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Cisco Refurbished
Original Part No : C2960S-STACK=

Catalyst 2960S Flexstack Stack Module REMANUFACTURED

Availability: In stock

Available Quantity: 1315

Delivery Time: 2 to 4 week

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    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.

    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 built-in 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. The deployment scenario on the left shows four switches that are colocated in the same wiring closet, but are not stacked. Each standalone switch on the left has two uplinks to the distribution layer switch that are combined in an EtherChannel group. The four switches on the right are stacked together with FlexStack (FlexStack links show in red). The stack has four uplinks to the distribution layer switch. Because FlexStack supports EtherChannel grouping of Ethernet interfaces across the stack members, the four uplinks are grouped together into a single EtherChannel group. All the benefits of EtherChannel grouping are retained when switches are placed into a stack.

    Figure 1. Comparison of FlexStack and Nonstacked Configurations

    Stacking Ethernet switches provides the network administrator with three major operational benefits:

     Single point of management: All switches in the stack are managed as one.

     Built-in redundancy and high availability: The high-speed FlexStack connections provide redundant communication for each stack member to every other member.

     Scalability to fit network needs: Installation of a new switch to the stack is easy. As the need for additional access ports grows, adding a new switch to an existing stack is easier and faster than adding a new standalone switch to the network.

    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. In a Layer 2 network, the logical switch will appear as a single spanning-tree entity.

    The second operational benefit that stacking provides is built-in redundancy and increased availability. Data path redundancy is built into the stacking architecture as there are two physical paths between any two stack members. Connecting stack members with the stacking cables provides data path redundancy for all stack members. Stacking increases Ethernet switch availability by providing redundancy for both the physical switch and the uplink. Because different physical switches will connect to the upstream network, losing one switch or one uplink interface does not prevent connectivity to the network. Since the logical switch has multiple uplinks, the logical switch still has network connectivity because at least one uplink is still active.

    In a logical switch, a single physical switch is acting as the stack master. The stack master manages all physical switches, including itself. If the master fails, another member automatically becomes the stack master following a well-documented election process (covered later). The configuration of the stack is preserved through a single switch failure or a reboot of all stack members. FlexStack provides 1:N redundancy for the stack master, with the ability for any physical switch to back up the acting master. (See Figure 2.)

    Figure 2. FlexStack with Redundant Links

    Flexibility of FlexStack allows for modular stacking capability. Cisco Catalyst 2960 switches can be added to a stack at any time by adding the optional FlexStack module. As the demand for Ethernet access ports increases, Cisco Catalyst 2960 switches can be stacked together either to create a new stack or to add new Cisco Catalyst 2960 switches to an existing stack. This flexibility provides investment protection for the network administrator, who can add additional stack members as needed.

    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.

    Stacking and Clustering

    Stacking is not clustering. Clustering is a technology available on Cisco Catalyst fixed Ethernet switches that allows the network administrator to use a single public IP address to manage multiple physical switches. Clustering was created to assist network administrators by having a single point of management as well as in preserving valuable public IP addresses needed to manage the Ethernet switches. Stacking is much more than a single point of management and IP address preservation because it offers redundancy, availability, and ease of management. Cisco Catalyst 2960 supports clustering as well as stacking.

    What Are FlexStack and FlexStack-Plus?

    FlexStack is the name of the stacking technology used by the Cisco Catalyst 2960-S Series of fixed Ethernet switches. FlexStack is specific to Cisco Catalyst 2960-S switches, and only Cisco Catalyst 2960-S Series Switches use FlexStack.

    FlexStack-Plus is the name of the stacking technology used by the Cisco Catalyst 2960-X and 2960-XR Series of fixed Ethernet switches. FlexStack-Plus is specific to the 2960-X and 2960-XR Series of switches.

    Both FlexStack and FlexStack-Plus require a specific external module in order to stack together. In addition to theFlexStack and FlexStack-Plus modules (Figure 3), a special FlexStack cable is also required to interconnect the modules. There are two different modules for FlexStack. The FlexStack module (PID: 2960S-STACK) is for 2960-S, and the FlexStack-Plus module (PID: 2960X-STACK) is for 2960-X and 2960-XR. These two modules are different sizes and cannot be inserted into the wrong 2960 model. Each FlexStack module supports two FlexStack ports. The FlexStack module is inserted into the rear of the Cisco Catalyst 2960 switch. Two FlexStack cables, inserted into the FlexStack module, provide data path redundancy for traffic flowing across the stack. Using FlexStack cables, the physical members of the stack form a ring, providing the built-in redundant data path for each member of the stack. FlexStack and FlexStack-Plus share the same stack cable types. You do not need different FlexStack cable types for FlexStack and FlexStack-Plus.

