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Cisco Catalyst 2960-S, 2960-X, and 2960-XR Stacking

with FlexStack and FlexStack-Plus Technology:

Description, Usage, and Best Practices

Introduction

Cisco

FlexStack and FlexStack-Plus stacking for Cisco Catalyst

2960-S, 2960-X and 2960-XR Series Switches

provides a true stacking solution, with all switches in a FlexStack or FlexStack-Plus stack acting as a single

switching unit. FlexStack and FlexStack-Plus provide a unified data plane and single configuration for a group of

stacked Cisco Catalyst 2960-S, 2960-X, and 2960-XR switches.

FlexStack and FlexStack-Plus lower the total cost of ownership with built-in 1:N redundancy, high availability, and

preprovisioning, not available in standalone switches. High-availability features such as EtherChannel and

FlexLinks will work across stack members, increasing uptime and network connectivity.

FlexStack-Plus is based on FlexStack. FlexStack was introduced on the 2960-S in 2010. FlexStack-Plus is being

introduced in 2013 with the 2960-X and 2960-XR models of Cisco Catalyst Ethernet switches.

FlexStack-Plus is an improvement over FlexStack because it doubles the speed of the stack bandwidth and allows

for more members to join the stack. The FlexStack-Plus bandwidth for a single stack member is 40Gbps compared

to 20Gbps with FlexStack. With multiple stack members, the FlexStack-Plus bandwidth is 80Gbps, and the

FlexStack bandwidth is 40Gpbs. With FlexStack-Plus technology, eight 2960-X or XR members can be joined into

a single stack. With FlexStack only four 2960-S members could be joined into a single stack.

FlexStack-Plus is backward compatible with 2960-S and FlexStack. Mixing 2960-X and 2960-S members in a stack

is supported. When the stack membership is mixed with 2960-X and 2960-S models, FlexStack-Plus falls back to

FlexStack capabilities of 40Gbps stack bandwidth and four members maximum per stack.

For the remainder of this document, the term 2960 will apply to all the 2960-S, 2960-X, and 2960-XR switches

unless explicitly called out. Also, the term FlexStack will refer to FlexStack-Plus as well as FlexStack unless

explicitly called out.

The differences between FlexStack and FlexStack-Plus are identified in Table 1.

For more information about the 2960-X and 2960-XR, see the Campus LAN Access Switches product pages on

Cisco.com. “Campus LAN Access Switches on Cisco.com”

As part of the Borderless Network architecture, FlexStack and FlexStack-Plus allows scalable provisioning and

management to deploy any number of switches quickly and easily.

Summary of content (25 pages)

