd-s. I keep getting the dhcp conflict error messages everyday. I have an Asus GT AX-11000 router that is connected to my new Cisco 3560cx 12pd-s. I somehow managed to do a basic configuration to set it up within my LAN network at home.

Here is the log from the swith. What am I doing wrong here ? How should I fix these dhcp conflict messages ? If you guys can explain it to me simple steps because i do not have any knowledge of how to use CLI or setup the dhcp on my switch. 

Thanks.

 cisco Cisco WS-C3560CX-12PD-S

15.2(7)E10Welcome cisco  

English

     

TROUBLESHOOTING

PING

TRACEROUTE

DIAGNOSTIC

SWITCH REBOOT

LOGS

DEBUG

Number of latest log entries to display

100

May 17 10:47:02.641 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.194.

 

May 17 10:47:01.635 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.193.

 

May 17 10:47:00.625 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.192.

 

May 17 10:46:59.614 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.191.

 

May 17 10:46:58.611 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.190.

 

May 17 07:24:17.950 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.179.

 

May 17 07:20:17.941 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.174.

 

May 17 06:02:21.843 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.156.

 

May 17 06:02:10.595 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.150.

 

May 17 06:01:55.527 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.142.

 

May 17 06:01:54.517 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.141.

 

May 17 06:01:49.490 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.138.

 

May 17 06:01:19.046 EST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/13, changed state to up

 

May 17 06:01:17.032 EST: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/13, changed state to up

 

May 17 06:01:02.642 EST: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/13, changed state to down

 

May 17 06:01:01.632 EST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/13, changed state to down

 

May 17 06:00:55.847 EST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/13, changed state to up

 

May 17 06:00:53.834 EST: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/13, changed state to up

 

May 17 06:00:39.321 EST: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/13, changed state to down

 

May 17 06:00:38.314 EST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/13, changed state to down

 

May 17 04:01:13.233 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.122.

 

May 17 04:01:12.174 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.121.

 

May 16 21:45:32.628 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.102.

 

May 16 21:45:31.618 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.101.

 

May 16 21:45:09.552 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.98.

 

May 16 13:19:49.724 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.90.

 

May 16 13:12:26.704 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.88.

 

May 16 12:32:06.740 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.84.

 

May 16 11:33:50.258 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.79.

 

May 16 09:04:41.666 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.71.

 

May 15 18:30:28.932 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.49.

 

May 15 16:43:25.567 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.41.

 

May 15 13:29:53.913 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.35.

 

May 15 13:13:57.505 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.27.

 

May 15 13:00:07.700 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.21.

 

May 15 12:40:04.128 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.17.

 

May 15 12:40:02.618 EST: %DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 192.168.1.16.

 

May 15 12:23:03.458 EST: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/12, changed state to down

 

May 15 12:23:02.452 EST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/12, changed state to down

 

LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/12, changed state to up

 

Log Buffer (4096 bytes):

 

 

        Logging Source-Interface: VRF Name:

 

    Trap logging: level informational, 88 message lines logged

 

 

No active filter modules.

 

 

    Persistent logging: disabled

 

    File logging: disabled

 

    Count and timestamp logging messages: disabled

 

    Exception Logging: size (4096 bytes)

 

                    filtering disabled

 

    Buffer logging: level debugging, 85 messages logged, xml disabled,

 

                     filtering disabled

 

    Monitor logging: level debugging, 0 messages logged, xml disabled,

 

                     filtering disabled

 

    Console logging: level debugging, 85 messages logged, xml disabled,

 

 

 

No Inactive Message Discriminator.

 

 

 

 

No Active Message Discriminator.

 

 

Syslog logging: enabled (0 messages dropped, 1 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)

 

 

 

 

 

 

 

 

 

 

6 Replies 6

Hello,

What is likely happening is you have a bunch of hosts already with those IPs not issued by that DHCP server. So when a new device comes online requesting an IP before the DHCP server issues it it will ping that address. If it gets a reply then obviously that IP is in use and the DHCP server does not issue that IP. This continues until a usable IP is found and issued.

If this is an at home network then most network devices that connect to your internet provider act as a DHCP server. If you have manually configured IPs on your network this could pose conflict issues as you see in your logs.

-David

Thanks for your reply David. So there is no solution to this? is there anyway to avoid this, it doesn"t do any harm but it is kind of annoying to see all the dhcp conflict issues. I only have my ip cameras manually configured, the rest is wifi devices on my router.  thanks.

You could go into the device (DHCP sever) that's trying to hand out IPs and prevent it from handing out the block of IPs to other devices. Depending on what device that is it could be accomplish a multitude of ways. Either that or block that log message from showing up by using the logging discriminator command feature.

 

-David

I got you thank you so much

Show ip dhcp binding

If there is binding IP-MAC

Then check MAC are all MAC connect to one port (access port)

If there is binding and mac connect to one port 

Then increase the dhcp subnet 

If not then there is 

1- l2 attack

2- Some L3 device run NAT with arp proxy

MHM

I ll check that thanks.