Conference netcad::hub_mgnt

617.0. "DEChub 900, FDDI, Dual-Homing, redundancy etc" by SAC::KINDER_N (Neil Kinder TCC South (Communications)) Thu Jan 13 1994 15:25

Hi,
    
    Here are some general FDDI questions on and some on the specific 
implementation of FDDI within the DEChub 900.

A customer has a very high availability requirement. The main components will
be two Alpha OSF/1 Servers, 22 Alpha OSF/1 workstations and two DECnis. They
need to be interconnected on a high speed bus - hence FDDI. Because the network
has to offer a high availability the FDDI will have to be implemented over 2
DEChub 900's. Each system will have to be connected to both DEChub 900 via
Concentrator 900 ports. I have thought that Dual-Homing is the best way to
connect to the concentrators in each Hub 900 from an individual system /
DECnis.

	+---------+				+---------+
	| system  |				| system  |
	+-++---++-+				+-++---++-+
	  ||   ||				  ||   ||
	  ||   |+-------------------------+       ||   ||
          ||   +-------------------------+|       ||   ||
          ||             Backup Pairs    ||       ||   ||Live
     Live ||           +-----------------||-------+|   ||Pair
     Pair ||           |+----------------||--------+   ||
          ||           ||                ||            ||
	  ||	     +-++-----+    +-----++-+          ||
          |+---------+ DEChub |    | DEChub +----------+|
          +----------+        |    |        +-----------+
		     +-++--++-+    +-++--++-+
                       ||  |+--------+|  ||
                       ||  +----------+  ||
                       || Forming the    ||
		       || backbone ring  ||
                       |+----------------+|
                       +------------------+

Here are my questions:-

o	For Dual-Homing do the interfaces on the Systems have to be DAS or is
there such a thing as a SAS with Dual-pairs (one for redundancy in Dual-Homing)

o	If you do need a DAS interface for Dual-Homing, I understand that one
pair goes into a backup mode. Does this make it act as a SAS in the sense that
like a SAS it is not part of the ring or is it acting like a DAS with one ring
being unavailable. I ask this as it makes a difference as to whether you can
remove workstations/ systems without disturbing the ring.

o	With this kind of requirement are there any alternatives to provide a
redundant FDDI backbone?

The two DEChub 900's have to be connected together to form the
redundancy within the ring. A few questions arise from this. I would like 
to connect the A port of one concentrator on one DEChub to the B port of a 
concentrator in the other DEChub. Additionally I need to connect the 
reverse pair via two other concentrators in the hubs. This would avoid the
situation where - if only two concentrators were involved rather than 4 - the
failure of one concentrator would partition the two hubs.

o	Is it a valid configuration to connect the concentrators of one hub to
the concentrators on another hub in the fashion mentioned above or do I need 
to run FDDI bridges between the hubs?

o	Is it valid to take the A port from Concentrator-1 in Hub-1 to port B
Concentrator-2 Hub-2 and port A Concentrator-3 in Hub-2 to Concentrator-4 in
Hub-1?

Entered in the Hub_management and FDDI notes conferences.

Cheers
Neil