Does portfast disable Spanning-Tree?

This topic is to discuss the following lesson:

Hi Rene,

I realized when you show
SW1#show spanning-tree interface FastEthernet 0/24 detail

q1) The “bpdu receive” is 0 - why ? ( non-root bridges do not send bpdu to root bridge ?)

q2) What is the difference between “P2P Edge” and “P2P” ? What do that actually meant ?

q3) Do we use portfast on ports that we are sure will not cause a loop ?

Regards,
Alan

Hi Alan,

  1. With PVST, BPDUs are relayed from the root bridges down the tree to other non-root bridges.
  2. P2P Edge means that portfast has been enabled. Portfast enabled interfaces don't trigger a TCN. Take a look at the portfast tutorial here, I explained it there.
  3. That's right, Cisco IOS warns you when you enable it on interfaces. It doesn't disable STP though so it's not like you will have permanent loops.

Rene

Hi all,
i have a port in access but from the output i see that port is in blocking:

interface GigabitEthernet5/0/47
 switchport access vlan 201
 switchport mode access


show spanning-tree vlan 201 blockedports
Name                 Blocked Interfaces List
-------------------- ------------------------------------
VLAN0201             Gi5/0/47


Port 431 (GigabitEthernet5/0/47) of VLAN0201 is backup blocking 
   Port path cost 4, Port priority 128, Port Identifier 128.431.
   Designated root has priority 24777, address 00be.758e.31c0
   Designated bridge has priority 24777, address 00be.758e.31c0
   Designated port id is 128.430, designated path cost 0
   Timers: message age 16, forward delay 0, hold 0
   Number of transitions to forwarding state: 2
   Link type is point-to-point by default
   BPDU: sent 2644, received 3230774

Can you explain me that?

thank you

Hello Valero

Spanning Tree doesn’t only apply to trunk ports, but is also active on access ports as well. So it is perfectly normal to see access ports in the blocking state. This is the case even if you’re using portfast, as shown in the lesson.

In this particular case, GigabitEthernet5/0/47 is actually a backup blocking port. This is a port state that we see when we use Rapid Spanning Tree. A backup blocking port will be used when there are two or more physical links between two switches. More about the backup port state can be seen at the following lesson:

I hope this has been helpful!

Laz