An important aspect is that IPv4 and IPv6 are neither forward compatible nor backward compatible.
The generic definition of a 6PE is a dual-stack IPv4 and IPv6-enabled router, with at least an IPv4 legitimate and routed address in the MPLS cloud and identified as a Forwarding Equivalence Class (FEC) with a correspondingly allocated and distributed label binding to the rest of the network.6PE is typically deployed by ISPs that have MPLS core network and (possible) supports MPLS VPN (or other) services  .
Most connections to the Internet in the world nowadays rely upon IPv4
protocol, even though it is considered as a legacy protocol since IPv6 has been standardized in year 2000 .
(8) For the past two decades, many scholars and network administrators have warned that the world is rapidly approaching the exhaustion of IPv4
addresses, and as such, an alternative needs to be developed.
In this paper, we revisit IPv6 performance and make a comparison with IPv4
from several metrics, including network reachability, packet delay, packet loss, and packet reordering.
The most recent version of the Internet Protocol, IPv6, uses a 128-bit address length instead of IPv4
's 32-bit address, thus ensuring sufficient addresses for the foreseeable future.
and compare the results for IPv6 and IPv4
protocols using both TCP and UDP protocols.
In particular Internet content providers must serve content with both IPv4
and IPv6 services, in order to be fully reachable on the global Internet." (6) It will require more than just a flip of a switch for the DOD and the Air Force to transition.
They are skeptical with the real benefits from shifting to IPv6 from IPv4
as justifying costs would be difficult.
To address these issues, in this paper we perform a careful comparative measurement study between the IPv4
and IPv6 traffic to explore the traffic features of IPv6 from flow level.
Tunneling is a system that allows IPv6 packets to be transmitted over an IPv4
network and vice versa.
In 1977, Americans Vinton Cerf and Robert Kahn, recognized as the "internet pioneers" created the IPv4