The rapid proliferation of the Internet has exhausted Internet Protocol version 4 (IPv4) addresses offered by Internet Assigned Number Authority (IANA). The new version of the IP i.e. IPv6 was launched by Internet Engineering Task Force (IETF) with new features, such as a simpler packet header, larger address space, new anycast addressing type, integrated security, efficient segment routing, and better Quality of Services (QoS). Virtualized network architectures such as Network Function Virtualization (NFV) and Software Defined Network (SDN) have been introduced. These new paradigms have entirely changed the way of internetworking and provide a lot of benefits in multiple domains of applications that have used SDN and NFV. ISPs are trying to move from existing IPv4 physical networks to virtualized next-generation IPv6 networks gradually. The transition from physical IPv4 to software-based IPv6 is very slow due to the usage of IPv4 addresses by billions of devices around the globe. IPv4 and IPv6 protocols are different in format and behaviour. Therefore, direct communication between IPv4 and IPv6 is not possible. Both protocols will co-exist for a long time during transition despite the incompatibility issues. The core issues between IPv4 and IPv6 protocols are compatibility, interoperability, and security. The transition creates many challenges for ISPs during shifting the network toward a software-based IPv6 network. Packet traversing, routing scalability, the guarantee of performance, and security are the main challenges faced by ISPs. In this research, we focused on a qualitative and comprehensive survey. We summarize the challenges during the transition process, recommended appropriate solutions, and an in-depth analysis of their mitigations during moving towards the next-generation virtual IPv6 network.

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