| Title: | FDDI - The Next Generation |
| Moderator: | NETCAD::STEFANI |
| Created: | Thu Apr 27 1989 |
| Last Modified: | Thu Jun 05 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 2259 |
| Total number of notes: | 8590 |
I have had a couple of questions from customers recently on the requirement to provide a resilient network connection form an XMI machine to FDDI. They would like to see a DAS version of the DEMFA so that dual homing can be used. They generally accept our arguments on the need to keep nodes off the backbone, but see dual homing as a reason to have a DAS adapter as it still connects via a concentrator and doesn't go against out basic philosophy of a dual ring of trees. As far as I can see the only option at the moment is a second controller (FDDI or Ethernet) and the use of the VMS load balancing / failover mentioned in the Networks Buyers Guide. I have the following questions: 1. Are we planning to produce a DAS adapter for XMI nodes to be used as described above (dual homed)? 2. How does the VMS load balancing / autofailover work (just an outline will do or a pointer, I can not seem to find any description other than in the Networks Buyers Guide). 3. With 2 adapters will DECnet phase IV allow both circuits to be active at the same time (assuming it is a router of course). I know this is not allowed with two Ethernet connection to the same LAN because of the physical address conflict, but maybe its possible on FDDI. Thanks for any help, Dave
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 390.1 | ... | STAR::SALKEWICZ | It missed... therefore, I am | Wed Nov 13 1991 12:48 | 24 |
Answers:
1) None that I know of
2) Load balancing is done by the higher layers which are presented
with a "chice" of adapters to use. The ony product I know
of today that actually does anything with this is clusters.
The rest (DECnet Phase IV, LAT, etc) just use the one adapter,
and don;t balance anything. As to the "how" does it work, its
not really that simple,.. but in a nutshell,.. PEDRIVER
(clusters) is always monitoring the response time for a given
adapter, and when a transmit is initiated, the adapter that
has poresented the least round trip delay in recent history
is selected for the transmit.
3) No,.. DECnet will not work if the two adapters are attached
to the same ring,. or somehow attached to the same extended LAN
(ie, they can't be bridged either). These are the
architectural limiits for Phase IV. Phase IV+ supports the idea
of an end node having multiple circuits, but there again, they
must be on seperate (unbridged) network segments.
/Bill
| |||||
| 390.2 | KONING::KONING | Paul Koning, NI1D | Wed Nov 13 1991 12:55 | 13 | |
About your question 3: DECnet Phase IV (regular or IV+) does NOT support multi-link endnodes. DECnet/VAX makes them work somewhat, but that's outside the architecture. Phase V is where such nodes are fully supported. Meanwhile, you can certainly do this if your nodes are Phase IV routers. However, because of the addressing issue, the two FDDI adapters have to be connected to DISJOINT LANs. In other words, they cannot be connected to the same FDDI ring, as you would with ordinary dual-homing. Nor can the two FDDIs they are connected to be bridged together. This is nothing more than the normal LAN connection rule for Phase IV routers; the fact that the LANs are FDDI doesn't change things. paul | |||||