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FlexLink+ is supported only on Layer 2 trunk ports and port channels and is not supported on interfaces configured on Layer 3 ports and on VLANs.
 Note |
FlexLink+ is not supported on port channels configured with access mode. |
The following sections provide information about FlexLink+
The FlexLink+ feature enables the user to configure a pair of a Layer 2 interfaces (trunk ports or port channels) where one interface is configured to act as a backup to the other. FlexLink+ provides an alternative solution to the Spanning Tree Protocol (STP) when you require simple link redundancy between two network nodes. STP is a complete solution that provides link redundancy and prevents loops in the network. If you need fast link redudancy between two nodes in the network, it is simpler and quicker to use FlexLink+. Flexlinks are typically configured in service provider or enterprise networks where customers do not want to run STP on the device. If the device is running STP, Flexlinks are not necessary because STP already provides link-level redundancy or backup.
In FlexLink+, when one of the links is up and forwarding traffic, the other link is in standby mode, ready to begin forwarding traffic if the active link shuts down. If the primary link shuts down, the standby link starts forwarding traffic. When the active link comes back up, it goes into standby mode and does not forward traffic. When FlexLink+ is configured on a switch stack each of the two L2 interfaces in the pair can be on the same device or on different devices.
In the following figure, ports 1 and 2 on switch A are connected to uplink switches B and C. Because they are configured with FlexLink+, only one of the interfaces is forwarding traffic; the other is in standby mode. If port 1 is the active link, it begins forwarding traffic between port 1 and switch B; the link between port 2 (the backup link) and switch C is not forwarding traffic. If port 1 goes down, port 2 comes up and starts forwarding traffic to switch C. When port 1 comes back up, it goes into standby mode and does not forward traffic; port 2 continues forwarding traffic.
If STP is configured on the uplink switch interfaces that connect to the FlexLink+ ports (Switch B and Switch C in this case), we recommend running the spanning-tree portfast trunk command on such uplink switch interfaces, for faster convergence.
Flexlink+ includes an optimization for improved multicast traffic convergence. The optimization uses Layer 2 multicast snooping mechanisms and requires that the uplink switches connected to the Flexlink+ configured ports have the same Layer 2 multicast snooping feature enabled.
Note |
For IPv4 multicast IGMP snooping is on by default. If IGMP snooping needs to be disabled on the uplink switches it must also be disabled on the Flexlink+ host switch. Otherwise IGMP reports may be looped around the active and standby Flexlink+ ports leading to excessively high CPU utilization. |
The following sections provide information on how to configure Flexlink+.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
enable Example: |
Enables privileged EXEC mode. Enter your password if prompted. |
| Step 2 |
configure terminal Example: |
Enters global configuration mode. |
| Step 3 |
interface interface-id Example: |
Specifies the interface, and enters interface configuration mode. |
| Step 4 |
switchport trunk allowed vlan vlan-list Example: |
Configures the allowed VLANs for an interface. |
| Step 5 |
switchport mode trunk Example: |
Configures the interface as a Layer 2 trunk. |
| Step 6 |
rep segment segment-id edge no-neighbor primary Example: |
Specifies that the port is the primary edge port where you can configure the active port of FlexLink+. A segment has only one primary edge port. |
| Command or Action | Purpose | |||
|---|---|---|---|---|
| Step 1 |
enable Example: |
Enables privileged EXEC mode.
|
||
| Step 2 |
configure terminal Example: |
Enters global configuration mode. |
||
| Step 3 |
interface interface-id Example: |
Specifies the interface, and enters interface configuration mode. |
||
| Step 4 |
switchport trunk allowed vlan vlan-list Example: |
Configures the allowed VLANs for an interface. |
||
| Step 5 |
switchport mode trunk Example: |
Configures the interface as a Layer 2 trunk. |
||
| Step 6 |
rep segment segment-id edge no-neighbor preferred Example: |
Specifies the segment edge as one with no external REP neighbor. Specifies that the port is the standby port for FlexLink+.
|
The following sections provide examples for configuring FlexLink+.
This example shows how to configure the active port for FlexLink+.
Device# interface Port-channel2
Device(config-if)# switchport trunk allowed vlan 20-23,40,41
Device(config-if)# switchport mode trunk
Device(config-f)# rep segment 1023 edge no-neighbor primary
This example shows how to configure the standby port for FlexLink+.
Device# interface Port-channel7
Device(config-if)# switchport trunk allowed vlan 20-23,40,41
Device(config-if)# switchport mode trunk
Device(config-f)# rep segment 1023 edge no-neighbor preferred
This table provides release and related information for features explained in this module.
These features are available on all releases subsequent to the one they were introduced in, unless noted otherwise.
|
Release |
Feature |
Feature Information |
|---|---|---|
|
Cisco IOS XE Gibraltar 16.12.1 |
FlexLink+ |
The FlexLink+ feature enables the user to configure a pair of a Layer 2 interfaces (trunk ports or port channels) where one interface is configured to act as a backup to the other interface. |
|
Cisco IOS XE Amsterdam 17.2.1 |
VLAN Load Balancing for FlexLink+ Preemption for VLAN Load Balancing FlexLink+ Dummy Multicast Packets |
VLAN load balancing feature was introduced on FlexLink+. VLAN load-balancing allows you to configure a FlexLink+ pair so that both ports can simultaneously forward the traffic for some mutually exclusive VLANs. You can trigger VLAN load balancing either by manually triggering it or by configuring a preempt delay. When a primary link fails, FlexLink+ transmits dummy multicast packets over the new active interface. These packets help learn the source MAC address. |
Use Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.
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