Howto: Configure DHCP-Relay on JunOS EX4300 Switch

The way to configure DHCP-Relay (maybe also called IP-Helper or DHCP-Forwarder) differs from common JunOS-configuration. Find out here how it works.

Environment

  • JunOS 13.x
  • EX4300 Switches, standalone, virtual-chassis or compatible
  • Multi-VLAN environment
    • For example:
      • VLAN A with IP 192.168.168.20 DHCP Server
      • VLAN B Clients with enabled routing and 192.168.178.0/24 clients in it
      • VLAN C Clients with enabled routing on EX and for example 192.168.179.0/24 clients in it
      • The need to provide VLAN B and C with DHCP-Service from DHCP-Server in VLAN A

Problem

The public and documented way from Juniper with the forwarding BOOTP helper is not working on this Juniper device.

 

forwarding-options {
helpers {
bootp {
interface {
vlan.0 {
server 192.168.168.20;

Solution

Juniper provides you with a different way to enable DHCP-relay from VLAN to VLAN across the Juniper enabled-Layer3-Switch.

  • First you have to define a dhcp-relay group with the DHCP-Server in it
  • Afterwards you have to define a DHCP-Client-Group with the internal-routing-bridge interface (irb.xx) from the Client-VLAN in it
  • Third you have to enable the dhcp-relay-function
  • Commit and have fun 🙂

Configuration-Example:

forwarding-options {
storm-control-profiles default {
all;
}
dhcp-relay {
server-group {
DHCP-Server {
192.168.168.20;
}
}
active-server-group DHCP;
group DHCP-Client {
interface irb.xx;
interface irb.xy;
}
}
}

Description:

Interface irb.xx is the IRB-Interface from EX-Switch from VLAN B (Client)

Interface irb.xy is the IRB-Interface from EX-Switch from VLAN C (Client)

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