v6ops Working Group C. Ma Internet-Draft C. Xie Intended status: Informational China Telecom Expires: 29 August 2025 25 February 2025 Considerations of Gradual IPv6-only Deployment in 5G Mobile Networks draft-ma-v6ops-5g-ipv6only-00 Abstract This document describes the approach of gradually deploying 464XLAT based IPv6-only technology on user plane in 3GPP 5G networks. It also discusses the challenges and potential solutions. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 29 August 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Ma & Xie Expires 29 August 2025 [Page 1] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terms and abbreviation . . . . . . . . . . . . . . . . . . . 3 3. 5GS IPv6-only Architecture on User Plane . . . . . . . . . . 4 3.1. Non-roaming Network Scenario . . . . . . . . . . . . . . 4 3.2. Roaming Network Scenario with Home Routed . . . . . . . . 4 3.3. Roaming Network Scenario with Local Break Out . . . . . . 5 4. Deployment Challenges . . . . . . . . . . . . . . . . . . . . 5 4.1. Roaming Challenge . . . . . . . . . . . . . . . . . . . . 5 4.2. UE Challenge . . . . . . . . . . . . . . . . . . . . . . 5 4.3. UP Layer Challenge . . . . . . . . . . . . . . . . . . . 6 4.4. DNS64 Configuration Challenge . . . . . . . . . . . . . . 6 5. Deployment Solution . . . . . . . . . . . . . . . . . . . . . 6 5.1. IMEI Configuration at Network Side . . . . . . . . . . . 6 5.2. Option 108 . . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. Normative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Currently, IPv6 has been widely in mobile networks of operators worldwide, and it has even gained the dominant position from the perspective of traffic. However, IPv4 applications still exist in the network, and the support for IPv4 services must still be considered to guarantee the users’ experience. Furthermore, operators have begun experimenting with deploying IPv6-only approach in their mobile networks. The 5G system is defined in the 3GPP standards organization. In the 5G system architecture, the session related to the endpoint's access to the internet is called the Packet Data Unit (PDU) session, and its type determines the IP protocol used for user access. In the 5G standards, the PDU session supports both IPv6 and IPv4 protocols, and it also provides policies to ensure that user equipment (UE) can access the internet. When a UE only supports the IPv4 protocol while the network supports dual-stack (IPv4 and IPv6), the network will provide an IPv4 protocol stack configuration for the UE. Accordingly, for UE only supporting IPv6,the network will provide an IPv6 protocol stack configuration for the UE. Additionally, there are policy configuration schemes related to static addresses and other aspects, but It does not specify the requirements related to IPv6-only technology. Ma & Xie Expires 29 August 2025 [Page 2] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 There are several IPv6-only transition technologies described in [RFC9313] . Most existing deployments utilize 464XLAT technology in cellular network. This document describes the architecture for deploying 464XLAT based IPv6-only technology on user plane in 3GPP 5G system. Based on the field trail, this document also discusses the major issues encountered and potential solutions to address them. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14[RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Terms and abbreviation The following terms are defined in this document: * 464XLAT: IPv6-Only Transition Mechanism (IPv6-to-IPv4 Translation) * 5GC: 5G Core * 5GS: 5G System * AMF: Access and Mobility Management Function * CLAT: CLAT is customer-side translator (XLAT) that compiles with [RFC6146] * PLAT: PLAT is provider-side translator (XLAT) that compiles with [RFC7915] * PDU：Protocol Data Unit * IMEI: International Mobile Equipment Identity * SMF：Session Management Function * UE: User Equipment, e.g., mobile phone. * LBO：Local Break Out Ma & Xie Expires 29 August 2025 [Page 3] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 3. 