Lab Objective
Configure two physical switches as a StackWise Virtual pair using a dedicated SVL connection, verify they present as a single logical switch with one shared control plane, and confirm a Dual-Active Detection link correctly identifies a split-brain scenario if the SVL itself fails.
Lab Purpose
Unlike HSRP or VRRP, covered earlier in this series, which provide redundancy between two independently managed devices sharing a virtual IP, StackWise Virtual merges two physical chassis into one logical switch with a single control plane, single configuration, and single management point — a fundamentally different redundancy model worth distinguishing clearly from FHRP-based approaches.
Lab Topology
Switch1 ---- SVL (dedicated high-bandwidth
link, e.g. TenGig1/0/1-2) ---- Switch2
Switch1 ---- DAD link (separate, lower
bandwidth, e.g. Gi1/0/1) ---- Switch2
Both switches will merge into a single
logical switch identified as "Switch 1"
after configurationTask 1: Designate Switch Domain and Switch Numbers
Configure a matching StackWise Virtual domain on both switches, with Switch1 as switch 1 and Switch2 as switch 2.
Task 2: Configure the SVL Interfaces
Designate the dedicated high-bandwidth ports as SVL links on both switches.
Task 3: Configure the Dual-Active Detection Link
Configure a separate link as the DAD (Dual-Active Detection) connection, distinct from the SVL itself.
Task 4: Reload Both Switches and Verify They Form a Single Logical Switch
Reload both switches and confirm they present as a single logical entity with one active supervisor role.
Task 5: Simulate an SVL Failure and Verify DAD Prevents a Split-Brain Condition
Shut down the SVL links while leaving the DAD link intact, and confirm the switches correctly detect the dual-active condition rather than both continuing to act as the active switch.
Solution and Verification
Switch1(config)# stackwise-virtual
Switch1(config-stackwise-virtual)# domain 1
Switch1(config)# switch 1 stackwise-virtual link 1
Switch2(config)# stackwise-virtual
Switch2(config-stackwise-virtual)# domain 1
Switch2(config)# switch 2 stackwise-virtual link 1Switch1(config)# interface tengigabitethernet1/0/1
Switch1(config-if)# stackwise-virtual link 1
Switch1(config-if)# exit
Switch1(config)# interface tengigabitethernet1/0/2
Switch1(config-if)# stackwise-virtual link 1
Switch2 configured identically on its
corresponding TenGig1/0/1-2 interfacesSwitch1(config)# interface gigabitethernet1/0/1
Switch1(config-if)# stackwise-virtual dual-active-detection
Switch2(config)# interface gigabitethernet1/0/1
Switch2(config-if)# stackwise-virtual dual-active-detection
-- The DAD link is deliberately separate
-- from the SVL -- its sole purpose is
-- detecting whether the SVL itself has
-- failed, so it cannot share the same
-- physical path as what it is monitoringSwitch1# reload
Switch2# reloadSwitch1# show switch
Switch/Stack Mac Address : 00aa.bb00.1111
H/W Current
Switch# Role Mac Address Priority Version State
-------------------------------------------------------
*1 Active 00aa.bb00.1111 1 V02 Ready
2 Standby 00aa.bb00.2222 1 V02 Ready
-- Both physical switches now present as
-- a single logical "Switch," with one
-- Active and one Standby role -- a single
-- running-config and a single management
-- IP now govern both physical chassis-- Simulating SVL failure while DAD remains up:
Switch1(config)# interface range tengigabitethernet1/0/1-2
Switch1(config-if-range)# shutdownSwitch2# show switch stack-ports
... SVL link down detected ...
Switch2# show logging | include DAD
%STACKMGR-4-DAD_DETECTED: Dual-active
condition detected via DAD link -- switch 2
transitioning to recovery mode
-- The DAD link successfully detected that
-- both switches might otherwise believe
-- themselves to be Active simultaneously
-- once the SVL failed -- one switch
-- automatically enters a recovery/
-- shutdown-of-non-critical-ports mode to
-- prevent both halves from actively
-- forwarding traffic as independent,
-- conflicting switchesKey Takeaway
StackWise Virtual's single logical switch model means a single configuration, a single management IP, and a single control plane spanning two physical chassis — a fundamentally different redundancy approach from the FHRP protocols (HSRP, VRRP, GLBP) covered earlier in this series, which keep two independently configured devices synchronized via a shared virtual IP; the dedicated DAD link exists specifically to prevent the dangerous split-brain scenario where an SVL failure could otherwise cause both physical switches to simultaneously believe they are the sole active member.