The 13 DNS Root Server Constellation Monitor
Comprehensive architectural audit of the 13 authoritative DNS root server letters (a.root-servers.net through m.root-servers.net) coordinating top-level domain delegations across the global Internet. Details operational custodians, anycast node counts, BGP routing ASNs, and software implementations.
Why Exactly 13 Root Server Letters?
In the original DNS specification (RFC 1035), UDP datagrams were strictly capped at 512 bytes to prevent IP fragmentation over low-bandwidth transit paths. To ensure that an answer to a primer query (requesting the list of root name servers and their IP addresses) fits into a single 512-byte UDP packet, the number of distinct server hostnames had to be limited to thirteen letters (A through M).
Today, thanks to BGP Anycast routing (RFC 4786) and EDNS0 buffer extensions (RFC 6891), those 13 logical IP addresses are actually served by more than 1,600 physical server clusters distributed across six continents.
| Root | Custodian / Operator | Headquarters | Anycast Nodes | Routing ASN | IPv4 Address | IPv6 Address | Software Stack |
|---|---|---|---|---|---|---|---|
| A a.root-servers.net | Verisign, Inc. Original root server operated by Verisign under US government agreements. High resilience anycast fabric. | United States | 38 Global Anycast | AS3661 | 198.41.0.4 | 2001:503:ba3e::2:30 | Verisign Atlas Engine |
| B b.root-servers.net | USC Information Sciences Institute (ISI) Operated by the birthplace of DNS (Jon Postel and Paul Mockapetris at USC-ISI). Academic non-profit stewardship. | United States | 6 Regional Anycast | AS394380 | 199.9.14.201 | 2001:500:200::b | BIND 9 & Knot DNS |
| C c.root-servers.net | Cogent Communications Tier 1 transit backbone provider providing extensive native peering across major international exchange points. | United States | 14 Global Anycast | AS2149 | 192.33.4.12 | 2001:500:2::c | BIND 9 |
| D d.root-servers.net | University of Maryland Pioneered massive anycast expansion among university operators, deploying over 160 points of presence globally. | United States | 165 Global Anycast | AS10886 | 199.7.91.13 | 2001:500:2d::d | NSD & BIND 9 |
| E e.root-servers.net | NASA Ames Research Center The sole remaining unicast root server instance, hosted directly at NASA Ames in Mountain View, California. | United States | 1 Single Unicast | AS2153 | 192.203.230.10 | 2001:500:a8::e | BIND 9 |
| F f.root-servers.net | Internet Systems Consortium (ISC) & Cloudflare Pioneered hardware anycast root deployment in 2002. ISC partnered with Cloudflare to scale across 300+ global data centers. | United States | 320 Global Anycast | AS3557 | 192.5.5.241 | 2001:500:2f::f | BIND 9 & Knot DNS |
| G g.root-servers.net | US Department of Defense (DISA) Defense Information Systems Agency operational node. Highly secured US military network infrastructure. | United States | 6 Regional Anycast | AS5927 | 192.112.36.4 | 2001:500:12::d0d | NSD |
| H h.root-servers.net | US Army Research Laboratory Army research facility at Aberdeen Proving Ground, Maryland. Strict security and autonomous routing profile. | United States | 4 Regional Anycast | AS1508 | 198.97.190.53 | 2001:500:1::53 | NSD |
| I i.root-servers.net | Netnod (Autonomica) First root server situated in Europe. Stockholm-based neutral Internet exchange operator with high European presence. | Sweden | 78 Global Anycast | AS8674 | 192.36.148.17 | 2001:7fe::53 | Knot DNS |
| J j.root-servers.net | Verisign, Inc. Second Verisign root server letter. Engineered specifically for massive DDoS absorption and line-rate query processing. | United States | 195 Global Anycast | AS26415 | 192.58.128.30 | 2001:503:c27::2:30 | Verisign Atlas Engine |
| K k.root-servers.net | RIPE NCC Regional Internet Registry for Europe, Middle East, and parts of Central Asia. Broad distribution across emerging regions. | Netherlands | 115 Global Anycast | AS25152 | 193.0.14.129 | 2001:7fd::1 | NSD & Knot DNS |
| L l.root-servers.net | ICANN Operated directly by ICANN. The largest individual root constellation in the world with over 650 nodes across 120 nations. | United States | 650 Global Anycast | AS20144 | 199.7.83.42 | 2001:500:9f::42 | Knot DNS & BIND 9 |
| M m.root-servers.net | WIDE Project First root server operated in Asia. Run by the pioneering Japanese Internet research consortium founded by Jun Murai. | Japan | 32 Global Anycast | AS7506 | 202.12.27.33 | 2001:dc3::35 | NSD & BIND 9 |
The historic standard of internet name resolution, utilized by A, B, C, D, E, F, L, and M roots.
Compact C implementation engineered strictly for authoritative operations without caching overhead. Utilized by D, G, H, K, and M.
Modern multithreaded server written in C, favored by I, K, and L roots for maximum packet throughput per core.
Hardware-accelerated custom packet engine powering A and J roots, capable of handling tens of millions of queries per second.