To enable the
persistent MAC address feature, use the
stack-mac persistent
timer command in global configuration mode on the switch stack or
on a standalone switch. To disable the persistent MAC address feature, use the
no form of
this command.
stack-mac persistent timer [ 0 | time-value ]
no stack-mac persistent timer
Syntax Description
0
|
|
time-value
|
(Optional)
Time period in minutes before the stack MAC address changes to that of the new
stack master. The range is 1 to 60 minutes.
|
Command Default
Persistent MAC
address is disabled. The MAC address of the stack is always that of the first
stack master.
Command Modes
Global configuration
Command History
Release
|
Modification
|
Cisco IOS Release 15.0(2)EX1
|
This command was introduced.
|
Usage Guidelines
The MAC address of
the switch stack is determined by the MAC address of the stack master. In the
default state (persistent MAC address disabled), if a new switch becomes stack
master, the stack MAC address changes to the MAC address of the new stack
master.
When persistent
MAC address is enabled, the stack MAC address does not change for a time
period. During that time, if the previous stack master rejoins the stack as a
stack member, the stack retains its MAC address for as long as that switch is
in the stack. If the previous stack master does not rejoin the stack during the
specified time period, the switch stack takes the MAC address of the new stack
master as the stack MAC address.
You can set the
time period to be from 0 to 60 minutes.
-
If you enter
the command with no value, the default delay is 4 minutes.
-
If you enter
0 , the stack
continues to use the current stack MAC address until you enter the
no stack-mac persistent
timer command.
-
If you enter a
time delay of 1 to 60 minutes, the stack MAC address of the previous stack
master is used until the configured time period expires or until you enter the
no stack-mac persistent
timer command.
Note |
When you
enter the
stack-mac persistent
timer command with or without keywords, a message appears warning
that traffic might be lost if the old master MAC address appears elsewhere in
the network domain. You should use this feature cautiously.
|
If you enter the
no stack-mac persistent
timer command after a switchover, before the time expires, the
switch stack moves to the current stack master MAC address.
If the whole stack
reloads, when it comes back up, the MAC address of the stack master is the
stack MAC address.
Examples
This example shows
how to configure the persistent MAC address feature, with the warning messages
for each configuration. It also shows how to verify the configuration:
Device(config)# stack-mac persistent timer
WARNING: Use of an explicit timer value with the command is recommended.
WARNING: Default value of 4 minutes is being used.
WARNING: The stack continues to use the base MAC of the old Master
WARNING: as the stack-mac after a master switchover until the MAC
WARNING: persistency timer expires. During this time the Network
WARNING: Administrators must make sure that the old stack-mac does
WARNING: not appear elsewhere in this network domain. If it does,
WARNING: user traffic may be blackholed.
Device(config)# stack-mac persistent timer 0
WARNING: Stack MAC persistency timer value of 0 means that, after a
WARNING: master switchover, the current stack-mac will continue
WARNING: to be used indefinitely.
WARNING: The Network Administrators must make sure that the old
WARNING: stack-mac does not appear elsewhere in this network
WARNING: domain. If it does, user traffic may be blackholed.
Device(config)# stack-mac persistent timer 7
WARNING: The stack continues to use the base MAC of the old Master
WARNING: as the stack-mac after a master switchover until the MAC
WARNING: persistency timer expires. During this time the Network
WARNING: Administrators must make sure that the old stack-mac does
WARNING: not appear elsewhere in this network domain. If it does,
WARNING: user traffic may be blackholed.
Device(config)# end
Device(config)# show switch
Switch/Stack Mac Address : 0cd9.9624.dd80
Mac persistency wait time: 7 mins
H/W Current
Switch# Role Mac Address Priority Version State
----------------------------------------------------------
*1 Master 0cd9.9624.dd80 1 4 Ready
You can verify
your settings by entering either of two privileged EXEC commands:
-
show
running-config —If enabled,
stack-mac persistent timer and the time in minutes
appears in the output.
-
show
switch —If enabled,
Mac
persistency wait time and the number of minutes appears in the
output.