With the exhaustion of global IPv4 addresses, all operators cannot apply to the IPv4 address pool of the public network. All countries have adopted IPv6 as the direction of the next-generation Internet, and China has also clearly accelerated the strategy of building IPv6-based next-generation Internet.

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IPv6 application in 5G bearer network
Witten By Calio Huang
With the exhaustion of global IPv4 addresses, all operators cannot apply to the IPv4 address pool
of the public network. All countries have adopted IPv6 as the direction of the next-generation
Internet, and China has also clearly accelerated the strategy of building IPv6-based
next-generation Internet.
Driven by national policies, the domestic IPv6 industry chain has accelerated its maturity, and the
development of terminals and service platforms has also accelerated the pace of IPv6 network
construction. As the carrier's basic network, the bearer network is also facing the demand for
IPv6 evolution.
VPN supports IPv6
With the IPv4/IPv6 dual-stacking of the interface carried by the base station and the core
network, the bearer network needs to support the 6vPE to provide a dual-stack VPN, which
satisfies the evolution of the IPv6 on the customer side. 6vPE superimposes IPv6 VPN on the IPv4
MPLS network. The operator only needs to upgrade the IPv6 and IPv6 dual stacks on the ingress
PE and egress PE of the service to support the IPv6 requirements of the service. The intermediate
node can still be an IPv4 MPLS network. The 6vPE control plane protocol is also MP-BGP. By
adding a new address family to advertise IPv6 routes between BGP neighbors, you can build an
L3VPN that supports IPv6.
The dual-stack VPN can support both the 4G base station and the newly built 5G base station
bearer. The user side provides dual-stack access based on the existing model. For the 4G base
station, only the IPv4 address is assigned, and the VPN sub-interface is used to access the VPN.
For the 5G base station supporting IPv6, the IPv4 and IPv6 addresses are allocated, and two

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access modes are supported. You can configure IPv4/IPv6 addresses on the same VLAN
sub-interface or IPv4/IPv6 addresses on different VLAN sub-interfaces. The first approach is
recommended to simplify the VLAN configuration. Similarly, the core network also needs to
support IPv4 and IPv6 dual stacks.
Within the VPN, the 5G base station communicates with the inventory 4G base station using the
IPv4 address, communicates with the core network using the IPv6 address, and the 4G base
station still communicates with the core network using the IPv4 address. The dual-stack VPN is
simple to implement and can avoid complex conversion between IPv4 and IPv6 while meeting the
service requirements.
The public network supports IPv6
A dual-stack VPN can provide IPv6 services to customers, but the bearer network ad hoc network
can be IPv4.
As the carrier network evolves to IPv6, the bearer network devices and protocols also need to
fully support IPv6. The control plane of the IPv6 bearer network of the control plane mainly
includes the DCN, the service control plane, and the southbound interface channel. In a
traditional IPv4 network, due to insufficient management address space or some limitations of
the external DCN network, the management IP allocated to the bearer network is very limited,
and the gateway network element function needs to be supported. The entire bearer network
only needs to assign an IP address to the gateway network element. The non-gateway network
element can communicate with the network management system by using a private IP address or
ID. At the same time, the gateway network element performs address translation, and the
complexity brought by the conversion makes the capability of the gateway network element
limited. After the DCN is evolved to IPv6, there is no longer any problem that the IPv4
management address is insufficient. Therefore, there is no need to support the gateway network
element and address translation function. All network elements can directly communicate with
the network management system, which simplifies. In addition, the DCN self-pass requires the
device to generate a default IP address. In the traditional IPv4 network, the default address of
each manufacturer is generated in a private manner, and the default address of IPv6 can use the
standard IEEE EUI-64 (64bit prefix + EUI-64). ) or RFC 3041 (64bit prefix + 64bit random address)
two schemes, compared to IPv4 is more conducive to unify the DCN implementation of each
manufacturer, easy to achieve DCN interoperability. The DCN generally adopts the OSPF protocol,
and the corresponding IPv6 DCN needs to support the OSPFv3 protocol.
The deployment of the service control plane is similar to IPv4. For the planning and allocation of
IP addresses, it should correspond to the network topology hierarchy, not only to effectively
utilize the address space, but also to reflect the scalability, flexibility and hierarchy of the network,
and to meet the requirements of the routing protocol, so as to facilitate Implement route
aggregation in the network, reduce entries in the routing table, reduce CPU and memory
consumption, and improve routing algorithm efficiency. Specifically, cities use a /48 for loopback
addresses and each loopback address uses /128 for addresses. Each city uses one or more /48 for
interface interconnect addresses, with one /64 reserved for each connection and /127 for the
address segment. The main difference between IPv4 and IPv4 is that the protocol supporting IPv6
needs to be deployed. In addition to the routing protocols such as ISISv6, the corresponding SR

