Loop Layer 2 by Cisco IP Phone

[francisco del cura ferreira]

Hi all

I hope someone could help with a very strange problem.

When an user connects both cables (voz and data) from an IP Phone to the switch by mistake, it creates a layer 2 loop generating lost of service. I would like to know how to avoid such as situation, the configuration of the access ports is this:

 switchport access vlan 30
 switchport trunk native vlan 30
 switchport mode access
 switchport voice vlan 51
 spanning-tree portfast
 spanning-tree bpdufilter enable
 spanning-tree bpduguard enable

What could be the root of the problem?

Thanks in advanced

Hi all

I hope someone could help with a very strange problem.

When an user connects both cables (voz and data) from an IP Phone to the switch by mistake, it creates a layer 2 loop generating lost of service. I would like to know how to avoid such as situation, the configuration of the access ports is this:

 switchport access vlan 30
 switchport trunk native vlan 30
 switchport mode access
 switchport voice vlan 51
 spanning-tree portfast
 spanning-tree bpdufilter enable
 spanning-tree bpduguard enable

What could be the root of the problem?
 

Thanks in advanced

[Reza Sharifi]

Hi,

You don't need to have the "switchport trunk native vlan 30" in the config.

In this case, your data vlan is 30, your voice vlan is 51 and that is all you need.

Also, your native vlan should be different than your voice vlan.

for example

data 30

voice 51

native 61

than you only add the native vlan statement to your trunk (uplinks), so they can carry untagged traffic.

HTH

[francisco del cura ferreira]

First of all, thanks for your answer Reza.

I'd like to ask you whether that misconfiguration could be the root of the layer 2 loops on the nework.

Thanks in advanced

[francisco del cura ferreira]

Hi,

The problem is in the next command:

 spanning-tree bpdufilter enable

When a user connects one Cisco IP Phone to the network with two wires at once, the switch filters the packet BPDUs and the command spanning-tree bpduguard enable doesn´t works.

I hope it has been helpful.

[paolo bevilacqua]

It is even mentioned in the manual by two big warning signs:

Configure Port Fast only on interfaces that connect to end stations; otherwise, an accidental topology loop could cause a data packet loop and disrupt switch and network operation.

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Caution Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in spanning-tree loops.

Usually this type of commands are given by people that doesn't not fully undertarstand when they have to be used, still they want to add commands.