There are currently 13 root name servers specified, with names in the form letter.root-servers.net, where letter ranges from A to M. (Six of these are not actual single servers, but represent several physical servers each in multiple geographical locations; cf. below.):
Letter IP address Old name Operator Location
A 18.104.22.168 ns.internic.net VeriSign Dulles, Virginia, USA
B 22.214.171.124 ns1.isi.edu USC-ISI Marina Del Rey, California, USA
C 126.96.36.199 c.psi.net Cogent Communications distributed using anycast
D 188.8.131.52 terp.umd.edu University of Maryland College Park, Maryland, USA
E 184.108.40.206 ns.nasa.gov NASA Mountain View, California, USA
F 220.127.116.11 ns.isc.org ISC distributed using anycast
G 18.104.22.168 ns.nic.ddn.mil U.S. DoD NIC Columbus, Ohio, USA
H 22.214.171.124 aos.arl.army.mil U.S. Army Research Lab Aberdeen Proving Ground, Maryland, USA
I 126.96.36.199 nic.nordu.net Autonomica distributed using anycast
J 188.8.131.52 VeriSign distributed using anycast
K 184.108.40.206 RIPE NCC distributed using anycast
L 220.127.116.11 ICANN Los Angeles, California, USA
M 18.104.22.168 WIDE Project distributed using anycast
Approximate geograpical location of all DNS root name servers (as of March 2007)
Older servers had their own name before the policy of using similar names was established.
No more names can be used because of protocol limitations - UDP packet can only carry 512 bytes reliably and a hint file with more than 13 servers would be larger than 512 bytes - but the C, F, I, J, K and M servers now exist in multiple locations on different continents, using anycast announcements to provide a decentralized service. As a result most of the physical, rather than nominal, root servers are now outside the United States.
There are also quite a few alternative namespace systems with their own set of root nameservers that exist in opposition to the mainstream nameservers. The first, AlterNIC, generated a substantial amount of press. See Alternative DNS root for more information.
Root name servers may also be run locally, on provider or other types of networks, synchronized with the US Department of Commerce delegated root zone file as published by ICANN. Such a server is not an alternative root, but a local implementation of A through M.
As the root nameservers function as part of the Internet backbone, they have come under attack several times, although none of the attacks have ever been serious enough to severely hamper the performance of the Internet.