[nsp] PVST+ BPDU frame format

[Clinton Work]

For compatibility reasons Cisco sends both regular BPDUs and PVSTP+ BPDUs on
the native vlan (confirmed with a sniffer). The regular BPDUs are sent for
non-cisco
switches which only have a single spanning tree instance for all VLANs. The
PVSTP+
BPDUs are sent on the native VLAN and every VLAN allowed on the trunk. The
PVSTP+
BPDUs use ethertype 0x010b and are sent to multicast MAC 01-00-0c-cc-cc-cd.


----- Original Message ----- 
From: "Even Glemmestad" <even at supras.nu>


> Afaik, BPDUs sent from a Cisco over .1q trunks are not PVST BPDUs; when
> Cisco uses a .1q trunk it uses normal STP on the link. I have created
> connections between Cisco and 3rd-party switches using PVST+ on the
> Cisco end, and STP on the 3rd-party end, running a .1q link in between.
> The result, without any other configuration than setting the trunk mode
> to dot1q, was that the BPDUs sent across the .1q trunks were normal STP
> BPDUs for VLAN1, and interpreted correctly by the 3rd-party switches.
>