[c-nsp] spanning-tree for local switching on ASR920

[Peter Rathlev]

On Thu, 2018-03-15 at 13:29 +0000, Nick Cutting wrote:
> In the output of show spanning tree - is the port with the untagged
> service instance forwarding on vlan 4093?
> Unless something changed from 16.6 -> 16.7 I imagine that it is only
> forwarding and processing BPDU's on vlans 2 and 10.

Correct, just VLANs 2, 10 and 2302 are STP enabled. There is no PVST
instance for the untagged bridge domains 4093/4094. So it indeed seems
like there's no way to run STP for untagged traffic.

If your primary concern is to react to cabling errors then maybe you
could use ports that sends BPDUs on an arbitrary tagged VLAN and has
"spanning-tree bpduguard enable" configured. On top of having a service
instance take the untagged traffic of course. Something like this:

  interface GigabitEthernet0/0/0
   no ip address
   negotiation auto
   spanning-tree bpduguard enable
   service instance 1 ethernet
    encapsulation untagged
    l2protocol peer cdp lldp
    bridge-domain 500
   !
   service instance 2 ethernet
    encapsulation dot1q 3000
    l2protocol peer stp
    bridge-domain 3000
   !
  !

I haven't had the opportunity to test it, but it should at least shut
down two such ports that are connected directly. Indirect connection
via other equipment should lead to shutdown unless they discard the
tagged BPDUs.

-- 
Peter