Читаем внимательнее определение VPN
A virtual private network (VPN) is a private data network that makes use of the public telecommunication infrastructure, maintaining privacy through the use of a tunneling protocol and security procedures.
Читаем RFC2516:
PPP over Ethernet (PPPoE) provides the ability to connect a network
of hosts over a simple bridging access device to a remote Access
Concentrator. With this model, each host utilizes it's own PPP stack
and the user is presented with a familiar user interface. Access
control, billing and type of service can be done on a per-user,
rather than a per-site, basis.
To provide a point-to-point connection over Ethernet, each PPP
session must learn the Ethernet address of the remote peer, as well
as establish a unique session identifier. PPPoE includes a discovery
protocol that provides this.
И далее:
PPPoE has two distinct stages. There is a Discovery stage and a PPP
Session stage. When a Host wishes to initiate a PPPoE session, it
must first perform Discovery to identify the Ethernet MAC address of
the peer and establish a PPPoE SESSION_ID. While PPP defines a
peer-to-peer relationship, Discovery is inherently a client-server
relationship. In the Discovery process, a Host (the client)
discovers an Access Concentrator (the server). Based on the network
topology, there may be more than one Access Concentrator that the
Host can communicate with. The Discovery stage allows the Host to
discover all Access Concentrators and then select one. When
Discovery completes successfully, both the Host and the selected
Access Concentrator have the information they will use to build their
point-to-point connection over Ethernet.
The Discovery stage remains stateless until a PPP session is
established. Once a PPP session is established, both the Host and
the Access Concentrator MUST allocate the resources for a PPP virtual
interface.
Да и в самом RFC1661 не нашел упоминаний про туннелирование.
Мне в принципе без разницы, просто самому интересно стало.