Configuring DHCP DHCP
Configuration Guide
407
The switch supports two kinds of DHCP Relay: DHCP Interface Relay and DHCP VLAN
Relay.

DHCP Interface Relay
DHCP Interface Relay is used to process and forward DHCP packets between different
subnets.
Before DHCP Interface Relay configurations, you should configure IP addresses for the
layer 3 interfaces connected to the clients. The layer 3 interface can be configured as
either VLAN interface, routed port, or port channel interface according to your network
scheme. When receiving DHCP packets from clients, the switch will fill the corresponding
interface’s IP address in the relay agent IP address field of the DHCP packets, and forwards
the packets to the DHCP server. The DHCP server assigns IP addresses to the clients base
on the relay agent IP address field.
As the following figure shows, the IP address for VLAN20 is 192.168.2.1/24 and for the
routed port Gi1/0/1 is 192.168.3.1/24. With DHCP Interface VLAN configured, the switch
uses IP address of VLAN 20 (192.168.2.1/24) when applying for IP addresses for clients in
VLAN 20, and uses IP address of Gi1/0/1 (192.168.3.1/24) when applying for IP address for
PC 1. As a result, the DHCP server will assign IP addresses in Pool A (the same subnet with
the IP address of VLANî™»20) to clients in VLAN 20, and assign IP address in Pool B (the same
subnet with the Gi1/0/1) to PC 1.
Figure 1-2 Application Scenario of DHCP Interface Relay
VLAN 20
192.168.2.1/24
Gi1/0/1
Routed Port
192.168.3.1/24
DHCP Server
Pool A:192.168.2.0/24
Pool B:192.168.3.0/24
DHCP Clients
VLAN 20
192.168.2.0/24
PC 1
DHCP Client
192.168.3.2/24
Switch
DHCP Relay

DHCP VLAN Relay
DHCP VLAN Relay allows clients in different VLANs to obtain IP addresses from the DHCP
server using a single agent interface IP address.
In DHCP Interface Relay, to assign IP addresses to clients in different VLANs, you need to
create a layer 3 interface for each VLAN to ensure the reachability.
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