24-3
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 24 Configuring Flex Links and MAC Address-Table Move Update
MAC Address-Table Move Update
Figure 24-2 VLAN Flex Links Load Balancing Configuration Example
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:
• 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.
Note Local administrative shut down or a link that starts forwarding again due to preemption is not considered
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.
MAC Address-Table Move Update
In Figure 24-3, ports 1 and 2 on switch A are connected to uplink switches B and D through a Flex Links
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.
Switch A
Uplink
switch B
gi2/0/6
Forwarding
(1-50)
gi2/0/8
Forwarding
(51-100)
Uplink
switch C
201398
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