Building The Address Table; Mac Addresses And Vlans - Cisco WS-C3750-48PS-S Software Configuration Manual

Chapter 7 Administering the Switch
This section contains this configuration information:
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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.
When private VLANs are configured, address learning depends on the type of MAC address:
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Building the Address Table, page 7-21
MAC Addresses and VLANs, page 7-21
MAC Addresses and Switch Stacks, page 7-22
Default MAC Address Table Configuration, page 7-22
Changing the Address Aging Time, page 7-22
Removing Dynamic Address Entries, page 7-23
Configuring MAC Address Notification Traps, page 7-23
Adding and Removing Static Address Entries, page 7-25
Configuring Unicast MAC Address Filtering, page 7-26
Displaying Address Table Entries, page 7-28
Dynamic MAC addresses learned in one VLAN of a private VLAN are replicated in the associated
VLANs. For example, a MAC address learned in a private-VLAN secondary VLAN is replicated in
the primary VLAN.
Static MAC addresses configured in a primary or secondary VLAN are not replicated in the
associated VLANs. When you configure a static MAC address in a private VLAN primary or
secondary VLAN, you should also configure the same static MAC address in all associated VLANs.
Managing the MAC Address Table
Catalyst 3750 Switch Software Configuration Guide
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