DHCP Relay Configuration on 300 Series Managed Switch

Objective

Dynamic Host Configuration Protocol (DHCP) is a technology that automatically configures IP addresses to hosts on a network. DHCP relay is a feature that is used by a switch (referred to as a relay agent) to allow DHCP communication between hosts and remote DHCP servers that are not on the same network. When a client sends out a DHCP broadcast for an IP address, the relay agent forwards the request to the subnet at which the remote DHCP server resides. The Properties page is used to globally enable DHCP relay and establish a connection between the switch and a remote DHCP server. The Interface Settings page is used to enable DHCP relay on specified interfaces.

The objective of this article is to explain how to configure DHCP Relay on the 300 Series Managed Switches.

Applicable Devices

• SF/SG 300 Series Managed Switches

Software Version

• v1.2.7.76

DHCP Relay Configuration

Properties

Step 1. Log in to the web configuration utility and choose IP Configuration > DHCP > Properties. The Properties page opens:

Step 2. (Optional) Check Enable in the Option 82 field to enable option 82 for DHCP packets. Option 82 is used to protect the switch from attacks such as IP and MAC address spoofing. Option 82 provides information about the location of the DHCP client through the insertion of the circuit ID (interface name at which the DHCP client is connected and the VLAN name that corresponds to the interface) and the remote ID (MAC address of the switch) in the packet header of the DHCP packet. The DHCP server then uses this information to assign an IP address.

Step 3. Check Enable in the DHCP Relay field to globally enable DHCP relay on the switch.

Step 4. Click Save. DHCP Relay is configured on the switch.

Step 5. Click Add to establish a path from the switch to the DHCP server. The Add DHCP Server window appears.

The IP Version field displays the IP version of the DHCP server. The 300 switches currently only supports DHCP relay to IPv4 DHCP servers.

Step 6. Enter the IP address of the DHCP server in the DHCP Server IP Address field.

Step 7. Click Apply. The DHCP server is configured to use the DHCP Relay Server Table.

DHCP Relay Interfaces

Step 1. Log in to the web configuration utility and choose IP Configuration > DHCP > Interface Settings. The Interface Settings page opens:

Step 2. Click Add to configure an Interface to allow DHCP relay. The Add DHCP Snooping VLAN window appears.

Step 3. Choose an interface from the Interface drop-down list.

Step 4. Check Enable in the DHCP Relay field to enable DHCP relay on the specified interface. In Layer 2 mode, the switch only supports DHCP relay on VLANs. In Layer 3 mode, the switch supports DHCP relay on ports, LAGs, and VLANS.

Step 5. Click Apply. DHCP relay is enabled on the interface.