How to configure DHCP Interface Relay on L2 Managed switches using the new GUI

This article applies to:

T1600G-52TS v3 or above, T1600G-52PS v3 or above, T1600G-28PS v3 or above, T1600G-28TS v3 or above, T1600G-18TS v2 or above, T1700X-16TS v3 or above, T2600G-52TS v3 or above, T2600G-28TS v3 or above, T2600G-28MPS v3 or above, T2600G-28SQ v1 or above.

Generally, if a client needs to get an IP address from the DHCP server, they should be in a same subnet, because the DHCP packet transmission is restricted in a LAN. This mechanism may bring inconvenience when the administrator needs to assign IP addresses to clients in different subnets or VLANs. Because under normal circumstances, he has to deploy one DHCP server for each subnet, which is inconvenient and uneconomical.

You can configure DHCP Relay to solve this problem. Through DHCP Relay, you can just deploy one DHCP server and this server can offer IP addresses to clients in different subnets or VLANs.

DHCP Relay includes DHCP Interface Relay and DHCP VLAN Relay.

DHCP Interface Relay:

DHCP Interface Relay can be applied in such scenario: a DHCP server is deployed to offer IP addresses to clients in multiple subnets. These subnets all have their own Layer 3 gateway (L3 Interface or VLAN Interface).

With DHCP Interface Relay enabled, when the switch receives the DHCP request packets, it will forward the packets through the Layer 3 gateway to the DHCP server, and forward the DHCP offers from the DHCP server to the corresponding subnets afterwards. The DHCP server will determine which IP address of subnet should be assigned to the clients based on the Layer 3 gateway.

DHCP VLAN Relay:

DHCP VLAN Relay can be applied in such scenario: a DHCP server is deployed to offer IP addresses to clients in multiple VLANs. These VLANs do not have VLAN interfaces.

DHCP VLAN Relay can manually designate an L3 interface for all the VLANs as the default relay agent interface. All the DHCP packets can be forwarded through this interface so that the clients can get IP addresses from the DHCP server.

Here we use an example to introduce the configurations of DHCP Interface Relay.

PC 1 and PC 2 are in different VLANs, both of the VLANs have their own VLAN interface. Now the administrator deploys one DHCP server on the network, and want the server to assign IP addresses to both PC 1 and PC 2.

Configuration Scheme

In the given situation, the DHCP server and the computers are isolated in different network subnets, so the DHCP request from the clients cannot be directly forwarded to the DHCP server. In this case, you can configure DHCP Interface Relay to satisfy the requirement.

Note：Please set static routes for the DHCP server to make sure that the DHCP offers from the DHCP server can reach to the clients in the VLANs.

In this example, the DHCP server is demonstrated with T2600G-52TS and the DHCP relay agent is demonstrated with T2600G-28TS. We will show you the configurations on both DHCP server and DHCP relay agent.

Configuring DHCP Server

1.Go to L3 FEATURES > DHCP Service > DHCP Server > DHCP Server page, enable DHCP server globally.

2.Go to L3 FEATURES > DHCP Service > DHCP Server > Pool Setting page, create two DHCP IP pools on the DHCP server. One is for PC 1 in 192.168.2.0/24 subnet and the other for PC 2 in 192.168.3.0/24 subnet.

3.Create two static routing entries for the server to guarantee the DHCP offers can reach to both VLAN interfaces.

Configuring VLAN on DHCP Relay Agent

1.Go to L2 FEATURES > VLAN > 802.1Q VLAN > VLAN Config page, create VLAN 10 and VLAN 20. Add the corresponding ports to the VLAN.

2.Go to L2 FEATURES > VLAN > 802.1Q VLAN > Port Config page, set the PVID of port 1/0/1 as 10 and 20 of port 1/0/2.

Configuring the VLAN Interface and Routed Port on the DHCP Relay Agent.

1.Go to L3 FEATURES > Interface page, click to load the following page. Create VLAN interface 10 and VLAN interface 20. Configure port 1/0/5 as the routed port.

Configuring DHCP Interface Relay on the switch.

1.Go to L3 FEATURES > DHCP Service > DHCP Relay > DHCP Relay Config page, enable DHCP Relay feature globally.

2.Go to L3 FEATURES > DHCP Service > DHCP Relay > DHCP Interface Relay page, click to load the following page. Specify the DHCP server for the clients in VLAN 10 and VLAN 20.

Now, all the configurations are finished.

For the detailed introduction of the related functions, you can also refer to the User Guides of the corresponding functions:

Configuring DHCP Service at: configuration-guides/configuring_dhcp_t1600g_t2600g/?configurationId=18203

Configuring 802.1Q VLAN at: configuration-guides/configuring_802_1q_vlan/?configurationId=18026.

Configuring Layer 3 Interfaces at: configuration-guides/configuring_layer3_interface/?configurationId=18212.