37-7
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 37 Configuring DHCP Snooping
DHCP Snooping Configuration Restrictions and Guidelines
DHCP Snooping Configuration Restrictions and Guidelines
These sections provide DHCP snooping configuration restrictions and guidelines:
•
DHCP Snooping Configuration Restrictions, page 37-7
•
DHCP Snooping Configuration Guidelines, page 37-7
•
Minimum DHCP Snooping Configuration, page 37-8
DHCP Snooping Configuration Restrictions
When configuring DHCP snooping, note these restrictions:
•
The PFC2 does not support DHCP snooping.
•
With releases earlier than Release 12.2(18)SXF5, the DHCP snooping database stores a maximum
of 512 bindings. If the database attempts to add more than 512 DHCP bindings, all bindings are
removed from the database.
•
With Release 12.2(18)SXF5 and later releases, the DHCP snooping database stores at least 8,000
bindings.
•
When DHCP snooping is enabled, these Cisco IOS DHCP commands are not available on the router:
–
ip dhcp relay information check
global configuration command
–
ip dhcp relay information policy
global configuration command
–
ip dhcp relay information trust-all
global configuration command
–
ip dhcp relay information option
global configuration command
–
ip dhcp relay information trusted
interface configuration command
If you enter these commands, the router returns an error message, and the configuration is not
applied.
DHCP Snooping Configuration Guidelines
When configuring DHCP snooping, follow these guidelines:
•
DHCP snooping is not active until you enable the feature on at least one VLAN, and enable DHCP
globally on the router.
•
Before globally enabling DHCP snooping on the router, make sure that the devices acting as the
DHCP server and the DHCP relay agent are configured and enabled.
•
For DHCP server configuration information, refer to “Configuring DHCP” in the
Cisco IOS IP and
IP Routing Configuration Guide
at:
http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfdhcp.html
•
If a Layer 2 LAN port is connected to a DHCP server, configure the port as trusted by entering the
ip dhcp snooping trust
interface configuration command.
•
If a Layer 2 LAN port is connected to a DHCP client, configure the port as untrusted by entering the
no ip dhcp snooping trust
interface configuration command.