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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 0.5-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.