DHCP Configuration

The main IPv4 DHCP configuration mode, entered with dhcp4 server, defines global options for IPv4 DHCP that affect the general behavior of DHCP as well as options that cover all subnets and pools.

To enter IPv4 DHCP configuration mode, enter:

tnsr# configure
tnsr(config)# dhcp4 server

From this mode, there are a variety of possibilities, including:


Subnet configuration, see Subnet Configuration.

authoritative (true|false):

Specifies whether or not this DHCP server is authoritative globally.

When not set as authoritative, clients may not trust leases from this server unless no other servers respond to requests, which may cause significant delays for clients obtaining addresses after switching subnets.

In most cases this will be true, which is the default value.


Description of the DHCP server


A DHCP Option declaration, see DHCP Options.

decline-probation-period <n>:

Decline lease probation period, in seconds.

echo-client-id <boolean>:

Controls whether or not the DHCP server sends the client-id back to the client in its responses.

interface listen <if-name>:

The interface upon which the DHCP daemon will listen. This is required.

interface socket (raw|udp):

Controls whether the DHCP daemon uses raw or UDP sockets.

lease filename <path>:

Lease database file

lease lfc-interval <n>:

Lease file cleanup frequency, in seconds.

This value defaults to 3600 which cleans up old lease data at one hour (3600 second) intervals.


Avoid setting this to a value of 0 which causes lease data to be retained indefinitely. This allows the lease database to continually grow in size over time without limitations.

lease persist <boolean>:

Whether or not the lease database will persist.

logging <logger-name>:

Controls which events are logged by the DHCP daemon. Enters config-kea-dhcp4-log mode. See DHCP Logging for more information.

match-client-id <boolean>:

When true, DHCP will attempt to match clients first based on client ID and then by MAC address if the client ID doesn’t produce a match. When false, it prefers the MAC address.

next-server <IP Address>:

Specifies a TFTP server to be used by a client.

rebind-timer <n>:

Sets the period, in seconds, at which a client must rebind its address.

renew-timer <n>:

Sets the period, in seconds, at which a client must renew its lease.

valid-lifetime <n>:

The period of time, in seconds, for which a lease will be valid.

Some of these values may be set here globally, and again inside subnets or pools. In each case, the more specific value will be used. For example, if an option is defined in a pool, that would be used in place of a global or subnet definition; A subnet option will be favored over a global option. In this way, the global space may define defaults and then these defaults can be changed if needed for certain areas.