Accton Technology ES3552XA, ES3526XA manual Dhcp Relay and Option 82 Information, Command Usage

Basic Configuration 3

Web – If the address assigned by DHCP is no longer functioning, you will not be able to renew the IP settings via the web interface. You can only restart DHCP service via the web interface if the current address is still available.

CLI – Enter the following command to restart DHCP service.

Console#ip dhcp restart	4-246
Console#

DHCP Relay and Option 82 Information

The switch supports DHCP relay service for attached host devices. If a subnet does not include a DHCP server, you can relay DHCP client requests to a DHCP server on another subnet.

When DHCP relay is enabled and the switch sees a DHCP request broadcast, it inserts its own IP address into the request (so that the DHCP server knows the subnet of the client), then forwards the packet to the DHCP server. When the server receives the DHCP request, it allocates a free IP address for the DHCP client from its defined scope for the DHCP client’s subnet, and sends a DHCP response back to the switch. The switch then broadcasts the DHCP response to the client.

DHCP also provides a mechanism for sending information about the switch and its DHCP clients to the DHCP server. Known as DHCP Option 82, it allows compatible DHCP servers to use the information when assigning IP addresses, or to set other services or policies for clients.

Using DHCP Relay Option 82, clients can be identified by the VLAN and switch port to which they are connected rather than just their MAC address. DHCP client-server exchange messages are then forwarded directly between the server and client without having to flood them to the entire VLAN.

In some cases, the switch may receive DHCP packets from a client that already includes DHCP Option 82 information. The switch can be configured to set the action policy for these packets. Either the switch can discard the Option 82 information, keep the existing information, or replace it with the switch’s relay information.

Command Usage

You must specify the IP address of at least one DHCP server. Otherwise, the switch’s DHCP relay agent will not operate and all DHCP request and reply packets will be flooded to the entire VLAN.

Command Attributes

•DHCP Relay Option 82 – Enables the DHCP relay agant with Option 82 support.

•DHCP Relay Option 82 Policy – Sets the DHCP relay policy for DHCP client packets that include Option 82 information. (Default: Drop)

•Replace – Overwrites the DHCP client packet information with the switch’s relay information.

•Keep – Retains the client’s DHCP information.

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