Wednesday, January 12, 2005

Q: What are all of these Cisco extensions to Spanning Tree protocol (STP)?

A:
Backbone Fast Convergence
Provides fast convergence after a spanning-tree topology change caused by indirect link failures.
Loop Guard
The loop guard feature checks that a root port or an alternate root port is receiving BPDUs. If a port is not receiving BPDUs, the loop guard feature puts the port into an inconsistent state, isolating the failure and letting spanning tree converge to a stable topology until the port starts receiving BPDUs again.
Portfast
STP PortFast causes a Layer 2 LAN interface configured as an access port to enter the forwarding state immediately, bypassing the listening and learning states.
Portfast BPDU Guard
Provides a means to shut the port down when any received BPDUs are detected.
Root Guard
The STP root guard feature prevents a port from becoming root port or blocked port. If a port configured for root guard receives a superior BPDU, the port immediately goes to the root-inconsistent (blocked) state.
Uplink Fast Convergence
Uplink Fast Convergence provides rapid switchover to a redundant uplink for wiring closet switches when the spanning-tree root port fails or when the spanning-tree topology is recalculated.
Uplink Load Balancing
Uplink Load Balancing by VLAN enables traffic load balancing across uplinks by providing direct control over the spanning-tree port cost for VLANs on a trunking port.

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