I am pretty much a newbie when it comes to networks so forgive me in advance if this question seems odd.

So here's a situation I am trying to figure out. There's a company who operates in 2 adjacent buildings, separated by 75m, and there is an underground pipe where a network cable could be passed. Let's assume that there is no network configured at the moment. One single static IP adress will be provided by a telco and the router will be installed in Building A's equiment room.

Each building has its own equipment room. There are 2 groups of workers in Building A (lets call them Sales and Accounting) and one group in Building B (Development). I want to have one switch per team (so 3 switches in total). The ultimate goal is to setup a VLAN. Assuming I would run a fiber optic cable from building A to Building B, what type of equipment would be required to connect the switches together to create a single network ?

  • 1
    You could directly connect the switches with the fiber optic cable. I'm not sure what other equipment you think you may need.
    – Ron Maupin
    Mar 30, 2020 at 0:59
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin
    Dec 17, 2020 at 16:25

4 Answers 4


There are honestly a bunch of different ways that this could be approached and we'd need to know a lot more about the scale of the requirement.

That said, in broad terms you might take the approach of a small L3 switch as a core in the primary building. It would have a fiber connection through the conduit to an L2 switch in the secondary building. The L3 core would also connect to the L2 switches in the primary building supporting sales and accounting. Finally, the L3 switch would also connect to a firewall that connects to the Internet router to provide security, NAT, etc.

The L3 switch could be configured with multiple VLAN's that are distributed to the L2 switches as needed (...so the development VLAN via the inter-building link, etc). The particulars of speeds and feeds and model numbers would depend on a bunch of the unknowns mentioned above (scale, performance requirements, budget, etc).


Use single-mode fiber (the kind with a yellow outer-jacket) to connect different buildings. It's best to get a professional fiber contractor to help you pass the fiber through the existing conduit; they can supply materials, too.

Use SFP+ or other plug-able optics marked 10km range for this application. Since you are new to this, buy the optics sold by the manufacturer of your switches; don't get "generics." Generics will almost always work, but I don't advise their use by folks unfamiliar with troubleshooting optic compatibility issues.

YOU MAY use the same switches for multiple teams or departments. I recommend it. VLANs allow you to segment users from each-other by configuring the switch-ports into logical groups connected via routing. Separate switches let you do the same thing, but the invention of VLANs makes it easier and less-costly.

DO NOT use a shorter-range multi-mode fiber & plugable module for this. That can seem like a good way to save money, but it will limit your options in the future for only a tiny, tiny cost savings.

  • SM fiber seems like overkill to me, given the distance is well within MM range. Why do you think it won't be suitable?
    – Ron Trunk
    Apr 1, 2020 at 18:19
  • The reason to use MMF is cost savings. When the number of units (of optics & cables) is this small, the flexibility lost by installing MMF is a big deal, and the cost-conservation is small. Since SMF is the industry standard for inter-building, inter-suite, or inter-company connectivity, and MMF is rarely used for these applications, I don't recommend MMF (at all, for any use) unless it's a large installation and the decision-makers understand the trade-offs. Apr 1, 2020 at 21:35
  • I don’t understand: what flexibility is the OP likely to lose?
    – Ron Trunk
    Apr 1, 2020 at 22:17
  • A common situation I run into is carriers being able to terminate circuits more easily (or cheaply) in one building/suite/floor than another. If you have SMF available, you can almost certainly extend such circuits passively to wherever you want them. If you use MMF for your internal cabling, you'll find your options for things like extending a demarc suddenly more challenging. Since the cost savings from using MMF is so small, I therefore don't recommend it unless the quantity is high and customer understands the consequence. Apr 2, 2020 at 13:24

To adopt optimised and scalable network as of your requirement.. devices you can use are ..

1 ) Router - edge or perimeter devices ISP interface is connected

  1. Layer 3 switch - To create VLans(SVI) to segregate traffic among sales ,accounting ,and development .

  2. Layer2 switch 2 each in each building futher we can use more layer2 switch as business and users increases .

  3. Optical fiber cable connecting two building and enabling trunk port at both end ensure all vlan will get accessed in building 2 also .


The minimum equipment is one router, and one switch in each building connected by a VLAN trunk. Fiber is recommended when connecting buildings.

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