395
Configuring DHCP
Information About Configuring DHCP
DHCP Snooping Configuration Guidelines
You must globally enable DHCP snooping on the switch.
DHCP snooping is not active until DHCP snooping is enabled on a VLAN.
Before globally enabling DHCP snooping on the switch, make sure that the devices acting as the DHCP server and
the DHCP relay agent are configured and enabled.
Before configuring the DHCP snooping information option on your switch, be sure to configure the device that is
acting as the DHCP server. For example, you must specify the IP addresses that the DHCP server can assign or
exclude, or you must configure DHCP options for these devices.
When configuring a large number of circuit IDs on a switch, consider the impact of lengthy character serstrings on
the NVRAM or the flash memory. If the circuit-ID configurations, combined with other data, exceed the capacity of
the NVRAM or the flash memory, an error message appears.
Before configuring the DHCP relay agent on your switch, make sure to configure the device that is acting as the DHCP
server. For example, you must specify the IP addresses that the DHCP server can assign or exclude, configure DHCP
options for devices, or set up the DHCP database agent.
If the DHCP relay agent is enabled but DHCP snooping is disabled, the DHCP option-82 data insertion feature is not
supported.
If a switch port is connected to a DHCP server, configure a port as trusted by entering the ip dhcp snooping trust
interface configuration command.
If a switch port is connected to a DHCP client, configure a port as untrusted by entering the no ip dhcp snooping
trust interface configuration command.
Do not enter the ip dhcp snooping information option allow-untrusted command on an aggregation switch to
which an untrusted device is connected. If you enter this command, an untrusted device might spoof the option-82
information.
You can display DHCP snooping statistics by entering the show ip dhcp snooping statistics user EXEC command,
and you can clear the snooping statistics counters by entering the clear ip dhcp snooping statistics privileged EXEC
command.
DHCP snooping trust Untrusted
DHCP snooping VLAN Disabled
DHCP snooping MAC address verification Enabled
Cisco IOS DHCP server binding database Enabled in Cisco IOS software, requires configuration.
Note: The switch gets network addresses and configuration parameters
only from a device configured as a DHCP server.
DHCP snooping binding database agent Enabled in Cisco IOS software, requires configuration. This feature is
operational only when a destination is configured.
1. The switch responds to DHCP requests only if it is configured as a DHCP server.
2. The switch relays DHCP packets only if the IP address of the DHCP server is configured on the SVI of the DHCP client.
3. Use this feature when the switch is an aggregation switch that receives packets with option-82 information from an edge
switch.
Table 46 Default DHCP Snooping Settings (continued)
Feature Default Setting
To Next Page
Loading...
Need help?
General