## 7 Conclusions  
The transition of legacy IPv4 networks into hybrid SoDIP6 networks and then to pure SoDIP6 networks are steps to be considered for network migrations with optimized OpEX and CapEX for Internet service providers. Through this study, communications among multiple ASes with legacy IPv4 networks and SoDIP6 networks as hybrid/SDN networks were achieved using ONOS/SDN-IP in the service provider carrier-grade networks. We proposed an approach for the smooth migration of existing legacy IPv4 network routers into SoDIP6-enabled switches with better placement of the controller during network migration by considering minimum control path latency using optimal path routing and BFR technique. The proposed approach gave a better result for the smooth migration of network routers with the suitable placement of the controller during the migration of carrier-grade service provider networks. **Supplementary Materials:** The program code for SoDIP6 network implementation using ONOS/SDN-IP with experimental snapshots including network/BGP router configuration over virtual environment using the Mininet emulator is available online at [[https://github.com/baburd/SoDIP6](https://github.com/baburd/SoDIP6)]([https://github.com/baburd/SoDIP6](https://github.com/baburd/SoDIP6)), in the folders \"sdhip\" and \"sodip6\". **Author Contributions:** Conceptualization, B.R.D., P.M.; Methodology, B.R.D., D.B.R., and P.M.; Software, B.R.D. ; Validation, D.B.R., S.R.J., and P.M.; Formal Analysis, B.R.D. ; Investigation, B.R.D., D.B.R., P.M.; Resources, S.R.J., P.M.; Data Curation, B.R.D. ; Writing--Original Draft Preparation, B.R.D. ; Writing--Review and Editing, D.B.R., S.R.J., and P.M.; Visualization, B.R.D. ; Supervision, D.B.R., S.R.J., and P.M.; Project Administration, B.R.D. and S.R.J. ; Funding Acquisition, B.R.D., P.M. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was partially funded by the Norwegian University of Science and Technology, Trondhiem, Norway (NTNU) under Sustainable Engineering Education Project (SEEP) financed by EnPE, University Grant Commission (grant-ID: FRG/475 Eng01), Bhaktapur, Nepal, Nepal academy of Science and Technology (NAST), Kathmandu, Nepal, and U.S. National Science Foundation (NSF). The work of [PERSON] was partly supported by the U.S. National Science Foundation (NSF) under grants CNS 1650831 and HRD 1828811. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the NSF  
**Acknowledgments:** We are thankful to the ERASMUS+ KA107 project and the GRC lab team members at Universitat Politecnica De Valencia for the research support and facilitation. **Conflicts of Interest:** The authors declare no conflicts of interest. * (5) APNIC. IPv6 Capability Measurement. Available online: [[https://stats.labs.apnic.net/ipv6](https://stats.labs.apnic.net/ipv6)]([https://stats.labs.apnic.net/ipv6](https://stats.labs.apnic.net/ipv6)) (accessed on 22 April 2020). * (6) [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Towards energy efficiency and green network infrastructure deployment in Nepal using software defined IPv6 network paradigm. _Electron. J. Inf. Syst. Dev. Ctries._**2020**, _86_, e12114. [CrossRef]
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