STP Configuration Examples

Configuration Example: Fast Port Span

Fast Port Span is a system-wide parameter and is enabled by default.

The following configuration example disables fast port span and then re-enables the feature. You must use the write memory command to save the configuration.

device# configure terminal
device(config)# no fast port-span
device(config)# fast port-span
device(config)# write memory

Excluding Specific Ports from Fast Port Span

Use the exclude command to exclude a specific port or a set of ports from Fast Port Span as shown in the following examples.

The following example excludes a port from the Fast Port Span while leaving Fast Port Span enabled globally.

device(config)# fast port-span exclude ethernet 1/1/7
device(config)# write memory

The following example excludes a set of ports from Fast Port Span.

device(config)# fast port-span exclude ethernet 1/1/1 ethernet 1/2/2 ethernet 1/2/3
device(config)# write memory

The following example excludes a contiguous (unbroken) range of ports from Fast Port Span.

device(config)# fast port-span exclude ethernet 1/1/1 to 1/1/24
device(config)# write memory

Re-Enabling Fast Port Span on Excluded Ports

The following example re-enables Fast Port Span on a port.

device(config)# no fast port-span exclude ethernet 1/1/1
device(config)# write memory

The following example re-enables Fast Port Span on all excluded ports.

device(config)# no fast port-span
device(config)# fast port-span
device(config)# write memory

Configuration Example: Fast Uplink Span Port

The Fast Uplink Span feature enhances STP performance for wiring closet switches with redundant uplinks.

You can configure Fast Uplink Span for a group of ports of VLAN.

The following example configures a group of ports for Fast Uplink Span.

device(config)# fast uplink-span ethernet 1/1/1 to 1/1/4
device(config)# write memory

This example configures four ports from 1/1/1 through 1/1/4, as a Fast Uplink Span group. In this example, all four ports are connected to a wiring closet switch. Only one of the links is expected to be active at any time. The other links are redundant. For example, if the link on port 1/1/4 is the active link on the wiring closet switch but becomes unavailable, one of the other links takes over. Because the ports are configured in a Fast Uplink Span group, the STP convergence takes one second instead of taking at least 30 seconds using the standard STP forward delay.

Use show keyword to check the status of ports with Fast Uplink Span enabled.

device(config)# show span fast-uplink-span
STP instance owned by VLAN 1
Global STP (IEEE 802.1D) Parameters:
VLAN Root Root Root Prio Max He- Ho- Fwd Last Chg Bridge
ID ID Cost Port rity Age llo ld dly Chang cnt Address
Hex sec sec sec sec sec
1 000000c100000001 2 1/3/1 8000 20 2 1 15 65 15 000011111111
Port STP Parameters:
Port Prio Path State Fwd Design Designated Designated
Num rity Cost Trans Cost Root Bridge
Hex
1/1/2 80 0 DISABLED   0 0 0000000000000000 0000000000000000
1/1/3 80 0 DISABLED   0 0 0000000000000000 0000000000000000
1/1/4 80 4 FORWARDING 1 2 000000c100000001 8000000011111111
1/1/5 80 0 DISABLED   0 0 0000000000000000 0000000000000000
1/1/6 80 0 DISABLED   0 0 0000000000000000 0000000000000000
1/1/7 80 0 DISABLED   0 0 0000000000000000 0000000000000000
1/1/8 80 0 DISABLED   0 0 0000000000000000 0000000000000000
1/1/9 80 0 DISABLED   0 0 0000000000000000 0000000000000000

Use show keyword to check the status of Fast Uplink Span for a specified VLAN.

device(config-vlan-2)# show span vlan 2 fast-uplink-span
STP instance owned by VLAN 2
Global STP (IEEE 802.1D) Parameters:
VLAN Root Root Root Prio Max He- Ho- Fwd Last Chg Bridge
ID ID Cost Port rity Age llo ld dly Chang cnt Address
Hex sec sec sec sec sec
2 8000000011111111 0 Root 8000 20 2 1 15 29596 0 000011111111
Port STP Parameters:
Port Prio Path State Fwd Design Designated Designated
Num rity Cost Trans Cost Root Bridge
Hex
1/1/1 80 4 LISTENING 0 0 8000000011111111 8000000011111111