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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. 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
C2960-X
C2960-XR
C2960-S
3850
Bidirectional stack
bandwidth
80Gbps
80Gbps
40Gbps
480Gbps
Hot-swappable stack
module
Yes
Yes
Yes
No (built-in)
Max stack members
8
8
4
9
Supports FlexStack
Yes
No
Yes
No
Supports FlexStack-Plus
Yes
Yes
No
No
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.