DHCP¶

DHCP configuration is managed per interface under Device Settings → Network → Interfaces. Click on an interface to open its settings.

Three DHCP roles are supported:

DHCP Client — the interface obtains its IP address automatically from an upstream DHCP server
DHCP Relay — the interface forwards DHCP requests from connected clients to a remote DHCP server
DHCP Server — the interface assigns IP addresses to connected clients from a locally defined address pool

Warning

DHCP Server and DHCP Relay both use UDP ports 67/68. They cannot be enabled on the same interface simultaneously.

DHCP Client¶

When configured as a DHCP client, the interface automatically requests and obtains an IP address, subnet mask, default gateway, and DNS servers from an upstream DHCP server. This is the typical setting for WAN-facing interfaces connecting to an ISP or upstream router.

To configure, go to the interface Settings tab and set IPv4 Address to DHCP.

No further configuration is required. The interface will begin soliciting an IP address as soon as the setting is saved and applied.

By default, the default gateway assigned by the upstream DHCP server is installed as a kernel default route (with administrative distance 0), which takes precedence over static default routes (e.g., ip route 0.0.0.0/0 nexthop 61.13.198.165).

This works well for simple single-WAN deployments, but in multi-WAN scenarios where you need selective failover or traffic steering, automatic default route installation can cause unintended failover — all traffic will use whichever DHCP-learned default route is active, defeating selective routing.

Disabling Default Route with nodefault¶

To prevent the automatic installation of a default route, use the Ignore Default Route flag in the GUI, or the nodefault keyword in CLI:

interface eth0
 enable
 ip address dhcp nodefault

With nodefault: - The interface obtains an IP address from DHCP - The gateway IP is learned but not installed as a default route - You can then use static routes or Policy-Based Routing (PBR) to explicitly control how traffic is forwarded

Multi-WAN Failover Pattern¶

A common use case is selective failover: primary WAN uses DHCP (which installs a default route), while secondary WAN uses DHCP with nodefault. This ensures:

Normal state: All traffic uses the primary WAN's default route
Primary WAN down: Only explicitly routed traffic (via PBR) uses the secondary WAN; other traffic is dropped

For example:

interface eth0
 ip address dhcp                  ! Primary WAN - installs default route

interface wwan0
 ip address dhcp nodefault        ! Secondary WAN - no default route

! PBR routes traffic to primary WAN with tracking; falls back to secondary if primary fails
object-group ransnet_destinations
 fqdn ransnet.com

firewall-set 100 mark 100 inbound vlan1 ip dst_object ransnet_destinations

ip pbr policy 100 fwmark 100
ip pbr 100 nexthop eth0 track icmp 1.1.1.1 15    ! Primary with tracking
ip pbr 101 nexthop wwan0                          ! Fallback (no tracking)

For complete implementation details, see WAN Failover — Selective Traffic Failover.

DHCP Relay¶

DHCP Relay (also known as DHCP Helper) forwards DHCP requests from clients on a locally attached network to a centralized DHCP server on a different subnet. This is useful when a single DHCP server serves multiple network segments across routed boundaries.

To configure, go to the interface DHCP tab and select DHCP Relay.

Field	Description
Upstream Server IP 1	Primary DHCP server IP address to forward requests to
Upstream Server IP 2	Secondary DHCP server IP address (optional, for redundancy)

The device forwards all DHCP broadcasts received on this interface to the configured upstream server(s) and relays the responses back to the requesting client.

CLI Configuration¶

interface eth1
  ip address 10.89.4.245/24
  ip dhcp-helper 192.168.8.1

For redundancy, specify a secondary server:

interface eth1
  ip address 10.89.4.245/24
  ip dhcp-helper 192.168.8.1
  ip dhcp-helper 192.168.8.2

Note

The relay interface must have IP reachability to the upstream DHCP server. Ensure routing is configured accordingly.

DHCP Server¶

When configured as a DHCP server, the interface assigns IP addresses to clients connected to its local network from a defined address pool.

To configure, go to the interface DHCP tab and select DHCP Server.

