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Cisco was not going to sit and wait around for the standards bodies to enhance Spanning-Tree Protocol so that it would converge faster and be more safe to implement. Instead, Cisco has been hard at work creating tools that could improve the protocol. Here is some review about these various tools.
- PortFast – Causes an access port to enter the forwarding state immediately, bypassing the listening and learning states. This enhancement should be enabled on ports that are connected to devices that are powered on and off, such as workstations. This feature is still needed and should be configured in Rapid Spanning Tree environments.
- UplinkFast – Provides fast convergence after a direct link failure. This enhancement is most useful in wiring-closet switches. This feature is not required in RSTP environments as this functionality is built into that new protocol.
- BackboneFast – Provides fast failover when an indirect link failure occurs. This feature is initiated when a root port or blocked port on a network device receives inferior BPDUs from its designated bridge. This feature only operates correctly when enabled on all network devices in the network. This feature is not required in RSTP environments as this functionality is built into that new protocol.
- BPDUGuard – When enabled, shuts down a port that receives a BPDU (Bridge Protocol Data Unit). Provides a secure response to invalid configurations, because the administrator can manually put the port back in service.When configured at the interface level, shuts the port down as soon as the port receives a BPDU, regardless of PortFast configuration.NotesIn a valid configuration, PortFast-enabled ports do not receive BPDUs. Reception of a BPDU by a PortFast-enabled port signals an invalid configuration.When enabled globally, BPDUGuard applies to all interfaces that are in an operational PortFast state.
- BPDUFilter Prevents a port from sending or receiving BPDUs. When configured globally, BPDUFilter applies to all operational PortFast ports. When an operational PortFast port receives a BPDU in this configuration, three things occur. The port immediately loses its operational PortFast status; BPDU filtering is automatically disabled on the port; and STP resumes sending BPDUs on the port. Care must be taken when configuring BPDUFilter as a port-based configuration can lead to Layer 2 loops if a switch is connected on that port.
- RootGuard – Prevents a port from becoming root port or blocked port. When a RootGuard-configured port receives a superior BPDU, the port immediately goes to a root-inconsistent (blocked) state.
- LoopGuard – Helps prevent bridging loops that could occur because of a uni-directional link failure on a point-to-point link. When enabled, if a root or blocked port stops receiving BPDUs from its designated port, it transitions to a loop-inconsistent blocking state.
Anthony Sequeira CCIE, CCSI
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Tags: ccie outing & switching, Cisco, cisco stp toolkit, layer2, Routing & Switching, stp
