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DHCP Server

A DHCP Server is a network server that automatically provides and assigns IP addresses, default gateways, and other network parameters to client devices. It relies on the standard protocol known as Dynamic Host Configuration Protocol or DHCP to respond to broadcast queries by clients. Read this topic for more information on DHCP server operations, configuring DHCP server and extended DHCP server.

Understanding DHCP Server Operation

As a DHCP server, a Juniper Networks device can provide temporary IP addresses from an IP address pool to all clients on a specified subnet, a process known as dynamic binding. Juniper Networks devices can also perform static binding, assigning permanent IP addresses to specific clients based on their media access control (MAC) addresses. Static bindings take precedence over dynamic bindings.


All DHCP packets passing through a DHCP unconfigured interface might be dropped.

Enabling the DHCP relay or DHCP server feature also enables the DHCP snooping feature, which analyzes all DHCP packets received through any interface of the device (both DHCP configured and unconfigured interfaces) .

Interfaces not listed under DHCP settings are considered as unconfigured interfaces. Depending on the configuration, DHCP packets received on DHCP unconfigured interfaces are dropped.

This section contains the following topics:

DHCP Options

In addition to its primary DHCP server functions, you can also configure the device to send configuration settings like the following to clients through DHCP:

  • IP address of the DHCP server (Juniper Networks device)

  • List of Domain Name System (DNS) and NetBIOS servers

  • List of gateway routers

  • IP address of the boot server and the filename of the boot file to use

  • DHCP options defined in RFC 2132, DHCP Options and BOOTP Vendor Extensions

Compatibility with Autoinstallation

The functions of a Juniper Networks device acting as a DHCP server are compatible with the autoinstallation feature. The DHCP server automatically checks any autoinstallation settings for conflicts and gives the autoinstallation settings priority over corresponding DHCP settings. For example, an IP address set by autoinstallation takes precedence over an IP address set by the DHCP server.

Chassis Cluster Support

DHCP server operations are supported on all SRX Series Firewalls in chassis cluster mode.

Graceful Routing Engine Switchover for DHCP

For EX Series switches, only extended DHCP local server maintains the state of active DHCP client leases. The DHCP local server supports the attachment of dynamic profiles and also interacts with the local AAA Service Framework to use back-end authentication servers, such as RADIUS, to provide subscriber authentication. You can configure dynamic profile and authentication support on a global basis or for a specific group of interfaces. The extended DHCP local server also supports the use of Junos address-assignment pools or external authorities, such as RADIUS, to provide the client address and configuration information.

For MX Series routers, the extended DHCP local server and the DHCP relay agent applications both maintain the state of active DHCP client leases in the session database. The extended DHCP application can recover this state if the DHCP process fails or is manually restarted, thus preventing the loss of active DHCP clients in either of these circumstances. However, the state of active DHCP client leases is lost if a power failure occurs or if the kernel stops operating (for example, when the router is reloaded) on a single Routing Engine.

You can enable graceful switchover support on both EX Series switches and MX Series routers. To enable graceful switchover support for the extended DHCP local server or extended DHCP relay agent on a switch, include the graceful-switchover statement at the [edit chassis redundancy] hierarchy level. To enable graceful Routing Engine switchover support on MX Series routers, include the graceful-switchover statement at the [edit chassis redundancy] hierarchy level. You cannot disable graceful Routing Engine switchover support for the extended DHCP application when the router is configured to support graceful Routing Engine switchover.

For more information about using graceful Routing Engine switchover, see Understanding Graceful Routing Engine Switchover.