7-20
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
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 Change Notification Traps, page 7-22
• Configuring MAC Address Move Notification Traps, page 7-24
• Configuring MAC Threshold Notification Traps, page 7-25
• Adding and Removing Static Address Entries, page 7-27
• Configuring Unicast MAC Address Filtering, page 7-28
• Disabling MAC Address Learning on a VLAN, page 7-29
• Displaying Address Table Entries, page 7-30
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
s
witch 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
r
eceived 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
an
d 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
a
nother until it is learned or statically associated with a port in the other VLAN.
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