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Filters and QOS Configuration for Ethernet Routing Switch 5500
Technical Configuration Guide
32
January 2013
avaya.com
8. IP Security Features
This section covers the security features DHCP Snooping, ARP -Inspection, and IP Source Guard. DHCP
Snooping and A RP-Inspection where added in the 5.0 software release while IP Source Guard was
added in the 5.1 soft ware release. If you are using a software release prior to 5.0, please see the next
section.
8.1 DHCP Snooping
DHCP snooping is a security feature that builds a binding table on untrusted ports by monitoring DHCP
messages. On core or uplink ports, the port(s) is considered trusted and should be configured as such.
The DHCP snooping binding table consists of the leased IP address, MAC address, lease time, port
number, and VLAN ID. DHCP snooping is configured at a per VLAN basi s where, by default, all ports are
set to untrusted. You must configure the uplink ports as trusted.
Overall, DHCP snooping operates as follows:
Allows only DHCP requests form untrusted ports.
DHCP replies and all other DHCP messages from untrusted ports are dropped
Verifies the DHCP snooping binding table on untrusted ports to verify the traffic entering a port by
comparing the source MA C address against the DHCP lease IP address. If there is no match, the
packet is dropped
8.1.1 DHCP Snooping Configuration
To enable DHCP snooping, enter the following command assuming we wish to enable DHCP snooping
on VLANs 100 and 200 and the uplink port is 1/24.
5500(config)#
ip dhcp-snooping vlan 100
5500(config)#
ip dhcp-snooping vlan 200
5500(config)#
ip dhcp-snooping enable
5500(config)#
interface fastEthernet 1/24
5500(config-if)#
ip dhcp-snooping trusted
5500(config-if)#
exit