DHCP Option 82
DHCP Option 82
DHCP Relay Agent Information Option 82 is an extension to the Dynamic Host Configuration Protocol (DHCP), and is defined in RFC 3046 and RFC 3993.
DHCP Option 82 can be used to send information about DHCP clients to the authenticating DHCP server. DHCP Option 82 will identify the VLAN number, port number and, optionally a customer ID of a client, during any IP address allocation. When DHCP Option 82 is enabled on the switch, it inserts the above information into the DHCP packets as they pass through the switch on their way to the DHCP server. The DHCP server stores the IP allocation record.
DHCP Option 82 can work in either layer 2 forwarding or layer 3 routing modes. There are significant differences in operation and configuration of these two modes – the latter needing BOOTP Relay support. Some configuration examples and operation descriptions are provided in a later section of this document.
Although Option 82 is titled the DHCP Relay Agent Information Option, the device that inserts the Option 82 information into a DHCP packet does not have to be acting as DHCP relay. A layer 2 switch can insert the Option 82 information into the DHCP packets (if snooping is enabled). The Option 82 information needs to be inserted into the DHCP packets by a switch at the edge of the network, because only the edge switch knows the information that uniquely identifies the subscriber that the IP address was allocated to.
It is quite likely that the edge switch will be a layer 2 switch, rather than a
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