The sys admin's daily grind: Dnstop

Save the Day

Article from Issue 185/2016
Author(s):

In last month's issue, Charly sent the lean pdnsd DNS cache down the catwalk. To see whether pdnsd really does the work expected of it, he now puts dnstop through infinite rounds in the name of names.

Most distributions include dnstop. If you prefer to build it yourself, you will find the source code online [1], but make sure you download and build the matching Libpcap [2] first. I launched the tool on the computer hosting my DNS cache with the following command:

dnstop -l 3 eth0

The -l 3 parameter tells dnstop to explore name requests up to the third level. For a request like www.linux-magazine.com, com is the first or top-level domain, linux-magazine is thus the second-level domain, and www is the third level.

When I press the 1 button on a computer running the command listed above, I can see which top-level domains are most frequently queried (Figure 1). What I am interested in here is which device on my network is asking for .xyz domains – but hey ho, if I press 2 or 3, I can extend the view to include the second and third levels.

Figure 1: Pressing the 1 key displays statistics with the requested top-level domains. It comes as little surprise that .com tops the list, but who is looking for .xyz?

Frequent and Rare Resource Records

Pressing T takes you to another practical statistic. It shows you what resource record types are most frequently requested. It is unsurprising to see requests for A (IPv4) and AAAA records (IPv6) topping the list (Figure 2). Well back in the field, is the A6 record, which comes from the early days of IPv6 and is about as widespread as gas streetlamps today. Other fairly sparsely represented records include DNSKEY, which come from DNSSEC (DNS Security). In contrast to A6 IPv6, DNSSEC is increasing steadily but still not well established.

Figure 2: Pressing T shows you the Resource Record overview. The A records typical of IPv4 have a two-thirds majority.

Pressing R (for Result) shows you how many requests were successful. In my short observation period, this was all of them, thankfully:

code       Count      %
------- --------- ------
Noerror     23987  100.0

If I use dnstop for evaluations at work – and then save them somewhere – I need to think about data protection. To avoid problems from the outset, I tend to launch the tool with -a for "anonymize." Then, dnstop replaces the client IP addresses with consecutive numbers, while all the other evaluations work as expected.

Charly Kühnast

Charly Kühnast is a Unix operating system administrator at the Data Center in Moers, Germany. His tasks include firewall and DMZ security and availability. He divides his leisure time into hot, wet, and eastern sectors, where he enjoys cooking, freshwater aquariums, and learning Japanese, respectively.

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

SINGLE ISSUES
 
SUBSCRIPTIONS
 
TABLET & SMARTPHONE APPS
Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Top Ten Tops

    The famous Unix admin utility known as Top has many imitators. We take a look at some of the top Top tools.

  • Charly's Column – Pdnsd

    Cache it, if you can! When the latencies of his Internet connection seem to take longer than Napoleon's reign, sys admin Charly comes up with a solution for name resolution.

  • The sys admin's daily grind: Let's Encrypt wildcards

    The pleasure of owning a nice domain like sensorenresidenz.de is clouded by the requirement of an X.509 certificate for every subdomain that the admin wants or has. Columnist Charly can help boost the webmaster's spirits.

  • darkstat

    Thanks to its minimal footprint, 20-year-old darkstat hardly generates any noticeable load even on low-powered systems, making it the perfect monitoring tool for Charly's home utility room.

  • Charly's Column – Doorbell Pi

    When Charly puts on his headphones at home, he often fails to hear the doorbell. So, he dreamed up a solution with a Raspberry Pi Zero, a noise detector, and a power outlet with a LAN connection.

comments powered by Disqus

Direct Download

Read full article as PDF:

Price $2.95

News