Tuesday, 18 January 2011

Spanning Tree Protocol

Hi some key points I would like to share with you on STP


setup Layer 2 LAN interface of the switch as an access port to enter the forwarding state immediately, bypassing the listening and learning states. Use PortFast only when connecting a single end station to a Layer 2 access port.


Provides from three to five seconds convergence after a direct link failure and achieves load balancing between redundant Layer 2 links using uplink groups.


Cuts convergence time by max_age for indirect failure.

BackboneFast is initiated when a root port or blocked port on a network device receives inferior bridge protocol data units (BPDU) from its designated bridge.

Loop guard:

Prevents an alternate or root port from becoming designated in the absence of BPDUs. Loop guard helps prevent bridging loops that could occur because of a unidirectional link failure on a point-to-point link.

Root guard:

Secures the root on a specific switch by preventing external switches from becoming roots.

BPDU guard:

When configured on a PortFast-enabled port, BPDU guard shuts down the port that receives a BPDU.

Unidirectional Link Detection (UDLD):

UDLD monitors the physical configuration of fiber-optic and copper connections and detects when a one-way connection exists. When a unidirectional link is detected, the interface is shut down and the system alerted.