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Cisco IE 3010 Switch Software Configuration Guide
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Chapter 20 Configuring Flex Links and the MAC Address-Table Move Update Feature
Understanding Flex Links and the MAC Address-Table Move Update
because the FastEthernet0/2 is blocked. When the active link, FastEthernet0/1 goes down, the backup
port, FastEthernet0/2, begins forwarding. You do not need to send any proxy reports because the
multicast data is already being forwarded by the upstream router. By leaking reports to the backup port,
a redundant multicast path has been set up, and the time taken for the multicast traffic convergence is
minimal.
MAC Address-Table Move Update
The MAC address-table move update feature allows the switch to provide rapid bidirectional
convergence when a primary (forwarding) link goes down and the standby link begins forwarding traffic.
In Figure 20-3, switch A is an access switch, and ports 1 and 2 on switch A are connected to uplink
switches B and D through a Flex Link pair. Port 1 is forwarding traffic, and port 2 is in the backup state.
Traffic from the PC to the server is forwarded from port 1 to port 3. The MAC address of the PC has
been learned on port 3 of switch C. Traffic from the server to the PC is forwarded from port 3 to port 1.
If the MAC address-table move update feature is not configured and port 1 goes down, port 2 starts
forwarding traffic. However, for a short time, switch C keeps forwarding traffic from the server to the
PC through port 3, and the PC does not get the traffic because port 1 is down. If switch C removes the
MAC address of the PC on port 3 and relearns it on port 4, traffic can then be forwarded from the server
to the PC through port 2.
If the MAC address-table move update feature is configured and enabled on the switches in Figure 20-3
and port 1 goes down, port 2 starts forwarding traffic from the PC to the server. The switch sends a MAC
address-table move update packet from port 2. Switch C gets this pa cket on port 4 and immediately
learns the MAC address of the PC on port 4, which reduces the reconvergence time.
You can configure the access switch, switch A, to send MAC address-table move update messages. You
can also configure the uplink switches B, C, and D to get and process the MAC address-table move
update messages. When switch C gets a MAC address-table move update message from switch A,
switch C learns the MAC address of the PC on port 4. Switch C updates the MAC address table,
including the forwarding table entry for the PC.
Switch A does not need to wait for the MAC address-table update. The switch detects a failure on port 1
and immediately starts forwarding server traffic from port 2, t he new forwarding port. This change
occurs in 100 milliseconds (ms). The PC is directly connected to switch A, and the connection status
does not change. Switch A does not need to update the PC entry in the MAC address table.