Subject: Re: no can do

From: Choon Lee <[email-masked]>
Date: Fri, 20 Aug 1993 09:08:43 -0700

Shannon,

In my follow up mail to Scott, I mentioned that for that particular topology we
can indeed "convert" the full mesh topology to a "LAN" topology, and that would
work in this particular instance.

However, we cannot assume that the WAN connection is always full mesh. E.g., the
WAN link between the DLSw nodes on LAN B and C may be missing. The other thing is
that to equate the WAN links to a "LAN", the DLSw node will have to solve problems
of duplicate frames, and I simply have not thought all these through.

Regards,
Choon Lee
3Com Corp

>> 
>> On Thu, 12 Aug 1993 15:59:16 -0700, Choon Lee wrote:
>> 
>> Choon,
>> 
>> I must disagree with the following:-( explanation follows)
>> 
>> >
>> >it hit me suddenly that there are times that a "loop" should
>> >not be broken. An example is the triangular topology (full mesh)
>> >case:
>> >
>> >
>> >            LAN A
>> >           ========
>> >               |
>> >            -------
>> >            |     |
>> >            |     |
>> >            -------
>> >             |   |
>> >             |   |
>> >  -------    |   |     -------
>> >  |     |-----   ------|     |
>> >  |     |--------------|     |
>> >  -------              -------
>> >     |                    |
>> >  =======              ========
>> >  LAN B                   LAN C
>> >
>> >
>> >Spanning tree would detect a "loop" in the triangular topology, and
>> >will attempt to block one of the links. Since DLSw does not cascade,
>> >the network is broken!
>> >
>> >A case of spanning tree working too well! :-)
>> 
>> Let me redraw your picture:
>> 
>> 
>>             LAN A
>>            ========
>>                |
>>             -------
>>             |     |
>>             |     |
>>             -------
>>                |
>>   ============================ LAN D (DLSW CLOUD - it's virtual)
>>      |                    |                          
>>   -------              -------
>>   |     |              |     |
>>   |     |              |     |
>>   -------              -------
>>      |                    |
>>   =======              ========
>>   LAN B                  LAN C
>> 
>> No loops here! :-)
>> 
>> Rgds, Shannon
>> 
>> >
>> >Regards,
>> >Choon Lee
>> >3Com Corp
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