Wireless Terminal Acquiring Multiple Addresses via VLAN-Group Method Leading to Insufficient IP Address Pool Resources

Topology 1

The WX5540H is connected to the core switch, and the DHCP server is responsible for assigning IP addresses to wireless terminals. When binding service templates under the AP's radio, a vlan-group is used, with a total of 4 class C address segments, approximately 1000 IP addresses. 

On-site, it was found that newly connected wireless terminals cannot access the internet and cannot obtain an IP address. Checking the DHCP server revealed that the IP address resources are exhausted. Using the 'display wlan client' command, it was found that the number of currently online terminals is less than 100, and 4 class C addresses should be sufficient.

1. Check the relevant configuration, for example:

vlan-group lianjia
 
 vlan-list 52 to 55
 
wlan ap lianjia model WA4320-ACN
 
 radio 1
 
   radio enable
 
   service-template 102 vlan-group lianjia

2. Review the logs on the AC, which indicate that multiple terminal IP addresses are changing, for example:

STAMGR/6/STAMGR_CLIENT_SNOOPING: Detected client IP change: Client MAC: 4c34-XXXX-9aec, IP: 10.39.55.136, 10.39.53.240, -NA-, -NA-, Username: XXXX, AP name: lianjia, Radio ID: 3, Channel number: 11, SSID: ***.***, BSSID: dcda-XXXX-e7c0.

On the DHCP server, it is found that each terminal has obtained multiple addresses, and these addresses belong to different VLANs within the vlan-group. This results in a small number of terminals occupying addresses in the entire address pool. The logs on the AC show that a terminal will obtain an address from each VLAN in the vlan-list.

3. By default, the VLAN allocation method for clients is dynamic. When a client first comes online, the AP randomly assigns a VLAN from the VLAN group specified for the radio under the dynamic allocation method. When the client comes online again, the VLAN assignment will depend on the configured VLAN allocation method. If static allocation is used, the client directly inherits the VLAN assigned from the previous VLAN group. If the client's IP address is within the lease period, the client will still be assigned the same IP address. Using this allocation method can reduce IP address consumption.

Set the client VLAN allocation method to static under the wireless service template: 

wlan service-template lianjia 
 client vlan-alloc static