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
