Cisco Systems 3750E manual Building the Address Table, MAC Addresses and VLANs

Chapter 7 Administering the Switch

Managing the MAC Address Table

These sections contain this configuration information:

•Building the Address Table, page 7-20

•MAC Addresses and VLANs, page 7-20

•MAC Addresses and Switch Stacks, page 7-21

•Default MAC Address Table Configuration, page 7-21

•Changing the Address Aging Time, page 7-21

•Removing Dynamic Address Entries, page 7-22

•Configuring MAC Address Notification Traps, page 7-22

•Adding and Removing Static Address Entries, page 7-24

•Configuring Unicast MAC Address Filtering, page 7-25

•Displaying Address Table Entries, page 7-27

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 globally configured on a standalone switch or on the switch stack. 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 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.

MAC Addresses and VLANs

All addresses are associated with a VLAN. An address can exist in more than one VLAN and have different destinations in each. Unicast addresses, for example, could be forwarded to port 1 in VLAN 1 and ports 9, 10, and 1 in VLAN 5.

Each VLAN maintains its own logical address table. A known address in one VLAN is unknown in another until it is learned or statically associated with a port in the other VLAN.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

7-20 OL-9775-02