Configuring MAC Address Tables
This chapter contains the following sections:
Information About MAC Addresses
To switch frames between LAN ports, the switch maintains
an address table. When the switch receives a frame, it associates the media
access control (MAC) address of the sending network device with the LAN port on
which it was received.
The switch dynamically builds the address table by using the MAC
source address of the frames received. When the switch receives a frame for a
MAC destination address not listed in its address table, it floods the frame to
all LAN ports of the same VLAN except the port that received the frame. When
the destination station replies, the switch adds its relevant MAC source
address and port ID to the address table. The switch then forwards subsequent
frames to a single LAN port without flooding all LAN ports.
You can also enter a MAC address, which is termed a static MAC
address, into the table. These static MAC entries are retained across a reboot
of the switch.
Configuring MAC Addresses
Configuring Static
MAC Addresses
You can configure
static MAC addresses for the switch. These addresses can be configured in
interface configuration mode or in VLAN configuration mode.
SUMMARY STEPS1.
switch#
configure
terminal
2.
switch(config)
#
mac-address-table static
mac_address
vlan
vlan-id {drop |
interface {type
slot/port} |
port-channel
number} [auto-learn]
3.
(Optional) switch(config)#
no mac address-table
static
mac_address
vlan
vlan-id
DETAILED STEPS| | Command or Action | Purpose |
|---|
| Step 1 | switch#
configure
terminal
|
Enters global
configuration mode.
|
| Step 2 | switch(config)
#
mac-address-table static
mac_address
vlan
vlan-id {drop |
interface {type
slot/port} |
port-channel
number} [auto-learn]
|
Specifies a
static address to add to the MAC address table.
If you
enable the
auto-learn
option, the switch will update the entry if the same MAC address is seen on a
different port.
|
| Step 3 | switch(config)#
no mac address-table
static
mac_address
vlan
vlan-id
| (Optional)
Deletes the
static entry from the MAC address table.
Use the
mac address-table
static command to assign a static MAC address to a virtual
interface.
|
This example shows
how to put a static entry in the MAC address table:
switch# configure terminal
switch(config) # mac address-table static 12ab.47dd.ff89 vlan 3 interface ethernet 1/4
switch(config) #
Configuring the
Aging Time for the MAC Table
You can configure
the amount of time that an entry (the packet source MAC address and port that
packet ingresses) remains in the MAC table. MAC aging time can be configured in
either interface configuration mode or in VLAN configuration mode.
SUMMARY STEPS1.
switch#
configure
terminal
2.
switch(config)#
mac-address-table aging-time
seconds [vlan
vlan_id]
DETAILED STEPS| | Command or Action | Purpose |
|---|
| Step 1 | switch#
configure
terminal
|
Enters global
configuration mode.
|
| Step 2 | switch(config)#
mac-address-table aging-time
seconds [vlan
vlan_id]
|
Specifies the
time before an entry ages out and is discarded from the MAC address table.
The
seconds range
is from 0 to 1000000. The default is 300 seconds for Cisco NX-OS 5500 and 1800
for Cisco NX-OS 5600 and 6000 series. Entering the value 0 disables the MAC
aging. If a VLAN is not specified, the aging specification applies to all
VLANs.
|
This example shows
how to set the aging time for entries in the MAC address table to 300 seconds:
switch# configure terminal
switch(config) # mac-address-table aging-time 300
switch(config) #
Clearing Dynamic Addresses from the MAC Table
SUMMARY STEPS1.
switch#
configure
terminal
2.
switch(config)#
clear mac-address-table dynamic
{address
mac-addr} {interface [type
slot/port |
port-channel
number} {vlan
vlan-id}
DETAILED STEPS| | Command or Action | Purpose |
|---|
| Step 1 | switch#
configure
terminal
|
Enters global
configuration mode.
|
| Step 2 | switch(config)#
clear mac-address-table dynamic
{address
mac-addr} {interface [type
slot/port |
port-channel
number} {vlan
vlan-id}
| Clears the dynamic address entries from the MAC address
table.
|
Verifying the MAC
Address Configuration
Use one of the following commands to verify the configuration:
Table 1 MAC Address
Configuration Verification Commands|
Command
|
Purpose
|
|---|
|
show mac-address-table aging-time
|
Displays the
MAC address aging time for all VLANs defined in the switch.
|
|
show mac-address-table
|
Displays the
contents of the MAC address table.
| Note
|
IGMP
snooping learned MAC addresses are not displayed.
|
|
|
show mac address-table loop-detect
|
Displays the
currently configured action.
|
This example shows
how to display the MAC address table:
switch# show mac-address-table
VLAN MAC Address Type Age Port
---------+-----------------+-------+---------+------------------------------
1 0018.b967.3cd0 dynamic 10 Eth1/3
1 001c.b05a.5380 dynamic 200 Eth1/3
Total MAC Addresses: 2
This example shows
how to display the current aging time:
switch# show mac-address-table aging-time
Vlan Aging Time
----- ----------
1 300
13 300
42 300
This example shows
how to display the currently configured action:
switch# configure terminal
switch(config)# show mac address-table loop-detect
Port Down Action Mac Loop Detect : enabled
switch# configure terminal
switch(config)# no mac address-table loop-detect port-down
switch(config)# show mac address-table loop-detect
Port Down Action Mac Loop Detect : disabled
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