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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter20 Configuring Flex Link s an d the MAC Address-Table Move Update Feature
Understanding Flex Links and the MAC Add re ss-Table Move Update
Figure20-2 VLAN Flex Links Load Balancing Configuration Example
MAC Address-Table Move Update
The MAC address-table move update feature allows the switch to provide rapid bidirectional
convergence when a primary (for war ding) link goes d o wn and the sta ndb y lin k be gins forw ard ing tra f f ic.
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 s witc h C rem oves 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 po rt 4 a nd imm ed iately
learns the MAC address of the PC on port 4, which reduces the reconvergence time.
You can configure the access switch, swi tch 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 f rom swit ch A,
switch C learns the MAC address of the PC on port 4. Switch C updates the MAC addres s ta ble,
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 port1
and immediately starts forwarding server traffic from port 2, t he new f orward in g port. Th is ch an ge
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.
Switch A
Uplink
s
witch B
gi2/0/6
Forwarding
gi2/0/8
Not Forwarding
Uplink
switch
C
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