394 | Dynamic Host Configuration Protocol (DHCP)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m 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 ValidationThe following feature is available on platforms: c, s and .IP Source Address Validation validates the IP source address of an incoming packet against the DHCPSnooping binding table. IP+MAC Source Address Validation ensures that the IP source address and MACsource address are a legitimate pair, rather validating each attribute individually. IP+MAC Source AddressValidation cannot be configured with IP Source Address Validation.Task Command Syntax Command ModeEnable IP Source Address Validation ip dhcp source-address-validation INTERFACENote: If IP Source Guard is enabled using the ip dhcp source-address-validation command and there are187 entries or more in the current DHCP snooping binding table, Source Address Validation (SAV) maynot be applied to all entries.To ensure that SAV is applied correctly to all entries, enable the ip dhcp source-address-validationcommand before adding entries to the binding table.Task Command Syntax Command ModeEnable DHCP MAC Source Address Validation. ip dhcp snooping verify mac-address CONFIGURATIONStep Task Command Syntax Command Mode1 Allocate at least one FP block to theipmacacl CAM region.cam-acl l2acl CONFIGURATION2 Save the running-config to thestartup-config.copy running-config startup-config EXEC Privilege3 Reload the system. reload EXEC Privilege
