: Secure Internet Protocol Routed NETwork
The SIPRNET is the network used by the American government for information classified at the Secret level. The SIPRNET is mostly disjoint from the NIPRNET; the only overlap are point-to-point links across base backbones that are encrypted with NES boxes.
Layer 2 links are encrypted with KIV-7s or KG-84s.
Common infrastructure services (WHOIS) are maintained by DISA, even including popular websites.