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Cisco Stacking Switches—StackWise and StackWise Plus

Stackable Switch

Allows access to all switches with a single IP address
Provides the means to manage the stack via CLI or MIB
Can connect all switches in a physical ring topology
Traffic flows in either direction of the ring, some Resiliency
Automatic Master selection & backup 1:N
Automatic IOS versioning and Update!
Automatic configuration of new members
Automatic unit replacement (configuration of old switch retained)
Stateful switch over in case of master failures
Ring resiliency similar to FDDI, provides HA and Resiliency
Sub-millisecond Master failover
Smart Multicast
Cross-stack features (Etherchannel and QoS)

Cisco StackWise (Plus)


Logical and physical ring architecture of the Catalyst 3k
Comprises two 16 Gbps counter-rotating rings
-Data on both rings when fully connected:
Stackwise-32 Gbps
Stackwise Plus-64 Gbps

Internal Connection:

On Cisco 3750V2, 3750G: The Stack Ring is the switching fabric
Cisco 3750E, 3750X: The Stack Ring only interconnects the individual Switch

Understanding the Stack Cable


Eight TX/RCV pairs per ring
That is 16 pairs (8 channels per ring)

Each TX/RCV pair has 2 traces that use differential signaling.
That is 32 traces in total

Each TX/RCV pair runs at 2.5 Gbps
8B/10B encoding is used.
(for every ten bits sent, eight bits are data and two bits are overhead)

Understanding the Stack Ring Speed
16 Channels x 2.5 Gbps x 8B/10B = 32Gbps
Or bidirectional 16 Gbps per cable = 32Gbps
Or Two Rings running at 16Gpbs each = 32Gbps


Stackwise Vs Stackwise Plus
Spatial Reuse

Note: These are packets not tokens. There is only 1 token per ring.

Ring Healing

 The switch fabric or port ASIC closest to cable detects link down
-Criteria is coding violations in a period of time
-Loss of at most one packet that was being transmitted when ring broke
-Just microseconds for hardware to detect failure
 Each switch signals a bad link to stack its partner
 Both ends of the cable loop back on themselves

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