Edimax AC-M3000/AC-M1000
User’s Manual
155
11. Appendix G—DHCP Relay AC-M3000 supports DHCP Relay defined according to RFC 3046 . For scaling reasons, it is advantageous to set up
an external DHCP server other than having the internal DHCP server implemented in AC-M3000 to assign an IP.
When forwarding client-originated DHCP packets to a DHCP server, a new option called the “Relay Agent
Information option” is inserted by the DHCP relay agent. External DHCP servers that recognize the Relay Agent
Information option may use the information to implement IP address or other parameter assignment policies. The
external DHCP server then echoes the option back to the relay agent in server-to-client replies, and the relay agent
strips the option before forwarding the reply to the client.
A graphic example of connecting 2 gateways with an external DHCP server:
Please note that the Router and Gateway 1 connected to the DHCP Server have to be under the same network
segment as DHCP Server.
When a client requests IP address from Gateway 1 Public LAN through the build-in DHCP relay agent of AC-M3000,
the DHCP server will receive a DHCP REQUEST packet with Option 82 (a code defined in RFC 3046). Also a Circuit
ID will be sent by AC-M3000 when DHCP relay is enabled to define where the packet is sent from, and this Circuit ID
should have a format of MAC_IP, such as 00:E0:22:DF:AC:DF_192.168.1.254. Therefore, when the external DHCP
server gets the request packet, it knows where to reply to and which IP to assign.