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I have a special demand that to improve the redundancy of a network. (any of the cable between switches broken will NOT disconnect any clients)

   S = a switch    C = a computer   - = CAT5 cable

                  Internet
                     |
                  ROURTER              C
                     |                /
         S---S---S---S---S---S---S---S--C
         |                       |
      C--S---S---S---S---S---S---S
         /
        C

This seems should work, but:

  1. Does it work just out of the box?
  2. Any settings needed? (on router? or pc?)
  3. Will a packet gets passed around infinitely?

Thanks guys!

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3 Answers

up vote 4 down vote accepted
  1. Not usually
  2. Enable spanning tree protocol on all switches.
  3. If spanning tree is disabled, then yes. Else, no.
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Do managed switch has STP? a newbie Q? Whats the diff between Managed Switches and non-managed? –  c2h2 May 15 '11 at 14:56
    
@c2h2 - any managed switch (or even a "smart" switch) will have STP. The difference between a managed and non-managed switch (and there's even a few steps inbetween) really needs a question on its own, as there's usually a lot to it. –  Mark Henderson May 15 '11 at 21:36
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As @pavium says, your design is outdated, no networks need to be designed like that any more, it is much more standard to have a tree type structure:


                 Internet
                    |
                  Router
                    |
                   / \
                  /   \
                 SR----SR
                  |     |
                 SR1---SR2
                 /\     /\
                /  \   /  \
               /    \ /    \
              S1     S2    S3
               |      |     |
               C      C     C

SR = multilayer switch

Where S1 & S3 would also be cross connected to the multilayer switches SR1 & SR2. If multilayer switches are not available this is still valid using only layer 2 and much safer than using a straightforward loop.

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I don't see anything wrong with using the design the OP posted as long as he enables STP. I would posit that you'll find many more networks like his than like yours, especially in small businesses with limited budgets and expertise. For instance, A 25 employee insurance office looking to build some redundancy into their network is surely not going to implement a solution like yours... but a 2500 employee insurance office probably should. –  joeqwerty May 15 '11 at 13:46
    
@joeqwety I suspect that you are absolutely correct, but I also suspect that those networks just grew rather than being designed. As you say a small loop is perfectly fine and makes a lot of sense for a tiny network, but the OP has 15 switches in his design which suggests (to me at least) rather more than 25 users. The design I have suggested is scaleable, a loop is not and does the OP no favours at all by suggesting that it is a good design. –  blankabout May 15 '11 at 14:16
    
My bad, I took the S's in his diagram to be switch ports and not individual switches. –  joeqwerty May 15 '11 at 15:05
    
to be honest, this will be used in a subway train, around 4-6 cabins per train, each cabin has about 3-5 computers running linux. I am a software designer, but not too much knowledges about the network topologies. Q: is a noraml 200usd Switch like netgear one a multilayered switch? –  c2h2 May 15 '11 at 15:24
    
Interesting project. You are not likely to get a multilayer switch for 200USD so, if you have no other choice, you could adapt the design I suggested by removing SR1 & SR2 and cross connecting S1, 2 & 3 to the switches that are directly connected to the Internet gateway. In the absence of layer 3 capability, the important thing to check is that your switch supports spanning tree (STP, this can be checked on the Netgear site), and that it is enabled because that is what will prevent your frames endlessly (or until your network collapses). –  blankabout May 15 '11 at 17:46
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This seems like stepping back to the bad old days of coaxial-based ethernet http://en.wikipedia.org/wiki/10BASE2

The weakest point of such systems is often the connectors between nodes, and dramatically increasing the number of connections, as depicted in your diagram, will not give greater reliability.

The ring structure is similar to Token Ring http://en.wikipedia.org/wiki/Token_ring

This has largely been superseded by the improved technology of switched ethernet

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