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Configuring IP Source Guard
Information About IP Source Guard
If you enable IPSG on an interface on which IP source bindings (dynamically learned by DHCP snooping or manually
configured) are not configured, the switch creates and applies a port ACL that denies all IP traffic on the interface. If you
disable IPSG, the switch removes the port ACL from the interface.
Source IP and MAC Address Filtering
IP traffic is filtered based on the source IP and MAC addresses. The switch forwards traffic only when the source IP and
MAC addresses match an entry in the IP source binding table.
When address filtering is enabled, the switch filters IP and non-IP traffic. If the source MAC address of an IP or non-IP
packet matches a valid IP source binding, the switch forwards the packet. The switch drops all other types of packets
except DHCP packets.
The switch uses port security to filter source MAC addresses. The interface can shut down when a port-security violation
occurs.
IP Source Guard for Static Hosts
IPSG for static hosts extends the IPSG capability to non-DHCP and static environments. The previous IPSG used the
entries created by DHCP snooping to validate the hosts connected to a switch. Any traffic received from a host without
a valid DHCP binding entry is dropped. This security feature restricts IP traffic on nonrouted Layer 2 interfaces. It filters
traffic based on the DHCP snooping binding database and on manually configured IP source bindings. The previous
version of IPSG required a DHCP environment for IPSG to work.
IPSG for static hosts allows IPSG to work without DHCP. IPSG for static hosts relies on IP device tracking-table entries
to install port ACLs. The switch creates static entries based on ARP requests or other IP packets to maintain the list of
valid hosts for a given port. You can also specify the number of hosts allowed to send traffic to a given port. This is
equivalent to port security at Layer 3.
IPSG for static hosts also supports dynamic hosts. If a dynamic host receives a DHCP-assigned IP address that is
available in the IP DHCP snooping table, the same entry is learned by the IP device tracking table. When you enter the
show ip device tracking all EXEC command, the IP device tracking table displays the entries as ACTIVE.
Note: Some IP hosts with multiple network interfaces can inject some invalid packets into a network interface. The
invalid packets contain the IP or MAC address for another network interface of the host as the source address. The
invalid packets can cause IPSG for static hosts to connect to the host, to learn the invalid IP or MAC address bindings,
and to reject the valid bindings. Consult the vendor of the corresponding operating system and the network interface
to prevent the host from injecting invalid packets.
IPSG for static hosts initially learns IP or MAC bindings dynamically through an ACL-based snooping mechanism. IP or
MAC bindings are learned from static hosts by ARP and IP packets. They are stored in the device tracking database.
When the number of IP addresses that have been dynamically learned or statically configured on a given port reaches a
maximum, the hardware drops any packet with a new IP address. To resolve hosts that have moved or gone away for
any reason, IPSG for static hosts leverages IP device tracking to age out dynamically learned IP address bindings. This
feature can be used with DHCP snooping. Multiple bindings are established on a port that is connected to both DHCP
and static hosts. For example, bindings are stored in both the device tracking database as well as in the DHCP snooping
binding database.
IP Source Guard Configuration Guidelines
By default, IP source guard is disabled.
You can configure static IP bindings only on nonrouted ports. If you enter the ip source binding mac-address vlan
vlan-id ip-address interface interface-id global configuration command on a routed interface, this error message
appears:
Static IP source binding can only be configured on switch port.
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