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Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 7 Administering the Switch
Managing the MAC Address Table
Managing the MAC Address Table
The MAC address table contains address information that the switch uses to forward traffic between
ports. All MAC addresses in the address table are associated with one or more ports. The address table
includes these types of addresses:
• Dynamic address: a source MAC address that the switch learns and then ages when it is not in use.
• Static address: a manually entered unicast or multicast address that does not age and that is not lost
when the switch resets.
The address table lists the destination MAC address, the associated VLAN ID, and port number
associated with the address.
Note For complete syntax and usage information for the commands used in this section, refer to the command
reference for this release.
This section contains this configuration information:
• Building the Address Table, page 7-54
• MAC Addresses and VLANs, page 7-55
• Default MAC Address Table Configuration, page 7-55
• Changing the Address Aging Time, page 7-55
• Removing Dynamic Address Entries, page 7-56
• Configuring MAC Address Notification Traps, page 7-56
• Adding and Removing Static Address Entries, page 7-58
• Adding and Removing Secure Addresses, page 7-59
• Displaying Address Table Entries, page 7-60
Building the Address Table
With multiple MAC addresses supported on all ports, you can connect any port on the switch to
individual workstations, repeaters, switches, routers, or other network devices. The switch provides
dynamic addressing by learning the source address of packets it receives on each port and adding the
address and its associated port number to the address table. As stations are added or removed from the
network, the switch updates the address table, adding new dynamic addresses and aging out those that
are not in use.
The aging interval is configured on a per-switch basis. However, the switch maintains an address table
for each VLAN, and STP can accelerate the aging interval on a per-VLAN basis.
The switch sends packets between any combination of ports, based on the destination address of the
received packet. Using the MAC address table, the switch forwards the packet only to the port or ports
associated with the destination address. If the destination address is on the port that sent the packet, the
packet is filtered and not forwarded. The switch always uses the store-and-forward method: complete
packets are stored and checked for errors before transmission.