Setup
DHCP Relay
SPS208G/SPS224G4/SPS2024 Service Provider Switches User Guide 24
2
STEP 4 In the
DHCP Relay Screen
, select Enable DHCP Option 82 Insertion.
L2 DHCP Relay Operation
DHCP Snooping with Option 82 Insertion
Requests
DHCP broadcasts are trapped on the CPU, and replacement broadcasts are
forwarded with Option 82.
NOTE If Option 82 is present in the request received on an untrusted port, the following
options are available:
• Pass-through enabled — The packet is forwarded, unchanged, to a trusted
port.
• Pass-through disabled — The packet is discarded.
Replies
Replies from the DHCP servers are handled according to the DHCP Snooping
rules, such as checking if the port is trusted before forwarding the packet.
L2 DHCP Relay
Requests
The switch traps DHCP broadcast messages (DHCP DISCOVER and DHCP
REQUEST) from the DHCP clients:
• Packets arriving with Option-82 are discarded.
• If the giaddr field is 0.0.0.0 it is modified to the DHCP server’s IP address.
• The packet is duplicated and relayed per each DHCP Server.
NOTE If L2 DHCP relay is enabled; and the DHCP server is on the DHCP request ingress
VLAN, the outgoing relayed packet is sent as a broadcast.
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