I've been using Internet for long and it feels slow long before ping reports packet drops or streaming shows loader. It feels sluggish, but when ISP tech support is puzzled too, it leaves me to look deeper.

After struggling with the slow ISP AirTel, I wondered what really is slow from technical aspect and I wanted to see if the dns server was upto the mark. I'm looking at the router config and it shows 125.22.47.100 (2401:4900:50:9::280) - we'd stick to the IPv4 version for a while. Checking for one lookups seemed non conclusive so I wanted to test it for a bigger list this time. I'm on a macOS so flushing dns would be a step too. So I could think of the test to be as go to a list of 500 domains, look up every domain name, and measure the complete time taken to do so. And then repeat it with cloudflare dns 1.1.1.1.

The list should be the first thing. Somewhere on Internet, Moz has a great list of 500 domains, also downloadable as csv. After cleaning up the list looks like:

www.google.com
www.blogger.com
youtube.com
microsoft.com
apple.com
...

I made a copy at github gist for reference.

Next is to feed this list to dig - a dns lookup utility on unix machines.

dig -f hostnames.txt +noall +stats
-f to feed the long list of 500 domain names
+noall to suppress default list of outputs
+stats to show stats that includes resolution time

To sum up all time taken by the command, a time command is handy.

dig -f hostnames.txt +noall +stats
0.07s user 0.13s system 0% cpu 3:40.70 total
So 3 mins 40s. Okay.

How would 1.1.1.1 do:
dig @1.1.1.1 -f hostnames.txt +noall +stats
0.06s user 0.10s system 0% cpu 31.568 total
31s.

That is 7x faster, or Airtel's 125.22.47.100 is 7x slower.

The real problem is if I change dns on the router to forget about the problem, AirTel makes it a point to disconnect service and it is all unusable - don't understand this part very well but it is probably to discourage using public dns.

Anyway, for now it confirms this dns is 7x slow.