VANCOUVER, B.C. -- Members of the Internet engineering community have raised several new security concerns about Teredo, a mechanism for sending IPv6 traffic over IPv4 networks that comes turned on by default in Microsoft’s Vista software.

Symantec and Ericsson security experts who called attention to the issue say they are concerned that Teredo bypasses network security through such devices as firewalls. Microsoft says it is providing Symantec with feedback on its report, stressed that Teredo is primarily designed for consumers and emphasized that "Teredo gets disabled automatically for enterprises when a domain environment is detected" (full Microsoft response here).

IPv6 is a long-anticipated upgrade to IPv4, the Internet’s primary communications protocol.

IPv6 fixes the lack of IP addresses found in IPv4. IPv6 has a virtually unlimited number of IP addresses, while IPv4 has 4.3 billion IP addresses, the majority of which have been handed out.

Teredo is a tunneling technique used to send IPv6 traffic through IPv4 network address translators (NAT). Because of the lack of IPv4 addresses, NATs are commonly used in enterprise networks to mask many private IPv4 addresses behind a single public IPv4 address.

See IPv4 vs. IPv6: Networking’s 50 Greatest Arguments

With Teredo, IPv6 packets are sent as IPv4-based User Datagram Protocol messages to go through IPv4 NATs. Teredo provides IPv6 traffic with address assignment and host-to-host automatic tunneling. A network using Teredo requires Teredo clients, Teredo host-specific relays, Teredo servers and Teredo relays.

Teredo is enabled by default in Windows Vista, but it won’t be enabled by default in Windows Server Code Name 2008, according to Microsoft.

In a 20-page document titled "Teredo Security Concerns," James Hoagland of Symantec and Suresh Krishnan of Ericsson, outline several new security concerns about running Teredo in managed, corporate network environments. The document is the result of an independent analysis of Teredo’s security implications that was conducted by Symantec.

"Teredo is not recommended as a solution for managed networks," the document states. "Administrators of such networks may wish to filter all Teredo traffic at the boundaries of their networks. . . . The easiest mechanism for this would be to filter out incoming traffic with Source Port 3544 and outgoing traffic with Destination Port 3544."