Mac Address Aging; Mac Address Limit; Mac Address Withdrawal - Cisco ASR 9000 Series Configuration Manuallines

MAC Address Aging

MAC Address Aging
A MAC address in the MAC table is considered valid only for the duration of the MAC address aging time.
When the time expires, the relevant MAC entries are repopulated. When the MAC aging time is configured
only under a bridge domain, all the pseudowires and attachment circuits in the bridge domain use that configured
MAC aging time.
A bridge forwards, floods, or drops packets based on the bridge table. The bridge table maintains both static
entries and dynamic entries. Static entries are entered by the network manager or by the bridge itself. Dynamic
entries are entered by the bridge learning process. A dynamic entry is automatically removed after a specified
length of time, known as aging time, from the time the entry was created or last updated.
If hosts on a bridged network are likely to move, decrease the aging-time to enable the bridge to adapt to the
change quickly. If hosts do not transmit continuously, increase the aging time to record the dynamic entries
for a longer time, thus reducing the possibility of flooding when the hosts transmit again.

MAC Address Limit

The MAC address limit is used to limit the number of learned MAC addresses. The default value for the MAC
address limit is 32000 for Cisco NCS 5001 and Cisco NCS 5002 and it is 8000 for Cisco NCS 5011.The
bridge domain level limit is always configured and cannot be disabled. The default value of the bridge domain
level limit is 4000 and can be changed in the range of 1-512000.
When a limit is exceeded, the system is configured to perform these notifications:
• Syslog (default)
• Simple Network Management Protocol (SNMP) trap
• Syslog and SNMP trap
• None (no notification)

MAC Address Withdrawal

For faster VPLS convergence, you can remove or unlearn the MAC addresses that are learned dynamically.
The Label Distribution Protocol (LDP) Address Withdrawal message is sent with the list of MAC addresses,
which need to be withdrawn to all other PEs that are participating in the corresponding VPLS service.
For the Cisco IOS XR VPLS implementation, a portion of the dynamically learned MAC addresses are cleared
by using the MAC addresses aging mechanism by default. The MAC address withdrawal feature is added
through the LDP Address Withdrawal message. To enable the MAC address withdrawal feature, use the
withdrawal command in l2vpn bridge group bridge domain MAC configuration mode. To verify that the
MAC address withdrawal is enabled, use the show l2vpn bridge-domain command with the detail keyword.
Note
By default, the LDP MAC Withdrawal feature is enabled on Cisco IOS XR.
The LDP MAC Withdrawal feature is generated due to these events:
• Attachment circuit goes down. You can remove or add the attachment circuit through the CLI.
• MAC withdrawal messages are received over a VFI pseudowire. RFC 4762 specifies that both wildcards
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
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(by means of an empty Type, Length and Value [TLV]) and a specific MAC address withdrawal. Cisco
IOS XR software supports only a wildcard MAC address withdrawal.
Implementing Multipoint Layer 2 Services