This article provides information on how to configure the Legacy EX-series switch as a DHCP server. 

• The Dynamic Host Configuration Protocol (DHCP) server provides a framework to pass configuration information to client hosts (such as PCs) on a TCP/IP network.

• A router or interface that acts as a DHCP server can allocate network IP addresses and deliver configuration settings to client hosts, without user intervention.

• The DHCP access service minimizes the overhead that is required to add clients to the network by providing a centralized, server-based setup.

• You do not have to manually create and maintain IP address assignments for clients. DHCP is defined in RFC 2131 Dynamic Host Configuration Protocol.

The following steps are used to configure the EX-Series switch as a DHCP server:

1. Create DHCP services on the EX switch by creating a DHCP pool:

   juniper@EX# set system services dhcp pool 10.0.0.0/24

2. Add the lowest IP address and highest IP address in DHCP pool address-range (optional):

   juniper@EX# set system services dhcp pool 10.0.0.0/24 address-range low 10.0.0.2 high 10.0.0.252

3. Add the router IP address to be supplied with the IP address (optional):

   juniper@EX# set system services dhcp pool 10.0.0.0/24 router 10.0.0.1

4. Create a virtual interface associated to the DHCP pool:

   Juniper@EX# set interface vlan unit 0 family inet address 10.0.0.1/24

5. Associate virtual interface to a VLAN where DHCP client’s machines will be connected

   Juniper@EX> set vlan default l3-interface vlan.0

   Command List Summary:

   set system services dhcp pool 10.0.0.0/24 address-range low 10.0.0.2
set system services dhcp pool 10.0.0.0/24 address-range high 10.0.0.252
set system services dhcp pool 10.0.0.0/24 router 10.0.0.1
set interfaces vlan unit 0 family inet address 10.0.0.1/24
set vlans default l3-interface vlan.0

6. Repeat steps 1 to 3 to add more DHCP pools for different subnets.

Note: This article is just for setting up DHCP locally on the EX-series switch. You can also configure routed virtual interfaces on the EX switch for each pool; this is covered in the EX-Series documentation and other associated articles.

Verifying DHCP operations on EX switches:

Verify the statistics of DHCP messages between server and the clients

juniper@EX# run show system services dhcp statistics

Packets dropped:
Total 2233

Messages received:
BOOTREQUEST  0
DHCPDECLINE  0
DHCPDISCOVER 2
DHCPINFORM   0
DHCPRELEASE  0
DHCPREQUEST  8

Messages sent:
BOOTREPLY    0
DHCPOFFER    2
DHCPACK      4
DHCPNAK      0

Verify the DHCP IP address allocations (bindings) to DHCP clients:

juniper@EX# run show system services dhcp binding
IP address Hardware address Type Lease expires at
10.0.0.3 00:23:9c:04:e3:43 dynamic 2012-11-14 18:04:40 PDT
10.0.0.4 00:a0:12:00:13:02 dynamic 2012-11-14 18:04:42 PDT

To view the DHCP binding for a specific IP address, the following command has to be issued

juniper@EX> show system services dhcp binding 10.0.0.3 detail
Dynamic binding information:
    IP address 10.0.0.3
    Hardware address 00:23:9c:04:e3:43
    Pool 10.0.0.0/24
    Request received on vlan.0

Lease information:
    Type DHCP
    Obtained at 2012-11-13 18:04:40 PDT
    Expires at 2012-11-14 18:04:40 PDT
    State active

DHCP options:
    Code: 1, Type: ip-address, Value: 255.255.255.0
    Code: 28, Type: ip-address, Value: 10.0.0.255
    Name: router, Value: [ 10.0.0.1 ]

Debugging DHCP operations on the switches:

Set traceoptions under DHCP to capture packets in log file:

juniper@EX# set system services dhcp traceoptions file
juniper@EX# set system services dhcp traceoptions flag all

To view the log file:

juniper@EX# run file show /var/log/

or

juniper@EX# run monitor start

2020-05-02: Article reviewed for accuracy; added specific platforms (Legacy EX).