Cisco Systems EA6500 Manual De Usuario
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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
78-14099-04
Chapter 16 Configuring Optional STP Features
Understanding How UplinkFast Works
When you enable PortFast BPDU filtering globally and set the port configuration as the default for
PortFast BPDU filtering (see the
PortFast BPDU filtering (see the
), then
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.
BPDU filtering.
lists all the possible PortFast BPDU filtering combinations. PortFast BPDU
filtering allows access ports to move directly to the forwarding state as soon as the end hosts are
connected.
connected.
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.
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.
applications.
shows an example topology with no link failures. Switch A, the root bridge, is connected
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.
that is connected directly to Switch B is in the blocking state.
Figure 16-1 UplinkFast Example Before Direct Link Failure
Table 16-1 PortFast BPDU Filtering Port Configurations
Per-Port Configuration
Global Configuration
PortFast State
PortFast BPDU Filtering State
Default
Enable Enable
Enable
1
1.
The port transmits at least 10 BPDUs. If this port receives any BPDUs, then PortFast and PortFast BPDU filtering are disabled.
Default
Enable
Disable
Disable
Default
Disable
Not applicable
Disable
Disable
Not applicable
Not applicable
Disable
Enable
Not applicable
Not applicable
Enable
L1
L2
L3
Switch C
Switch A
(Root)
Switch B
Blocked port
1
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