My iMac randomly drops his Internet connection ?

[Synchronyme]

Hi,

I use my iMac for 3 stuff: mail, surfing (on Opera, Firefox and Safari) and World of Warcraft. But since a couple of weeks, my iMac has random and temporary networking problems : accessing a website becomes *very* slow (30 sec to load a page) and WoW shows a *huge* latency.

Now I know it's not my network because my linux pc, my macbook and my tablet have zero issues with our modem (fiber connection). Also, if I reboot the iMac the internet is fast again. It's only after a while (+2 hours) that the lags appears again.

I'm really not a Mac specialist so I'm not sure where to look for this: I checked the monitor utility/networking tab, but saw nothing special (no program that would have taken all the resources...). I ran Onyx and even Avast but fond nothing fishy neither.

So I don't know what could cause this... DNS ? But why WoW is impacted then ? And why it's only after a while ? If it's one of the browsers I use, why the issue stays after I close everything (but disappear for a while if I reboot) ?

I'm on Yosemite btw. (didn't upgrade yet: not sure if the bonus are greater than the fear of seeing my system -and not only my internet- becoming sluggish... but maybe I should ?)

 

[BrianBaughn]

Just using your provider's modem/router and no other networking devices?

 

[DeltaMac]

Are you using an ethernet (wired), or wireless?
If wireless, can you try a wired connection to see if that ethernet connection will help make your internet connection more reliable?

 

[Synchronyme]

The iMac is wired (ethernet) to my only provider's modem.

 

[BrianBaughn]

This doesn't sound like anything I can remember seeing.

What results do you get if you do an actual "Internet Speed Test" after booting and another after it gets sluggish?

 

[DeltaMac]

Which iMac do you have?
Do you still have the 2008 model?

Have you ever tried restarting your modem?

 

[kschendel]

Try Activity Monitor (in the Applications/Utilities folder) after a reboot and then once it's slow, maybe you picked up some adware / malware, or Spotlight reindexing, or something. If it's cpu or disk activity on the machine you should be able to see it via Activity Monitor. If nothing shows up there, look for bad packets / errors / retries on the Ethernet interface. Maybe try a new Ethernet cable. (Yes, they can sometimes go bad, I found out the hard way!)