Understanding How Uplinkfast Works - Cisco 7604 Configuration Manual

Chapter 21 Configuring Optional STP Features
PortFast BPDU filtering can also be configured on a per-port basis. When PortFast BPDU filtering is
explicitly configured on a port, it does not send any BPDUs and drops all BPDUs it receives.
Configuring PortFast BPDU filtering on a port that is not connected to a host can result in bridging loops.
Caution
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 21-1 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.
UplinkFast is most useful in wiring-closet switches. This feature may not be useful for other types of
Note
applications.
Figure 21-1
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.
OL-4266-08
"Enabling PortFast BPDU Filtering" section on page
Table 21-1 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
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
Understanding How UplinkFast Works
PortFast State PortFast BPDU Filtering State
1
Enable Enable
Disable Disable
Not applicable Disable
Not applicable Disable
Not applicable Enable
21-10), then
21-3