Cisco Systems 3130 Configuring Optional Spanning-Tree Features

19-11
Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
OL-13270-01
Chapter19 Configuring Optiona l Spa nning-Tree Features Configuring Optional Spanning-Tree Features
Figure19-9 Root Guard in a Data-Center Network
Understanding Loop Guard
You can use loop guard to prevent alternate or root ports from becoming designated ports b eca use o f a
failure that leads to a unidirectional link. This feature is most effective when it is enabled on the entire
switched network. Loop guard prevents alternate and root ports from becoming designated ports, and
spanning tree does not send BPDUs on root or alternate port s.
You can enable this feature by using the spanning-tree loopguard default global configuration
command.
When the switch is operating in PVST+ or rapid-PVST+ mode, loop gu ard prevents alter nate a nd root
ports from becoming designated ports, and spanning tree does not send BPDUs on root or alternate ports.
When the switch is operating in MST mode, BPDUs are not sent o n nonb oun da ry por ts onl y if the
interface is blocked by loop guard in all MST instances. On a bo und ar y po rt, loo p g uard bl ocks the
interface in all MST instances.
Configuring Optional Spanning-Tree Features
These sections contain this configuration information:
•Default Optional Spanning-Tree Configuration, page 19-12
•Optional Spanning-Tree Configuration Guidelines, page 19-12
•Enabling Port Fast, page 19-12 (optional)
•Enabling BPDU Guard, page 19-13 (optiona l)
•Enabling BPDU Filtering, page 19-14 (optional)
•Enabling UplinkFast for Use with Redundant Links, page 19-15 (optional)
•Enabling Cross-Stack UplinkFast, page19-16 (optional)
201771
Desired
root switc
h
Customer network
Potential
s
panning-tree root without
root guard enabled
Enable the root-guard feature
on these interfaces to prevent
switches in the customer
network from becoming
the root switch or being
in the path to the root.
Data-center network