Junos Basics – EX2200C Switch as a DHCP server

In my previous Junos Basics post I covered a simple OSPF configuration in Junos. In this post I’ll step through configuring a Juniper EX2200C switch as a DHCP server.

The EX2200C is a great little switch that’s ideal for a small branch office deployment, and one feature that you might look to take advantage of in such a network is the switch’s ability to function as a DHCP server.

The first step is to enable DHCP for a VLAN (in this case the SALES VLAN 192.168.1.0/24 that we created in a previous post):

set system services dhcp pool 192.168.1.0/24

Next, we’ll set the range of addresses that the server can dish out to clients to 192.168.1.10 – 100:

[edit system services dhcp pool 192.168.1.0/24]
set address-range low 192.168.1.10
set address-range high 192.168.1.100

Then we need to make sure our DHCP clients pick up the correct domain name, DNS server and default gateway IP addresses:

[edit system services dhcp pool 192.168.1.0/24]
set system services dhcp pool 192.168.1.0/24 domain-name small.biz
set system services dhcp pool 192.168.1.0/24 name-server 192.168.1.1
set system services dhcp pool 192.168.1.0/24 router 192.168.1.1 

That’s the basic configuration done so I’ll test it with a client machine connected to the SALES VLAN, and run a couple of show commands to verify our config is working:

To see stats for the client to server DHCP packets:

rich@EX2200C> show system services dhcp statistics
Packets dropped:
    Total                      0

Messages received:
    BOOTREQUEST                0
    DHCPDECLINE                0
    DHCPDISCOVER               1
    DHCPINFORM                 0
    DHCPRELEASE                0
    DHCPREQUEST                2

Messages sent:
    BOOTREPLY                  0
    DHCPOFFER                  1
    DHCPACK                    2
    DHCPNAK                    0

To view the IP address leases:

rich@EX2200C> show system services dhcp binding
IP address       Hardware address   Type     Lease expires at
192.168.1.66     00:26:6c:10:6d:ff  dynamic  2012-06-09 21:59:33 UTC

Finally, sometimes it is useful for a client machine to always receive the same IP address when it requests one from a DHCP server. This is achieved with a DHCP address reservation for the MAC address of the client machine.

To do this we have to go up a level in the configuration, and then set a static binding:

[edit system services dhcp]
set static-binding 00:26:6c:10:6d:ff fixed-address 192.168.1.10

To test this I’ll release/renew the IP address on the client machine, and then check the binding on the server:

rich@EX2200C> show system services dhcp binding
IP address       Hardware address   Type     Lease expires at
192.168.1.10     00:26:6c:10:6d:ff  static   never

I hope this has been a useful explanation.  In my next Junos Basics post I’ll cover automatic configuration archiving to an FTP server.

Thanks for reading.

Rich

Follow Rich on Twitter