Need assistance in extending the DHCP pool size to support 510 users.
Summary
How to extend ZDs DHCP scope to provide 512 leases?Question
How to extend ZDs DHCP scope to provide 512 leases?Customer Environment
ZD,AP, ZD manged DHCP PoolRoot Cause
The root cause was to configure start IP from middle of subnet range.Troubleshooting Steps
Seeing issues where DHCP server on the ZD is not giving IP's to more than 255 users. Initially when this setup was deployed, the requirement was less than 255 leases, however later have to add more users and hence need to extend the leases to 512. Tried to change the subnet mask to /23 for your entire network, however that did not help.By default ZD support 512 leases maximum and that is per design. We further gathered current configuration on the ZD and acknowledged that ZD is configured with following settings:
Starting IP: 192.168.91.20
Number of IPs: 235
ZD's IP : 192.168.91.2
Explained the subnet range which is available with above configuration. The DHCP pools subnet is derived from the ZDs IP, for example, if the ZDs IP is 192.168.91.x, the DHCP pool will start with 192.168.91.x. Since we do subnetting for third octet, the /23 scope consumes one bit from the network portion and hence the range becomes, 192.168.90.1- 192.168.91.255. Since ZDs DHCP was configured currently with start IP of 192.168.91.20, the available IPs with current config were reduced to 192.168.91.20- 192.168.91.254, Total 235.
Resolution
Extend the range the start IP of the scope have to be changed to 192.168.90.x; where "x" being the number after excluding reserved/static IP's including ZD, APs other network devices with static IP in the network. With this they would get 192.168.90.x-192.168.91.254 IP's for the users.Suggested to change the static IP of the APs to the excluded range to avoid IP conflict and that being the sole reason of having start IP option. The DHCP server will not know about the static IPs being assigned to the client, even you configure those IPs from the ZD.
The reason why we need to do so is "When a DHCP client requests a lease, a DHCP server checks its pool of available addresses and assigns the client a lease on an available IPv4 address. By default, the server checks only the list of current leases to determine whether an address is available. It does not actually query the network to see whether an address is in use".
Article Number:
000005098
Updated:
June 26, 2020 04:12 PM (over 4 years ago)
Tags:
Configuration, Troubleshooting, ZoneDirector
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