Configure a DHCP Relay

Let us learn to configure a DHCP relay.
DHCP Relay is a branch-site feature that is configured at the interface level on a device. Typically, a DHCP Relay agent is used to forward DHCP requests between clients and servers that are not on the same physical subnet. DHCP Relay can be configured on a controller port, a LAN port, or on a sub-interface that has a defined, static IP address.
When a ION device receives a DHCP request from a client on the interface configured with DHCP Relay, it forwards those requests to configured DHCP servers. It also listens to DHCP responses from all DHCP servers and relays them to the client. The DHCP Relay requests are forwarded only when the ION device is assigned to a site and the site is in active mode.
An ION device with DHCP Relay:
  • Forwards DHCP client broadcast requests to the configured DHCP server.
  • Forwards DHCP unicast request from another DHCP Relay agent downstream on the LAN-side to the configured DHCP server.
  • Forwards DHCP client/DHCP Relay agent broadcast/unicast requests to another DHCP Relay agent.
In the event of a DHCP server error, the ION device forwards all rejections back to the client. In the event of a client rejection, the ION device forwards all rejections from the client back to the DHCP server.
  1. Navigate to
    Claimed Devices
    , select a device and click
    Configure the device
  2. Select the
  3. Select a port.
  4. For
    Admin Up
    , select
  5. (Optional)
    Enter a
  6. For
    Interface Type
    , select
  7. For
    Use This Port For
  8. For
    , enter the
    IP Address/Mask
    , and
    Default Gateway
  9. For
    DHCP Relay
    , select
    to enable it.
    1. Define DHCP server IP addresses.
      Up to 16 DHCP server IP addresses may be added.
    2. (Optional)
      Define the source interface used to send DHCP requests to the servers.
      By default, the controller port is used. Make sure that the defined source interface can reach DHCP server IP addresses and vice versa. If the DHCP server is local to the branch the source interface must be the interface from which the DHCP server is accessible.
    3. (Optional)
      Enable Option 82 and configure the
      Circuit ID
      Remote ID
      , and
      Reforwarding policy
      The ION device DHCP Relay agent can include additional information by using DHCP Option 82, Circuit ID, and Remote ID, which the DHCP server uses to allocate the appropriate IP address.
  10. Save Port

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