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extension, BGP-LS, and PCEP protocols must support IPv6.
Network evolution is not a one-step process. From IPv4 control plane to IPv6 is a gradual upgrade
and evolution process, and the two need to coexist for a long period of time. In order to support
smooth evolution, the control plane also needs to support IPv4/IPv6 dual-stack. The deployment
of dual stacks can be divided into the following stages:
- Gradually upgrade the device's IPv6 capabilities;
- The IPv6 address of the NE and the interface is added, and the process of deploying ISISv6 or
OSPFv3 is completely independent of the original IPv4 control plane while maintaining the
original IPv4 DCN and service control plane configuration unchanged.
- During the transition period, if the device deploys both IPv4 and IPv6 addresses, IPv6 is
preferred for communication;
After the IPv6 deployment is complete, the original IPv4 control plane is deleted and only IPv6 is
reserved.
Forwarding plane IPv6
In the existing bearer network, the forwarding plane adopts MPLS technology. The elegant and
concise data plane of MPLS rarely encounters challenges, but the complex control plane makes
the network deployment more complicated. The SR technology simplifies and unifies the MPLS
control plane and has been favored by more and more operators. SR technology supports both
MPLS and IPv6 data planes, namely SR-MPLS and SRv6. After the network evolves to IPv6, does
the data plane continue to retain MPLS or IPv6?
Unlike SR-MPLS, which uses a 20-bit tag to indicate a different SID, the 128-bit SID used by SRv6 is
more scalable. The SRv6 SID can be divided into three parts: locator, function, and parameter. The
locator is used to express the routing information to the node, and the function and parameter
respectively represent the specific functions and parameters required to be executed at the
node.
In addition, SRv6 has good end-to-end characteristics. After the access network, metropolitan
area network, backbone network, and data center are unified to IPv6-only network, it can easily
provide end-to-end services for users. The problem with SRv6 is that it is incompatible with the
existing MPLS forwarding plane and cannot be smoothly evolved. The existing network devices
require hardware upgrades to support SRv6. Because the SRv6 SID overhead is too large, the
supported stack depth is also limited.
In order to solve the deep problem of SRv6 stack, there are some other options:
- The cascading model is adopted, and the service layer of the overlay uses SRv6, but the bearer
network still adopts SR-MPLS, and the client's SRv6 service is carried as a normal IPv6 packet;
- Performing the transformation of SRv6 and SR-MPLS at the border node, using the SR-MPLS to
establish a service path in the bearer network, and advertising the other routes to the other
network by means of the SRv6 Binding SID. The other network pushes the BSID into the SRv6
label stack, and the SRv6 packet After reaching the border node of the bearer network, the
border node performs the operation of End.BM to map the SRv6 BSID to the SR-MPLS label stack,
and forwards the label in the bearer network with MPLS label to save overhead.
- SRoUDP is used to build an end-to-end SR. SRoUDP is a technology that supports SR on a native
IP network. The MPLS label stack is used to represent the segment list of the SR. However, the

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MPLS label stack is not directly encapsulated in the Ethernet. Encapsulated in UDP packets, nodes
that do not support SRoUDP can be forwarded directly in native IP. SRoUDP has the advantages of
small SR-MPLS overhead and SRv6 support native IP forwarding plane, but its packaging is
relatively complicated.
In addition to the above methods, technologies such as CRH, Binding SID, PCEP FS, and IGP
flexible algorithms can help optimize the stack depth of SRv6. At present, various technologies
are in the stage of blooming, and it is necessary to pay attention to relevant standard progress
and industry trends to determine the mainstream development trend in the future.
Combined with the deployment progress and evolution strategy of the base station and the core
network IPv6, the bearer network can evolve to support IPv6 in a stepwise manner. In the first
phase, 6vPE is deployed to meet the bearer requirements of the base station and the core
network IPv6. In the second phase, the control plane is evolved to IPv6 to solve the DCN address
translation. The current node forwarding plane can still maintain a simple, efficient and mature
MPLS mechanism. The network programming capability of SRv6 technology is stronger, but the
technology is still immature. How to improve the packaging efficiency of SRv6 instructions is a key
issue of the industry. After the SRv6 technology matures Then consider fully supporting the
forwarding plane IPv6.