    FlexStack and FlexStack-Plus are optional. In order for a 2960 switch to stack, a separate FlexStack or FlexStack-Plus module (depending upon your exact 2960 model) must be inserted in the rear of the switch. Without this module, stacking cannot function. Figure 3 shows a FlexStack-Plus module to be inserted into the rear of a Cisco Catalyst 2960-X switch. All FlexStack module types are hot swappable.

    Cisco Catalyst 2960 switches running FlexStack and FlexStack-Plus use a hop-by-hop method of transferring Ethernet packets across the stack. Packets traverse the stack by going from one member to another over the FlexStack links until the packet reaches its destination. This is a behavior similar to that of multiple standalone Ethernet switches forwarding packets from one switch to another.

    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. The FlexStack protocol is the same for FlexStack on the 2960-S models and the 2960-X and XR models. Because it is the same protocol for all models of 2960, the different 2960 model types can be stacked together.

    Figure 3. FlexStack Module Inserted into Rear of 2960-X

    A single FlexStack connection between two 2960 stack members is a full-duplex 10Gbps connection. A single FlexStack-Plus connection between two 2960-X members is full-duplex 20Gbps. Each Cisco Catalyst 2960-S and 2960-X and 2960-XR member supports two FlexStack connections, which doubles the line rate. Each FlexStack member can simultaneously send and receive Ethernet traffic over both stack links at line rate, effectively giving 40Gbps of stack bandwidth per 2960-X member and 20Gbs of stack bandwidth per 2960-S member. When two or more 2960-X members are stacked together, the effective stack bandwidth is 80Gpbs because each member is capable of sending and receiving 40Gbps simultaneously. Same for 2960-S, the effective stack bandwidth is 40Gbps because multiple members are sending and receiving 20Gbps simultaneously. (See Table 1.)

    Table 1. Comparison of FlexStack-Plus, FlexStack and StackWise-480

    Stacking Item





    Bidirectional stack bandwidth





    Hot-swappable stack module




    No (built-in)

    Max stack members





    Supports FlexStack





    Supports FlexStack-Plus





    Mixed Stacks: FlexStack and FlexStack-Plus

    The 2960-S and 2960-X support a mixed stack of 2960 models. All these 2960 models run the FlexStack protocol, allowing them to be stacked together into a single stack. The exception is the 2960-XR does not stack with either the 2960-X or the 2960-S. The 2960-XR has the IP-Lite feature set, and this is not compatible with the LAN Base feature set on the 2960-X and 2960-XR. Table 2 shows all the allowed mixed stack combinations. What is crucial is the Cisco IOS Software feature set. All 2960 models with the LAN Base Cisco IOS Software feature set can stack together.

    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




    2960-X LAN Base




    2960-S LAN Base




    Table 3 shows FlexStack-Plus backward compatibility and performance of 2960-X and 2960-XR with the 2960-S switches.

    Table 3. Backward Compatibility

    Scale of Mixed Stack Combination

    Max Stack Bandwidth

    Stack Limit

    Cisco IOS Software Feature Set

    2960-XR IP Lite



    IP Lite

    2960-X LAN Base



    LAN Base

    2960-X, 2960-S LAN Base



    LAN Base

    When the 2960-S and 2960-X members are stacked together, the entire stack (even the 2960-X members) fall back to FlexStack capabilities. Mixing 2960 members limits the max stack members to four, and 20Gbps stack bandwidth per member, and 40Gbps per stack.

    FlexStack Cabling

    Special cables are used to connect Cisco Catalyst 2960 Series Switches together in a stack. These special FlexStack cables can only be used to stack Cisco Catalyst 2960 switches with other Cisco Catalyst 2960 switches that support FlexStack. Figure 4 shows a picture of two FlexStack cables connected to a fully inserted FlexStack module. Notice how the tabs on the cables are on opposite sides of each other. The FlexStack cables are keyed as well. Besides the tabs needing to be away from each other, the keying of the metal portion of the connector prevents the cable from being connected incorrectly.

    Figure 4. FlexStack Module with Cables

    When each member in the stack has two operational FlexStack links, then the stack is operating in a fully redundant mode. The dual FlexStack connections from each member to two other members are what provide the redundancy. Should any single FlexStack connection break or cease to operate, then the switches in the stack will use the remaining FlexStack connection that is provided.

