UMN:CLI
User Manual
V8102
412
A DHCP server may use the remote ID to select the IP address to be assigned. It may
permit static assignment of IP addresses to particular remote IDs, and disallow an ad-
dress request from an unauthorized remote ID.
IP Spoofing
A DHCP client may associate the IP address assigned by a DHCP server in a forwarded
DHCP_ACK message with the circuit to which it was forwarded. The circuit access device
may prevent forwarding of IP packets with source IP addresses, other than, those it has
associated with the receiving circuit. This prevents simple IP spoofing attacks on the cen-
tral LAN, and IP spoofing of other hosts.
MAC Address Spoofing
By associating a MAC address with a remote ID, a DHCP server can prevent offering an
IP address to an attacker spoofing the same MAC address on a different remote ID.
Client Identifier Spoofing
By using the agent-supplied remote ID option, the untrusted and as-yet unstandardized
client identifier field need not be used by the DHCP server.
shows how the DHCP relay agent with the DHCP option 82 operates.
Fig. 9.38
DHCP Option 82 Operation
9.6.6.1
Enabling DHCP Option 82
To enable/disable the DHCP option 82, use the following command.
Command
Mode
Description
ip dhcp option82
Global
Enables the system to add the DHCP option 82 field.
no ip dhcp option82
Disables the system to add the DHCP option 82 field.
