Security
IP Source Guard
370 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)
18
•DHCP Snooping must be globally enabled in order to enable IP Source
Guard on an interface.
•IP source guard can be active on an interface only if:
-DHCP Snooping is enabled on at least one of the port's VLANs
-The interface is DHCP untrusted. All packets on trusted ports are
forward ed.
•If a port is DHCP trusted, filtering of static IP addresses can be configured,
even though IP Source Guard is not active in that condition by enabling IP
Source Guard on the port.
•When the ports status changes from DHCP untrusted to DHCP trusted, the
static IP address filtering entries remain in the Binding database, but they
become inactive.
•Port security cannot be enabled if source IP and MAC address filtering is
configured on a port.
•IP Source Guard uses TCAM resources and requires a single TCAM rule per
IP Source Guard address entry. If the number of IP Source Guard entries
exceeds the number of available TCAM rules, the extra addresses are
inactive.
Filtering
If IP Source Guard is enabled on a port then:
•DHCP packets allowed by DHCP Snooping are permitted.
•If source IP address filtering is enabled:
-IPv4 traffic: Only traffic with a source IP address that is associated with
the port is permitted.
-Non IPv4 traffic: Permitted (Including ARP packets).