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White Paper Cisco Catalyst 2960-S, 2960-X, and 2960-XR Stacking with FlexStack and FlexStack-Plus Technology: Description, Usage, and Best Practices Introduction ® ® Cisco FlexStack and FlexStack-Plus stacking for Cisco Catalyst 2960-S, 2960-X and 2960-XR Series Switches provides a true stacking solution, with all switches in a FlexStack or FlexStack-Plus stack acting as a single switching unit.
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Why Stack Ethernet Switches? Stacking Ethernet switches reduces the network administrator’s total cost of ownership. The cost of maintaining the network is decreased because there are fewer devices to manage, and the network uptime is increased with builtin redundancy. Figure 1 shows two ways to deploy Ethernet switches at the access layer. In each case four switches are connected to a Cisco Catalyst 6509 Switch.
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The first operational benefit is fewer devices to manage. Multiple physical switches in a stack appear as a single logical switch. This eases management overhead because there are fewer devices in the network to manage. A single IP address is used to manage the logical switch. All manageable entities (for example, Ethernet interfaces and VLANs) on all physical switches can be configured and managed from the logical switch. The logical switch will appear as a single entity in the network.
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Adding members to a stack and replacing physical units are much easier when multiple switches are combined into a FlexStack group. Since the stack retains the configuration, there is no need to back up the configuration prior to removing the switch. Conversely, when a new member is inserted into the stack, the configuration of the stack is pushed to the new member. The network administrator need not explicitly recover the switch configuration since the stack took care of it.
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Switches in a stack communicate with each other using the FlexStack protocol. The FlexStack protocol allows the FlexStack members to behave as one logical switch. The FlexStack protocol runs on each member. The FlexStack protocol is used by the master switch to manage the other members. The master tracks the presence of each ® member, the member’s availability, the Cisco IOS Software image, and the status of each member’s FlexStack connections.
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Table 2. Allowed Mixed Stack Combinations Mixed Stack Combination 2960-XR IP Lite 2960-X LAN Base 2960-S LAN Base 2960-XR IP Lite Yes No No 2960-X LAN Base No Yes Yes 2960-S LAN Base No Yes Yes Table 3 shows FlexStack-Plus backward compatibility and performance of 2960-X and 2960-XR with the 2960-S switches. Table 3.
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Deployment Topologies Figure 5 shows a three-member stack with full bandwidth and with redundant FlexStack connections. Figure 5. Fully Redundant Three-Member Stack When one FlexStack link is not present, the stack still functions. Figure 6 shows a stack with incomplete FlexStack cabling. In Figure 6, all data traffic passes through the middle member. This stack is operating in a nonredundant mode.
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Figure 8 shows the conventional cabling deployment. The 3.0-meter cable is used to complete the redundant ring connection by connecting the top member with the bottom member. The other connections connect to directly adjacent members using the 0.5-meter cables. The 3.0-meter cable is not the default cable shipped for FlexStack and must be ordered. See the Cisco Catalyst 2960-S, 2960-X, or 2960-XR data sheet for ordering information. Figure 8. Four-Member Stack with 3.0-Meter Cable The 0.
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The same behavior is seen for management traffic. Simple Network Management Protocol (SNMP), HTTP, Telnet, and Secure Shell (SSH) Protocol type of management traffic is all forwarded to the master regardless of the ingress interface. The response from the master is sent through the stack to the destination interface. On configuration changes, the stack master pushes a copy of the configuration to every member. This way all members have a copy of the saved configuration. Stack upgrades occur on the master.
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FlexStack Operations To see FlexStack operation and member status, use the Cisco IOS Software CLI command “show switch.” This command gives the basic information, including number of members, which member is the master, and state of all members. The following is a sample output of the command for a stack of 2960-S members: C2960S-48# show switch Switch/Stack Mac Address : 0022.bdc4.
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Fully redundant three-member stack (Figure 5): C2960-FullRedundant#show switch stack-ports Switch # Port 1 Port 2 -------- ------ ------ 1 Ok Ok 2 Ok Ok 3 Ok Ok C2960-FullRedundant#show switch neighbors Figure 5: All stack ports are operational. Shows the member number of the Switch # Port 1 Port 2 neighbor on a stack link. -------- ------ ------ For example, member 1 connects 1 2 3 to member 2 on port 1 and member 2 3 1 3 on port 2.
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Making a Specific Switch the Stack Master and Master Election Rules Stack Election Rules When multiple physical members are present in the stack, one of the members will be elected as the stack master. There can only be one master and up to three backups 1:3. The election rules used by FlexStack in choosing a master are applied in this order: 1. Switch that is the current master 2. Switch with higher priority 3. Switch that has configuration file 4. Switch with longest uptime 5.
