Resilient Links

This chapter provides an overview, guidelines, and other important information about how to implement resilient links on Layer 2 Switching Modules in your Switch 4007 system.

The chapter covers these topics:

• Resilient Links Overview

• Key Concepts

• Key Guidelines for Implementation

• Resilient Link Define and Modify

• Resilient Link State

• Resilient Link Active Port

• Resilient Link Remove

After you log in to the Management Module (EME) and connect to a slot that houses a Layer 2 Switching Module, you can manage resilient links from the bridge link menu of the Administration Console. For more information on specific commands, see the Switch 4007 Command Reference Guide.

The management interfaces display "cb9000" and refer to the Management Module as the Enterprise Management Engine (EME) because the heritage of the Switch 4007 is the CoreBuilder^® 9000 switch.

Resilient links protect your network against an individual link or device failure by providing a secondary backup link that is inactive until it is needed. A resilient link comprises a resilient link pair that contains a main link and a standby link. If the main link fails, the standby link immediately takes over the task of the main link. Figure 12 shows a resilient link pair.

Figure 12 Resilient Link Pair

Under normal network conditions, the main link carries your network traffic. If a signal loss is detected, the device immediately enables the standby link so that it carries the data and sends a trap to the network management station to alert you of the signal loss. The standby port assumes the profile and carries the network traffic of the main port.

If the main link has a higher bandwidth than its standby link, traffic is switched back to the main link, provided that no loss of link is detected for 2 minutes. Otherwise, you must manually switch traffic back to the main link.

Switchover time to the backup link takes less than 1 second, ensuring no session timeouts and therefore seamless operation.

To keep you informed about network activity, configure the module to generate an SNMP trap whenever a switchover from one link to the other occurs or whenever the link state (up or down) of either link in the resilient pair changes. For more information about how to configure and enable SNMP traps, see Chapter 23.

Features

You can configure these features for resilient links:

• Define - Specify a name and the ports that you want to associate with the link.

• Link state - Enable or disable a resilient link pair.

• Active port - Define either port as the port that carries network traffic.

• Modify - Change the name and ports that are associated with a previously defined resilient link.

• Remove - Delete one or more resilient links from the module.

• Resilient links enable you to protect critical links and prevent network downtime if those links fail.

• 3Com recommends that you implement resilient links in these network configurations:

  • Switch-to-switch downlinks from the wiring closet to the data center. The resilient link pair must terminate on a Layer 2 data-center switch.

  • Server-to-switch connections in the data center and campus interconnect areas.

• When you define a resilient link pair, you define:

  • The main port - The port on which network traffic runs under normal operation.

  • The standby port - The port to which network traffic shifts if the main port fails.

• You can define either the main port or the standby port as the active port, that is, the port that is carrying network traffic. The main port is usually defined as the active port.

Consider these important factors when you implement and configure resilient links.

General Guidelines

• Create resilient links before you define your VLANs. If you plan to create resilient links to be part of a VLAN, create the resilient links before you create the VLAN.

• You must reboot the module when you finish defining the resilient links. (You can define multiple links in one define operation.)

• If you perform an nvData reset operation, the module erases all previous resilient link settings.

• Resilient links are a point-to-point technology; they do not react to "downstream" network failures.

• Inactive links take up ports but do not add to network capacity.

• You cannot set up resilient link pairs if the Spanning Tree Protocol (STP) is enabled.

• You cannot disable ports that are part of a resilient link unless a link failure occurs.

• You need to define a resilient link only at one end of the link.

• If an active standby port fails and you have defined a link on the main port, the ports toggle and the main port becomes active.

To define or modify a resilient link, specify the ports that you want to be in the resilient link.

Important Considerations

• When you define or modify a resilient link, you specify the name of the link and the ports that you want to associate with the link. You can specify all ports in one define operation.

• You can define more than one resilient link at a time, so that you reboot the module only once.

• When you create a resilient link that includes ports that are part of a VLAN, those ports are removed from the VLAN. You must modify the VLAN to add the new bridge port. This consideration does not apply to the Default VLAN. All ports are part of the Default VLAN.

• If you have already defined other resilient links on your module, you cannot select ports that are part of an existing resilient link to be part of an additional resilient link pair.

• You cannot select a trunked port nor the trunk itself as part of a resilient link.

• The resilient link name can be up to 32 characters long.

See the Switch 4007 Command Reference Guide for a complete description of the resilient link commands.

You can enable or disable one or more resilient link pairs with a single command.

Important Considerations

• When the link state is enabled, the resilient link can transmit and receive traffic.

• When the link state is disabled, the resilient link no longer transmits or receives frames.

The active port is the port that carries traffic. You can designate either the main port or the standby port as the active port.

Important Considerations

• Only one port in a resilient link pair is active at a time.

• By default, the module defines the main port in a resilient pair as the active port when you reboot, unless the main link is down.

• If the main link is of equal or lesser bandwidth than the active standby link, the switchover back to main link is not automatic. If you want the main link to be active, you must configure it as the active port.

You can remove one or more resilient links with a single remove command.

Important Consideration

• After you remove a resilient link pair, you must reboot the module.