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Good afternoon everyone.

I would like to know the textbook answer to a network I've been asked to assist with.

I have an IT cupboard which serves the location as the MDF. I then have a variety of zones (A,B and C) throughout the location. Unfortunately there has been no consistent plan whilst installing cabling to these zones so you have a situation something like this:

MDF <---1x 60m---> "A" <---2x 10m---> "B" <---2x 5m---> "C"

All cabling is Cat6a.

Is the best option here to connect the MDF-A cable to one of the A-B cables, with A and C connecting to B? All switches at A, B and C are identical.

Pros of this approach, traffic from B and C has one fewer hop to reach the MDF and there are no areas more than 3 layers deep. Cons of this approach, traffic from A has one more hop to reach the MDF.

Any input you have is appreciated!

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  • Layer-2 doesn't have hops. Hops are a layer-3 concept. At layer-2, all hosts are connected as peers, and the frame survives unchanged from one host to another host. There is no TTL or any other way of counting hops in layer-2.
    – Ron Maupin ♦
    May 30, 2017 at 14:00
  • Hi Ron, I understand this. Hop count was put in quotation marks for this purpose but I will edit the title to avoid confusion
    – eto.ttnflt
    May 30, 2017 at 14:02
  • 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 could provide and accept your own answer.
    – Ron Maupin ♦
    Aug 14, 2017 at 4:24

2 Answers 2

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A best practice would be to use a pair of switches as the primary and secondary root switches, and all access switches are connected to both the primary and secondary root switches.

Daisy-chaining switches is a poor practice that introduces SPoFs (single-points-of-failure). The failure of one switch in the chain will orphan all the devices downstream of the failed switch.

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  • in an ideal world this is what I would be installing, however I cannot run new cable to the MDF which is where our WAN links terminate therefore I have to use what I have. There is the alternative of creating a loop A-B-C but that still gives you two SPoFs at MDF and A. The example I gave currently has SPoFs at MDF and B.
    – eto.ttnflt
    May 30, 2017 at 14:22
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It's very common for environments to grow and have it built that way over time.

Each switch the packet will have to pass through is considered a hop as the individual switches have to process/tag/untag, unicast/broadcast packets, etc.

If you could direct connect your switches to the mdf with single-mode fibre, that would be a performance plus as you can upgrade to 10G or more. But that would have to be justified with a valid business case...

But in those unplanned environments where you have to piggy back from switch to switch with cat5e/cat6/cat6a/cat6a-shielded (mostly stuck with 1G per link due to distance) make sure your uplinks/downlinks are bonded in an etherchannel (or similar) and never go over the maximum number of hops.

Until you have your new fibre in place, I'd recommend to have a exact model spare switch on the side towards minimising downtime when one of the switches suffers from some fault.

For the hops, see this link from a manufacturer: www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/19120-122.html

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