MAC Address Table Overview
Managing Source Learning
page 2-4
OmniSwitch 6624/6648 Network Configuration Guide
April 2004
MAC Address Table Overview
Source learning builds and maintains the MAC address table on each switch. New MAC address table
entries are created in one of two ways: they are dynamically learned or statically assigned. Dynamically
learned MAC addresses are those that are obtained by the switch when source learning examines data
packets and records the source address and the port and VLAN it was learned on. Static MAC addresses
are user defined addresses that are statically assigned to a port and VLAN using the
mac-address-table
command.
Accessing MAC Address Table entries is useful for managing traffic flow and troubleshooting network
device connectivity problems. For example, if a workstation connected to the switch is unable to commu-
nicate with another workstation connected to the same switch, the MAC address table might show that one
of these devices was learned on a port that belonged to a different VLAN or the source MAC address of
one of the devices may not appear at all in the address table.
Using Static MAC Addresses
Static MAC addresses are configured using the
mac-address-table
command. These addresses direct
network traffic to a specific port and VLAN. They are particularly useful when dealing with silent network
devices. These types of devices do not send packets, so their source MAC address is never learned and
recorded in the MAC address table. Assigning a MAC address to the silent device’s port creates a record
in the MAC address table and ensures that packets destined for the silent device are forwarded out that
port.
When defining a static MAC address for a particular slot/port and VLAN, consider the following:
•
Configuring static MAC addresses is only supported on non-mobile ports.
•
The specified slot/port must already belong to the specified VLAN. Use the
vlan port default
command to assign a port to a VLAN before you configure the static MAC address.
•
Only traffic from other ports associated with the same VLAN is directed to the static MAC address
slot/port.
•
There are three types of static MAC addresses available:
permanent
(default),
reset
, or
timeout
. The
type selected determines the status of the MAC address in the event of a switch reboot or when the
MAC address age exceeds the aging timer. These types are defined as follows:
Note that static MAC addresses configured with a
reset
or
timeout
status are not captured when a
snapshot of the switch’s running configuration is taken.
•
There are two types of static MAC address behavior supported:
bridging
(default) or
filtering
. Enter
filtering
to set up a denial of service to block potential hostile attacks. Traffic sent to or from a filtered
MAC address is dropped. Enter
bridging
for regular traffic flow to or from the MAC address. For
more information about Layer 2 filtering, see
Chapter 21, “Configuring QoS.”
Status
Definition
permanent
MAC address remains in use even if MAC ages beyond the aging timer
value or the switch is rebooted.
reset
MAC address is removed the next time the switch is rebooted.
timeout
MAC address is removed when it ages beyond the aging timer value.
