Flex Links Failover Actions - Cisco Catalyst 4500 Series Software Configuration Manual

Chapter 24 Configuring Flex Links and MAC Address-Table Move Update
Figure 24-2
Uplink
switch B
Note A static MAC address must point to a Flex Links interface that is forwarding for given VLAN. For
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.
The show mac address-table command always shows static MAC addresses as associated with the
Note
interface on which it was configured even if it may have been moved to the standby link because of a
Flex Links failover.
MAC Address-Table Move Update
In Figure
pair. Port 1 is forwarding traffic, and port 2 is in the blocking state. Traffic from the PC to the server is
forwarded from port 1 to port 3. The MAC address of the PC was learned on port 3 of switch C. Traffic
from the server to the PC is forwarded from port 3 to port 1.
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.
24-3, ports 1 and 2 on switch A are connected to uplink switches B and D through a Flex Links
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Uplink
switch C
Forwarding
(51-100)
gi2/0/8
MAC Address-Table Move Update
24-3