UniFi DHCP Server

The DHCP Server on UniFi Gateways dynamically assigns IP addresses to devices and provides other information such as the location of the default gateway and DNS server.

How does it work?

DHCP Server is enabled on each individual Virtual Network by default. When devices connect to the network, they will send a broadcast message in order to obtain an IP address. The server then responds and provides the IP address and other information to the device. The following information is provided:

  • Subnet Mask (Netmask)
  • Default Gateway - By default this is the IP address of the UniFi Gateway.
  • DNS Server - By default this is the IP address of the UniFi Gateway.
  • Lease Time - By default this is 1 day (86400 seconds). 

And the following are optional:

  • Domain Name
  • Custom Options

Custom Options

DHCP options are flexible parameters that advanced users to pass additional information from their DHCP server to a client. Default options are already used by most devices on the network today. 

These are the pre-defined DHCP options available in the UniFi Network application:

  • UniFi Network application - Option 43
  • NTP Server - Option 42
  • Network Boot - Option 66 and Option 67
  • Time Offset - Option 2
  • TFTP Server - Option 66
  • WPAD URL - Option 252
  • WINS Server - Option 44

Additional custom options can be specified using the DHCP Option Code

Ping Conflict Detection

The UniFi Gateway sends a ping to the IP address it is intended to allocate before it is leased to a device. If there is a response to the ping, the IP address will not be leased. This detection depends on devices responding to the ping, which may not occur due to local firewall settings. Sending a ping before every lease is allocated introduces a small delay while the gateway is waiting for the response. This delay is amplified when more clients are on the network that request an IP address at the same time. If you are noticing delays before clients are able to obtain an address and connect to the internet, consider disabling the detection.

 

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