DHCP IP address conflict troubleshoot

Latest reply: Dec 3, 2018 16:32:12 604 2 1 0

This post highlights the DHCP IP address conflict troubleshoot process. Please have a read below.

 

[Problem description]


A customer finds some users that have duplicate IP addresses. The IP addresses were assigned by the switch configured as DHCP Server. The example configuration is as below:

interface Vlanif3000

ip address 10.10.10.1 255.255.255.224 // Only 29 available IP addresses

dhcp select interface

dhcp server dns-list 172.16.0.2


[Analysis]


Found the following logs indicating the IP conflict:


Oct  1 2018 18:54:59-03:00 DC-S12704-01 %DHCP/4/DHCP_DHCP_ALLOC_ADDRESS(l)[1]:Result of IP address allocation from the DHCP server to wireless users. [WLAN_STA_INFO_IP_CONNECTION]ACMAC:XX-XX-XX-XX-XX-XX;ACNAME:ACNAME;APMAC:XX-XX-XX-XX-XX-XX;APNAME:APNAME;USER:X;MAC:XX-XX-XX-XX-XX-XX;TIME:1538430899;ZONE:UTC-0300;DAYLIGHT:false;ERRCODE:105;RESULT:INCORRECT REQUEST IP OR MAC;

 

Also the command display ip pool shows many IP addresses in conflict:


<DC-S12704-01>display ip pool 

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

  Pool-name        : Vlanif3000

  Pool-No          : 0

  Lease            : 1 Days 0 Hours 0 Minutes

  Position         : Interface       Status             : Unlocked

  Gateway-0        : -              

  Network          : 10.10.10.0

  Mask             : 255.255.255.224

  VPN instance     : --

  Conflicted address recycle interval: -

  Address Statistic: Total       :29        Used        :24       

                     Idle        :0         Expired     :0         

                     Conflict    :5        Disable     :0     

 

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


[Root cause]


There are many possible root causes:


1. Addresses are assigned manually;


2. The IP pool is very small;


3. Lease time is too long.

 

[Suggestions]


To avoid the IP address conflict, we suggest your to check the following:


1. Verify if no IP address is assigned manually. If so, make sure that the IP address is available.


2. The moment the switch detects a conflict, renew the IP address from the terminal device.


3. Decrease lease time in order to reduce the IP Address conflict incidences:


<HUAWEI>system-view

[HUAWEI]interfave vlanif3000

[HUAWEI-Vlanif3000]dhcp server lease minute Z


4. Configure an IP address conflict detection system, sending the X number of ICMP packets with Y timeout to an IP before assigning it:


<HUAWEI>system-view

[HUAWEI]dhcp enable

[HUAWEI]dhcp server ping packet X

[HUAWEI]dhcp server ping timeout Y


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Mysterious.color
MVE Created Nov 27, 2018 18:27:31 Helpful(0) Helpful(0)

thanks
it's very helpful DHCP IP address conflict troubleshoot-2809547-1
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Core%20Engineer%2C%20Technical%20Department.%20High%20experience%20in%20Networking
RubenMonroy
Created Dec 3, 2018 16:32:12 Helpful(0) Helpful(0)

very good recommendations, thanks a lot
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