TP-Link T1600G-28PS Jetstream Smart Switches User Guide - Page 459
DHCP VLAN Relay, the Gi1/0/1 to PC 1.
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Configuring DHCP Service DHCP can assign IP addresses that are in the same subnet with the Relay Agent IP Address to the clients. The switch supports specifying a DHCP server for multiple Layer 3 interfaces, which makes it possible to assign IP addresses to clients in different subnets from the same DHCP server. As the following figure shows, the IP address of VLAN 20 is 192.168.2.1/24 and that of the routed port Gi1/0/1 is 192.168.3.1/24. With DHCP Interface VLAN configured, the switch fills in the Relay Agent IP Address field of the DHCP packets with the IP address of VLAN 20 (192.168.2.1/24) when applying for IP addresses for clients in VLAN 20, and fills with the IP address of Gi1/0/1 (192.168.3.1/24) when applying for an 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 VLAN 20) to clients in VLAN 20, and assign an 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 DHCP Server Pool A:192.168.2.0/24 Pool B:192.168.3.0/24 VLAN 20 192.168.2.1/24 Gi1/0/1 Routed Port 192.168.3.1/24 DHCP Clients VLAN 20 192.168.2.0/24 Switch DHCP Relay PC 1 DHCP Client 192.168.3.2/24 ■■ DHCP VLAN Relay DHCP VLAN Relay allows clients in different VLANs to obtain IP addresses from the DHCP server using the IP address of a single agent interface. In DHCP Interface Relay, to achieve this goal, you need to create a Layer 3 interface for each VLAN to ensure the reachability. In DHCP VLAN Relay, you can simply specify a Layer 3 interface as the default agent interface for all VLANs. The switch fills this default agent interface's IP address in the Relay Agent IP Address field of the DHCP packets from all VLANs. As the following figure shows, no IP addresses are assigned to VLAN 10 and VLAN 20, but a default relay agent interface is configured with the IP address 192.168.2.1/24. The switch fills in the Relay Agent IP Address field of the DHCP packets with the IP address of the default agent interface (192.168.2.1/24) when applying for IP addresses for clients in both VLAN 10 and VLAN 20. As a result, the DHCP server will assign IP addresses on 192.168.2.0/24 (the same subnet with the IP address of the default agent interface) to clients in both VLAN 10 and VLAN 20. User Guide 434
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