3

I was reading about daisy chaining PoE switches and I had a doubt regarding it. While implementing this configuration, do we daisy chain the power or the data or both? Is it dependent on the wiring configuration?

It would help me understand the concept a lot better if any of you can help me out.

Thanks! D

2 Answers 2

3

There are two kinds of PoE devices/ports: power-sourcing equipment/PSE (switches or injectors) and powered devices/PD which draw power from a PSE.

PoE devices come in three generations: IEEE 802.3af ("PoE") with up to 12.95 W delivery, 802.3at ("PoE+") with up to 25.4 W, and 802.3bt ("PoE++"/"4PPoE") with up to 51/71 W (two/four pair). bt devices are still somewhat scarce.

There are a few small switches with a PD port and some very few among them with PSE ports ("PoE pass-through"). Since each switch requires some power for itself, the pass-through capability is generally limited to two stages if you start with 802.at power.

As Ron Maupin already stated, chaining Ethernet switches is not considered good practice. Chains introduce multiple single points of failure, increase latency and constrict redundant linkage.

The 'natural' topology for Ethernet is a tree: a core switch where all access switches connect to, or - when more ports are required - a three-tier hierarchy with distribution switches between core and access. These topologies also much better support PD switches in the access tier.

1

do we daisy chain the power or the data or both?

You only daisy-chain data. Power is not supplied unless the connecting device asks for it, and a PoE switch interface does not ask for power, but it will supply it if asked. In fact, most enterprise-grade PoE switches will have higher-speed interfaces used for uplinks, although that is not necessary to chain switches, and those interfaces may probably not be PoE interfaces.

In any case, it really is not a good practice to daisy-chain switches.

2
  • Thanks for the clarification! Now if I plan on implementing daisy chain for PoE networks instead of switches, it wouldn't pose an issue right?
    – user86914
    Dec 29, 2022 at 10:03
  • There are PoE powered switches. (usually 8 or less port, desktop devices. and a few "industrial" switches can be PoE powered.) Chaining power will quickly become a problem as the available power falls off a cliff.
    – Ricky
    Dec 29, 2022 at 19:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.