Dell S4820T, Configuration Manual

Page: 352 / 1178

Source Address Validation
Using the DHCP binding table, Dell Networking OS can perform three types of source address validation
(SAV).
Table 21. 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.
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Dynamic Host Configuration Protocol (DHCP)