C
LIENT

S

ECURITY

7-8

CLI – This example configures a static source-guard binding on port 1.
Configuring DHCP Snooping
The addresses assigned to DHCP clients on unsecure ports can be
carefully controlled using the dynamic bindings registered with DHCP
Snooping (or using the static bindings configured with IP Source Guard).
DHCP snooping allows a switch to protect a network from rogue DHCP
servers or other devices which send port-related information to a DHCP
server. This information can be useful in tracking an IP address back to a
physical port.
Command Usage
Network traffic may be disrupted when malicious DHCP messages are
received from an outside source. DHCP snooping is used to filter DHCP
messages received on an unsecure interface from outside the network or
firewall. When DHCP snooping is enabled globally on the switch, and on
a specific VLAN interface, DHCP messages received on an untrusted
interface from a device not listed in the DHCP snooping table are
dropped.
Table entries are only learned for trusted interfaces. An entry is added or
removed dynamically to the DHCP snooping table when a client receives
or releases an IP address from a DHCP server. Each entry includes a
MAC address, IP address, lease time, VLAN identifier, and port
identifier.
The rate limit for the number of DHCP messages that can be processed
by the switch is 100 packets per second. Any DHCP packets in excess of
this limit are dropped.
Console(config)#ip source-guard binding 11-22-33-44-55-66 vlan 1
192.168.0.99 interface ethernet 1/5 23-14
Console(config)#interface ethernet 1/5
Console(config-if)#ip source-guard sip 23-11
Console(config)#