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.
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¶
For redundancy, specify a secondary server:
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.
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 |