328 | Dynamic Host Configuration Protocolw w w . d e l l . c o m | s u p p o r t . d e l l . c o m • DHCP MAC Source Address Validation on page 328 verifies a DHCP packet’s source hardwareaddress matches the client hardware address field (CHADDR) in the payload.• IP+MAC Source Address Validation on page 328 verifies that the IP source address and MAC sourceaddress are a legitimate pair.IP Source Address ValidationIP Source Address Validation (SAV) prevents IP spoofing by forwarding only IP packets that have beenvalidated against the DHCP binding table. A spoofed IP packet is one in which the IP source address isstrategically chosen to disguise the attacker. For example, using ARP spoofing an attacker can assume alegitimate client’s identity and receive traffic addressed to it. Then the attacker can spoof the client’s IPaddress to interact with other clients.The DHCP binding table associates addresses assigned by the DHCP servers, with the port on which therequesting client is attached. When IP Source Address Validation is enabled on a port, the system verifiesthat the source IP address is one that is associated with the incoming port. If an attacker is impostering as alegitimate 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.DHCP MAC Source Address ValidationDHCP MAC Source Address Validation (SAV) validates a DHCP packet’s source hardware addressagainst 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 CHADDRfield in the DHCP header only for packets from snooped VLANs.IP+MAC Source Address ValidationIP+MAC Source Address Validation is available on platforms: c sTask Command Syntax Command ModeEnable IP Source Address Validation ip dhcp source-address-validation INTERFACETask Command Syntax Command ModeEnable DHCP MAC Source AddressValidation.ip dhcp snooping verifymac-addressCONFIGURATION
