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I was reading about DNS some days ago and learned how the requests are processed. If you surf to www.example.com, then a request will go to the Root Name Servers to see who owns that .com address, then another request will go to another, more local, DNS server to see who owns the example.com address and so on.

How is it technically possible that the 13 Root Name Servers can handle all requests done by earth's billions of Internet users simultaneously without being overloaded leading to a Denial-of-Service?

Wouter
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Rox
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5 Answers5

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They're 13 highly available clusters of servers, not simply 13 servers.

Among other things, root nameserver operators are required to have enough capacity to handle three times their normal traffic load (RFC 2870). This leads to rather large clusters.

However, the root nameservers only serve responses for the top level domains themselves, i.e. com., net., uk., ae., etc., and the nameservers which query the root can cache this information up to 48 hours, which dramatically reduces the load at the root nameservers. This leads to smaller clusters.

The root nameservers are in over 130 physical locations in 53 countries; with only 13 server names, this is done through the magic of IPv4 anycast.

The root nameservers also have their own web site, which you may find interesting reading.

Community
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Michael Hampton
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They don't. The root nameservers just have to tell you what nameservers handle com. From then on, you don't need to go to them to handle any domain inside com. The root nameservers have no idea who owns example.com. They're root nameservers, not com nameservers.

What slimsuperhero said is also true. Many high-volume nameservers use anycast to have a single IP address served by a number of servers around the world.

David Schwartz
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Each root server is not actually a server, they are huge clusters of servers. In addition to this, DNS answers are cached so not every request reaches the root server.

gevial
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Note that you do not use the root servers. You usually use the DNS server provided by your Internet Service Provider which usually can respond immediately if the information you need is in their local cache. Only if not cached, their upstream DNS server is asked and only eventually is the root server asked (and that response is then cached)

Thorbjørn Ravn Andersen
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Actually Its 13 Anycast IP address which resolves to lot of servers around the globe. You can look at the Link to find those servers if needed. All these servers are managed by the concerned authority.

The fact that we are still using only 13 IP address (And cluster of servers having same IP address) is that to ensure that the packet size wont go beyond 512 bytes. Then why? we have TCP which can go beyond this packet size why cant we use it?. The thing is that, TCP involves very high overhead as it includes multiple steps and procedures to establish a TCP connection. Because of this, the entire process of a DNS query will go slow.

Things like DNS can never be slow and that's why we still use the same old system.

Jaison
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