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CCNP Enterprise Core (350-401) Cisco Datalink Layer

Spanning Tree Protocol – Portfast

Generating a Topology Change Notification for link state changes on single devices does not make sense in a network due device normally only having one connection to the network.

Using the Portfast feature on Cisco Catalyst switches disables the topology change notification being generated if a link state changes to a single user device.

An additional advantage of enabling portfast on the port is it skipped the listening and learning states of the spanning tree protocol process allowing a rapid connection to the network once the link comes online.

Whilst this does default some of the protection of spanning tree if a network switch device is accidentality connected the port will remove the portfast functionality if it detects a bridge protocol data unit (BPDU) on that port.

Portfast can be enabled on an individual interface in interface configuration mode by entering the command spanning-tree portfast

Portfast can be enabled globally across all interfaces with the command spanning-tree portfast default in global configuration mode. Individual interfaces can be removed from having portfast switched on by default with the interface configuration command spanning-tree portfast disable

Portfast in the forms above can only be enabled on access ports. For single host devices that can utilise VLANs portfast can be switched on for trunks too. Use the command spanning-tree portfast trunk.

The portfast trunk command is not to be used for switch to switch communication!

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