DNS Performance

This is typically the most important aspect regarding DNS because there are visible results that can be measured.
Here are a few things to consider regarding the performance of your DNS…

Where are your end users coming from? Are they in 1 single geographic location, or are they global? This
is where you need to make sure you place your servers. It may seem like common sense, but you’d be surprised
how many of us ignore this factor. You can’t expect your website to perform well if you require a user in
Europe to resolve the DNS in the US and vice versa. It doesn’t make sense when you consider how congested
the Internet is today. Someone in the UK would literally have to cross an ocean to find your DNS servers.
Over a period of time, you’ll notice that not all your users are reaching your site the first every time.
When a dns query experiences enough latency, it will go unanswered and your user will see a blank page with
a 404 error. You may think the simple solution is to setup multiple dns servers in case one doesn’t
respond, but what you may not realize is that redirections can cause enough latency to drop a query. We have all
seen this. You need to cut down on as much latency as possible and push your servers closer to your end users.

You also need to look into what routing technology is being used for your DNS. The most traditional approach
for DNS is Round Robin. In a Round Robin format, each DNS server has its own IP Address and queries are routed
in order. As queries come in, they are resolved in a predefined order of 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, etc…Lets
pretend that server 1 is located in California, server 2 in New York, server 3 in the UK, server 4 in Asia,
and server 5 in Australia. I might be in Asia, but if i’m 2nd in line, I’ll be resolved in New York. This
doesn’t make any sense, does it? This brings us back to my original point of placing your DNS servers close
to your end users.

A better technology than Round Robin is IP Anycast and BGP. Let’s take the example used before with 5 globally
distributed name servers. However, this time, all servers have the exact same IP address with no predefined
order of routing. Through BGP, users are routed to the closest topological server. So if I’m in Asia, I’m going
to be routed to the name servers in Asia. If the server in Asia goes offline, then I’ll be redirected to
Australia, assuming this is the next closest route based on my location. Now its not always the closest route,
but the shortest amount of hops based on network topology.

As you can see, Anycast and BGP combined is much more efficient than Round Robin, due to its redundancy and intelligence built in. This is going to speed up resolution to your site and reduce the amount of dropped DNS requests you may experience.

Another thing to consider with performance, are the extra services that DNS can provide such as Auto Failover
and Load Balancing. While these services don’t directly impact the performance of the DNS itself, they do help
in enhancing the performance of your over all network. There are several DNS providers out there that offer these
solutions and avoid the need in purchasing hardware appliances. Since DNS traffic is the first link into your network,
DNS queries can be controlled in a variety of ways. One of the more common and cutting edge technologies in the last few years has been Global Server Load Balancing. This is the ability to route users to your closest content servers
based on the geographic region they are coming from. A few DNS providers have partnered with Geo IP database companies that supply IP information of geographic locations around the world. By partnering with these companies, you can control where the DNS traffic is routed to by knowing the IP of your end user. There are also ways of routing traffic based on percentages across a pool of IP’s. DNS can also be used for disaster recovery by monitoring your content servers as a health check and redirect traffic to a backup server if need be.

So as you can see, there is a lot that effects the performance of your External DNS. You shouldn’t rule out any of these factors.

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