API Guide

Source Address Validation
Using the DHCP binding table, Dell Networking OS can perform three types of source address validation (SAV).
Table 27. Three Types of Source Address Validation
Source Address Validation Description
IP Source Address Validation Prevents IP spoofing by forwarding only IP packets that have been
validated against the DHCP binding table.
DHCP MAC Source Address Validation Verifies a DHCP packet’s source hardware address matches the
client hardware address field (CHADDR) in the payload.
IP+MAC Source Address Validation Verifies that the IP source address and MAC source address are a
legitimate pair.
Enabling IP Source Address Validation
IP source address validation (SAV) 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 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
INTERFACE PORT EXTENDER
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.
The system 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
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Dynamic Host Configuration Protocol (DHCP)