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Configuring a Switch as a DHCP Server (CLI Procedure)

Note: This topic applies to Junos OS for EX Series switches and QFX Series switches with support for the Enhanced Layer 2 Software (ELS) configuration style. If your switch runs software that does not support ELS, see Configuring a DHCP Server on Switches (CLI Procedure). For ELS details, see Getting Started with Enhanced Layer 2 Software.

A Dynamic Host Configuration Protocol (DHCP) server provides a framework to pass configuration information to client hosts on a TCP/IP network. A switch acting as a DHCP server can dynamically allocate IP addresses and other configuration parameters, minimizing the overhead that is required to add clients to the network.

A DHCP configuration consists of two components—an optional reconfiguration of default settings on DHCP clients and the configuration of a DHCP server. This topic covers configuration of the switch as a local DHCP server using DHCP for IPv4 (DHCPv4). For information about DHCPv6 local server, see DHCPv6 Local Server Overview.

This topic describes the following task:

1. Configuring the Switch as a Local DHCP Server

Configuring the Switch as a Local DHCP Server

1. Configure a Layer 3 interface with an IP address on which the DHCP server will be reachable:
   [edit]user@switch# set interfaces interface-name unit unit-number family family address address/prefix-lengthuser@switch# set vlans vlan-name vlan-id vlan-id user@switch# set vlans vlan-name l3-interface irb-name user@switch# set interfaces irb-name l3-interface irb-name family family address address/prefix-length

   For example:

   [edit]user@switch# set interfaces ge-0/0/1 unit 0 family inet address 40.1.1.2/24 user@switch# set vlans server vlan-id 301 user@switch# set vlans server l3-interface irb.301 user@switch# set interfaces irb.301 family inet address 50.1.1.2/24
2. Configure the DHCP server for the Layer 3 interface:
   [edit]user@switch# set system services dhcp-local-server group-name interface interface-name

   For example:

   [edit]user@switch# set system services dhcp-local-server group server1 interface ge-0/0/1user@switch# set system services dhcp-local-server group server1 interface irb.301
3. Create an address pool for IPv4 addresses that can be assigned to clients. The addresses in the pool must be on the subnet in which the DHCP clients reside. Do not include addresses that are already in use on the network.
   [edit]user@switch# set access address-assignment pool pool-name family family network address/prefix-length

   For example:

   [edit]user@switch# set access address-assignment pool pool1 family inet network 20.1.1.0/24
4. (Optional) Define a range of addresses in the address-assignment pool. The range is a subset of addresses within the pool that can be assigned to clients. If no range is specified, then all addresses within the pool are available for assignment. Configure the name of the range and the lower and upper boundaries of the addresses in the range:
   [edit]user@switch# set access address-assignment pool pool-name family family range range-name low low-IP-addressuser@switch# set access address-assignment pool pool-name family family range range-name high high-IP-address

   For example:

   [edit]user@switch# set access address-assignment pool pool1 family inet range range1 low 20.1.1.101 user@switch# set access address-assignment pool pool1 family inet range range1 high 20.1.1.110
5. (Optional) Configure one or more routers as the default gateway on the client’s subnet:
   [edit]user@switch# set access address-assignment pool pool-name family family dhcp-attributes router gateway-ip-address

   For example:

   [edit]user@switch# set access address-assignment pool pool1 family inet dhcp-attributes router 20.1.1.254
6. (Optional) Configure the IP address that is used as the source address for the DHCP server in messages exchanged with the client. Clients use this information to distinguish between lease offers.
   [edit]user@switch# set access address-assignment pool pool-name family family dhcp-attributes server-identifier ip-address

   For example:

   [edit]user@switch# set access address-assignment pool pool1 family inet dhcp-attributes server-identifier 20.1.1.254
7. (Optional) Specify the maximum time period, in seconds, that a client holds the lease for an assigned IP address if the client does not renew the lease:
   [edit]user@switch# set access address-assignment pool pool-name family family dhcp-attributes maximum-lease-time seconds

   For example:

   [edit]user@switch# set access address-assignment pool pool1 family inet dhcp-attributes maximum-lease-time 43,200
8. (Optional) Specify user-defined options to be included in DHCP packets:
   [edit]user@switch# set access address-assignment pool pool-name family family dhcp-attributes option option-id-number option-type option-value

   For example:

   [edit]user@switch# set access address-assignment pool pool1 family inet dhcp-attributes option 98 string test98