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Setting the MAC Learning Limit
To set a MAC learning limit on an interface, use the following command.
● Specify the number of MAC addresses that the system can learn off a Layer 2 interface.
INTERFACE mode
mac learning-limit address_limit
Three options are available with the mac learning-limit command:
○ dynamic
○ no-station-move
○ station-move
NOTE: An SNMP trap is available for mac learning-limit station-move. No other SNMP traps are available
for MAC Learning Limit, including limit violations.
mac learning-limit Dynamic
The MAC address table is stored on the Layer 2 forwarding information base (FIB) region of the CAM.
The Layer 2 FIB region allocates space for static MAC address entries and dynamic MAC address entries. When you enable
MAC learning limit, entries created on this port are static by default. When you configure the dynamic option, learned MAC
addresses are stored in the dynamic region and are subject to aging. Entries created before this option is set are not affected.
Dell EMC Networking OS Behavior: If you do not configure the dynamic option, the system does not detect station moves
in which a MAC address learned from a MAC-limited port is learned on another port on the same system. Therefore, any
configured violation response to detected station moves is not performed. When a MAC address is relearned on any other
line card (any line card except the one to which the original MAC-limited port belongs), the station-move is detected and the
system takes the configured the violation action.
mac learning-limit mac-address-sticky
Using sticky MAC addresses allows you to associate a specific port with MAC addresses from trusted devices. If you enable
sticky MAC, the specified port retains any dynamically-learned addresses and prevents them from being transferred or learned
on other ports.
If you configure mac-learning-limit and you enabled sticky MAC, all dynamically-learned addresses are converted to
sticky MAC addresses for the selected port. Any new MAC addresses learned on this port is converted to sticky MAC
addresses.
To save all sticky MAC addresses into a configuration file that can be used as a startup configuration file, use the write
config command. If the number of existing MAC addresses is fewer than the configured mac learn limit, any additional MAC
addresses are converted to sticky MACs on that interface. To remove all sticky MAC addresses from the running config file,
disable sticky MAC and use the write config command.
When you enable sticky mac on an interface, dynamically-learned MAC addresses do not age, even if you enabled mac-
learning-limit dynamic. If you configured mac-learning-limit and mac-learning-limit dynamic and you
disabled sticky MAC, any dynamically-learned MAC addresses ages.
mac learning-limit station-move
The mac learning-limit station-move command allows a MAC address already in the table to be learned from another
interface.
For example, if you disconnect a network device from one interface and reconnect it to another interface, the MAC address is
learned on the new interface. When the system detects this “station move,” the system clears the entry learned on the original
interface and installs a new entry on the new interface.
Layer 2
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