[nsp] 1483 Bridging & Spanning Tree

[Clinton Work]

My main experience is with the WS-X5158 card and it will pass Spanning-Tree
BPDUs depending upon the Supervisor configuration. If you disable spanning
tree on the Supervisors used at both ends (vlan 100 and 500). Any BPDUs
entering the switch via vlan 100 or 500 will be sent across the 1483 ATM
PVC. If spanning tree is enabled on the Supervisor then it treats the ATM
port like a  like a seperate interface. The Supervisor will send
Spanning-Tree BPDUs out the VLAN attached to the 1483 PVC on the ATM card.
Incoming BPDUs on Ethernet interfaces attached to vlan 100 or 500 will be
processed by the Supervisor.

Things to watch out for:
 - The Cat5K SupII allows you to disable spanning tree per vlan. The SupIII
is all or nothing.
 - If you attach multiple ATM VCs to the same VLAN on the ATM card there is
still only one port
  from the view of the Supervisor. A bad BPDU on one ATM VCs can cause the
VLAN to go blocking
  on the ATM port and affect all the ATM VCs attached to the VLAN.
 - Disabling spanning-tree on the native VLAN of a 802.1q trunk is a bad
idea. The Supervisor will
  forward the 802.1q BPDU over 1483 ATM VC attached to the same VLAN. The
far end
  Catalyst 5500/6500 won't like it.
 - I've seen a far number of spanning-tree issues with invalid frames being
confused by the SupII/III
  as BPDUs with bridge MAC of 00-00-00-00-00-00 (valid by the RFC spec).
Every time one the of the
  bad frames is receivied it causes a new root bridge on the VLAN. If there
are lot of ATM VCs
  attached to the same VLAN it can be hard to find the source.


----- Original Message ----- 
From: "Dan Armstrong" <dan at beanfield.com>
Cc: <cisco-nsp at puck.nether.net>
Sent: Tuesday, March 02, 2004 12:22 PM
Subject: [nsp] 1483 Bridging & Spanning Tree


> I have a bit of a mind bender here...
>
> If you bridge 2 VLANs together over ATM 1483 (with say a WS-X5161 card),
does 1483 pass the Spanning Tree PDUs?
>
> Assuming it does, if I am bridging VLAN 100 on the local switch to VLAN
500 on the other end, how does spanning tree handle that?
>