Conference 7.286::fddi

783.0. "DB600 with backup LB200" by CGOS01::DMARLOWE (PDP 11: MOV -(PC),-(PC)) Mon Nov 16 1992 01:22

I have a customer that has a very large extended LAN using Vitalink 
bridges.  They are just now putting a pile of DB5xx/6xxs.  The network is 
generally stable but every now and then a link goes down and then the 
network reconfigures.  That means a 20-30 second outage.  Now when the FDDI 
gear is added their concerns are growing as to how all this will react.  
Below is a small slice of the network and some questions.


                        TRANSLAN  root bridge
                          |    \
                          |     \
                          |    TRANSLAN
                          |     /
                          |    /
                        TRANSLAN
                           |
                   ====================================
                         |                       |
                       DB600                   LB200
                       +   +                     |
                       +   + dual                |
                       +   + ring                |
                       +   +                     |
                       DB600                     |
                         |                       |
                   ====================================

The DB600s will be the primary path to the lower Ethernet.  If one of the 
Vitalink bridge links fail then spanning tree kicks in to get around the 
problem.  With spanning tree on, in the DB600s, I take it that the lower 
LAN will see an outage to other LANs as all bridges get involved in the 
attempted reconfig?

Secondly.  I thought I read something in one of the notes files about 
disabling spanning tree in the DB5xx/6xx bridges.  If you do that does that 
mean you will get duplicated packets on the lower LAN as packets will come 
in via both the DB5xx/6xx and the LB200?

Any other comments about spanning tree in this config greatly appreciated.

dmm