CCIE Routing & Switching v5 Workbook -
CCIE R&S v5 Advanced Technology Labs -
LAN Switching
STP PortFast Default
A Note On Section Initial Configuration Files: You must load the
initial configuration files for the section, named LAN Switching Initial
Spanning Tree, which can be found in
. Reference the Virtual Routers &
Physical Switches Diagram to complete this task.
Task
Configure Spanning-Tree PortFast on SW1 - SW4 so ports in access mode do not
have to wait for the Spanning-Tree listening and learning phases to begin forwarding.
Configure FastEthernet0/1 on SW1 as an access port in vlan 146.
Do not use any interface-level Spanning-Tree commands to accomplish this.
Configuration
SW1:
spanning-tree portfast default
!
interface FastEthernet0/1
switchport mode access
switchport access vlan 146
SW2, SW3, SW4:
spanning-tree portfast default
Verification
Portfast default has the same effect as the interface-level portfast command, but it is
automatically enabled at the same time only on interfaces statically configured in
access mode. This command is equivalent to issuing the
spanning-tree portfast
command under an interface range that encompasses all interfaces. The port must
be an access port for this to work, however. If the port is configured as a trunk, the
global portfast command will not convert the port to an edge port; you must
manually configure the port with the
spanning-tree portfast trunk
command.
Regardless of how portfast is enabled, if BPDUs are received on the port, the port
will lose its portfast and edge status, and STP port state will be negotiated, thus the
port may actually transition to blocking.
Verify that PortFast is enabled at the global level, appearing as by default.
SW1#show spanning-tree summary
Switch is in pvst mode
Root bridge for: VLAN0001, VLAN0005, VLAN0007-VLAN0010, VLAN0022, VLAN0043
VLAN0058, VLAN0067, VLAN0079, VLAN0146
Extended system ID
is enabledPortfast Defaultis enabled
PortFast BPDU Guard Default
is disabled
Portfast BPDU Filter Default is disabled
Loopguard Defaultis disabled
EtherChannel misconfig guard is enabled
UplinkFast
is disabled
BackboneFast
is disabled
Configured Pathcost method used is short
NameBlocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN000100033
VLAN000500033
VLAN000700033
VLAN000800033
VLAN000900033
VLAN001000033
VLAN002200033
VLAN004300033
VLAN005800033
VLAN006700033
VLAN007900033
VLAN014600044
---------------------- -------- --------- -------- ---------- ----------
12 vlans0003737
Verify that PortFast is actually also enabled at the interface level, thus port is an
STP Edge port, because it is in access mode and no BPDUs have been received
inbound.
SW1#show interfaces fastEthernet0/1 switchport
Name: Fa0/1
Switchport: EnabledAdministrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 146 (VLAN0146)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
<output omitted>
!
!SW1#show spanning-tree interface fastEthernet0/1 portfast
VLAN0146enabled
!
!SW1#show spanning-tree interface fastEthernet0/1 detail
Port 3 (FastEthernet0/1) of VLAN0146 is designated forwarding
Port path cost 19, Port priority 128, Port Identifier 128.3.
Designated root has priority 4242, address 0013.605f.f000
Designated bridge has priority 4242, address 0013.605f.f000
Designated port id is 128.3, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1The port is in the portfast mode by default
Link type is point-to-point by default BPDU: sent 72,received 0
Enable STP debugging to verify that ports transitions into forwarding state on link up.
SW1#debug spanning-tree event
Spanning Tree event debugging is onSW1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#service timestamp debug datetime msec
SW1(config)#logging console 7
SW1(config)#interface FastEthernet0/1
SW1(config-if)#shutdown
!
*Mar 3 06:03:34.735: STP: VLAN0146 we are the spanning tree root
2d05h: %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to administratively down
2d05h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down
When interface Fa0/1 is shut down and subsequently brought back up, it
immediately transitions to the forwarding state.
SW1(config-if)#no shutdown
!
*Mar 3 06:04:03.634: set portid: VLAN0146 Fa0/1: new port id 8003*Mar 3 06:04:03.634:
STP: VLAN0146 Fa0/1 ->jump to forwarding from blocking
!
2d05h: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
2d05h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up