With DHCP Server, the switch hosts the server thereby removing the need to deploy an external DHCP server. The hosted DHCP Server has the same basic functionality as a standalone external DHCP server. The switch listens for DHCP requests from clients on the network and assigns IP addresses dynamically from a preconfigured address pool.
In addition to IP addresses, you can configure DHCP Server to provide clients with standard DHCP settings such as DNS, NTP, and TFTP servers, boot image files and NetBios servers. The server also lets you customize non-standard DHCP settings that the server passes to clients.
DHCP Server includes the following support options:
DHCP Server supports IPv4 deployments. With IPv6-only deployments, you must deploy an external DHCP Server on a standalone server or other network device.
Note
The DHCP Server configuration information in this chapter applies to the DHCP Server feature, which is hosted on the switch. If you are deploying an external DHCP server, refer to the documentation that comes with your server for information on how to configure DHCP on the external server.You can deploy DHCP Server with clients that are in the GRT as well as user-defined VRFs.
You can configure DHCP Server and DHCP Relay to provide DHCP services to clients in local VLANs as well as clients that connect from a remote switch.
You can configure the server to listen for DHCP messages or BOOTP messages (by default, the server listens for both message types).
You can deploy DHCP Server in authoritative mode or non-authoritative mode (the default setting is authoritative mode). In authoritative mode, the server is the authority on the network and assigns all addresses within that network. In non-authoritative mode, the server listens for DHCP messages and forwards these messages to another server for processing.
Note
In authoritative mode, the switch rejects INT_REBOOT messages from clients with a DHCPNAK message. In non-authoritative mode, the switch sends a DHCPNAK only if a lease is present for the same client, but using a different IP address.You can deploy DHCP Server as a standalone server or in a High Availability (HA) pairing on two switches in a primary-standby configuration. In an HA pair, the primary DHCP Server manages the DHCP service for clients and shares lease information with the standby server. The standby server takes over only if the primary server becomes inactive.
If you want to deploy High Availability:
You must configure DHCP Server on both peer switches. You can assign the primary and standby roles to each switch manually or you can allow the switches to assign roles automatically. By default, the switch with the lower IP address is primary.
You must configure the network so that clients can connect to both peer switches.
You must synchronize the clocks on the two HA peer switches using a protocol such as NTP or by configuring the system clocks on the two HA peers manually.
In addition to standard DHCP options, DHCP Server supports the customization of non-standard parameters that the DHCP Server provides to clients in response to DHCP requests. The following conditions apply:
You must assign a DHCP code in the unassigned range from 224 to 254.
You must define the option using DHCP global parameters. After the option is defined, you can assign a data value to the option using global parameters or subnet settings. If you use subnet settings, you can assign different data values for different subnets.
In the Custom Option definition, you must assign one of three data types: IPv4 address, string, or integer. After you define a data type, all data values for that option, irrespective of which subnet they're assigned in, must use that data type.
Custom Options do not support the assignment of arrays or the override of standard DHCP options.