Is FDDI still a relevant technology?

[terrywilson]

We are looking at implementing a WAN on a new site for a client; they have specified fibre ring which to me means FDDI (correct me if I'm wrong!) but I didn't think that it was that common these days. My thought would have been a pair of 24 port fibre switches with failover on the devices themselves. Opinions or suggestions welcomed

 

[baddos]

Depending on the local telephone company, they may be able to provide you with a dark fiber network, but you probably wouldn't use fddi.

I would be curious as to why you would need such a WAN and couldn't use a MPLS wan setup.

 

[terrywilson]

Why did I write WAN? I meant LAN; its a factory environment with processing equipment. In the spec's Ive been giving they specifically mention fibre ring and all tha tcomes to mind is FDDI which I haven't struck in person before, only in text books. Sorry to cause confusion.

 

[baddos]

Oh ok, well simple enough then. You can create a "ring" with gigabit fiber sure enoug with just regular ethernet. Using spanning tree you can have physical loops to ensure redundant paths in case a line gets cut or such. FDDI is similar to token ring which is what got you thinking about that, but it most likely will not be used as it would cost more and be slower than using todays gigabit fiber.

If this is just wiring for a single building or such you'll probably be using multimode fiber.

 

[terrywilson]

I had seen reference to relying upon stp to handle network failure in this way in some automation documents I was reading earlier. I was going to test it out in the lab and see how it behaves. One question though, how does it physically appear; for redundancy we will need two NICs per device and two switches; in terms of cabling, in my mind I'm seeing it look more like a traditional ethernet layout with teaming on the adaptors (if they support it) but what if the controllers don't support teaming; how would it work then?

 

[baddos]

If you are talking about a host connecting to two different switches, then yes you are correct. You would need to have a NIC and/or operating system that could support teaming.

STP or spanning tree would be a protocol that runs on your switches to handle the switches redundant paths.

 

[terrywilson]

I'll have to wait until I get more info from the customer. I have added the two different switches part myself; on the spec there are multiple switches, I am ssuming they will be splitting the devices across those. Am I right in thinking that to get the fail-over capabilities I have two choices:

- An FDDI network with dual rings and appropriate controller/switches

- An intelligent device that supports teaming and multiple adaptors

Are there any other ways that we could achieve the network redudancy that you could think of? Thanks.

 

[dgrizzard]

You can use fiber, but you need to make sure they need fiber.

Are they using 10GB?

Is there a distance issue?

Regardless if you're using fiber or copper you can just use port channels to connect the two switches together. This will allow redundancy on the link and it will allow both links to be utilized. If you used STP (which you should enable anyway!) then one of the links would be blocked and essentially wasted unless there was a failure. The second thing you have to remember is that there is a convergence time for STP (if you're using RSTP then it is faster), but when using port channels/etherchannel there is no convergence time since it sees both cables (up to 8) as one link.

I have attached a diagram as an example. The diagram though shows two switch chassis. Basically what I show here are 4 switches with two on each side in a chassis (they are connected together on the back end with 2 stack link cables). This allows redundancy in the hardware and logically each chassis will appear as one switch when you console into them. So each switch will have a fiber or copper cable running between them (or more than one) and then you will put all of those cables into one stack link. If you really wanted to be redundant then run two cables between each switch (so 6 cables) that way up to two switches can fail (hardware wise) and everything would still be up.

Link to image just in case it doesn't show up ....

http://img138.imageshack.us/img138/9249/diagramj.jpg

 

[terrywilson]

Nike, very good explanation there. Unfortunately we were involved after the cabling was installed so we only have one fibre run between each cabinet. The main driver for fibre in this case isnt distance but interference; its going its going into a mill with lots of noisy electric equipment. Thanks for the post though, I had read about Etherchannel and wondered if that would have been a better way to do it as well, unfortunately I think that ship has sailed

 

[dgrizzard]

Ah well in that case then just stick a couple of fiber modules into the switches and link it up Just make sure if it SMF or MMF, and you probably want to turn on UDLD (unidirectional link detection).

Best of luck