GeoDNS is easily the most powerful set of tools on the DNS level. These services can be used to improve the performance of your domains on a global scale, build your own CDN, and deliver unique content based on qualities of your end-users. We are going to show you how GeoDNS services work and how you can leverage them to optimize your global network.

Basic DNS Lookup

Every time you type a domain into your browser, you are performing a query. This query is looking for the IP address that maps to the your domain. We are going to look at the path your query takes to find that answer, so that we can better understand how DNS and GeoDNS work.

Click the diagram on the right to see DNS in action. For a more detailed explanation please go to our knowledge base.

basic DNS lookup

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Terms You Need to Know


An end-user or querying client is perceived as the resolving name server. The resolving name server is specific to the the end user trying to access the domain.

Every client that accesses the Internet will go thorugh a resolving name server to resolve an FQDN (fully qualified domain names) to an IP address.

geoDNS DNS lookup

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Standard GeoDNS Lookup

When you add GeoDNS into the mix, things get a little more complicated. GeoDNS services allow you to make routing decisions based on the location of your end-users.

For the next two illustrations, we will be using an IP Filter to make routing decisions. We'll talk more about IP Filters in just a minute.

Do you see the problem? Routing decisions aren't specific to the end-user's true location. Instead, decisions are made based on the location of the resolving name server, which could be close by or a Public DNS server.


But things are changing! Recently there has been a big push to have more resolving name servers support RFC 7871 which is the EDNS client subnet. This means that actual clients' IP addresses are making the original query.

The resolving name server actually says “I am asking this information on behalf of xx.xx.xx.xx/24”. This is very important to understand because the response provided by the authoritative name server can be much more specific than if the normal IP of the resolving name server is used.

GeoDNS with EDNS

When you use an EDNS client subnet with GeoDNS, the response to the querying client would look like this.

Now that we have a basic understanding of how queries can be answered with GeoDNS and EDNS client subnet, we can start looking at more advanced configurations.

geo DNS lookup

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Types of GeoDNS Configurations

Region Traffic Direction (GTD)

GTD uses region-specific rules to answer queries in the originating region. For example, a user in Europe wants to visit mydomain.com. The DNS provider would return a region-specific record that is only used for European traffic.

GeoIP Services

GeoIP uses a database to automatically map users' IP addresses to a location and network. You can use GeoIP to filter traffic or to automatically route users to the closest resource in your network.


hat makes Constellix so unique as a GeoDNS provider, is that you can combine regional traffic direction (GTD) with GeoIP services to effectively fix incorrectly mappings.

Sometimes, an IP may be mapped to a location it no longer resides in. In that case, GeoIP services would continue treated the IP as if it were in its original location. Since GTD doesn't rely on a database, and instead looks at the true location of the querying IP, it's able to override incorrectly geo-targeted IP addresses.

GeoIP Configurations

IP Filters

You can use filters to send end-users to a specific IP or hostname; or restrict access. Users can be filtered based on their network, ASN, IP address, or location. The diagram illustrates the four different types of IP Filters you can create with Constellix.

If you want to set up this configuration for your own domains, you can follow the tutorial or watch this video.

IP Filter DNS lookup

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DNS lookup with GeoProximity

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GeoProximity uses our GeoIP engine to automatically calculate which of your predefined servers is closest to your end-users. If you have multiple web or application servers in a high traffic region, this is a great way to slash resolution times and deliver location-specific content.

If you want to set up this configuration for your own domains, you can follow the tutorial or watch this video.

GeoProximity + IP Filters

You can combine GeoProximity rules with IP Filters for even more granularity. Queries will first be answered based on IP Filter rules(s). If there is no matching rule, then the query will be answered based on the GeoProximity rule(s).

IP Filter and GeoProximity DNS lookup

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Global Traffic Director


Constellix’s Global Traffic Director (GTD) uses our powerful IP Anycast+ network to identify the geographical location of the querying client. When GTD is enabled for a domain, you can create regionally defined rules for answering queries.

GTD DNS lookup

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You can create a different version of your domain for each of the five GTD regions. GTD effectively decreases resolution times and offers the most accurate location-based routing.

If you want to set up this configuration for your own domains, you can follow the tutorial or watch this video.

GTD + GeoIP Services

When you combine the GTD with GeoIP services (IP Filters and GeoProximity) you can correct any errors caused by incorrect IP to Location mapping databases; as well as incorrect lookups by poor peering practices.

The illustrations shows how GTD is able to detect the true location of a user with a European IP address and accurately route them to a nearby server in US East.

Constellix is the only platform that offers these two services together, giving you the most accurate configurations in the industry. (Patent pending)

GTD + GeoIP DNS lookup

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