DHCP Relay Agent Information and Option 82 Insertion
DHCP relay agent information, also known as DHCP option 82, enables a DHCP relay agent (the RUCKUS ICX device) to insert Option 82 information about a client's identity into a DHCP client request being sent to a DHCP server. This option can be used to assist DHCP servers to implement dynamic address policy.
On the ICX 8200 device, the dhcp-relay information
command is used to enable relay information and configure client
identifiers. Other ICX devices use the dhcp snooping relay
information command.
The RUCKUS device inserts DHCP option 82 when relaying DHCP request packets to DHCP servers. When the DHCP server reply packets are forwarded back to DHCP clients, and the Remote ID (RID) matches the local port MAC address, then DHCP option 82 is deleted by the agent prior to forwarding the packet to the client. The VLAN and port information is used to forward the DHCP reply.
DHCP packets use the following process:
- Before relaying a DHCP discovery packet or DHCP request packet from a client to a DHCP server, the ICX switch adds agent information to the packet.
- Before relaying a DHCP reply packet from a DHCP server to a client, the ICX switch removes relay agent information from the packet.
The ICX switch deletes DHCP option 82 attributes before forwarding a server reply packet back to a DHCP client.
DHCP option 82 insertion or deletion is available only when DHCP snooping is enabled on both client and server ports.