Dell PowerEdge FX2 Dell PowerEdge FN I/O Aggregator Configuration Guide 9.6(0 - Page 66
Option 82, Option, Number and Description, Parameter Request, Renewal Time, Rebinding Time, Circuit ID
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Option Number and Description • 5: DHCPACK • 6: DHCPNACK • 7: DHCPRELEASE • 8: DHCPINFORM Parameter Request Option 55 List Clients use this option to tell the server which parameters it requires. It is a series of octets where each octet is DHCP option code. Renewal Time Option 58 Specifies the amount of time after the IP address is granted that the client attempts to renew its lease with the original server. Rebinding Time Option 59 Specifies the amount of time after the IP address is granted that the client attempts to renew its lease with any server, if the original server does not respond. End Option 255 Signals the last option in the DHCP packet. Option 82 RFC 3046 (the relay agent information option, or Option 82) is used for class-based IP address assignment. The code for the relay agent information option is 82, and is comprised of two sub-options, circuit ID and remote ID. Circuit ID This is the interface on which the client-originated message is received. Remote ID This identifies the host from which the message is received. The value of this suboption is the MAC address of the relay agent that adds Option 82. The DHCP relay agent inserts Option 82 before forwarding DHCP packets to the server. The server can use this information to: • track the number of address requests per relay agent. Restricting the number of addresses available per relay agent can harden a server against address exhaustion attacks. • associate client MAC addresses with a relay agent to prevent offering an IP address to a client spoofing the same MAC address on a different relay agent. • assign IP addresses according to the relay agent. This prevents generating DHCP offers in response to requests from an unauthorized relay agent. The server echoes the option back to the relay agent in its response, and the relay agent can use the information in the option to forward a reply out the interface on which the request was received rather than flooding it on the entire VLAN. The relay agent strips Option 82 from DHCP responses before forwarding them to the client. To insert Option 82 into DHCP packets, follow this step. 66 Dynamic Host Configuration Protocol (DHCP)