from the Teredo tunnel, from anywhere except Teredo (the default), or only from the local intranet. The Teredo protocol also encapsulates detailed information about the tunnel's endpoint in its data packets. This information can help potential attackers by increasing the feasibility of an attack, and/or by reducing the effort required. Firewalling, filtering, and blocking For a Teredo pseudo-tunnel to operate properly, outgoing UDP packets to port 3544 must be unfiltered. Moreover, replies to these packets (i.e., "solicited traffic") must also be unfiltered. This corresponds to the typical setup of a NAT and its stateful firewall functionality. Teredo tunneling software reports a fatal error and stops if outgoing IPv4 UDP traffic is blocked. DoS via routing loops In 2010, new methods to create denial of service attacks via routing loops that use Teredo tunnels were uncovered. They are relatively easy to prevent. Default use in MS-Windows Microsoft Windows as of Windows 10, version 1803 and later disable Teredo by default. If needed, this transitional technology can be enabled via a CLI command or Group Policy. Implementations Several implementations of Teredo are currently available: Windows XP SP2 includes a client and host-specific relay (also in the Advanced Networking Pack for Service Pack 1). Windows Server 2003 has a relay and server provided under the Microsoft Beta program. Windows Vista and Windows 7 have built-in support for Teredo with an unspecified extension for symmetric NAT traversal. However, if only a link-local and Teredo address are present, these operating systems don't try to resolve IPv6 DNS AAAA records if a DNS A record is present, in which case they use IPv4. Therefore, only literal IPv6 URLs typically use Teredo. This behavior can be modified in the registry. Windows 10 version 1803 and later disable Teredo by default. If needed, this transitional technology can be enabled via a CLI command or Group Policy. Miredo is a client, relay, and server for Linux, *BSD, and Mac OS X, ng_teredo is a relay and server based on netgraph for FreeBSD from the LIP6 University and 6WIND. NICI-Teredo is a relay for the Linux kernel and a userland Teredo server, developed at the National Chiao Tung University. Choice of the name The initial nickname of the Teredo tunneling protocol was Shipworm. The idea was that the protocol would pierce through NAT devices, much as the shipworm (a kind of marine wood-boring clam) bores tunnels through wood. Shipworms have