With the introduction of 5G, network operators will face the challenge of a large variety of use cases with different network requirements. Taking also into account the large number of new connected devices and fast response times of network infrastructure needed, the introduction of new architectures and flexible routing techniques for the transport network is considered vital. IPv6, on top of the apparent advantage of a significantly larger number of IP addresses, can be the foundation on which efficient 5G transport techniques can be implemented. Segment Routing is a technique where its main advantage for 5G is that it will allow Mobile Carriers to steer traffic based on policies via predefined paths. This will enable the network to select low-latency paths, for example, for URLLC traffic, or to avoid low-latency paths for normal, best-effort internet traffic. At the same time, specific links between neighbor nodes can be selected, an operation that is not possible with standard routing protocols. Segment Routing runs natively on an MPLS or IPv6 data plane. It can either be built based on MPLS, where a path through the transport network is defined via an MPLS label or based on IPv6, where a new IPv6 Routing Extension Header (SRH) identifies the path via an IPv6 address list.
5G & IPv6 drivers
The main driver for IPv6 is a possible IPv4 (RFC1918) address shortage and the need for address harmonization in 5G, across all networks from day one. Taking into account 5G with network slicing, slice specific networks might be placed, depending on the use case, either close to the cell site (for example, for URLLC use cases) or somewhere centrally to provide a centralized service for all network segments. A harmonized 5G address concept offers the freedom to gradually evolve 5G networks and services, without the need of usual IP hacks like dedicated backbone VPNs per network segment.
From an early deployment aspect, IPv6 is seen as mandatory for specific 5G traffic flows, such as the 5G Control Plane (CP) and the 5G User Plane (UP). For the Management Plane (MP) and IPSec, IPv6 deployment in the early phase is not seen as mandatory but optional if available.
IP Dual-stack
Due to the mixed nature of current transport networks and the long time it takes to transition from IPv4 to IPv6, Dual-Stack support becomes essential. All Dual-Stack scenarios that can occur during the early deployment phase and later must be supported by the 5G nodes. The main idea is to use specific (Global Unicast Addresses) GUA IPv6 addresses on the same network for LTE and 5G infrastructure. That would even allow Operators to include new network segments in the future or to run standard services on shared platforms. It would, of course, be the ideal solution to introduce IPv4/IPv6 dual-stack initially on 4G to allow IPv6 also on 5G nodes. However, it would be unrealistic and costly to change the entire installed base of LTE nodes to IPv6 before a 5G massive rollout. Furthermore, a great number of the existing 4G radio nodes nowadays, do not fully support IPv6. For example, some vendors introduce IPv6 for LTE at the same time as for 5G, while others, even if they already support IPv6, do not plan to support IPv4/IPv6 dual-stack on 4G nodes.
IPv6 deployment
The extent to which IPv6 can be deployed depends on the IPv6 support at the peer nodes. That is mainly the IPsecGW and the NMS. One option is to run IPsec, management traffic, and 5G user plane with IPv6, and the other option is to have a minimum IPv6 solution, with IPv6 only on the 5G user plane.
All IP addresses within the en-gNB can be configured with an IPv4 and an IPv6 address right from the start. This will enable the operator to prepare for future migration activities. As a next step, the 4G radio nodes should also be migrated to IPv6. It has to be mentioned that in some networks, not pure 4G eNodeBs are deployed, but 2G/3G/4G multi-standard combined nodes. As most of the radio vendors, based on the current hardware platform roadmaps, do not have IPv6 support for 2G and 3G interfaces, the IPv6 migration will only be possible for the 4G part of multi-standard base stations.
Native IPv6
The migration of LTE to IPv6, therefore, is significant in the case of LTE rollout of multi-standard base stations, which require further IP prefixes. With this requirement, some Mobile Carriers would consider the use of IPv6 directly, since it would help them not to spend additional effort with migration in the near future. In the case where Operators do not have plans to swap LTE running on the standalone nodes, the need to migrate to IPv6 becomes essential only at the time of running 5G NSA on IPv6. From the long term perspective, it is not wise to operate RAN on two IP stacks. Therefore it is much efficient to migrate to IPv6 as soon as possible. IPv6 is now the direction where the industry is moving. The sooner the Carrier is able to make this change and transition of their existing networks to IPv6, the less effort is to be spent in the future.
IPv6 in MPLS networks
The migration of 4G and 5G S1 interfaces to IPv6 does not require a migration of the whole existing backbone and backhaul infrastructure to native IPv6 since, in most transport networks, IP MPLS is already used. It is sufficient that the edge routers of the IP MPLS backhaul/backbone are configured to route IPv6 packets into existing VPNs. Within the MPLS network, backbone/backhaul packets are switched based on MPLS labels, regardless of which IP version the payload has. In this case, even the control plane of the IP MPLS backbone/backhaul can remain on IPv4.
IPv6 Challenges
Considering the time it will take for native IPv6 network implementation and the critical drivers for such a transformation, only the introduction of a new generation of services, such as 5G, could push the introduction of IPv6 forward. For existing networks, 5G MPLS-based segment routing can also be used, starting at the cell site and extended through the whole mobile backhaul segment. MPLS advantages over IPv6 technology are that many networks are already based in IP MPLS, which makes migration to MPLS Segment Routing a relatively easy task. Furthermore, security concerns have been raised regarding the usage of IPv6 extension headers. However, IPv6 has excellent advantages in creating future proof networks that can support and lay the foundations of any future technology. 5G is one of these technological milestones where IPv6 expansion can be based upon. It is apparent that if IPv6 is not adopted for 5G networks from the very beginning, then it is more likely that IPv6 network transformation for the industry as a whole will not be fully implemented within the next following years.
