DHCP Relay

This section describes how to configure the Dynamic Host Configuration Protocol Relay on the switch.

DHCP Relay (Dynamic Host Configuration Protocol Relay) agent is a host or an IP router that allows the DHCP client and DHCP server in different subnets to communicate with each other, so that the DHCP client can obtain its configuration information while booting.

DHCP Relay agent is used to forward DHCP packets between client and server when they are not in the same subnets. The relay receives packets from the client and inserts certain information such as network from which the packet is removed and then forwards it to the server. The server identifies the client’s network from this information and allocates IP accordingly, then sends the reply to the relay. The relay strips the information inserted and broadcasts the packets into the client’s network.

To access DHCP Relay screens, go to Layer 3 Management > DHCP Relay.

The DHCP Relay related parameters are configured through the screens displayed by the following tabs:

DHCP Relay Configuration

DHCP Relay Interface Configuration

DHCP Relay Configuration

By default, the tab Basic Settings displays the DHCP Relay Configuration screen.

Figure 1. DHCP Relay Configuration

Screen Objective	This screen allows the user to configure the basic DHCP Relay information.
Note: To enable DHCP Relay, DHCP Server Status should be disabled.
Navigation	Layer 3 Management > DHCP Server > Basic Settings
Fields	Select—select the interface for which configuration need to be applied or deleted. Service DHCP-Relay—select the Service DHCP relay status in the switch. The default option is Disabled. The list contains: Enabled—enables the DHCP relay service i.e. Relay Agent becomes active in the switch. DHCP relay agent relays DHCP messages between DHCP client and DHCP server located in different subnets. Disabled—disables the DHCP relay service in the switch Note: The service DHCP relay can be set as Enabled, only if the DHCP Server is set as Disabled. IP DHCP Relay Information Option—select the Service DHCP relay status in the switch. The default option is Disabled. The list contains: Enabled—enables the controlling status of the processing related to the Relay Agent Information options for inserting the necessary information while relaying a packet from a client to a server and examining/stripping of the inserted information when relaying a packet from a server to a client. Disabled—disables the controlling status of the processing related to the Relay Agent Information options Server Address—displays the IP address of the DHCP Server to which the Relay Agent needs to forward the packets from the client. A maximum of 5 servers can be configured. If no servers are configured, the DHCP packets will be broadcast to entire network, except the network from which packet was received.
Buttons	Apply—modifies attributes and saves the changes. Add—adds and saves new configuration. Delete—deletes the selected entry.

DHCP Relay Interface Configuration

Figure 2. DHCP Relay Interface Configuration

Screen Objective	This screen allows the user to configure a DHCP address pool. A DHCP address pool is used by the servers to allocate IP addresses to clients.
Navigation	Layer 3 Management > DHCP Server > Interface Settings
Fields	Select—select the interface for which configuration need to be applied or deleted. Interface—select the VLAN Interface which is already created in the system. Note: VLAN interface can be created using Layer 2 Management > VLAN > Static VLANs screen. Circuit ID—enter the Circuit ID value for an interface. The circuit ID uniquely identifies a circuit over which the incoming DHCP packet is received. In DHCP relay, it is used to identify the correct circuit over which the DHCP responses should be relayed. The configured circuit ID is used in the DHCP relay agent information option to inform the DHCP server about the interface from which a DHCP packet is received. The minimum value depends upon the number of interfaces that can be created. For example, if a total of 160 interfaces are allowed to be created in the switch, the circuit ID value range starts from 161 only. The interfaces include all physical interfaces, port channels, and logical L3 interfaces. This value ranges from 1 to 2147483647. Note: String of length zero will reset the configuration. Remote ID—enter the Remote ID value for an interface. The configured remote ID is used to inform the DHCP client about the remote circuit to which the DHCP packets should be forwarded from the interface. The remote ID is globally unique and an octet string of maximum size of 32. Note: The remote ID should not be same as that of the default value. Note: String of length zero will reset the configuration.
Buttons	Create—adds and saves new configuration. Reset—resets to default value for respective fields and discards all user input. Apply—modifies attributes and saves the changes. Delete—deletes the selected entry.