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> I am a bit confused about the way switching works on the DECswitch
> 900EF and how the backplane segments get interconnected.
>
> Let us assume we have, in a DECHUB 900, two 900EF, two PORTswitch
> 900TPs, and two DECrepeater 90TS. Out of the Flex Channels, we create five
> Ethernet channels (Ethernet 2 through 6) and one FDDI channel.
> We then create the following configuration:
To be more precise, you create 5 ethernet LAN segments and
one FDDI ring segment, which at this point are an abstract concept
since you have not yet connected anything - channels get assigned
only after you make a connection. Think virtual LAN. So let's forget
about channels, you never see them anyway and they are causing
confusion I think. The connection between modules is what counts.
> - one 90TS is connected to the Thinwire Ethernet, the other 90TS is
> connected to the Thinwire and to Ethernet 2.
> - some ports on the first 900TP are connected to Ethernet 2 and some to
> Ethernet 3. on the second 900TP some ports are connected to Ethernet 3
> and some are connected to Ethernet 4.
> - one the first 900EF two ports are to be used for external connections
> (one server on each port) and the other four are to be used to connect
> to Ethernets 1 to 4 on the backplane. the second 900EF is to be
> configured in a similar way. None of the 900EFs is connected to
> Ethernet 5 or 6.
>
> Some questions:
>
> 1- If I connect a module to Ethernet 5 or 6 will stations on that
> module be able to reach the rest of the network? How?
>
Assuming that the connection to LAN 5 or 6 is the only connection
that module will have:
The only way to have a module reach anywhere is to connect it to
another module. Since there would be only 1 module on LAN 5 or 6
it cannot talk to anyone. You will need to connect a switch port
each on LAN 5 and 6. "Imagine the sound of one hand clapping".
> 2- If the answer to 1 is no, How do I configure my switchs to have all
> segments see each other?
>
Since you have 12 ethernet ports available from the 2 900EF switches,
use 6 of those ports to provide connectivity to the Hub LAN segments.
Use the other six to connect to your servers on the front panel
of the switches. Connectivity-wise, it doesn't really matter which 6,
barring media concerns (UTP/AUI), you can use them from either switch.
Performance-wise, you will want to try to keep stations that tend
to talk to each other on the same switch. Or the same LAN.
Connect the two switches together on an FDDI LAN in the hub.
Because the switches are connected together on FDDI, it makes no sense
to connect more than one switch port to each LAN, unless you wish
to take advantage of the spanning tree protocol to provide backup
connectivity in the event of a switch failure, which is perfectly
reasonable, but you did not express this need.
> 3- If two ports on a 900EF want to communicate, do they do it over a
> backplane segment? do they use the FDDI? or do they get switched inside
> the switch?
>
All ports are interconnected within the switch itself, including
fddi <--> ethernet. flooding is taken care of by the forwarding
database, loops are taken care of by spanning tree. All ports see
all other ports.
> 4- If two external ports on two different 900EFs want to communicate,
> do they do it over the FDDI channel?
>
Yes. This assumes you have manually connected the two switches, via a
Hub FDDI LAN using Hubwatch, which you didn't mention.
> 5- Does each 900EF have to be connected to all backplane Ethernet segments
> to be able to switch between them? or can I connect one 900EF to 3
> Ethernet segments and the other 900EF to another 3 Ethernet segments
> and this will give me switching abilities between all my segments
> through the FDDI?
>
Yes you can do 3 and 3 and the switches will pass packets over
the FDDI.
> 6- What is the best way to configure the above hub if I want to have 4
> servers each on its dedicated Ethernet segmnet and about 100 clients
> on the port switches?
>
See question #2.
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