Mesh Wireless network as a backup link for existing fiber links

Unanswered Question
Jan 24th, 2009


we are planning to have a wireless mesh network as a backup link to our existing network with fiber uplinks.

Currently some of the uplinks are directly connected to our core switch (Layer 2 connectivity) and some of the uplinks are connected via nearby switch with single mode/muilti mode fibers. All the existing switches are mix of 2950/3560 and 3750 etc.

Can someone advise how can we configure automatic switchover to wireless network when there's a fiber link failure on particualr uplink(s). Our wireless solution is a mesh since there are many access switches currently connected with long distance with fiber cables.

I have this problem too.
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wesleyterry Sun, 01/25/2009 - 18:20

If you aren't routing between these sites, and just trunking your VLANs, Won't spanning tree do this for you?

If you already have the bridging path between your switches, then they should see multiple paths back, and choose the best path. So, wouldn't basic spanning tree keep the wireless from being used until it is the best option?

Now, the better question is, what are you doing for the mesh? Are you converting 1131 or 1242's into Enterprise Wireless Mesh, or are you implementing 15XX outdoor APs?

pemasirid Mon, 01/26/2009 - 11:50

Many thanks for your response. Could you please advise me how we can achieve with STP. Ofcause STP is the best solution if work in my senario.

yes we are going to implement with 1522 outdoor mesh AP.

Also I would appreciate if you can send me any reference URL to get more clear understanding about trigering wireless network as back.

thanks in advance

pemasirid Wed, 01/28/2009 - 11:55

Hi Westley,

Could you please clarify more with STP how this can be achieved. Can both ends mesh (MAP/RAP) conigured for STP. We have already STP running on the L2 switches.

Appreciate if you can share any documents on this senario.

Thanks in advance.

wesleyterry Wed, 01/28/2009 - 13:45

I don't have any documentation to back this up, so this is just a theory, but this is what I would do:

Configure the AP wired closest to your core (or main resources) as a RAP (root). Configure (for test purposes) all of your other APs as MAPs (mesh). Wire the MAP into your switches with the appropriate VLAN as the native trunked vlan (assuming you are doing any vlans). I believe all of your APs are going to need the same native vlan as your RAP.

Be sure to enable "ethernet bridging" which is an option in the GUI on the same screen you specify MAP or RAP.

Now in this scenario, all of your AP's will be building a mesh network back to your RAP and each MAP will be treating its wired connection like a workgroup bridge (providing the uplink to the switch from the RAP)...

Again, I am assuming that spanning tree will block this port if the fiber link is up, but as soon as the fiber link is down, this should be a valid path to send all traffic across..

Now, what I don't know about ROOT APs is if the uplink to the controller dies (the fiber goes down), can the RAP then function as a MAP? If so, then you could turn everything into RAPs. If all of your AP's are RAPs, then they will be using the faster fiber network as the connection to your controller. If they are all MAPs, im pretty sure they will all be using the backhaul of the radio to get back to the controller (but this might not be a problem if you aren't using these devices for client access).

Long story short, I can't prove it but it sounds like it should work fine.

Spanning tree may need some tweaking if for some reason it uses the mesh as the primary link, but I'm pretty sure it won't. The default nature of spanning-tree should use the best path, and if your fiber connections are gig, it should weigh them much better than the link to the Mesh AP.

Does this make any sense? It sounds reasonable to me, but I haven't tested it.


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