If the physical interfaces are configured under a VLAN/RETH, the VLAN/RETH interface has to be added under forwarding-options helpers bootp, or else the DHCP relay service will not work. This article describes how to configure an SRX Series device as a relay agent to forward incoming requests from BOOTP or DHCP clients to a BOOTP or DHCP server.

If the physical interfaces are configured under a VLAN/RETH, the VLAN/RETH interface has to be added under forwarding-options helpers bootp, or else the DHCP relay service will not work:

set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan members vlan-trust
set interfaces ge-0/0/2 unit 0 family ethernet-switching vlan members vlan-trust
set vlans vlan-trust vlan-id 3
set vlans vlan-trust l3-interface vlan.0
set interfaces vlan unit 0 family inet address 192.168.1.1/24

user@host# set forwarding-options helpers bootp interface ge-0/0/1.0 (incorrect)
user@host# set forwarding-options helpers bootp interface ge-0/0/2.0 (incorrect)


Generally, if a logical interface (such as the VLAN/RETH interface) is configured for a set of physical interfaces, the VLAN/RETH interface has to be referred, instead of the physical/child interface. This is similar to the behavior in the Security zone hierarchy.

When configuring the DHCP Relay agent, make sure that the interface that is specified to receive the bootp requests is the VLAN/RETH interface, not the physical/ child interface.

user@host# set forwarding-options helpers bootp interface vlan.0

To configure an SRX Series device as a relay agent to forward incoming requests from BOOTP or DHCP clients to a BOOTP or DHCP server, perform the following procedure:

1. Provide a description for the relay service. In this example, Global DHCP relay service is the descriptive text:
   

   user@host# set forwarding-options helpers bootp description "Global DHCP relay service"

2. Specify the IP address of the server, to which requests are forwarded. In this example, the IP address is 192.18.24.38 :
   

   user@host# set forwarding-options helpers bootp server 192.18.24.38

3. Specify the maximum number of hops to be allowed per packet. In this example, the hop count is 4 :
   

   user@host# set forwarding-options helpers bootp maximum-hop-count 4

4. Specify the interface on which bootp requests will be received:
   

   user@host# set forwarding-options helpers bootp interface vlan.0
   
   OR
   
   user@host# set forwarding-options helpers bootp interface reth1.0
   

   Note :

   • The DHCP client which will send the DHCP-request side interface should be bound; that is, from where DHCP requests are received (refer to the diagram). If the interfaces are configured as Ethernet switching, then the VLAN/RETH interface must be added, instead of the physical interface.
   
   
5. DHCP relay is supported on chassis cluster only as of Junos OS 12.1X46. Prior to this, DHCP features are not supported on a chassis cluster. (DHCP Server and Client features on a cluster are supported from 12.1X47 onwards). Thus RETH interfaces can be specified only as of Junos OS 12.1X46, though the commit might succeed on Junos releases prior to this.

• For further information, refer to

  KB25925 - DHCP is not supported on J and SRX series devices in chassis cluster before Junos 12.1X46 [juniper.net]

  Junos Release Notes 12.1R46 (page 8)

• Specify DHCP as an allowed inbound service for each interface that is associated with it:
  

  user@host# set security zones security-zone untrust interfaces vlan.0 host-inbound-traffic system-services DHCP
  OR
  user@host# set security zones security-zone untrust interfaces reth1.0 host-inbound-traffic system-services DHCP
  

• KB15755 - SRX Getting Started - Configure Global DHCP Relay Service [juniper.net]