how to disable stp on port

Unanswered Question
Jul 22nd, 2009

hi experts,

1 > we can not disable stp on switch. we can disable stp on vlan basis or port basis Is this correct or wrong

2> i Want explanation of spanning-tree bpdufilter enable command

thanks in advance

suryakant

I have this problem too.
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nwmerc1224 Sun, 11/01/2009 - 08:36

Enable the spanning-tree bpdufilter feature on the interface level to prevent

1. port from sending BPDU

2. ignore incoming BPDU's receive

Remember, enable on interface level only.

YANGCCIE4 Sun, 11/01/2009 - 09:07

hi,

1> Yes, we can not disable stp on switch, by default the switch will be configured by pvst, you can change it to mst, the switch must be configured one of the two choices.

2> BPDUfilter enable command enable the filter function on the interface, filter out the BPDU packet,the purpose is a)in order to avoid the STP re-calculating. b)to save system resource consumption. c) to avoid the new device has the higher priority then grap the root-bridge from the original network.

hope it helps

Yang

Muhammad Anser Khan Sun, 11/01/2009 - 09:33

Dear Suryakant,

As per my knowledge we can not disable STP on the port forcefully, But It will happen when we enable bpdufilter on the interface:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# spanning-tree bpdufilter enable

BPDU filtering allows you to prevent a port from sending and receiving BPDUs. If it receives BPDU It will disable the Spanning tree from this port.

Although it is not recommended, you can turn off Spanning Tree Protocol (STP) on a per-VLAN basis, or globally on the switch.

Use the no spanning-tree vlan vlan-id command in order to disable STP on a per virtual LAN (VLAN) basis.

NOTE: Cisco does not recommend this command to apply on the interface because It may cause loops in the network when STP becomes disable.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_se/configuration/guide/swstpopt.html#wp1046220

Regards,

Anser

Peter Paluch Sun, 11/01/2009 - 10:07

Hello Suryakant,

To add to other gentlemen's answers:

1.) On a per-VLAN basis, the STP is disabled by saying no spanning-tree vlan N. Regarding disabling the STP on a port, there are two different forms of doing it. The first is the PortFast feature, i.e. declaring the port as an edge port by the command spanning-tree portfast. This actually isn't disabling STP at all. It just allows the port to transition immediately from Blocking (or Discarding) to Forwarding. However, the STP is still fully active on that port - it still sends and receives BPDUs, and if a BPDU is indeed received on a PortFast port, the PortFast feature is deactivated until the port is disconnected and connected again.

The second way to disable STP on a port is the BPDU Filter - read further.

2.) The BPDU Filter feature prevents a port from sending and optionally from receving updates. Its behavior is different depending on how the feature is activated.

If the feature is activated in global configuration mode using the spanning-tree portfast bpdufilter default command, then the feature is automatically activated on all PortFast-enabled ports. In this case, after port is connected, it sends 11 BPDUs in usual intervals. If no BPDU is received during this time or anytime after it, the port will stop sending BPDUs. If a BPDU is received on such a port, the Filter feature is deactivated for that port and the port becomes a normal STP port - it again starts sending and receiving BPDUs in a usual way.

If the BPDU Filter feature is activated directly on a port using the command spanning-tree bpdufilter enable, the port will never send or receive BPDUs and will remain completely unblocked under all circumstances. This is the way to disable STP on a port.

Best regards,

Peter

Muhammad Anser Khan Thu, 11/05/2009 - 02:22

Dear Peter,

How can you get this "it sends 11 BPDUs in usual intervals" ?

Can you provide me any link or theory behind this?

I will be thankful

Regards,

Anser

Peter Paluch Thu, 11/05/2009 - 02:26

Hello Anser,

It was mentioned in Cisco Networking Academy CCNP3 curricula, and you can also trivially verify it by sniffing a switchport that has the BPDU Filter functionality enabled in global configuration mode.

There is no special theory behind this. The port simply sends a couple of BPDUs to possibly elicit a STP response from the other switch if there is any. The count of 11 BPDUs was probably chosen to span the entire max_age period where the port on the second switch can be blocked and therefore unresponsive to BPDUs.

Best regards,

Peter

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