DNSMON User Guide
Domain Name System (DNS) queries are sent approximately once per minute to DNS root and Top-Level Domain (TLD) name servers. The queries are sent from about 60 locations worldwide, with the main concentration of queries coming from the RIPE NCC service region (Europe, the Middle East and parts of Central Asia). The elapsed time from sending the query to receiving the answer is measured.
The query types used in our measurements are not typically applied in real name resolution. However, both the capability and the time to answer these queries are very similar to the referral queries used in name resolution. The server has to be running and correctly configured to answer our test queries.
Graphs are provided to depict the measurements from three separate views:
The 'Probe' view shows a number of graphs, one to each server as seen from the test-box that you select. You can use this view to look at DNS root and TLD service quality at one particular location. Because name servers are well connected and geographically dispersed, this view can also be helpful as an indicator of connectivity between the test-box location and the rest of the world.
The 'Server' view shows measurements from all locations to a particular server. You can use this to assess the quality of the service provided by this particular server.
The 'Domain' view shows a number of graphs for each domain, one for the root and each monitored TLD as seen from almost all locations. You can use this view to assess the generic DNS root and TLD service quality provided to the collective pool of Test Traffic Measurement (TTM) test-boxes.
The DNS Monitoring Service provides a good assessment of the DNS root and TLD service at each TTM test-box location. You can work out which name servers serve a particular location better than others, and what the typical delay is. You can also see the effect that server and/or network infrastructure problems have on general DNS service quality.
The measurements allow you to rapidly evaluate any past or present DNS problem, and to work out if the problem is caused by poor root or TLD name service. By looking at measurements from all locations to a particular server, you can estimate the service quality of that instance. This comprehensive view lets you offset most local influences on metrics. This will give you a more complete picture than if the measurements were only from a single point on the Internet. It is possible to see if the server itself or the network infrastructure is behind poor quality service. You can also assess how 'close' any network infrastructure problems are to a given server.
'Global' DNS root and TLD service quality
We measure from around 60 specific points. While this is much more accurate than inferring DNS quality using only measurements from a single point, it is by no means comprehensive. Our measurement locations are concentrated in the RIPE NCC Service Region. This provides a reasonably accurate view of service quality in this region with some locations outside the region for comparison.
The general quality of DNS name resolution
There are many additional factors to take into account like DNS caching, service quality of lower level DNS servers, their network connectivity and the quality of DNS implementations. For instance, due to caching only a tiny fraction of all DNS name resolutions are directly affected by the quality of DNS root service.
Effects that last less than a minute
This is the interval between queries sent from test-boxes to name servers.
Notes on IP anycasting:
The scope of our measurements is the DNS service provided at each particular test-box location from each particular name server address. Some name server operators provide service at their address from different locations by means of IP anycasting. Our measurements differentiate between the different instances of such a server by querying every minute for 'hostname.bind' or 'id.server'. The instance can only be determined when there is a valid reply from the server. Currently, we are working on presentational aspects of this data. Watch this space for notes on progress.
You can get around the DNSMON site by using the menu that is at the top of each page. Each option will take you to a different part of the site and will also be the place to go if you need help.
If you select domains, servers or probes, you will see a second level menu appear.
Each second level menu is specific to the view selected. On overview pages, you can select another overview (as shown above). When you have chosen the overview that you want to see from the drop-down menu, you must click on the 'show' button.
On the third level invidual plot pages, you can select the time interval to plot and configure the plot (see above).