Для туннелирования IPv6 в IPv4, мелкософт пользует протокол Teredo. Если это он, то ipconfig /all должен выдавать помимо отображаемых в “Сетевых устройствах”, туннельные адаптеры.
Если у вас установлен какой-нибудь снифер инструмент анализа протоколов, например, Wireshark, можно глянуть что передают через этот порт.
Судя по описанию Teredo на technet Teredo Overview | Microsoft Learn, клиенты teredo, подключённые к сетям IPv4 и IPv6, выступают в качестве ретрансляторов, туннелирующих трафик IPv6 хостов через своё IPv4 соединение. Но! Как серверы, так и ретрансляторы слушают udp 3544 для входящих teredo-соединений:
Teredo server
A Teredo server is an IPv6/IPv4 node that is connected to both the IPv4 Internet and the IPv6 Internet, supports a Teredo tunneling interface over which packets are received. The general role of the Teredo server is to assist in the address configuration of Teredo client and to facilitate the initial communication between Teredo clients and other Teredo clients or between Teredo clients and IPv6-only hosts. The Teredo server listens on UDP port 3544 for Teredo traffic.
For more information about the role of the Teredo server in facilitating initial communication, see “Teredo Processes” in this article.
Windows XP SP2, Windows XP SP1 with the Advanced Networking Pack for Windows XP, Windows Server 2003 with Service Pack 1, Windows Vista, and Windows Server “Longhorn” do not include Teredo server functionality.
Teredo relay
A Teredo relay is an IPv6/IPv4 router that can forward packets between Teredo clients on the IPv4 Internet (using a Teredo tunneling interface) and IPv6-only hosts. In some cases, the Teredo relay interacts with a Teredo server to help it facilitate initial communication between Teredo clients and IPv6-only hosts. The Teredo relay listens on UDP port 3544 for Teredo traffic.
For more information about the role of the Teredo relay in facilitating initial and ongoing communication between Teredo clients and IPv6-only hosts, see “Teredo Processes” in this article.
Windows XP SP2, Windows XP SP1 with the Advanced Networking Pack for Windows XP, Windows Server 2003 with Service Pack 1, Windows Vista, and Windows Server “Longhorn” do not include Teredo relay functionality. Microsoft does not plan to deploy any Teredo relays on the IPv4 Internet. Individual Internet service providers (ISPs) could deploy their own Teredo relays. The Windows-based Teredo client will work with a Teredo relay when sending traffic to an IPv6-only host on the IPv6 Internet. Teredo relays are not needed to communicate with Teredo host-specific relays.
Teredo host-specific relay
Communication between Teredo clients and IPv6 hosts that are configured with a global address must go through a Teredo relay. This is required for IPv6-only hosts connected to the IPv6 Internet. However, when the IPv6 host is IPv6 and IPv4-capable and connected to both the IPv4 Internet and IPv6 Internet, then communication should occur between the Teredo client and the IPv6 host over the IPv4 Internet, rather than having to traverse the IPv6 Internet and go through a Teredo relay.
A Teredo host-specific relay is an IPv6/IPv4 node that has an interface and connectivity to both the IPv4 Internet and the IPv6 Internet and can communicate directly with Teredo clients over the IPv4 Internet, without the need for an intermediate Teredo relay. The connectivity to the IPv4 Internet can be through a public IPv4 address or through a private IPv4 address and a neighboring NAT. The connectivity to the IPv6 Internet can be through a direct connection to the IPv6 Internet or through an IPv6 transition technology such as 6to4, where IPv6 packets are tunneled across the IPv4 Internet. The Teredo host-specific relay listens on UDP port 3544 for Teredo traffic.
Windows XP SP2, Windows XP SP1 with the Advanced Networking Pack for Windows XP, Windows Server 2003 with Service Pack 1, Windows Vista, and Windows Server “Longhorn” include Teredo host-specific relay functionality, which is automatically enabled if the computer has a global address assigned. A global address can be assigned from a received Router Advertisement message from a native IPv6 router, an ISATAP router, or a 6to4 router. If the computer does not have a global address, Teredo client functionality is enabled.
The Teredo host-specific relay allows Teredo clients to efficiently communicate with 6to4 hosts, IPv6 hosts with a non-6to4 global prefix, or ISATAP or 6over4 hosts within organizations that use a global prefix for their addresses, provided both hosts are using a version of Windows that supports Teredo.
Так что если это и инкапсуляция, то не от мелкософта.