HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 190

Information About STP Extensions Chapter 10 Configuring STP Extensions Send feedback to [email protected] Table 10-1 BPDU Filtering Configurations BPDU Filtering Per Port Configuration Default BPDU Filtering Global Configuration Enable STP Edge Port Configuration Enable BPDU Filtering State Enable1 Default Enable Disable Disable Default Disable Not applicable Disable Disable Not applicable Not applicable Disable Enable Not applicable Not applicable Enable 1. The port transmits at least 10 BPDUs. If this port receives any BPDUs, the port returns to the spanning tree normal port state and BPDU Filtering is disabled. Understanding Loop Guard Loop Guard protects networks from loops that are caused by the following: • Network interfaces that malfunction • Busy CPUs • Anything that prevents the normal forwarding of BPDUs An STP loop occurs when a blocking port in a redundant topology erroneously transitions to the forwarding state. This transition usually happens because one of the ports in a physically redundant topology (not necessarily the blocking port) stops receiving BPDUs. Loop Guard is only useful in switched networks where devices are connected by point-to-point links. On a point-to-point link, a designated bridge cannot disappear unless it sends an inferior BPDU or brings the link down. Note Loop Guard can be enabled only on network and normal spanning tree port types. You can use Loop Guard to determine if a root port or an alternate/backup root port receives BPDUs. If the port does not receive BPDUs, Loop Guard puts the port into an inconsistent state (blocking) until the port starts to receive BPDUs again. A port in the inconsistent state does not transmit BPDUs. If the port receives BPDUs again, the protocol removes its loop-inconsistent condition, and the STP determines the port state because such recovery is automatic. Loop Guard isolates the failure and allows STP to converge to a stable topology without the failed link or bridge. Disabling Loop Guard moves all loop-inconsistent ports to the listening state. (See Chapter 8, "Configuring Rapid PVST+" for information on STP port states.) You can enable Loop Guard on a per-port basis. When you enable Loop Guard on a port, it is automatically applied to all of the active instances or VLANs to which that port belongs. When you disable Loop Guard, it is disabled for the specified ports. 10-4 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide OL-16597-01