Allied Telesis AT-FS970M Series - Manual (Page 461)

AT-FS970M Switch Command Line User’s Guide
461
A routing interface that receives a BOOTP reply from a server inspects the
broadcast flag field in the packet to determine whether the client, in its
original request to the server, set this flag to signal that the response must
be sent as a broadcast datagram. Some older nodes have this
dependency. If the flag is not set, the routing interface forwards the packet
to the originating client as a unicast packet. If the flag is set, the packet is
forwarded as a broadcast by the interface.
You configure the BOOTP relay agent on the switch by specifying the IP
address of the BOOTP server on your network with the ADD BOOTP
RELAY command. You can enter up to eight BOOTP or DHCP servers.
The IP addresses apply to all the routing interfaces on the switch. BOOTP
requests are forwarded to all the specified servers, simultaneously.
You activate the BOOTP relay agent on the switch with the ENABLE
BOOTP RELAY command. As soon as the agent is enabled, the routing
interfaces begin to forward BOOTP requests from the clients. Activating
the client applies to all routing interfaces on the switch. You cannot
activate the agent on some interfaces and not on others. The default
setting for the agent on the switch is disabled.
To view the status of the agent and the IP addresses of the servers, use
the SHOW BOOTP RELAY command.
These guidelines apply to the DHCP relay agent:
 You can specify up to five DHCP or BOOTP servers on the switch.
 Because both BOOTP and DHCP use BOOTP messages, the
DHCP relay agents can relay both their packets.
 The relay agent supports IPv4 address interfaces, but not IPv6
address interfaces.
DHCP Relay
Agent Option 82
The DCHP option-82 feature enables the switch to insert extra information
into the DHCP packets it relays. This information enables more accurate
identification of a subscriber, as it states which switch port on which relay
switch the subscriber is connected to. The information is stored in a
specific optional field in the DHCP packet, namely, the agent-information
field, which has option ID 82.
The DHCP relay agent inserts the option 82 information into the DHCP
packets that it is relaying to a DHCP server. DHCP servers that are
configured to recognize option 82 may use the information to implement IP
addresses, or other parameter assignment policies, based on the network
location of the client device. Alternatively, the server can simply log this
information to create a detailed audit trail of the locations of the clients to
which given addresses were allocated at given times.
To set the DHCP relay option 82, refer to “Configuring the DHCP Relay
Option 82” on page 467