Field	Description
DHCP Server	Enable or disable the DHCP server on this interface
DNS 1 / DNS 2	DNS server addresses distributed to clients (default: `8.8.8.8` / `8.4.4.4`)
Router (default gateway)	Default gateway address advertised to clients
DHCP Pool Range: Start	First IP address in the allocatable address pool
DHCP Pool Range: End	Last IP address in the allocatable address pool
DHCP Description	Optional label for this DHCP server instance

Note

Only the primary IP address of an interface can be used as the basis for the DHCP pool range. Secondary IP addresses on the same interface are not eligible.

DHCP Options¶

Additional DHCP options can be enabled to pass supplementary configuration to clients:

Option	Description
Static MAC-IP	Define static lease bindings — assign a fixed IP to a specific MAC address
MTU	Advertise a specific MTU value to clients (Option 26)
Domain	Distribute a DNS search domain to clients
Lease Time	Override the default IP lease duration
Option 42	NTP server addresses
Option 43	Vendor-specific information (e.g., pushing controller IP to lightweight APs for automatic registration)
Option 66	TFTP server hostname (used for PXE boot or IP phone provisioning)
Option 150	TFTP server IP address (Cisco IP phone provisioning)
Option 242	IP phone configuration (Avaya IP phone provisioning)
Enable Tracking	Log client lease activity for visibility and troubleshooting

CLI Configuration¶

DHCP server on a physical interface:

interface eth1
  ip address 192.168.8.1/24
  dhcp-server
    description "DHCP pool for LAN"
    router 192.168.8.1
    dns 8.8.8.8 8.8.4.4
    range 192.168.8.10 192.168.8.254
    enable

DHCP server on a VLAN interface:

interface vlan 1 10
  ip address 10.10.10.1/24
  dhcp-server
    description "DHCP pool for VLAN-10"
    router 10.10.10.1
    dns 8.8.8.8 8.8.4.4
    range 10.10.10.2 10.10.10.254
    enable

Note

After modifying DHCP server settings, the service must be restarted to apply changes. Disable and re-enable the DHCP server to restart it.

Additional DHCP Pools¶

Note

This feature is available on gateway-series devices only.

Additional DHCP pools allow a single device's DHCP server to assign addresses to networks that are not directly attached to the server interface — for example, remote subnets reachable via relay agents on downstream devices.

These pools appear under the Additional DHCP Pools (non-attached networks) section at the bottom of the DHCP tab.

Click + Add DHCP Pool to define a new pool. Each pool supports the same configuration fields as the primary DHCP server — DNS servers, default gateway, pool range, and DHCP options — but is scoped to a specific non-attached network.

Field	Description
Network	The target subnet this pool serves
Range	Start and end IP addresses for the pool
Router	Default gateway advertised to clients in this pool
Enable	Toggle to activate or suspend this pool without deleting it

CLI Configuration¶

For each remote network pool, define the pool and add a host route back to the relay agent:

ip dhcp-pool 10.30.30.0/24
  description "DHCP pool for remote VLAN-30"
  router 10.30.30.1
  dns 8.8.8.8 8.8.4.4
  range 10.30.30.2 10.30.30.254
  enable

ip route 10.30.30.1/32 nexthop 192.168.8.9

The host route (/32) to the relay agent's interface IP is required so the DHCP server can return responses to the correct relay.

Note

Multiple dhcp-pool entries can be configured. Each pool serves a remote network range (not directly attached to the HSG).
The interface receiving relay requests must have DHCP Server enabled to listen for DHCP requests from both local and remote relay agents. If you want to limit local address allocation, use a small pool range (e.g., range 10.x.x.1 10.x.x.5).
Each dhcp-pool must be explicitly enabled; configuration changes require restarting the DHCP service.
Routing and firewall rules must permit bidirectional communication between the DHCP server and relay agents on UDP ports 67/68:
Relay agent → DHCP server (outbound)
DHCP server → Relay agent (return traffic via host route)

Verification and Troubleshooting¶

Use the following CLI commands to verify DHCP operation and diagnose issues:

Command	Description
`show ip dhcp-server`	Display DHCP server configuration and status
`show ip dhcp-lease`	List all active DHCP leases and their assigned IP/MAC bindings
`show ip dhcp-log`	Show DHCP service logs for debugging lease assignment issues
`tcpdump interface <ifname> port 67`	Capture live DHCP traffic on a specific interface to verify relay or server operation