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This problem has plagued me across multiple networks (Ethernet and Wi-Fi, across multiple ISP's) and multiple operating systems (Snow Leopard, Mountain Lion, Mavericks). While browsing, my internet will completely slow down, images will load terribly slowly and youtube just won't work.

If I change my DNS in network prefs, everything starts working beautifully again for the next 10 minutes or so until it slows down again.

I need to keep switching between Google's DNS and my ISP's DNS continuously so I can use the internet.

Does anyone know the issue and what could fix it? Thanks for your help!

Edit:

  1. Further information - Images / videos take super long to come through but most of the time text will show up with / without styling.

  2. The laptop was purchased from outside the US but I'm currently residing in the US.

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  • Does the problem happen with multiple ISPs and in different locations e.g. Work, an internet cafe, a friend's house? You should include that information in your question as it isn't obvious and if the connection is fine in a different physical location it might be your ISP or router.
    – codecowboy
    Commented Jan 13, 2014 at 18:20
  • I implied that by mentioning 'multiple networks' but I'll update my question nonetheless; thanks for pointing that out.
    – Siddharth Iyer
    Commented Jan 13, 2014 at 18:22
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    Presumably there are other machines / devices on the same network(s) not experiencing these issues? Instead of changing the dns info back and forth, does 'dscacheutil -flushcache' at the terminal have the same effect?
    – codecowboy
    Commented Jan 13, 2014 at 18:34
  • Yes most of the networks I've used have a bunch of other devices on them. I'm facing these issues on my personal Macbook Pro. The one I have from work faces no such issues on the same networks so I'm certain there's something going on in my personal macbook. I will try the dscacheutil -flushcache when I get home and let you know how it goes. Could you please post an answer with your comment? I'd like to upvote it for helpfulness (and accept it if it works) :)
    – Siddharth Iyer
    Commented Jan 13, 2014 at 19:13
  • I'm not an authority on this stuff so I would wait for a proper answer if I were you ;)
    – codecowboy
    Commented Jan 14, 2014 at 9:33

2 Answers 2

Reset to default
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+50

I can think of 4 possible reasons:

Bad hardware config

It's worth re-setting the NVRAM in your machine by holding Command, Shift, P and R while booting. You'll hear a chime - keep holding, then you hear another chime - let go. This is safe to do.

Bad/Broken Network (Filter) Driver

There's also a possibility you have a bad network driver installed, perhaps against your knowledge, or maybe a leftover from some software. Try booting in Safe Mode (hold Shift as your machine boots) and see how the internet performance is (everything will be slow in this mode, but if it's a driver issue you should see a difference in the browsing).

Malware Infection

The last time I saw this behaviour turned out to be a rampant malware infection on the computer which was saturating the internet connection by sending out spam email. Changing the network/IP details temporarily interrupted the malware until it work up again. You may be able to see this in Activity Monitor (all processes, look at network tab, anything using a lot of networking while you don't do any browsing?). It is worth doing an anti-malware and/or virus scan to eliminate this risk.

It's time to do a fresh install

Have you upgraded your OS from Leopard thru Mavericks? Ever done a 'nuke-and-pave' / erase-and-reinstall? Might be worth it in your case - you can restore your data from a TimeMachine backup (make sure you have one!), but do not have to restore the whole system. It depends on how much software you'd have to spend time reinstalling, but this has worked well in the past for people I've worked with.

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  • That's it! Network monitor showed me that a process from a VPN client I had installed on my machine at my last job was still sending and receiving a substantial amount of network packets even though the client wasn't running. The amount was sizeable.... 1.5 MB of data sent and received, which is pretty large considering that Chrome was listed at 2 MB. I uninstalled the client and so far so good. This is the longest I've had my mac running without any network connectivity issues.
    – Siddharth Iyer
    Commented Jan 20, 2014 at 22:19
  • Your statement - "Changing the network/IP details temporarily interrupted the malware until it work up again." was what helped me most.
    – Siddharth Iyer
    Commented Jan 21, 2014 at 1:17
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    Splendid! So glad you found the root cause!
    – JBRWilkinson
    Commented Jan 21, 2014 at 13:01
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I'm betting you are outside the US.

If you use the Google DNS Server then you will find that a lot of Content Delivery Networks (CDNs) will deliver you content from a US server. This will be slower than a closer server.

The delay in the problem is because your Mac is caching the DNS answer for a short time. Why some machines and not others is a bit of a puzzle but I suggest you try using your ISPs DNS servers for both secondary and primary for a few days and see if the problem goes away.

Check this out http://apcmag.com/why-using-google-dns-opendns-is-a-bad-idea.htm and this http://joemaller.com/2577/itunes-slowdowns-with-google-dns/

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  • Hi Tony, thanks for your response. I'm currently residing in the US and all my DNS settings are set to default to my ISP as of now. I keep switching between Google / my ISP to make things work for a short time. Not sure how relevant this is, but the Macbook Pro was purchased outside the US. I'll add that to my answer.
    – Siddharth Iyer
    Commented Jan 15, 2014 at 14:20

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