Additional Considerations When The Switch Itself Is A Dhcp Client; Configuring Dhcp Relay And Option 82 Information - AMX NXA-ENET8-2POE Operation/Reference Manual

Additional Considerations When The Switch Itself Is a DHCP Client

The port(s) through which the switch submits a client request to the DHCP server must be configured as
trusted. Note that the switch will not add a dynamic entry for itself to the binding table when it receives an
ACK message from a DHCP server.
Also, when the switch sends out DHCP client packets for itself, no filtering takes place. However, when the
switch receives any messages from a DHCP server, any packets received from untrusted ports are dropped.
1.
Click Configuration, Security, Network, DHCP, Snooping.
2.
Set the status for the global DHCP snooping process, and set any ports within the local network or
firewall to trusted.
3.
Click Apply

Configuring DHCP Relay and Option 82 Information

Use the DHCP Relay Configuration page to configure 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.
FIG. 57 DHCP Relay Configuration
DHCP Relay Configuration parameters
• Relay Mode
• Relay Server
• Relay Information
Mode
• Relay Information
Policy
• Replace
• Keep
• Drop
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.
NXA-ENET8-2POE Gigabit Ethernet Layer 2 PoE Switch
If a DHCP packet from a client passes the filtering criteria above, it will only be forwarded to

trusted ports in the same VLAN.
If a DHCP packet is from server is received on a trusted port, it will be forwarded to both trusted

and untrusted ports in the same VLAN.
If the DHCP snooping is globally disabled, all dynamic bindings are removed from the binding

table.
Enables or disables the DHCP relay function. (Default: Disabled)
IP address of DHCP server to be used by the switch's DHCP relay agent.
Enables or disables the DHCP Relay Option 82 support. Note that Relay Mode
must also be enabled for Relay Information Mode to take effect. (Default: Dis-
abled)
Sets the DHCP relay policy for DHCP client packets that include Option 82 infor-
mation.
Overwrites the DHCP client packet information with the switch's relay information.
(This is the default.)
Retains the client's DHCP information.
Drops the packet when it receives a DHCP message that already contains relay
information.
Configuring the NXA-ENET8-2POE
79