Cisco Systems 3750E 用户手册
20-6
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 20 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 20-5
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
Catalyst 3750-E switch stack
StackWise Plus
port connections
port connections
159891
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