Building The Address Table; Mac Addresses And Vlans - Cisco 3845 - Security Bundle Router Software Manual

Managing the MAC Address Table
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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. 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 1, 9, and 10 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.
You can disable MAC address learning on a per-VLAN basis. Customers in a service provider network
can tunnel a large number of MAC addresses through the network and fill up the available MAC address
table space. You can control MAC address learning on a VLAN and manage the MAC address table space
that is available on the switch by controlling which VLANs, and therefore which ports, can learn MAC
addresses.
Before you disable MAC address learning, be sure that you are familiar with the network topology and
the switch system configuration. Disabling MAC address learning on a VLAN could cause flooding in
the network. See the
information.
Cisco ME 3800X and 3600X Switch Software Configuration Guide
5-20
Default MAC Address Table Configuration, page 5-21
Changing the Address Aging Time, page 5-21
Removing Dynamic Address Entries, page 5-21
Configuring MAC Address Change Notification Traps, page 5-22
Configuring MAC Address Move Notification Traps, page 5-24
Configuring MAC Threshold Notification Traps, page 5-25
Adding and Removing Static Address Entries, page 5-26
Configuring Unicast MAC Address Filtering, page 5-27
Disabling MAC Address Learning on a VLAN, page 5-28
Displaying Address Table Entries, page 5-29
"Disabling MAC Address Learning on a VLAN" section on page 5-28
Chapter 5 Administering the Switch
for more
OL-23400-01