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For brand-new switches, with no configuration, all powered at the same time, the switch with the lowest MAC address will be the master. It is not practical to orient and deploy switches in a stack based on MAC address. To create a new stack with the correct physical member as the master, the network administrator must use the “uptime” rule. To reliably make any new switch the master, it must be powered up first.
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Configuring a Backup Master It is a good practice to configure another switch to be the backup should the primary master fail. Configuring a backup master enables a predictable master election in case of primary master failure. To configure a secondary (or backup) master, assign a priority value less than that of the primary master but greater than that of the other members. In the example just given, the primary master has priority 14, and all other members have priority 1.
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It is recommended that FlexStack operate in a fully redundant mode. In order to add a member to an existing stack, at least one FlexStack link must be disconnected, causing the existing stack to operate in nonredundant mode. This disconnection will cause a minor traffic outage across the stack. Traffic will resume while the stack is in nonredundant mode. The network administrator does not need to connect the FlexStack link in a fully redundant mode for traffic to flow.
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Figure 9. Adding a New Member to an Existing Stack If all went well, traffic on the exiting members was minimally interrupted. There were at least two interruptions. The first occurred when the FlexStack cable was removed in step 3. The other interruption occurred when the new switch joined the stack after being powered on (step 7). In between the two interruptions, traffic will continue to be switched over the existing members and the operational FlexStack links.
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If the network admin chooses not to “clean up” the configuration after a member has been removed, the configuration will remain the running-config and the startup-config for the stack. This extra configuration will make the configuration file “config.text” larger than it should be. In a switch replacement situation, replacing a member switch with an identical model is very convenient with FlexStack stacking. FlexStack remembers the member model number, but not the MAC address.
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Here is another example showing how to update a FlexStack stack that has a mix of 2960-S and 2960-X models. The same “archive download-sw” command is used. This time, two Cisco IOS Software images are identified on the command line. Since the 2960-S runs a different Cisco IOS Software image from the 2960-X, two different images are required. Even though two separate images are required, it is recommended that both images be on the same release. Keeping members on the same release is important.
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C2960-48#show switch Switch/Stack Mac Address : 0022.bdc4.1d80 H/W Switch# Role Mac Address Priority Version Current State ---------------------------------------------------------*1 Master 0022.bdc4.1d80 1 1 Ready 2 Member 0022.bdc4.2300 1 1 Ready 3 Member ec30.912e.
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C2960-48(config-if-range)# switchport mode trunk C2960-48(config-if-range)# exit C2960-48(config)# !!!!! C2960-48(config)# !! now configure the access ports.
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Figure 10. Four-Member Stack with Two Uplinks FlexStack and FlexStack-Plus Comparison with StackWise Plus and StackWise-480 ® The FlexStack and FlexStack-Plus feature is based on StackWise Plus. For those network administrators familiar with managing Cisco Catalyst 3750-E or 3750-X stacks running StackWise Plus, managing FlexStack is very similar. There are some differences between FlexStack, FlexStack-Plus, and StackWise Plus. This section will describe the similarities as well as the differences.
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Stack Features Cisco Catalyst 2960-S FlexStack Stacking Cisco Catalyst 2960-X FlexStack-Plus Stacking Cisco Catalyst 3750-X StackWise Plus Cisco Catalyst 3850 StackWise- 480 Dynamic ring load balancing No No Yes Yes Stack convergence 1-2 seconds 100 milliseconds Few milliseconds Few milliseconds Stack link failure detection Software Hardware Hardware Hardware Stack quality of service (QoS) Applied hop by hop Applied hop by hop Applied on ingress Applied on ingress Management Single
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With StackWise-480, once a packet is on the ring, it is guaranteed to be delivered to the destination interface. Add to this that StackWise-480 rings will dynamically load balance, and you can see that ring congestion is not an issue on StackWise-480. Troubleshooting Tips and Operational Details FlexStack Member Addition When a new switch joins an existing stack (that is, a stack that has already elected a master), then the new switch will be rebooted after it joins.
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Figure 12 shows a stack without redundant connections. When the FlexStack link indicated by B breaks, the FlexStack will break into two logical switches. The top two members will form one logical stack with two members, and the other logical stack will contain a single member. Figure 12. Broken Stack Since the stack in the connection in Figure 12 has broken into two, only two members will have their stack port status shown. The third member has been removed from the stack.
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Conclusion FlexStack and FlexStack-Plus technology provides network administrators the ease of use for managing multiple switches. Cisco Catalyst 2960-S, 2960-X, and 2960-XR switches are the fully featured Layer 2 switches that use FlexStack and FlexStack-Plus. FlexStack and FlexStack-Plus have built-in hardware redundancy along with built-in ease of use. Printed in USA © 2013 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information.