<h3>
<a href="http://www.circleid.com/posts/20120217_measuring_root_server_performance/" class="blue">Measuring Root Server Performance</a>
</h3><b><a href="http://www.circleid.com/posts/20120217_measuring_root_server_performance/">http://www.circleid.com/posts/20120217_measuring_root_server_performance/</a><br></b>By <a href="http://www.circleid.com/members/3167/" class="blue"><strong>Daniel Karrenberg</strong></a><div class="byline">
</div>
<img src="http://www.circleid.com/images/member_photos/photo_3167.jpg" alt="Daniel Karrenberg" class="memPhoto" border="0" width="80"> <p>Root name servers are a core service of the Internet (For more information on root name servers, please see the <a href="http://internetsociety.org/dns-root-name-server-frequently-asked-questions">DNS Root Name Server FAQ</a>).
As such they receive a huge amount of queries and need to answer
reliably with acceptable delay. The RIPE NCC is responsible for
operating one of the 13 DNS root name servers K-root which responds to
10,000 — 15,000 queries per second. Most root servers are operated as a
network of distributed "instances" using <a href="http://aharp.ittns.northwestern.edu/papers/k5-anycast/">anycast</a>.
That means a single IPv4 or IPv6 address is announced simultaneously by
a set of name server "instances" deployed in different geographical
locations.
</p>
<p>
K-root operates 18 instances; You can find a map <a href="http://k.root-servers.org/">http://k.root-servers.org/</a> on the RIPE NCC's website.
</p>
<p>
<a href="http://k.root-servers.org/visualk/">VisualK</a> is a new tool
that monitors the load of the K-root name server supported by each
instance. It further shows load migrations between pairs of instances
over time. ViskalK is one of the tools our operations staff use to
monitor the health of K-root.
<br>
The image below is a screenshot of the output of the tool. Each instance of K-root is represented by two concentric circles:
</p>
<ul><li>The first one, filled with colour, has a size proportional to the number of queries per second received on that instance;</li><li>The other one, indicated by a dotted line, shows the average load
over the previous 30 minutes. This is used as a reference value.</li></ul>
<p>
In most cases, these circles overlap. But in some cases you can see that
the dotted line is much larger, for example at the root name server
instance in Poznan, Poland. This means that something has changed
recently: the number of queries has dropped significantly.
</p>
<p>
<img src="http://www.circleid.com/images/uploads/6397.gif" style="display:block;margin:0 auto;" border="0" height="473" width="558">
</p>
<p>
In the image you can also see that pairs of instances are connected by
links (or "tentacles") if they are considered topologically adjacent.
Links between root name server instances are generally invisible, but
become active when traffic migration is detected: colour and size of the
link indicate the origin and volume of traffic flow, together with
bubbles pouring into the instance receiving the traffic. In our example
you can see that some load has moved from the instance at NAP (in Miami,
Florida) to the one located at LINX (in London, UK).
</p>
<p>
In addition, VisualK highlights unusual behaviour. Flashing arrows show
load migrations between instances that are not considered adjacent. Root
name server instances start to blink if their traffic load decreases
significantly. The goal is to help spot unexpected changes while they
are happening and to allow root name server operators to investigate
what causes these changes.
</p>
<p>
For more information, please refer to the background article on RIPE Labs: <a href="https://labs.ripe.net/Members/csquarce/visualk">VisualK — Monitoring K-root in Near Real Time</a>
</p>
<p>
<em>VisualK has been developed by Claudio Squarcella, intern at the RIPE NCC, in collaboration with the <a href="http://www.dia.uniroma3.it/%7Ecompunet/www/view/group-members.php?id=compunet">Compunet Lab</a> at Roma Tre University.</em>
</p>
<p><strong>By <a href="http://www.circleid.com/members/3167/" class="blue">Daniel Karrenberg</a>, Chief Scientist at the RIPE NCC</strong></p>