Organization: Stanford Linear Accelerator Center
Date: Friday, 9 Oct 1992 16:09:05 PST
From: Martin L. Dart (415) 926-2745, DART@SLACVM.SLAC.STANFORD.EDU.
 <DART@SLACVM.SLAC.STANFORD.EDU>
Newsgroups: comp.dcom.lans.fddi
Subject: Dual Homing II


Thank you all for your response about Dual Homing.  As it happens I now
have more detailed questions about this subject.  While it is clear that
Dual Homing can be done I need to clarify a question that has been raised.
Does one connect a DAS station as per FIG.1 or FIG. 2 below.  Figure 1 shows
a  DAS station plugged directly into two concentrators.  Figure 2 shows
the concentrators cross-coupled.  I believe, and I will be testing this,
that FIG. 2 is the correct configuration as it's the only way I can see
that normal token rotation will be maintained.   Does anyone have Dual
Homing in place?  (My original note follows the figures.)



          |----------|            |----------|
 TO     ->|A  CON    |->->->->->->|A         |
        <-|          |<-<-<-<-<-<-|  SERVER  |
 DUAL     |    1     |            |    1     |
        ->|B         |       -->->|B         |
 RING   <-|   DAS    |      /-<-<-|   DAS    |
          |----------|     //     |----------|
                          //
          |----------|   //
 TO     ->|A  CON    |-> /
        <-|          |<-<
 DUAL     |    1     |            FIG. 1
        ->|B         |            Direct Dual Homing.
 RING   <-|   DAS    |
          |----------|




          |----------|            |----------|
 TO     ->|A  CON    |->->->->->->|A         |
        <-|          |<--       <-|  SERVER  |
 DUAL     |    1     |   \     /  |    1     |
        ->|B         |    <-<-<-<-|B         |
 RING   <-|   DAS    |      /-<-<-|   DAS    |
          |----------|     //     |----------|
                          //
          |----------|   //
 TO     ->|A  CON    |<- /
        <-|          |-->
 DUAL     |    1     |            FIG. 2
        ->|B         |            Cross-Coupled Dual Homing.
 RING   <-|   DAS    |
          |----------|



>My original request:
>
>I need some advice on dual homing.  I want to use DH, Dual Homing,
>to satisfy a conflict; our users want redundant access to some
>servers on the FDDI and, even though the servers have DAS cards,
>I don't want them on my main ring.  What I was planing on doing
>as a fix was cross couple the stations across two concentrators,
>which I understand is called dual homing.   This is a picture of
>what I want to do.  Can I just plug these guys in and expect them
>to work this way?
>  *
>  *  ------------------                       -------------
>  ***|A               |***********************|A          |
>     | Concentrator 1 |                       |  SERVER 1 |
>  ***|B               |                      *|B          |
>  *  ------------------                    *  -------------
>  *                                     *
>  *                                  *
>  *->(Main Ring)                  *
>  *                            *
>  *                         *
>  *  ------------------  *
>  ***|A               |*
>     | Concentrator 2 |
>  ***|B               |
>  *  ------------------
>  *



Thanks,
Marty Dart.

My opinions are mine and mine alone.