[c-nsp] Cisco RSTP interop with 802.1w equipment

[Phil Mayers]

Marian Ďurkovič wrote:
> Hi all,
> 
>   I wonder if there's any solution to the following interoperability issue:
> 
> Cat6500 with IOS 12.2(18)SXF16 running spanning-tree mode rapid-pvst,
> 802.1w compliant switch running IEEE version of rapid STP
> 
> When those are connected by access ports, everything works as expected.
> However, when connected by 802.1Q trunk with vlans 1500-1520, the
> behaviour is this:
> 
> 802.1w switch sending BPDUs to IEEE STP MAC address (0180.c200.0000)
> Cat6500 sending per-vlan BPDUs to Cisco MAC address (0100.0ccc.cccd)
> but nothing to IEEE STP MAC address
> 
> Aren't Cisco switches supposed to send BPDUs also to IEEE STP MAC address

Generally, no. Vlan 1 is treated specially.

> on 802.1Q trunks? Or is there any special config needed for this?

Vlan number 1 will interop, so if you do this:

int Gi1/1
   switchport mode trunk
   switchport trunk native vlan 1
   switchport trunk allowed vlan 1,2,3

...then vlan 1 will form an 802.1w adjacency with the neighbour, vlans 2 
and 3 will just pass straight through it.

In general, PVST passes straight through non-PVST switches; the non-PVST 
switches appear as if they're shared segments.