Configuring The Dhcp Relay Agent - Cisco Catalyst 2928 Software Configuration Manual

Configuring DHCP Snooping
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Note

Configuring the DHCP Relay Agent

Beginning in privileged EXEC mode, follow these steps to enable the DHCP relay agent on the switch:
Command
Step 1 configure terminal
Step 2
service dhcp
Step 3
end
Step 4 show running-config
Step 5 copy running-config startup-config
To disable the DHCP server and relay agent, use the no service dhcp global configuration command.
See the "Configuring DHCP" section of the "IP Addressing and Services" section of the Cisco IOS IP
Configuration Guide, Release 12.2 from the Cisco.com page under Documentation > Cisco IOS
Software > 12.2 Mainline > Configuration Guides for these procedures:
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Catalyst 2928 Switch Software Configuration Guide
19-10
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.
Follow these guidelines when configuring the DHCP snooping binding database:
Because both NVRAM and the flash memory have limited storage capacity, we recommend that
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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
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configure NTP. For more information, see the
If NTP is configured, the switch writes binding changes to the binding file only when the switch
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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.
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.
Purpose
Enter global configuration mode.
Enable the DHCP server and relay agent on your switch. By default, this
feature is enabled.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Checking (validating) the relay agent information
Configuring the relay agent forwarding policy
Chapter 19 Configuring DHCP Features and IP Source Guard Features
"Configuring NTP" section on page 7-4.
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