Understanding How Portfast Bpdu Filtering Works; Understanding How Uplinkfast Works - Cisco WS-C6506 Software Manual

Chapter 9 Configuring Spanning-Tree PortFast, UplinkFast, BackboneFast, and Loop Guard

Understanding How PortFast BPDU Filtering Works

BPDU filtering allows you to avoid transmitting BPDUs on a port that is connected to an end system.
When you enable BPDU filtering on the switch, spanning tree places that port in the forwarding state
immediately, instead of going through the listening, learning, and forwarding states. When you enable
BPDU filtering globally and set the port configuration as the default for BPDU filtering (see the
"Configuring PortFast BPDU Filtering on the Switch" section on page
disables the BPDU filter.
If the port configuration is not set to default, then the PortFast configuration will not affect BPDU
filtering.
to move directly to the forwarding state as soon as the end hosts are connected.
Table 9-2 BPDU Filter Port Configurations
Per-Port Configuration
Default
Default
Default
Disable
Enable
1. The port transmits at least 10 BPDUs. If this port receives any BPDUs, then the operational PortFast value is set to disable and the operational BPDU filter
is then disabled.

Understanding How UplinkFast Works

UplinkFast provides fast convergence after a spanning-tree topology change and achieves load balancing
between redundant links using uplink groups. An uplink group is a set of ports (per VLAN), only one of
which is forwarding at any given time. Specifically, an uplink group consists of the root port (which is
forwarding) and a set of blocked ports. The blocked ports do not include self-looping ports. The uplink
group provides an alternate path in case the currently forwarding link fails.
UplinkFast is most useful in wiring-closet switches. This feature may not be useful for other types of
Note
applications.
Figure 9-1
directly to Switch B over link L1 and to Switch C over link L2. The port on Switch C that is connected
directly to Switch B is in the blocking state.
OL-8978-04
Table 9-2 lists all the possible BPDU filter combinations. The BPDU filter allows access ports
Global Configuration
Enable
Enable
Disable
X
X
shows an example topology with no link failures. Switch A, the root switch, is connected
PortFast Operational Value
Enable
Disable
X
X
X
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Understanding How PortFast BPDU Filtering Works
9-13), then PortFast enables or
Operational BPDU Filter
1
Enable
Disable
Disable
Disable
Enable
9-3