    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. This stack provides only half of the possible bandwidth between members and does not have redundant connections. Only the middle member has full stack bandwidth. The top and bottom members are operating at half the fully redundant stack bandwidth. The fully redundant stack bandwidth for 2960-X and 2960-XR is 40Gbps per member. The fully redundant stack bandwidth for 2960-S is 20Gbps per member.

    Figure 6. Nonredundant Three-Member Stack

    Three different FlexStack-Plus cable lengths are available, as shown in Table 4.

    Table 4. FlexStack Cable Lengths

    Product ID




    0.5 meters

    This is the default cable that ships with the FlexStack or FlexStack-Plus module.


    1.0 meters



    3.0 meters


    The different lengths allow for deployment flexibility. Figure 7 shows how to stack four switches using only the 0.5-meter cables. The stack member connections are interweaved using the stack cables. No cable extends more than two stack members. The interweaving of the stack links still provides redundant connections for the stack.

    Figure 7. Four-Member Stack with 0.5-Meter Cables

    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 0.5-meter cable can be used to connect two Cisco Catalyst 2960 switches that are 4 rack units away from each other. In a stack of four, with all four members racked directly on top of each other, 0.5-meter cables can be used to connect all stack members. When stack members are more than 4 rack units apart, then longer stack cables are required.

    FlexStack Protocol

    FlexStack protocol allows every stack member to be in constant communication with the adjacent member and with the stack master. Each member is aware of the operational state of every stack port in the stack. FlexStack protocol is used to detect new member additions as well as member removal. The operational status for all stack members and their interfaces is communicated to each member through the FlexStack protocol.

    The 2960-X with FlexStack-Plus has better reaction time to changes in the operation state of the FlexStack links than the 2960-S with FlexStack. The 2960-X has special hardware that is capable of detecting the change in the stack port operational state. The special hardware is capable of changing how packets are forwarded across the stack. This is the FlexStack link recovery time. Because it is being done in hardware, it is very fast. For packets traversing across the FlexStack-Plus stack, the traffic recovery time is 100ms or less.

    The 2960-S with FlexStack is not as fast. The recovery time for loss of a FlexStack link is 1 to 2 seconds. On the 2960-S with FlexStack, the change in stack port operational state is managed by the CPU in software. Because it is in software, the operational state change has to be processed, and the software has to reprogram the forwarding logic to forward traffic around the now nonoperational FlexStack link.

    Role of the Stack Master

    The stack master controls the configuration and is the central point for management. All Layer 2 protocol traffic (for example, VLAN Trunking Protocol [VTP], Dynamic Trunking Protocol [DTP], Cisco Discovery Protocol, and Link Layer Discovery Protocol [LLDP]) is forwarded to the master regardless of where the protocol packet ingresses. The master will also transmit all Layer 2 protocol packets. If the egress interface is on another member, then the protocol packet is passed from the master along the stack interfaces to the destination member.

    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. The master pushes new Cisco IOS Software images to all members. Each member stores a copy of the Cisco IOS Software image on its local Flash.

    FlexStack LED Operation

    The LEDs on the front of the Cisco Catalyst 2960-S, 2960-X, and 2960-XR can be used to view stack operation. When multiple Cisco Catalyst 2960 switches are stacked together, only the stack master will have the “MSTR” LED solid green. Other members of the same stack will have this LED dark.

    To find the switch member number, press the mode button until the stack LED goes green. At this point the LEDs over the Ethernet ports are used. The port number matching the member will start to blink. For member 2, the LED for port 2 will blink. For member 3, port 3 will blink. Depending upon the number of members in the stack (up to four for 2960-S and up to 8 for 2960-X), the other ports will go solid green. This allows the network administrator to see the number of stack members just from the LEDs over the ports.

    When a switch is operating standalone, the MSTR LED will be solid green.

    FlexStack Details

    Inserting the FlexStack Module

    The FlexStack module will insert easily into the slot. Just before it is fully inserted, there will be “minor” resistance. This is normal. Push the module completely into the switch chassis. Tighten the screws no more than “finger” tight. The screws are meant to keep the module from slipping out, not to maintain stack link connectivity. Finger tight is sufficient to maintain a fully operational stack connection.

    FlexStack Redundant Power

    Redundant power for each Cisco Catalyst 2960-S and 2960-X is provided by the Cisco Redundant Power System 2300 (Cisco RPS 2300). The 2960-XR has its own dual redundant power supplies and does not support the RPS2300. If the RPS2300 is being used to provide redundant power, then each stack member must have its own connection to the Cisco RPS 2300.


    Additional Information

    Weight (Kg) 1
    Datasheet URL http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-2960-x-series-switches/white_paper_c11-728327.html
    Condition Refresh
    Module Type Switching Module



    AED 0