Cisco Systems 3130 User Manual
19-6
Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
OL-13270-01
Chapter 19 Configuring Optional Spanning-Tree Features
Understanding Optional Spanning-Tree Features
How CSUF Works
CSUF ensures that one link in the stack is elected as the path to the root. As shown in
, the
stack-root port on Switch 1 provides the path to the root of the spanning tree. The alternate stack-root
ports on Switches 2 and 3 can provide an alternate path to the spanning-tree root if the current stack-root
switch fails or if its link to the spanning-tree root fails.
ports on Switches 2 and 3 can provide an alternate path to the spanning-tree root if the current stack-root
switch fails or if its link to the spanning-tree root fails.
Link 1, the root link, is in the spanning-tree forwarding state. Links 2 and 3 are alternate redundant links
that are in the spanning-tree blocking state. If Switch 1 fails, if its stack-root port fails, or if Link 1 fails,
CSUF selects either the alternate stack-root port on Switch 2 or Switch 3 and puts it into the forwarding
state in less than 1 second.
that are in the spanning-tree blocking state. If Switch 1 fails, if its stack-root port fails, or if Link 1 fails,
CSUF selects either the alternate stack-root port on Switch 2 or Switch 3 and puts it into the forwarding
state in less than 1 second.
Figure 19-5
Cross-Stack UplinkFast Topology
When certain link loss or spanning-tree events occur (described in
), the Fast Uplink Transition Protocol uses the neighbor list to send fast-transition
requests to stack members.
The switch sending the fast-transition request needs to do a fast transition to the forwarding state of a
port that it has chosen as the root port, and it must obtain an acknowledgement from each stack switch
before performing the fast transition.
port that it has chosen as the root port, and it must obtain an acknowledgement from each stack switch
before performing the fast transition.
Switch 1
Spanning-
tree root
Backbone
Blade switch stack
StackWise Plus
port connections
port connections
201790
Switch 2
StackWise Plus
port connections
port connections
Forward
Link 1
(Root link)
(Root link)
Link 2
(Alternate
redundant
link)
(Alternate
redundant
link)
Link 3
(Alternate
redundant
link)
(Alternate
redundant
link)
100 or 1000 Mbps
100 or 1000 Mbps
100 or 1000 Mbps
Forward
Forward
Switch 3 StackWise Plus
port connections
Stack-root port
Alternate stack-
root port
root port
Alternate stack-
root port
root port