I just purchased a Samsung M2830DW  You can run it either wired via 
USD/Ethernet or via Wifi.  Meets you 600 DPI requirements.  A local 
office supply shop had one on sale with free next day delivery for $50 
USD and it works with  Google Cloud Print, so it was a buy for me.
It was a pain to set up Wifi, but once I got it on the wired network, 
it was relatively straight forward to configure via a web interface.
On 2015-11-21 12:48, Adam John Trickett wrote:
> Hi,
>
> My elder Epson ink-jet printer has become increasingly unstable 
> (mechanical
> failure I'm sure). I'm looking for a laser printer to replace it. 
> Requirements
> are:
>
> 1) Wired networked
>
> 2) 600dpi, I don't need to pay for higher, but it's okay if it's 
> higher
>
> 3) Duplex would be nice but is not essential.
>
> 4) Must work with Linux
>
> 5) USB or parallel port okay but not essential if wired network is 
> there.
>
> 6) Postscript nice but not essential if Linux (CPUS) driver works 
> perfectly
>
> 7) Low volume printing - don't need heavy duty cycle but don't want 
> toner to
> "go off" if unused for months at at time
>
> 8) Don't need a scanner function etc
>
> 9) A4 Only.
>
> Any suggestions? I've no brand loyalty.
>
> --
> Adam Trickett
> Overton, HANTS, UK
>
> In a world without walls - who needs windows?
>     -- anon
-- 
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