Configuring The Dhcp Server; Dhcp Server And Switch Stacks - Cisco WS-CBS3032-DEL Software Configuration Manual

Configuring DHCP Features
•
•
•
•

Configuring the DHCP Server

The switch can act as a DHCP server. By default, the Cisco IOS DHCP server and relay agent features
are enabled on your switch but are not configured. These features are not operational.
For procedures to configure the switch as a DHCP server, see the "Configuring DHCP" section of the
"IP addressing and Services" section of the Cisco IOS IP Configuration Guide, Release 12.2.

DHCP Server and Switch Stacks

The DHCP binding database is managed on the stack master. When a new stack master is assigned, the
new master downloads the saved binding database from the TFTP server. If the stack master fails, all
unsaved bindings are lost. The IP addresses associated with the lost bindings are released. You should
configure an automatic backup by using the ip dhcp database url [timeout seconds | write-delay
seconds] global configuration command.
When a stack merge occurs, the stack master that becomes a stack member loses all of the DHCP lease
bindings. With a stack partition, the new master in the partition acts as a new DHCP server without any
of the existing DHCP lease bindings.
For more information about the switch stack, see
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
22-10
Follow these guidelines when configuring the DHCP snooping binding database:
Because both NVRAM and the flash memory have limited storage capacity, we recommend that
–
you store the binding file on a TFTP server.
For network-based URLs (such as TFTP and FTP), you must create an empty file at the
–
configured URL before the switch can write bindings to the binding file at that URL. See the
documentation for your TFTP server to determine whether you must first create an empty file
on the server; some TFTP servers cannot be configured this way.
To ensure that the lease time in the database is accurate, we recommend that you enable and
–
configure NTP. For more information, see the
on page 5-4.
If NTP is configured, the switch writes binding changes to the binding file only when the switch
–
system clock is synchronized with NTP.
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.
Starting with Cisco IOS Release 12.2(37)SE, 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.
Do not enable Dynamic Host Configuration Protocol (DHCP) snooping on RSPAN VLANs. If
DHCP snooping is enabled on RSPAN VLANs, DHCP packets might not reach the RSPAN
destination port.
Chapter 22 Configuring DHCP Features and IP Source Guard
"Configuring Time and Date Manually" section
Chapter 7, "Managing Switch Stacks."
OL-13270-06