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Just recently I had an interview for a network Engineer position. The interviewer asked me the following: You have a building of 5 floors, where each floor has around 30 employees. What is your way of structuring such a network?

I tried my best and then he told me that I should have a network room in the basement. There I have my routers connected with LA. In each floor I have my switches connected also with LA and forming a ring with the routers in the basement. Of course, spanning tree is on.

His answer is not so clear to me. Can anyone point out the standard way of structuring such a network?

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    This is simply too vague. There's no "one-size fit all" answer and the one they provided is very poor. A switch ring is an awful topology.
    – JFL
    Jul 8, 2020 at 6:22
  • Sorry but I have been working in Networks field for only 18 months now. So I'm not an expert. But I've seen many of my employers customers use the switch ring topology. I though it's a good way. Could you please clarify why it's so bad? Thanks in advance.
    – AhmedWas
    Jul 8, 2020 at 10:03
  • 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 18:49

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Sorry for being blunt but if you can't answer that you should reconsider applying for that position.

When asked such a question you should counter with "what are the requirements?" - how redundant, resilient, fast, future-proof does the network need to be? Are there hot spots (data center, power users)? Is there a budget?

The usual structure is to run horizontal cabling within each floor, usually twisted-pair copper, distributed by one or more L2 switches. For high bandwidth demands (>10 Git/s), fiber may be necessary.

The floor cabinets are connected to a central cabinet via vertical cabling, usually fiber. For smaller buildings and low bandwidth demands, copper may also be used. The central cabinet should use L3 distribution to the floor cabinets - fast routers or L3 switches. Again, with low requirements, you can also use simple, "flat" L2 distribution.

Note that you shouldn't use rings for L2 connections, only trees. If redundancy is required, start at central distribution with dual switches and dual downlinks.

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  • Thanks for your answer. I have 3 questions. Thanks in advance: 1- If I have more employees in each floor that I need to install four L2 switches instead of one per floor. These four switches should be connected to each other as ST mesh? 2- Only switch no.1 should be connected to the base L3 switch? or both switch no1 and no4 should be connected to the base? 3- Why L2 rings are bad for redundancy?
    – AhmedWas
    Jul 8, 2020 at 10:42
  • 1+2) If you need more switches, just add them to your floor cabinet - make sure you uplink each of them to the central switch(es) individually and don't chain them. Interconnecting them isn't required but may be useful for redundant uplinking. 3) Standard Ethernet is not designed for rings or meshes, and long chains need to be avoided generally. The spanning-tree protocol (RSTP/MSTP) blocks all redundant ports anyway, so they're only actually used in failover scenarios.
    – Zac67 ♦
    Jul 8, 2020 at 11:38
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For building 5 floor network .. just chossen

  1. layer 3 switch as core
  2. 5 layer2 as access switch
  3. router connecting for internet access

Use horizontal cabling peer to peer

Consider 6 vlan in total 5 vlans for each floor &1vlan for management . Configure 6Svi and DHCP configuration , intervlan concept ,access-list in layer3 core switch.choose one router connecting for internet and router has to connect with layer3 core switch so that internet access cann provided for all six floor .. each 5 floor access configuration should be done 5 trunk links should be configured from layer3 core switch to layer2 access switch

Dchp configuration in layer3 switch will used to allocate ips dynamically to desktops on all floors

Access-list in layer3 switch will used to restrict vlan between them to communicate according to organisation requirements . U can setup layer3 and router in baseroom of building and all trunk links will connect from layer3 switch to access switch towards upwards...

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  • Excellent.. Thanks for explanation. I designed and configured my company network infrastructure upon fallowing your posts... Really helpfull..
    – user73775
    May 18, 2021 at 12:43

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