Cisco WS-C2960-24TC-S Software Guide - Page 359
Understanding Loop Guard, Configuring Optional Spanning-Tree Features, Default Optional Spanning-
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Chapter 17 Configuring Optional Spanning-Tree Features Configuring Optional Spanning-Tree Features Understanding Loop Guard You can use loop guard to prevent alternate or root ports from becoming designated ports because of 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 ports. 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 guard prevents alternate and 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 on nonboundary ports only if the interface is blocked by loop guard in all MST instances. On a boundary port, loop guard blocks the interface in all MST instances. Configuring Optional Spanning-Tree Features These sections contain this configuration information: • Default Optional Spanning-Tree Configuration, page 17-9 • Optional Spanning-Tree Configuration Guidelines, page 17-10 • Enabling Port Fast, page 17-10 (optional) • Enabling BPDU Guard, page 17-11 (optional) • Enabling BPDU Filtering, page 17-12 (optional) • Enabling UplinkFast for Use with Redundant Links, page 17-13 (optional) • Enabling BackboneFast, page 17-13 (optional) • Enabling EtherChannel Guard, page 17-14 (optional) • Enabling Root Guard, page 17-15 (optional) • Enabling Loop Guard, page 17-15 (optional) Default Optional Spanning-Tree Configuration Table 17-1 shows the default optional spanning-tree configuration. Table 17-1 Default Optional Spanning-Tree Configuration Feature Port Fast, BPDU filtering, BPDU guard UplinkFast BackboneFast EtherChannel guard Root guard Loop guard Default Setting Globally disabled (unless they are individually configured per interface). Globally disabled. Globally disabled. Globally enabled. Disabled on all interfaces. Disabled on all interfaces. OL-8603-04 Catalyst 2960 Switch Software Configuration Guide 17-9
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