Theory:

DHCP relay is used when DHCP server is not on same subnet as client. When relayed DHCP packet is added giaddr field as defined in RFC2131 which has relay agent IP address used by DHCP server to choose right pool.

Network Configuration:

In  this example we will setup two VLANs, one for internal users and one for guests with following settings.

VLAN 1: Network: 192.168.1.0/24

VLAN 10: Network: 192.168.10.0/24

VLAN 20: Network: 192.168.20.0/24

SERVER IP: 192.168.1.123

SERVER is in VLAN 1DXS

PC1: Connected to VLAN 10

PC2: Connected to VLAN 20 

Devices:
DXS-3600-32S/SI

Firmware Used: 
2.40.046

Note: Please always check our website for updates for firmware

Topology Example:

 
Step 1 –  Login via SSH, telnet or console and enter Privileged EXEC Mode
                    
 DXS-3600-32S TenGigabit Ethernet Switch

                             Command Line Interface
                           
Firmware: Build 2.40.046

           Copyright(C) 2015 D-Link Corporation. All rights reserved.

Switch>enable

Switch#

Switch#configure terminal

Create VLANs and assign switch IP interface on each VLAN. In this example we create two VLANs, VLAN 10 for corporate users and VLAN 20 for guest users. Change this settings to suite your VLANs and IPs.

Switch(config)#vlan 10

Switch(config-vlan)#exit

Switch(config)#vlan 20

Switch(config-vlan)#exit

Switch(config)#interface vlan 10

Switch(config-if)#ip address 192.168.10.1 255.255.255.0

Switch(config-if)#exit

Switch(config)#interface vlan 20

Switch(config-if)#ip address 192.168.20.1 255.255.255.0

Switch(config-if)#exit

Step 2.

We assign port member of VLANs. In this example port 7 is in VLAN 10, port 8 is in VLAN 20 and DHCP server is on port 24 member of VLAN 1.

Switch(config)#interface ethernet 1/0/7

Switch(config-if)#switchport mode access

Switch(config-if)#switchport access vlan 10

Switch(config-if)#exit

Switch(config)#interface ethernet 1/0/8

Switch(config-if)#switchport mode access

Switch(config-if)#switchport access vlan 20

Switch(config-if)#exit

Switch(config)#interface ethernet 1/0/24

Switch(config-if)#switchport mode access

Switch(config-if)#switchport access vlan 1

Switch(config-if)#exit 

Step 3.

We enable DHCP relay and define pools and DHCP relay source and destination. Where source is switches VLAN IP and destination DHCP server IP. Finally we save configuration.

Switch(config)#service dhcp

Switch(config)#ip dhcp relay information option

Switch(config)#ip dhcp pool corporate

Switch(config-dhcp-pool)#relay source 192.168.10.90 255.255.255.0

Switch(config-dhcp-pool)#relay destination 192.168.1.100

Switch(config-dhcp-pool)#exit

Switch(config)#ip dhcp pool guest

Switch(config-dhcp-pool)#relay source 192.168.20.90 255.255.255.0

Switch(config-dhcp-pool)#relay destination 192.168.1.100

Switch(config-dhcp-pool)#end

Switch#copy run start

Destination filename startup-config? [y/n]:  y

Saving all configurations to NV-RAM.......... Done.

Step 4.

Finally we check that clients are getting correct IP.