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Cisco IE 3010 Switch Software Configuration Guide
OL-23145-01
Chapter 21 Configuring DHCP Features and IP Source Guard Features
Understanding IP Source Guard
Note The port ACL takes precedence over any router ACLs or VLAN maps that affect the same interface.
The IP source binding table bindings are learned by DHCP snooping or are manually configured (stat ic
IP source bindings). An entry in this table has an IP address with its associated MAC address and VLAN
number. The switch uses the IP source binding table only when IP source gu ard is enabled.
IPSG is supported only on Layer 2 ports, including access and trunk ports.You can configure IPSG with
source IP address filtering or with source IP and MAC address filtering.
• Source IP Address Filtering, page 21-16
• Source IP and MAC Address Filtering, page 21-16
• IP Source Guard for Static Hosts, page 21-16
Source IP Address Filtering
When IPSG is enabled with this option, IP traffic is filtered based on the source IP address. The switch
forwards IP traffic when the source IP address matches an entry in the DHCP snooping binding database
or a binding in the IP source binding table.
When a DHCP snooping binding or static IP source binding is added, chan ged, or deleted on an interface,
the switch modifies the port ACL by using the IP source binding changes and re-applies the port ACL to
the interface.
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 IP source guard, 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 swit ch 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
Note Do not use IPSG (IP source guard) for static hosts on uplink po rts or trunk ports.
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