Understanding How Uplinkfast Works - Cisco 6500 Series Software Configuration Manual

Chapter 16 Configuring Optional STP Features
When you enable PortFast BPDU filtering globally and set the port configuration as the default for
PortFast BPDU filtering (see the
PortFast enables or disables PortFast BPDU filtering.
If the port configuration is not set to default, then the PortFast configuration will not affect PortFast
BPDU filtering.
filtering allows access ports to move directly to the forwarding state as soon as the end hosts are
connected.
Table 16-1 PortFast BPDU Filtering 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 PortFast and PortFast BPDU filtering are disabled.

Understanding How UplinkFast Works

UplinkFast provides fast convergence after a direct link failure and achieves load balancing between
redundant Layer 2 links using uplink groups. An uplink group is a set of Layer 2 LAN interfaces (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, except for self-looping ports. The uplink group
provides an alternate path in case the currently forwarding link fails.
Note UplinkFast is most useful in wiring-closet switches. This feature may not be useful for other types of
applications.
Figure 16-1
directly to Switch B over link L1 and to Switch C over link L2. The Layer 2 LAN interface on Switch C
that is connected directly to Switch B is in the blocking state.
Figure 16-1 UplinkFast Example Before Direct Link Failure
Switch A
(Root)
78-14099-04
"Enabling PortFast BPDU Filtering" section on page
Table 16-1 lists all the possible PortFast BPDU filtering combinations. PortFast BPDU
Global Configuration
Enable
Enable
Disable
Not applicable
Not applicable
shows an example topology with no link failures. Switch A, the root bridge, is connected
L1
L2
Blocked port
Switch C
Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
PortFast State
Enable
Disable
Not applicable
Not applicable
Not applicable
Switch B
L3
Understanding How UplinkFast Works
16-10), then
PortFast BPDU Filtering State
1
Enable
Disable
Disable
Disable
Enable
16-3