Owner`s manual

100 | Dynamic Host Configuration Protocol (DHCP)
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IP Source Address Validation
IP source address validation prevents IP spoofing by forwarding only IP packets that have been validated
against the DHCP binding table. A spoofed IP packet is one in which the IP source address is strategically
chosen to disguise the attacker. For example, using ARP spoofing, an attacker can assume a legitimate
client’s identity and receive traffic addressed to it. Then the attacker can spoof the client’s IP address to
interact with other clients.
The DHCP binding table associates addresses assigned by the DHCP servers, with the port on which the
requesting client is attached. When you enable IP source address validation on a port, the system verifies
that the source IP address is one that is associated with the incoming port. If an attacker is impostering as a
legitimate client, the source address appears on the wrong ingress port and the system drops the packet.
Likewise, if the IP address is fake, the address will not be on the list of permissible addresses for the port,
and the packet is dropped.
To enable IP source address validation, follow this step:
DHCP MAC Source Address Validation
DHCP MAC source address validation validates a DHCP packet’s source hardware address against the
client hardware address field (CHADDR) in the payload.
FTOS Release 8.2.1.1 ensures that the packet’s source MAC address is checked against the CHADDR
field in the DHCP header only for packets from snooped VLANs.
To enable DHCP MAC source address validation, follow this step:
IP+MAC Source Address Validation
IP source address validation validates the IP source address of an incoming packet against the DHCP
snooping binding table. IP+MAC source address validation ensures that the IP source address and MAC
source address are a legitimate pair, rather than validating each attribute individually. You cannot configure
IP+MAC source address validation with IP source address validation.
Task Command Syntax Command Mode
Enable IP Source Address Validation
ip dhcp source-address-validation
INTERFACE
Task Command Syntax Command Mode
Enable DHCP MAC Source Address
Validation.
ip dhcp snooping verify mac-address
CONFIGURATION