DHCP server configuration settings

Here are the configuration settings for the DHCP server. Typically, you can modify these settings without restarting the DHCP server for the changes to become effective on the running server.

• Enable Dynamic Host Configuration Protocol (DHCP) Server: Enables the DHCP server feature on this Digi device. Note that for the DHCP server to operate, the Digi device must be configured to use a static IP address. For information on how to configure static IP settings, see IP Settings.
  • Scope Name: The name of the physical network interface associated with the subnet being served by the DHCP server. Most Digi device models have a single network interface, so there is no choice for the scope name. For models that have multiple network interfaces, such as an Ethernet interface and a Wi-Fi (802.11) interface, this DHCP Server may be configured to provide services on either of those interfaces.
  • IP Addresses: The starting and ending IP addresses for the scope being served by this DHCP server. These addresses must be in the same subnet as the Digi device itself.
  • Lease Duration: The length of the leases for the scope being served by this DHCP server. The default lease duration is 24 hours. A DHCP client may request a lease duration other than this setting, and the DHCP server will grant that request if possible.
• Wait specified delay before sending DHCP offer reply: The interval of time in milliseconds to delay before offering a lease to a new client. The default delay is 500ms, and the range is 0 to 5000ms. Use of this delay permits this Digi device to reside on a network with other DHCP servers, yet not offer leases to new clients unless the other DHCP servers do not make such an offer. This provides a measure of protection against inadvertently connecting a Digi device to a network that is running its own DHCP server(s), and offering leases to clients in a manner inconsistent with that network.
• Check that an IP address is not in use before offering it: When a DHCP client requests a new IP address lease, before offering an IP address to that client, use “ping” to test whether that IP address is already in use by another host on the network but is unknown to the DHCP server. If an IP address is determined to be in use, it is marked as Unavailable for a period of time, and it will not be offered to any client while in this state. Enabling this test adds approximately one second of delay before the IP address is offered to the client, since the “ping” test must not receive a valid reply for that test to successfully determine that the IP address is not already in use. This option is off (disabled) by default. This option does not apply to Static Lease Reservations, since the “ping” test is not used for them.
• Send the DHCP Server IP address as a DNS Proxy Server: This option configures the DHCP Server to send its IP address to a DHCP client as the first DNS server in its lease information. This Digi device supports a DNS Proxy feature that will relay DNS requests and responses between DNS clients and servers. The DNS Proxy is not a feature of the DHCP Server itself, but rather it is managed elsewhere in the configuration settings for this Digi device. For DHCP client to use DNS Proxy effectively, you must enable DNS proxy in the DHCP server configuration and the DNS Proxy settings. For more information, see the description of the Enable DNS Proxy Service setting in Advanced Network Settings. This option is on (enabled) by default.

• Static Lease Reservations: A static lease reservation is a specific IP address paired with a client's MAC address, which reserves the IP address for that client's use only. This assures that a client always receives a lease for the same IP address and that no other client obtains a lease for that address.

  To add a reservation, type the IP address and MAC Address values, select or clear the Enable check box, and then press the Add button.

  After adding a reservation, you may click the IP address or MAC address of that entry in the table, permitting you to specify or modify the lease duration for this reservation.

  The Enable check box for the entry permits a reservation to be disabled without actually removing the entry, then enabled again at a later time.

  Use the Remove link to permanently remove a reservation from the DHCP server configuration.

  Use the Remove All link to permanently remove all reservations from the DHCP server configuration.

• Address Exclusions: A specific set of IP addresses to exclude from the scope. The DHCP server will not grant leases to clients for any IP address in the exclusion range.

  To add an exclusion, type the starting and ending IP addresses, select or clear the Enable check box, and then press the Add button.

  The Enable check box for the entry permits an exclusion to be disabled without actually removing the entry, then enabled again at a later time.

  Use the Remove link to permanently remove an exclusion from the DHCP server configuration.

  Use the Remove All link to permanently remove all exclusions from the DHCP server configuration.

• Apply button: You must click Apply to save changes you make to the DHCP server settings. If you leave this page without applying the changes, those changes will be discarded.