Cisco-proprietary enhancements to 802.1D

PortFast

PortFast, shown in Figure 2-3, is a Cisco-proprietary enhancement to the 802.1D STP implementation. You apply the command to specific ports, and that application has two effects:

■ Ports coming up are put directly into the forwarding STP mode.
■ The switch does not generate a TCN when a port configured for

PortFast is going up or down—for example, when a workstation power-cycles. Therefore, consider enabling PortFast on ports that are connected to end-user workstations. Caution must be used with PortFast ports to ensure that hubs, switches, bridges, or any other device that could cause a loop are not connected to these ports.

UplinkFast

Configure UplinkFast on wiring closet switches. It detects a directly
connected failure and allows a new root port to come up almost immediately.
When you are configuring UplinkFast, the local switch has a priority
set to 49,152, and it adds 3000 to the cost of all links. Finally, a mechanism
is included that causes the manipulation of MAC address tables
for other bridges.

BackboneFast

Configure BackboneFast on all switches. It speeds convergence when
the failure occurs and is indirectly located, such as in the core of the
backbone. It reduces convergence from about 50 seconds to about 30
seconds.