DHCP IP Address Conflict Troubleshoot

Created: Nov 28, 2018 01:44:06Latest reply: Dec 4, 2018 00:32:12 332 2 1 0

DHCP IP Address Conflict Troubleshoot

 

[Problem Description]

Customer finds some users that have duplicate IP Address, 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 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.    IP pool is very small.

3.    Lease time is too long.

 

[Suggestions]

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

1.    Verify no IP Address is assigned manually. If so make sure that IP Address is available.

2.    At 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 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  Visitor   Created Nov 28, 2018 02:27:31 Helpful(0) Helpful(0)

thanks
it's very helpful
  • x
  • convention:

find what you love and let it kill you.
RubenMonroy     Created Dec 4, 2018 00:32:12 Helpful(0) Helpful(0)

very good recommendations, thanks a lot
  • x
  • convention:

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