Wireless – Will spanning tree allow/support point the use of multi-point wireless links for redundancy

spanning treewireless

I've got a network, with a shared wireless link, I want to add the links identified by the "+"s. After reading up on spanning tree protocol I'm concerned the shared wireless link could be a problem.

           A
           |
         (WAP)--
          /|\   \
        /  |  \    \
      /    |    \     \
   (WAP) (WAP) (WAP)    \
     |     |     |     (WAP)
     B+++++C+++++D+++    |
                     ++++E+
                    (WAP)  +
                      |    +
                      F++++

I have control over the brand of switch, but not the WAPs. *WAP Info Added:* The WAPs are a combination of Tranzeo TR-5a-Nf and UBiQUiTi NanoStation5; specifically the WAPs at A, E & F are TR-5aNf, and the WAPs at B, C & D are NanoStation5.

The redundant links are standard Cat5E copper and connect as shown by the "+" lines in the diagram.

Any helpful suggestions or pointers would be greatly appreciated!

Backstory:
The current network is the diagram without the "+" links. B,C,D, etc. (there's actually five points) are on a farm spread out over about a 15,000 sqft area with about 1,000' between point A and the closest point and 2,000' between point A and the farthest point. Individual links go down occasionally (equipment blocks them, damaged, etc.) and we're trying to route around failed wireless links automatically.

I don't know all that much about spanning tree, but when I did some research it seemed to indicate that the redundant links had to be on separate ports and in this scenario they will all be connected to the same port on the root hub (A) by virtue of the multi-point wireless network.

Best Answer

After you have added your links, you will end up with something with the same issue as a mesh network: You have several wireless path toward a destination and you need to use the "best" and forget about the others. "best" being defined by some metric (capacity, loss rate, latency/jitter ...) which

  • is not trivial to retrieve
  • is invasive, you need traffic to get them
  • can change dramatically over time.

This kind of problem require a very specific solution. Your best bet would be to use something like 802.11s or another mesh routing protocol that support mixing wireless and wired links.

Using a wireless-unaware protocol like STP is asking for trouble. If a wireless link degrades but remain usable enough for STP, you will have horrible performance.

Alternatively, if your hardware does not support any mesh technology and you are not willing to change it, i would set A as a 4addr wireless client, so it can try roaming to the 'best' AP. But i admit i haven't understood the situation with E and F.

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