[c-nsp] Spantree .1Q packets received on non-trunk port.

[Lee Starnes]

Thanks Chris for breaking it down. Makes sense.


On Wed, Aug 27, 2014 at 6:14 AM, Chris Marget <chris at marget.com> wrote:

> On Tue, Aug 26, 2014 at 7:32 PM, Lee Starnes <lee.t.starnes at gmail.com>
> wrote:
> > they are providing an "access" port for us.
> > This is "un-tagged" traffic at the remote site
> > if I connect a cisco switch to it with the
> > port on the cisco configured as an access port, I get the error below.
> >
> > 00:06:52: %SPANTREE-7-RECV_1Q_NON_TRUNK: Received 802.1Q BPDU on non
> trunk
> > FastEthernet0/3 VLAN638.
> > 00:06:52: %SPANTREE-7-BLOCK_PORT_TYPE: Blocking FastEthernet0/3 on
> > VLAN0638. Inconsistent port type.
>
> untagged != access in Cisco land.
>
> Cisco switches (at least those running rapid-pvst+) send an extra TLV in
> their spanning tree BPDUs. The TLV indicates the VLAN associated with the
> STP instance.
>
> The switch configuration probably looks something like:
>
> interface x/y
>  switchport mode trunk
>  switchport trunk native vlan 638
>  switchport trunk allowed vlan 638
>
> The configuration you're expecting is:
>
> interface x/y
>  switch port mode access
>  switchport access vlan 638
>
> Transit traffic in vlan 638 is handled identically by both configurations.
>
> The spanning tree BPDUs are not the same. The first case (untagged traffic
> via native VLAN on a trunk) marks the VLAN number in the extra TLV in the
> BPDU, which will upset Cisco STP speakers which know to interpret it.
>
> I think the error which results is the one you're seeing.
>
> /chris
>