ISATAP

ISATAP stands for Intra-Site Automatic Tunnel Addressing Protocol. It is an IPv6 transition mechanism that enables IPv6 traffic to be carried over an IPv4 network within a single administrative site. ISATAP allows IPv6 hosts on an IPv4 infrastructure to communicate with each other without a dedicated IPv6 tunnel server by using a built-in, automatic tunneling interface.

Operation and addressing: An ISATAP-enabled host creates a virtual IPv6 interface and assigns itself an ISATAP IPv6 address, typically of the form 2001:5efe:w.x.y.z, where w.x.y.z is the host’s IPv4 address on the IPv4 network. IPv6 traffic is encapsulated within IPv4 packets and transmitted to an ISATAP router or relay inside the site. The tunnel endpoints and routes are discovered automatically, often using Router Advertisements or equivalent discovery mechanisms, providing connectivity to the site's IPv6 prefix.

Scope and deployment: ISATAP is designed for intra-site use, contrasting with other mechanisms such as 6to4 (which spans across the wider Internet) and Teredo (NAT traversal). It was specified in RFC 5214 (2008) as a means to ease IPv6 rollout over existing IPv4 infrastructure within an organization.

Status and considerations: While ISATAP can simplify IPv6 transition on IPv4-laden networks, it has declined in prominence as native IPv6 deployment increases and other transition technologies mature. Some operating systems provide ISATAP support but may disable it by default due to security considerations or changing network design practices.