Alcatel-Lucent 6850-48 Guida Di Rete
Managing Source Learning
MAC Address Table Overview
OmniSwitch AOS Release 6 Network Configuration Guide
September 2009
page 2-5
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
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
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.
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
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.
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
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.
• Static MAC addresses are permanent addresses. This means that a static MAC address remains in use
even if the MAC ages out or the switch is rebooted.
• 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
MAC address is dropped. Enter bridging for regular traffic flow to or from the MAC address. For
more information about Layer 2 filtering, see
• If a packet received on a port associated with the same VLAN contains a source address that matches a
static MAC address, the packet is discarded. The same source address on different ports within the
same VLAN is not supported.
same VLAN is not supported.
• If a static MAC address is configured on a port link that is down or disabled, an asterisk appears to the
right of the MAC address in the show mac-address-table command display. The asterisk indicates
that this is an invalid MAC address. When the port link comes up, however, the MAC address is then
considered valid and the asterisk no longer appears next to the address in the display.
that this is an invalid MAC address. When the port link comes up, however, the MAC address is then
considered valid and the asterisk no longer appears next to the address in the display.