Why There Are Only 13 DNS Root Name Servers

13 server names is a constraint of IPv4

The DNS root name servers translate URLs into IP addresses. Each root server is a network of hundreds of servers in countries worldwide. However, they are identified as 13 named authorities in the DNS root zone.

Illuminated server room panel
Hoxton / Tom Merton / Getty Images

Why Are There Only 13 DNS Servers?

There are a couple of reasons the internet Domain Name System uses exactly 13 DNS servers at the root of its hierarchy. The number 13 is a compromise between network reliability and performance. It's also based on a constraint of Internet Protocol version 4 (IPv4), which most networks use.

While only 13 designated DNS root server names exist for IPv4, each root server name represents not a single computer but a server cluster consisting of many computers. This use of clustering increases the reliability of DNS without any adverse effect on its performance. These 13 IPv4 root servers can support up to 4.3 billion addresses.

Will There Be More DNS Servers?

Because the emerging IP version 6 standard doesn't have as low limits on the size of individual packets, the DNS will, over time, contain more root servers to support IPv6. In theory, IPv6 supports an infinite number of addresses, but only a relatively small number of networks use this new protocol.

DNS IP Packets

Because DNS operation relies on potentially millions of other internet servers finding the root servers at any time, the addresses for root servers must be distributed over IP as efficiently as possible. Ideally, all these IP addresses should fit into a single packet (datagram) to avoid the overhead of sending multiple messages between servers.

With IPv4 in widespread use today, the DNS data that fits inside a single packet is as small as 512 bits after subtracting the other protocol supporting the information contained in packets. Each IPv4 address requires 32 bits.

Accordingly, the designers of DNS chose 13 as the number of root servers for IPv4, taking 416 bits of a packet and leaving up to 96 bits for other supporting data. That allows the flexibility to add a few more DNS root servers in the future if needed.​

Practical DNS Use

The DNS root name servers are not important for the average computer user. The number 13 also does not constrain the DNS servers you can use for your devices. There are many publicly accessible DNS servers that anyone can use to change the DNS servers that their devices use.

For example, make a tablet use a Cloudflare DNS server so that internet requests run through that DNS server instead of a different one, such as a Google DNS server. Doing this might be helpful if the Google server is down, or you can browse the web faster using the Cloudflare DNS server.

This article was updated on June 6, 2022, to correct an error. Each IPv4 address requires 32 bits, not bytes.

Was this page helpful?