I've posted this over on the Ubuntu forums too....


Having a very strange problem with Ubuntu 12.04.

On the whole it connects to the internet fine, but every now and again when I try to use a website (even Google) it will instantly fail and say that the server is not responding. After a few attempts to refresh, it usually works.

We're talking maybe 1 in 10 or 1 in 20, but it happens frequently enough to be annoying.

Here's the thing:
They are two completely different machines. One is a home built desktop (Hackintosh) with a wired network. One is a MacBook Air 4,2 with its Broadcom Wifi. It happens with both Firefox and Chrome.
It's fine under OS X and Windows.

There is no physical connection drop i.e. the wifi stays connected on the laptop and there is no "cable has been removed" message on the desktop or anything like that.

Personally I think that rules out the hardware and drivers, which leaves me with the network infrastructure.
Anyone know of any compatibility problems between Ubuntu/Linux networking and Draytek 2830 series routers, perhaps? (I have updated the router firmware to no avail). These routers, whilst reliable, are admittedly known for these strange little bugs. (Yes I'm leaving that comment in my copy to here as I've had a few little quirks on Draytek routers over the years heh... but the support IS usually good......)

After a few attempts to refresh, it usually works.

So I guess there's a finite time when the problem is apparent. So.... if you can catch it try: -

ping 192.168.x.x #whatever address your router is, probably will always work on wired.
#What about the next hop gateway (from routers online status)
ping 8.8.8.8 #one of google's dnss, easy to type quickly
dig www.google.com

The idea being to try to see how far up the line the problem goes.

also, have you got two dnss in /etc/resolve.conf one working and the other not (bit of a long shot)?
Could the browsers be trying to do ipv6 dns lookup, it can be turned off on firefox so easy to test.

If you cannot catch it, leave a ping running in a term and see if theres any seq nums missing at the time.

Thanks for the ideas. I'll have to try and catch it, thing is it seems to be a split-second thing normally. A page will not work, then I'll press refresh and it's there (albeit maybe with broken images if it fails to connect for those), and it's extremely rare that it'll take more than a couple of seconds of refreshing.

Also it's not happened on my desktop since. It's happened a few times on the laptop, and makes a little more sense there as it's a dodgy Broadcom wifi driver. It's still "not quite often enough to easily troubleshoot but often enough to be irritating" so I guess I'll have to try different things over a long period of time.

Weird indeed. There must be others using this combination of router and OS, but admittedly both are very small percentages of the population.

My resolv.conf uses 127.0.0.1 as in the latest Ubuntu it appears to act as a server to itself and pass it through to a GUI network management tool. In the worst case I could probably see if I can bypass this mechanism and use something more traditional and low-level. The DNS configuration that I do get though is the router as the primary and the ISP's first DNS as its secondary. I've set up manual IP and specified each of those individually and both are working fine. I even specified the ISP's secondary DNS (which it would fall to if the router's DNS relay doesn't hit the primary) and that is fine also.

I wasn't sure from what you said but did you have any success by bypassing the router's DNS proxy? I.e. resolf.conf or your dns cache config set directly to your ISP's DNSs?

I have never really trusted the draytek DNS proxy function (though I may be paranoid) and my DNS (bind) forwards directly to the external DNSs.