5GS IPv6-only Architecture on User Plane Examples of 5GS IPv6-only architectures on user plane are shown in the figures in the following sections. In production 5GS network, there is roaming behavior which specifies where the PDU session anchor and its controlling SMF are located in. That decides whether UE’s PDU sessions get IP configuration and access the Internet from home 5GS network or visited 5GS network. Regarding roaming, 5GS contains three scenarios including non-roaming, roaming with home routed, and roaming with local break out. 3.1. Non-roaming Network Scenario Based on wireless 3GPP network architecture defined in [RFC6877], the non-roaming network architecture is depicted as figure 1. When a mobile network operator run only a 5GC, there is just non-roaming network scenario. In this csae, the CLAT function is deployed on the UE, while the PLAT/stateful NAT64 function and DNS64 function are deployed on the network side. +-------+ +------------+ _________ |UE | |5GC | / \ |+----+ | | +-----+ | / \ ||CLAT| +--+--+UPF +---+---+ Internet | |+----+ | | +-----+ | \ / +-------+ +---/-----\--+ +--------+ / \ +------+ +------+ |NAT64 | |DNS64 | +------+ +------+ 3.2. Roaming Network Scenario with Home Routed Generally, large mobile operators run multiple 5GCs divided by administrative divisions or other geographical methods. The roaming network scenario with home routed is shown in figure 2. In this case, UEs acquire IP network configuration and access the Internet in their home 5GS network. The IP address allocation strategy and traffic exit interface are decided by their home 5GC. The CLAT function is deployed on the UE, while the PLAT/stateful NAT64 function and DNS64 function are deployed on the home network. Ma & Xie Expires 29 August 2025 [Page 4] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 3.3. Roaming Network Scenario with Local Break Out The roaming network scenario with LBO is shown in figure 3. In this case, UEs get IP network configuration and access the Internet in the visited network. The CLAT function is deployed on the UE, while the PLAT/stateful NAT64 function and DNS64 function are deployed on the visited network. Home network also need to support NAT64 and DNS64 when UE is in the non-roaming case. The following table 1 summarizes 5GC's network capabilities where the mobile network shall have to provide IPv6-only connectivity service. +------------------+-----+-------------+---------------+ |Scenario |UE |Home Network |Visited Network| +------------------+-----+-------------+---------------+ |Non-roaming |CLAT |NAT64 DNS64 | | +------------------+-----+-------------+---------------+ |Roaming with Local|CLAT |NAT64 DNS64 |NAT64 DNS64 | |Breakout | | | | +------------------+-----+-------------+---------------+ |Roaming with Home |CLAT |NAT64 DNS64 | | |Routed | | | | +------------------+-----+-------------+---------------+ Table 1. Network Capabilities for IPv6-only 5G Scenarios 4. Deployment Challenges Based on our practices, for large-size mobile network operators, it’s very difficult for operators to deploy IPv6-only capabilities across the whole network at once. There is a transition period that the IPv6-only capability is deployed gradually. This section identifies the major challenges when applying 464XLAT in a production network. 4.1. Roaming Challenge In the scenario where 5GC A supports IPv6-only capability while 5GC B doesn’t. When UE A from 5GC A roams to 5GC B, it only obtains IPv6 configuration and accesses Internet according to the local breakout roaming policy. In this case, the access to IPv4 Internet may fail due to 5GC B lacks NAT64 and DNS64 capabilities. 4.2. UE Challenge Regarding UE challenge, a significant number of terminals have not enabled CLAT functionality. The vast majority of Android terminals support and have enabled the CLAT functionality. Most new terminals like smart watch do not support this feature. Moreover, Apple's iOS in China does not enable CLAT functionality. Ma & Xie Expires 29 August 2025 [Page 5] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 4.3. UP Layer Challenge When IPv6-only users access IPv4 sites, the actual address they reach is generated by the DNS64 server, which combines a special IPv6 prefix with the IPv4 site address to form an IPv6 address. Existing layer 3&layer 4 content billing rules based on IPv4 addresses will no longer be effective and will need to be adjusted to accommodate the IPv6 addresses formed by DNS64. 