Dhcp Snooping; Ip Source Guard - Cisco 500 Series Administration Manual

Security

DHCP Snooping

STEP 4
DHCP Snooping

IP Source Guard

Cisco 500 Series Stackable Managed Switch Administration Guide
Click Apply. The IP fragmentation is defined, and the Running Configuration file is
updated.
See DHCPv4 Snooping/Relay.
IP Source Guard is a security feature that can be used to prevent traffic attacks
caused when a host tries to use the IP address of its neighbor.
When IP Source Guard is enabled, the device only transmits client IP traffic to IP
addresses contained in the DHCP Snooping Binding database. This includes both
addresses added by DHCP Snooping and manually-added entries.
If the packet matches an entry in the database, the device forwards it. If not, it is
dropped.
Interactions with Other Features
The following points are relevant to IP Source Guard:
• 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
forwarded.
• 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.
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