Interpreting UI/Reports, PNM Viz Overview

RDn: DNS

Description

This shows the speed of response from your DNS service.

The DNS service is a network resident service to which your computers pass the name of the thing they want to access and it replies with the IP address to use when connecting to it.

For example, if you want to access CNN to read the news, your computer will send “www.CNN.com” to the DNS service. As at the time of writing this article, the DNS service will resolve that host name for CNN to the IP address “151.101.17.67”. Your computer and browser then uses this IP address to communicate with the CNN website.

Your DNS may be provided by your service provider or you may use a third party.

There is a link on this page to a short article outlining the typical components of a home internet service.

Real-world impacts

If you are suffering from poor DNS performance then you may be seeing slow initial responses from web sites.

This is a “slow down” issue – your network is working but just taking too long to do things.

If the DNS fails to resend altogether then you will see a message saying you cannot access that website at all.

Both issues can be intermittent.

Remember that some web pages will gather content from multiple sources so you could see parts of a page fail to load or be very slow to load due to DNS issues affecting just a single DNS.

Of course, if your DNS service is running slow or failing for all lookups then the whole page will be very slow or fail altogether regardless of how many places the content comes from.

What to look for

In this visualization, a higher number means slower (worse) performance.

Usually, these lookup times would just a few ms (milliseconds) greater than the ping time to the DNS server that can resolve your request.

DNS can get a little complicated because it is a chained service. The server you initially call may, in turn, ask a higher authority for the resolution to be made and in turn, that server will likely ask yet another.

Further, DNS is cached in multiple places. This means that if you (or someone else) has asked for a particular web server to be resolved recently then there is no need to go all the way up the “chain of command” to resolve it for you. Your computer or one of the DNS servers in the chain may already have the answer for you.

Sometimes a DNS server may fail to respond at all – this will result in hard failures to access a website rather than just slow performance

How do we test

We do a DNS lookup via the DNS configured on your computer. We bypass the caching on your computer so that we are always testing the chain of command and not just whether your computer has recently been asked for that particular host to be resolved.

We measure the time taken to resolve the hostname by the configured DNS server

What could cause poor DNS performance or DNS failures

It is important to reiterate that with the chaining of DNS servers and the caching use by your computer and each DNS along the chain, DNS performance issues can be very intermittent and a little hard to track down.

Don’t despair though, with a little logical thought and structured testing these things can be tracked down.

Performance issues can be down to your service provider’s DNS capacity to misconfiguration or any of the DNS servers further up the chain.

The web server (or destination of any kind) provider will also use a name server to do the final resolution of name to IP address and capacity or configuration issues there could cause problems.

Network loss between servers in that DNS chain can also lead to performance issues or failures. Remember this is not the same network path as we test in our loss visualization so the only way to figure this out is to pass the problem to your service provider (or DNS provider if that is different)

Remember though that other things could cause DNS failures or performance issues too. Examples include:

      • Loss in your home network or your service provider network will cause DNS retries which induce delay
      • Heavy loss in these networks could even cause lookup failures rather than just delays

Next steps to diagnose or repair for Residential Trial Customers

Firstly you will want to establish if this is a ‘sometimes fails’ fault, an ‘always slow’ problem or more of a ‘sometimes slow’ intermittent issue.

Then try to eliminate some of the steps along the way. A great way of doing this is to use a public DNS (such as Google or openDNS) to see if it is your service provider DNS that is causing the issues – if it is then just forward them the TelcoSI email and PDF and ask them to take a look.

If it is not them then you are going to have to see if the issue is down to just one website/domain name or many – this will point you towards the right place to look next. If it is only one then contacting that website/domain owner is the next step.

If the loss visualization shows significant loss at the same time you see DNS issues then the loss may be causing the performance issues so it may be sensible to address that first.

More visualization Overviews:

TelcoSIAdmin

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