[EX] Example - Configuring an EX Series switch as a DHCP server (including gateway, DNS, and others)

Defining a DHCP pool

The DHCP pool name is identified by a subnet on the EX switch, which is configured on a physical layer 3 interface or on a VLAN interface (IRB). For example, if the switch has ports on VLAN 20, and interface VLAN 20 has IP address 20.20.20.1/24, then the pool to assign IP addresses for this subnet will be configured as set system services dhcp pool 20.20.20.0/24.

Alternately the IP address could also be assigned to a physical L3 interface. In either case, when the switch receives DHCP DISCOVER / REQUEST packets on either the layer 2 VLAN 20 ports, or the layer 3 port with an interface IP address, the switch knows to assign IP addresses from the pool identified by 20.20.20.0/24. This is how the switch can map DHCP requests to a specific pool.

You can create more pools for other subnets as needed.

Configuring the DHCP pool parameters

Reference the DHCP pool by name and configure these parameters.

Address range for IP assignment
Lease time in seconds
DHCP Server Identifier
Gateway / Router, WINS, DNS addresses
DHCP Options if any, etc

Configure L2 ports with correct VLAN assignment, or assign appropriate IP addresses to the layer 3 interface. Attach DHCP clients to those ports.

Example

[edit]
root@4200-48-2# show system services dhcp 
pool 20.20.20.0/24 {
    address-range low 20.20.20.50 high 20.20.20.100;
    default-lease-time 3600;
    name-server {
        20.20.20.1;
    }
    wins-server {
        20.20.20.1;
    }
    router {
        20.20.20.1;
    }
    server-identifier 20.20.20.1;
}

[edit]
root@4200-48-2# show system services dhcp | display set 
set system services dhcp pool 20.20.20.0/24 address-range low 20.20.20.50
set system services dhcp pool 20.20.20.0/24 address-range high 20.20.20.100
set system services dhcp pool 20.20.20.0/24 default-lease-time 3600
set system services dhcp pool 20.20.20.0/24 name-server 20.20.20.1
set system services dhcp pool 20.20.20.0/24 wins-server 20.20.20.1
set system services dhcp pool 20.20.20.0/24 router 20.20.20.1
set system services dhcp pool 20.20.20.0/24 server-identifier 20.20.20.1

[edit]
root@4200-48-2# show interfaces vlan.20   
family inet {
    address 20.20.20.1/24;
}

[edit]
root@4200-48-2# show interfaces ge-0/0/0 
unit 0 {
    family ethernet-switching {
        vlan {
            members 20;
        }
    }
}

Attach a PC to ge-0/0/0 and a DHCP assignment takes place.

Verifying the DHCP service

root@4200-48-2> show system services dhcp pool 
Pool name           Low address      High address     Excluded addresses
20.20.20.0/24       20.20.20.50      20.20.20.100  

root@4200-48-2> show system services dhcp ?      
Possible completions:
  binding              Show DHCP client binding information
  conflict             Show DHCP address conflict
  global               Show DHCP global scope information
  pool                 Show DHCP address pool information
  statistics           Show DHCP statistics

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