STP error when trunking between two switches across a L2 service provider

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Mar 8th, 2010
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I'm trying to configure trunking on our two switches,  the switches are in two different location, that are inter-connected via L2 service provider.

SW1(3550) --- Service Provider ---  SW2(3550)

Site A                                         Site B

Here are some logs to help you on understanding my issue.

From SW1:


interface FastEthernet0/18

description *** This connects to Equinix ***

switchport trunk encapsulation dot1q

switchport mode trunk

speed 100

duplex full


Trunk Status:

Port        Mode         Encapsulation  Status        Native vlan

Fa0/18      on           802.1q         trunking      1

Port      Vlans allowed on trunk

Fa0/18      1-4094

Port        Vlans allowed and active in management domain

Fa0/18      1,3-4,100

Port        Vlans in spanning tree forwarding state and not pruned

Fa0/18      none


Mar  2 03:36:05.238: %SPANTREE-7-RECV_1Q_NON_TRUNK: Received 802.1Q BPDU on non trunk FastEthernet0/18 VLAN1.

Mar  2 03:36:05.238: %SPANTREE-7-BLOCK_PORT_TYPE: Blocking FastEthernet0/18 on VLAN0001. Inconsistent port type.

Mar  2 03:41:28.187: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/18, changed state to down

Mar  2 03:41:31.199: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/18, changed state to up

Mar  2 03:41:31.227: %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan id 25 on FastEthernet0/18 VLAN1.

Mar  2 03:41:31.227: %SPANTREE-2-BLOCK_PVID_LOCAL: Blocking FastEthernet0/18 on VLAN0001. Inconsistent local vlan.

From SW2:


interface FastEthernet0/1

description *** this connects to Global Switch ***

switchport trunk encapsulation dot1q

switchport mode trunk

duplex full


According to the our service provider "vlan untagged" was configured on their equipment where SW1 was connected.

Please help, I need to setup the trunking between the two switch ASAP.



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KARUPPUCHAMY MA... Mon, 03/08/2010 - 00:34
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I am suspecting the config with ISP switch.In ISP switches they used to configure QinQ tunneling to give service to multiple customers via the same switch.

If they have not configured properly for your connectivity then you night face this issue.

From cisco web


Error Message  

%SPANTREE-7-RECV_1Q_NON_TRUNK  : Received 802.1Q BPDU on non trunk [chars] [chars].

Explanation   An SSTP BPDU that was not operationally a trunk has been received on the specified  interface.

Recommended Action   Verify that the configuration and operational state of the listed interface and that  of the interface to which it is connected have the same mode (access or trunk). If the mode is trunk,  verify the same encapsulation (none, ISL or 802.1Q). Once these parameters are consistent, spanning  tree will automatically unblock the interfaces as appropriate.

For more information about qinq tunneling just have a look into the below URL




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