8-28
Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
78-11380-10
Chapter8 Administering the Switch
Managing the ARP Table
To disable unicast MAC address filtering, use the no mac address-table static mac-addr vlan vlan-id
global configuration command.
This example shows how to enable unicast MAC address filtering and to configure the switch to drop
packets that have a source or destination address of c2f3.220a.12f4. When a packet is received in
VLAN 4 with this MAC address as its source or destination, the packet is dropped:
Switch(config)# mac address-table static c2f3.220a.12f4 vlan 4 drop

Displaying Address Table Entries

You can display the MAC address table by using one or more of the privileged EXEC commands
described in Tabl e 8-4:
Managing the ARP Table
To communicate with a device (over Eth ernet, for e xam ple), the softw are f irst m ust dete rmine the 48-bi t
MAC or the local data link address of that device. The process of determining the local data link address
from an IP address is called address resolution.
The Address Resolution Protocol (ARP) associates a host IP address with the corresponding media or
MAC addresses and the VLAN ID. Taking an IP address as input, ARP determines the associated MAC
address. Once a MAC address is determined, the IP-MAC address asso ciation is store d in an ARP cach e
for rapid retrieval. Then the IP datagram is encapsulated in a lin k-laye r frame and s ent o ver the ne two rk.
Encapsulation of IP datagrams and ARP requests and replies on IEEE 802 networks other than Et hernet
is specified by the Subnetwork Access Protocol (SNAP). By default, standard Ethernet-style ARP
encapsulation (represented by the arpa keyword) is enabled on the IP interface.
ARP entries added manually to the table do not age and must be manually removed.
For CLI procedures, refer to the Cisco IOS Release 12.1 documentation on Cisco.com.
Step4 show mac address-table static Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Table8-4 Commands for Displaying the MAC Address Table
Command Description
show mac address-table address Displays MAC address table information for the specified MAC address.
show mac address-table aging-time Displays the aging time in all VLANs or the specified VLAN.
show mac address-table count Displays the number of addresses present in all VLANs or the specified VLAN.
show mac address-table dynamic Displays dynamic MAC address table entries only.
show mac address-table interface Displays the MAC address table information for the specified interface.
show mac address-table multicast Displays the Layer 2 multicast entries for all VLANs or the specified VLAN.
show mac address-table static Displays static MAC address table entries only.
show mac address-table vlan Displays the MAC address table information for the specified VLAN.