Cisco Catalyst 2950 Command Reference

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Catalyst 2950 and Catalyst 2955 Switch Command Reference
OL-10102-01
Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
ip dhcp snooping information option allow-untrusted
ip dhcp snooping information option allow-untrusted
Use the ip dhcp snooping information option allow-untrusted global configuration command on an
aggregation switch to configure it to accept DHCP packets with option-82 information that are received
on untrusted ports that might be connected to an edge switch. Use the no form of this command to
configure the switch to drop these packets from the edge switch.
ip dhcp snooping information option allow-untrusted
no ip dhcp snooping information option allow-untrusted
Syntax Description This command has no arguments or keywords.
Defaults The switch drops DHCP packets with option-82 information that are received on untrusted ports that
might be connected to an edge switch.
Command Modes Global configuration
Command History
Usage Guidelines You might want an edge switch to which a host is connected to insert DHCP option-82 information at
the edge of your network. You might also want to enable DHCP security features, such as DHCP
snooping, IP source guard, or dynamic Address Resolution Protocol (ARP) inspection, on an
aggregation switch. However, if DHCP snooping is enabled on the aggregation switch, the switch drops
packets with option-82 information that are received on an untrusted port and does not learn DHCP
snooping bindings for connected devices on a trusted interface.
If the edge switch to which a host is connected inserts option-82 information and you want to use DHCP
snooping on an aggregation switch, enter the ip dhcp snooping information option allow-untrusted
command on the aggregation switch. The aggregation switch can learn the bindings for a host even
though the aggregation switch receives DHCP snooping packets on an untrusted port. You can also
enable DHCP security features on the aggregation switch. The port on the edge switch to which the
aggregation switch is connected must be configured as a trusted port.
Note 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.
Examples This example shows how to configure an access switch to not check the option-82 information in
untrusted packets from an edge switch and to accept the packets:
Switch(config)# ip dhcp snooping information option allow-untrusted
Release Modification
12.1(22)EA3 This command was introduced.

Cisco Catalyst 2950 Specifications

General

Forwarding Bandwidth	8.8 Gbps
Switching Capacity	13.6 Gbps
Forwarding Rate	6.6 Mpps
Weight	3.6 kg
RAM	16 MB
Flash Memory	8 MB
Operating Humidity	10% to 85% non-condensing
Uplink Ports	2 x 10/100/1000Base-T
Dimensions	4.4 cm x 44.5 cm x 24.2 cm
Remote Management Protocol	SNMP, Telnet, HTTP
Features	Quality of Service (QoS), VLAN support
Compliant Standards	IEEE 802.3, IEEE 802.3u, IEEE 802.1D, IEEE 802.1Q, IEEE 802.1p
Status Indicators	system
Operating Temperature	0 to 45°C
Ports	24 x 10/100 Ethernet ports
MAC Address Table Size	8, 192 entries
Power Supply	Internal 100-240V AC, 50-60Hz