Configuring The Dhcp Relay Agent - Cisco IE 3000 Software Configuration Manual
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Configuring DHCP Features
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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
Cisco IE 3000 Switch Software Configuration Guide
20-8
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.
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.
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
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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.
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To ensure that the lease time in the database is accurate, we recommend that you enable and
configure NTP. For more information, see the
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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.
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.
Chapter 20
Configuring DHCP Features
"Configuring NTP" section on page
7-3.
OL-13018-01
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