15.1.8 MAC address update function

<Structure of this section>

(1) Transmit Operation

When the active port is changed due to a failure on the communication link or when an operation command is executed to change the active port, the Switch can send an MAC address update frame to have an upstream switch relearn the MAC address of a terminal. The MAC address update frame has the following features:

The MAC address update frame is a multicast frame.
You specify the MAC address to be learned by upstream switches as the source MAC address.
Upstream switches do not need a special receiving functionality.

You can configure the functionality for updating MAC addresses for each uplink port pair. You can also specify VLANs to which MAC address update frames are not to be sent.

The following figure shows the difference in switchover operation according to the use of MAC address update frames.

Figure 15-5 Difference in switching operation due to use of MAC address update frame

Normal operation: The primary port on the Switch performs communication. Upstream switches learn the MAC address of the user terminal via the current communication path.
If the primary port fails (when MAC address update frames are not sent): If the Switch is not configured to send MAC address update frames, although the secondary port is now active, upstream switch B retains the MAC address of the user terminal on the previous port. Therefore, communication is not restored until the MAC address learned by upstream switch B is erased or the user terminal sends traffic to upstream switch B.
If the primary port fails (when MAC address update frames are sent): If the Switch is configured to send MAC address update frames, it sends an MAC address update frame to request that upstream switch B change the port on which it learns the MAC address of the user terminal as soon as the secondary port becomes active. Therefore, communication can be restored immediately.

The following table describes the specifications of the functionality for updating MAC addresses.

Table 15-2 Specification of MAC address update function
Item	Description
Unit for ports that send MAC address update frames	Per uplink port
Sending port	Enabled active port
Number of times frames are sent^#	1 to 3 times
MAC address entries to be sent	Entries must concurrently satisfy the following conditions: They must be entries that are learned on the VLANs containing the applicable uplink port pair. These entries do not include entries learned on the VLANs not subject to the sending MAC address update frames as specified in the applicable configuration. They must be entries that are learned on ports other than the applicable uplink port pair.
Types of MAC address entries to be sent	Dynamic entries Static entries Entries authenticated by IEEE 802.1X Entries authenticated by Web-based authentication Entries authenticated by MAC-based authentication Switch MAC address Virtual MAC address
Maximum number of MAC address entries to be sent	3000 entries. If the number of entries to be sent exceeds 3000, only 3000 entries are sent and an operation log message indicating that the capacity limit has been exceeded is output.
Sending rate	300 pps at maximum

#: Set in the configuration

(2) Reception operation

As with other frames, when the Switch relays MAC address update frames, it learns the source MAC addresses contained in the frames and registers them in its MAC address table. For more information, refer to the "Configuration Guide Vol.1" "25 MAC Address Learning".