Administrator Guide

The DHCP binding table associates addresses the DHCP servers assign with the port or the port channel interface on which the
requesting client is attached and the VLAN the client belongs to. 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 and optionally that the client belongs to the permissible
VLAN. If an attacker is impostering as a legitimate client, the source address appears on the wrong ingress port and the system drops the
packet. If the IP address is fake, the address is not on the list of permissible addresses for the port and the packet is dropped. Similarly, if
the IP address does not belong to the permissible VLAN, 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-validation command and if there are
more entries in the current DHCP snooping binding table than the available CAM space, SAV may not be applied to all
entries. To ensure that SAV is applied correctly to all entries, enable the ip dhcp source-address-validation
command before adding entries to the binding table.
• Enable IP source address validation.
INTERFACE mode
ip dhcp source-address-validation
• Enable IP source address validation with VLAN option.
INTERFACE mode
ip dhcp source-address-validation vlan vlan-id
NOTE:
Before enabling SAV With VLAN option, allocate at least one FP block to the ipmacacl CAM region.
DHCP MAC Source Address Validation
DHCP MAC source address validation (SAV) validates a DHCP packet’s source hardware address against the client hardware address
field (CHADDR) in the payload.
Dell EMC Networking OS ensures that the packet’s source MAC address is checked against the CHADDR field in the DHCP header only
for packets from snooped VLANs.
• Enable DHCP MAC SAV.
CONFIGURATION mode
ip dhcp snooping verify mac-address
Enabling IP+MAC Source Address Validation
IP source address validation (SAV) validates the IP source address of an incoming packet and optionally the VLAN ID of the client against
the DHCP snooping binding table. IP+MAC SAV 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 SAV with IP SAV.
1. Allocate at least one FP block to the ipmacacl CAM region.
CONFIGURATION mode
cam-acl l2acl
2. Save the running-config to the startup-config.
EXEC Privilege mode
copy running-config startup-config
3. Reload the system.
EXEC Privilege
reload
4. Do one of the following.
• Enable IP+MAC SAV.
INTERFACE mode
ip dhcp source-address-validation ipmac
• Enable IP+MAC SAV with VLAN option.
INTERFACE mode
ip dhcp source-address-validation ipmac vlan vlan-id
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Dynamic Host Configuration Protocol (DHCP)