|The encapsulation method used by a tunnel. The value
direct indicates that a packet is encapsulated
directly within a normal IP header, with no
intermediate header, and unicast to the remote tunnel
endpoint (e.g., an RFC 2003 IP-in-IP tunnel, or an RFC
1933 IPv6-in-IPv4 tunnel). The value minimal indicates
that a Minimal Forwarding Header (RFC 2004) is
inserted between the outer header and the payload
packet. The value UDP indicates that the payload
packet is encapsulated within a normal UDP packet
(e.g., RFC 1234).
The values sixToFour, sixOverFour, and isatap
indicates that an IPv6 packet is encapsulated directly
within an IPv4 header, with no intermediate header,
and unicast to the destination determined by the 6to4,
6over4, or ISATAP protocol.
The remaining protocol-specific values indicate that a
header of the protocol of that name is inserted
between the outer header and the payload header.
||other(1), direct(2), gre(3), minimal(4), l2tp(5), pptp(6), l2f(7), udp(8), atmp(9), msdp(10), sixToFour(11), sixOverFour(12), isatap(13), teredo(14)