Cisco 7609 User Manual

16-8
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
78-14064-04
Chapter 16 Configuring Optional STP Features
Enabling PortFast
– If a channel is blocked by loop guard and the channel breaks, spanning tree loses all the state
information. The individual physical ports may obtain the forwarding state with the designated
role, even if one or more of the links that formed the channel are unidirectional.
Note You can enable UniDirectional Link Detection (UDLD) to help isolate the link failure.
A loop may occur until UDLD detects the failure, but loop guard will not be able to
detect it.
• Loop guard has no effect on a disabled spanning tree instance or a VLAN.
Enabling PortFast
Caution Use PortFast only when connecting a single end station to a Layer 2 access port. Otherwise, you might
create a network loop.
To enable PortFast on a Layer 2 access port, perform this task:
This example shows how to enable PortFast on Fast Ethernet interface 5/8:
Router# configure terminal
Router(config)# interface fastethernet 5/8
Router(config-if)# spanning-tree portfast
Router(config-if)# end
Router#
This example shows how to verify the configuration:
Router# show running-config interface fastethernet 5/8
Building configuration...
Current configuration:
!
interface FastEthernet5/8
no ip address
switchport
switchport access vlan 200
switchport mode access
spanning-tree portfast
end
Router#
Command Purpose
Step 1
Router(config)# interface {type
1
slot/port} |
{port-channel port_channel_number}
1. type = ethernet, fastethernet, gigabitethernet, or tengigabitethernet
Selects an interface to configure.
Step 2
Router(config-if)# spanning-tree portfast
Enables PortFast on a Layer 2 access port connected to a
single workstation or server.
Step 3
Router(config-if)# spanning-tree portfast default
Disables PortFast.
Step 4
Router(config-if)# end
Exits configuration mode.
Step 5
Router# show running interface {type
1
slot/port} |
{port-channel port_channel_number}
Verifies the configuration.

Cisco 7609 Specifications

General

Brand	Cisco
Model	7609
Category	Network Router
Language	English