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I have a PoE+ switch (ZyXEL GS1100-8HP) that has a button on the front to toggle IEEE 802.3az compliance. I looked this up and found that it was a power management specification known as "Energy-Efficient Ethernet".

From the Wikipedia page, it seems that the primary effect is that the transmit path of the physical layer is put to sleep when idle. The user manual for the device says about the same thing.

Granted that for home use (the Wikipedia page mentions this and also it seems logical) savings are probably minimal. Also, at pretty much any given time something on my network is sending something -- a quick glance at Wireshark shows a typical stream of whatever; ARP, Dropbox stuff, SSDP, etc. and the activity lights on my switches confirm.

That said, I don't know why I would disable it. Without knowing more about it it seems benefits will be either zero or positive, i.e. it can't hurt.

So my question is: Why wouldn't I want to enable 802.3az? The fact that there's a toggle button on the front of this switch means that somebody somewhere seems to know that there's a reason to disable it; what is that reason?

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  • I would assume the reason there is a toggle, is because you should only enable it, if all clients on the network support 802.3az
    – Ramhound
    Sep 26 '16 at 14:45
  • @Ramhound Is your implication that no change happens in the switch's own power-management regardless of client support? Also the question still remains: Why not just leave it enabled anyways? Does it cause harm to devices that don't support it? If 9 out of 10 connected devices support it does that still mean I'd want to turn it off anyways?
    – Jason C
    Sep 26 '16 at 14:49
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From the user guide of the product:

An EEE-enabled device initiates Low Power Idle (LPI) signals to negotiate and wake up the remote device when there is data to be transmitted. To use EEE, both devices should be EEE compliant.

EEE is configured on a per-system basis in the Switch. If one of the networking devices that connect to the Switch doesn't support EEE, EEE may not work in the Switch to save power.

Press in the IEEE 802.3az EEE ON/OFF button on the front panel to turn on the EEE feature. Disable it if you don't want the network performance to be impacted due to the latency from the additional time required for the sleep and wake transition or if the remote side doesn't support it.

This basically says that if one device connected to the switch does not support 802.3az then the power saving function might not work, hard to tell so just try it. But it does lead to a slight latency so if that is an issue then turn off the energy saving function.

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  • Thanks. I did see that although it's about the same info as Wikipedia. I figured it was a performance issue, but in practice does the wake up time have a non negligible effect? There are a lot of "performance" statements in a lot of areas that don't have much of an impact in reality, is this one of them? I notice no change in network speeds with the feature off or on, although this could be because not all my devices support it. Also does it hurt to leave it enabled if a device doesn't support it?
    – Jason C
    Sep 26 '16 at 17:12
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    It all depends on what your needs are in the network, a home network with normal usage does not feel any difference I would guess if this is turned on or not but a professional network would be very vary of using this feature. Also, once the devices are turned on then you won't feel any lag on the network, its only in the beginning when the switch is sending out signals to turn on the device that this has any effect.
    – ojs
    Sep 26 '16 at 17:51
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In my case [router does not support it, laptop does], the connection kept on dropping and reconnecting very quickly (within a couple of seconds). I had to disable Energy-Efficient Ethernet to get a functional connection.

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  • Interesting. So the 802.3az switch was in the laptop side in your case, yeah?
    – Jason C
    Oct 21 '18 at 0:01
  • By switch, if you mean the setting which I could toggle, yes.
    – Milind R
    Oct 24 '18 at 5:04
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    That's what I meant; too many things, not enough English words, lol.
    – Jason C
    Oct 24 '18 at 12:48
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There are some usages, that need EEE disabled. For example Dante audio networking will not work with energetically efficient switches.

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