Defense Against Bogus DHCP Message Attacks

Mechanism

An authorized DHCP client that has obtained an IP address sends a DHCP Request message or Release message to extend the lease or to release the IP address. If attackers continuously send DHCP Request messages to the DHCP server to extend the lease, the IP addresses cannot be reclaimed or obtained by authorized users. If attackers forge DHCP Release messages of authorized users to the DHCP server, the authorized users may be disconnected.

Solution

To prevent bogus DHCP message attacks, use the DHCP snooping binding table. The device checks DHCP Request messages and Release messages against binding entries to determine whether the messages are valid. (The device checks whether the VLAN IDs, IP addresses, MAC addresses, and interfaces in messages match binding entries.) If a message matches a binding entry, the device forwards the message; if a message does not match a binding entry, the device discards the message.