Conference 7.286::fddi

387.0. "FDDI Config Question ?????? " by LTLKNG::DOUGHTY () Fri Nov 08 1991 16:19

	Heelo,

	I am putting together a system for a customer that will be a five
	node VAXcluster.  The customer has a baseband ethernet installed
	throughout his large plant (several miles square - many buildings).
	The ethernet was the orignal network in the facility.  Now, they
	have installed an FDDI network that connects several off-sites (10
	to 20 miles away) to the main plant.  Also, they ran FDDI fiber 
	to each building in the main plant from a central site.  The FDDI
	to each building is used for the primary network path, but the coax
	is still there and functions as a backup.

	In installing this cluster, the customer wants to run FDDI into the
	cluster members, but also connect each member to the baseband for
	backup.  (see below).   

	====================================FDDI===========================
          ||                     ||                      ||        ||
          ||                     ||                      ||        ||fiber
          ||                     ||                      ||       ---------
          ||                     ||                      ||       |       |
          ----------             ----------       ----------      | Bridge|
          |  6000  |             |  6000  |       |  6000  |      ---------
          |        |             |        |       |        |        |xceiver
          ----------             ----------       ----------        |
             |                      |                |              |
             |                      |                |              |
         ----+----------------------+----Ethernet----+--------------+--------

	Elsewhere in the network, the Ethernet and FDDI are bridged together
	as well (actually, in each building to allow for single building
	fail over).  

	The question????

	Since you ask.....Will this work?  Will this provide primary access 
	by the FDDI and go to the coax ONLY if the FDDI fails?  Will the
	bridge shown drop into backup mode automatically?  Have I provided
	enough information to ask this question?

	My gut says it will work, but I have been burned before by my gut....
	so any thoughts from out there would be appreciated.  Thanks in 
	advance.

	Alvin

This will work for the VAXcluster software.  The FDDI path will be used if 
available, otherwise the Ethernet path will used.  The bridge is optional
as far as failover of the cluster traffic is concerned.

One thing to consider is how DECnet is effected by this.  If all of these
systems are routers and they have circuits on both FDDI and Ethernet
DECnet will fail over.  If the systems are not routers they should only
have circuits on one adapter.  In this case DECnet will not failover.

		Tony

    .1 is not correct.
    
    If you try to run DECnet on both the Ethernet and the FDDI devices
    in your vaxes, you will have a duplicate address problem. This is
    because the FDDI is bridged (in several places) to the Ethernet.
    The problem exists regardless of whether the nodes are routers
    or not. You can only run DECnet on "one side of the bridge" or
    on only one of the two (FDDI/EThernet) controllers for each
    system. These are the limits of the phase IV architecture. Phase
    V will fix this problem when it ships.
    
    So your options ofr DECnet are:
    	- only run on one of the two (FDDI/Ethernet) controllers
    	- remove the bridges and run DECnet on both
    
    Clusters will work correctly if you use VMS V5.4-3 or later.
    
    
    							/Bill