4.4. DNS64 Configuration Challenge After enabling the DNS64 functionality, there is an increase in the processing load due to the additional handling of IPv6 queries and the DNS64 conversion, which consumes some device performance. The extent of this performance demand increase depends on the scale of IPv6 queries. In a 5G network, once the DNS64 functionality is enabled, DNS resolution requests from both IPv6-only and dual-stack users will be processed by the DNS64 server. Even IPv4 resolution requests from dual-stack users will be treated as if they were from IPv6-only users, which place a significant load pressure on the DNS server. This may futher impact the service logic of the existing dual-stack users. 5. Deployment Solution 5.1. IMEI Configuration at Network Side One solution is to enhance the core network's capability to configure IP addresses and DNS server addresses based on IMEI number ranges. The IMEI is a unique sequence of 14 to 15 digits assigned to each mobile phone. It serves as a device identification number, enabling service providers to recognize the phone within the network. The primary purpose of the IMEI is to uniquely identify each device, allowing the network to determine whether the UE supports CLAT functionality. By configuring a whitelist of IMEIs that support CLAT functionality in the network, the network can assign an IPv6-only environment to UEs listed in the whitelist. 5.2. Option 108 One possible solution is to use the option108 [RFC 8925] method, allowing UE to choose whether to join the IPv6-only environment. Additionally, a method for configuring DNS64 server addresses needs to be considered. However, in practical deployments, core network support for DHCPv4 functionality is optional and may not be applicable to all networks. Ma & Xie Expires 29 August 2025 [Page 6] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 Another possible solution is to transmit Pref64 and DNS64 address information through the RA option. In 5G systems, RA is used to advertise IPv6 prefixes in the SLAAC, which is a mandatory functionality. Transmitting this information through RA is also a favorable option. Currently, the IETF has produced two RFCs, namely [RFC 8106] and [RFC 8781]. In practical implementations, the mobile core network supporting IPv6-only environments (IPv6-only mode) should include these two options in the RA messages. Upon receiving this message, the UE can abandon the IPv4 interface and operate in IPv6-only mode. In this solution, the core network does not need to be aware of the protocol stack ultimately used by UE. 6. Security Considerations TBD. 7. IANA Considerations TBD. 8. Acknowledgements The comments and suggestions of the following are gratefully acknowledged: 9. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3587] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global Unicast Address Format", RFC 3587, DOI 10.17487/RFC3587, August 2003, . [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011, . [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: Combination of Stateful and Stateless Translation", RFC 6877, DOI 10.17487/RFC6877, April 2013, . Ma & Xie Expires 29 August 2025 [Page 7] Internet-Draft 5G IPv6-only Deployment Considerations February 2025 [RFC7915] Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont, "IP/ICMP Translation Algorithm", RFC 7915, DOI 10.17487/RFC7915, June 2016, . [RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, "IPv6 Router Advertisement Options for DNS Configuration", RFC 8106, DOI 10.17487/RFC8106, March 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8781] Colitti, L. and J. Linkova, "Discovering PREF64 in Router Advertisements", RFC 8781, DOI 10.17487/RFC8781, April 2020, . [RFC8925] Colitti, L., Linkova, J., Richardson, M., and T. Mrugalski, "IPv6-Only Preferred Option for DHCPv4", RFC 8925, DOI 10.17487/RFC8925, October 2020, . [RFC9313] Lencse, G., Palet Martinez, J., Howard, L., Patterson, R., and I. Farrer, "Pros and Cons of IPv6 Transition Technologies for IPv4-as-a-Service (IPv4aaS)", RFC 9313, DOI 10.17487/RFC9313, October 2022, . Authors' Addresses Chenhao Ma China Telecom Beiqijia Town, Changping District Beijing 102209 China Email: machh@chinatelecom.cn Chongfeng Xie China Telecom Beiqijia Town, Changping District Beijing 102209 China Email: xiechf@chinatelecom.cn Ma & Xie Expires 29 August 2025 [Page 8]