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Chapter 3
Configuring Ethernet Switching
MAC Addresses and VLANs
Changing the Address Aging Time
Configuring the Aging Time
OL-2031-02
Figure 3-3
Contents of the Address Table
All MAC addresses are associated with one or more VLANs. An address can exist
in more than one VLAN and have different destinations in each. Multicast
addresses, for example, could be forwarded to port 1 in VLAN 1 and ports 9, 10,
and 11 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. An address can be secure in one VLAN and dynamic in
another. Addresses that are statically entered in one VLAN must be static
addresses in all other VLANs.
Dynamic addresses are source MAC addresses that the switch learns and then
drops when they are not in use. Use the Aging Time field to define how long the
switch retains unseen addresses in the table. This parameter applies to all VLANs.
Setting too short an aging time can cause addresses to be prematurely removed
from the table. When the switch receives a packet for an unknown destination, the
switch floods the packet to all ports in the same VLAN as the receiving port. This
unnecessary flooding can impact performance. Setting too long an aging time can
cause the address table to be filled with unused addresses; it can cause delays in
establishing connectivity when a workstation is moved to a new port.
Catalyst 4224 Access Gateway Switch Software Configuration Guide
Managing the Catalyst 4224 Access Gateway Switch
3-19
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Table of Contents
Troubleshooting
