Source Address ValidationUsing the DHCP binding table, Dell Networking OS can perform three types of source address validation(SAV).Table 11. Three Types of Source Address ValidationSource Address Validation DescriptionIP Source Address Validation Prevents IP spoofing by forwarding only IP packetsthat have been validated against the DHCP bindingtable.DHCP MAC Source Address Validation Verifies a DHCP packet’s source hardware addressmatches the client hardware address field(CHADDR) in the payload.IP+MAC Source Address Validation Verifies that the IP source address and MAC sourceaddress are a legitimate pair.Enabling 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 is strategically chosen to disguise the attacker.For example, using ARP spoofing, an attacker can assume a legitimate client’s identity and receive trafficaddressed to it. Then the attacker can spoof the client’s IP address to interact with other clients.The DHCP binding table associates addresses the DHCP servers assign, with the port on which therequesting client is attached. When you enable IP source address validation on a port, the system verifiesthat the source IP address is one that is associated with the incoming port. If an attacker is impostering asa legitimate client, the source address appears on the wrong ingress port and the system drops thepacket. Likewise, if the IP address is fake, the address is not on the list of permissible addresses for theport and the packet is dropped.To enable IP source address validation, use the following command.NOTE: If you enable IP source guard using the ip dhcp source-address-validationcommand and there are 187 entries or more in the current DHCP snooping binding table, SAV maynot be applied to all entries. To ensure that SAV is applied correctly to all entries, enable the ipdhcp source-address-validation command before adding entries to the binding table.• Enable IP source address validation.INTERFACE modeip dhcp source-address-validationDHCP MAC Source Address ValidationDHCP MAC source address validation (SAV) validates a DHCP packet’s source hardware address againstthe client hardware address field (CHADDR) in the payload.Dell Networking OS ensures that the packet’s source MAC address is checked against the CHADDR fieldin the DHCP header only for packets from snooped VLANs.• Enable DHCP MAC SAV.Dynamic Host Configuration Protocol (DHCP) 269
