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Unicast DNS vs. Anycast DNS

In Unicast DNS, there is a one-to-one association between network address and network edpoint: each destination address uniquely identifies a single receiver endpoint.


So, if your Unicast DNS network had three name server records - ns1, ns2, and ns3 - each of those corresponds to exactly one name server.

As long as everything is working properly, your DNS will be fine. However, if one of those servers goes down for any reason, suddenly one of your name server records does not work, because that one server is down. So, you have ns1, ns2, and ns3 listed as your name servers, but due to a severe storm, ns3 has gone down. Now, 1/3 of your queries are going to be dropped because that server is no longer available on your network.

In Anycast DNS, there is a one-to-many association between network addresses and network endpoints: each destination address identifies a set of receiver endpoints, but only one of them is chosen at any given time to receive information from any given sender.


So, if your Anycast DNS network has three name server records - ns1, ns2, and ns3 - each of those corresponds to a group of name servers located in many different geographical regions. So, if one of the servers on the network goes down, it's ok, because there are several other servers that can respond for the same name server record.

In addition, an Anycast DNS network will automatically route queries to the name server that is closest to the client geographically. So even though the servers listed for ns1 could be located in the US, Europe, and Asia, a client in China will only be getting responses from the name server in Asia rather than having their queries routed to several different continents.

Clearly, Anycast DNS is vastly superior to Unicast DNS in terms of reliability and speed.

 

 

 

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