Flex Links Failover Actions - Cisco Catalyst 4500 series Administration Manual

Chapter 23 Configuring Flex Links and MAC Address-Table Move Update
rest on the other port. If one of the ports fail, the other active port forwards all the traffic. When the failed
port reactivates, it resumes forwarding traffic in the preferred VLANs. In addition to providing the
redundancy, this Flex Links pair can be used for load balancing. Also, Flex Links VLAN load balancing
also does not impose any restrictions on uplink switches
Figure 23-2
Uplink
switch B
A static MAC address must point to a Flex Links interface that is forwarding for given VLAN. For
Note
example, if a backup interface is forwarding VLAN X, then a static MAC address in VLAN X must point
to the backup interface. Misconfiguration might cause unexpected results.

Flex Links Failover Actions

When a Flex Links primary fails, the following important actions are taken:
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Local administrative shut down or a link that starts forwarding again due to preemption is not considered
Note
a link failure. In those cases, flush the dynamic hosts and not move them.
Static MAC addresses configured on a Flex Links member interface are moved over to the backup, if it
fails. Static MAC addresses configured on a Flex Links member interface are restored when it starts
forwarding again.
Note The show mac address-table command always shows static MAC addresses as associated with the
interface on which it was configured even if it may have been moved to the standby link because of a
Flex Links failover.
OL_28731-01
VLAN Flex Links Load Balancing Configuration Example
Forwarding
(1-50)
gi2/0/6
Switch A
Detects link failure.
Moves static unicast MAC addresses that are configured on the primary link to the standby link.
Moves dynamic unicast MAC addresses that are learned on the primary link to the standby link.
Moves the standby link to a forwarding state.
Transmits MAC address-table move updates over a new active link, if you enter the
mac move update transmit command.
Transmits dummy multicast packets over a new active interface.
(Figure
Forwarding
(51-100)
gi2/0/8
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
About Flex Links
23-2).
Uplink
switch C
23-3