Internet Engineering Task Force (IETF)                         R. Koodli
Request for Comments: 6212                                 Cisco Systems
Category: Informational                                        July 2011
ISSN: 2070-1721
Internet Engineering Task Force (IETF)                         R. Koodli
Request for Comments: 6212                                 Cisco Systems
Category: Informational                                        July 2011
ISSN: 2070-1721

Mobile Networks Considerations for IPv6 Deployment




Mobile Internet access from smartphones and other mobile devices is accelerating the exhaustion of IPv4 addresses. IPv6 is widely seen as crucial for the continued operation and growth of the Internet, and in particular, it is critical in mobile networks. This document discusses the issues that arise when deploying IPv6 in mobile networks. Hence, this document can be a useful reference for service providers and network designers.


Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.


This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

本文件是互联网工程任务组(IETF)的产品。它代表了IETF社区的共识。它已经接受了公众审查,并已被互联网工程指导小组(IESG)批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准;见RFC 5741第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2011 IETF信托基金和确定为文件作者的人员。版权所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本,并提供简化BSD许可证中所述的无担保。

Table of Contents


   1. Introduction ....................................................2
   2. Reference Architecture and Terminology ..........................3
   3. IPv6 Considerations .............................................4
      3.1. IPv4 Address Exhaustion ....................................4
      3.2. NAT Placement in Mobile Networks ...........................7
      3.3. IPv6-Only Deployment Considerations ........................9
      3.4. Fixed-Mobile Convergence ..................................12
   4. Summary and Conclusion .........................................14
   5. Security Considerations ........................................15
   6. Acknowledgements ...............................................15
   7. Informative References .........................................15
   1. Introduction ....................................................2
   2. Reference Architecture and Terminology ..........................3
   3. IPv6 Considerations .............................................4
      3.1. IPv4 Address Exhaustion ....................................4
      3.2. NAT Placement in Mobile Networks ...........................7
      3.3. IPv6-Only Deployment Considerations ........................9
      3.4. Fixed-Mobile Convergence ..................................12
   4. Summary and Conclusion .........................................14
   5. Security Considerations ........................................15
   6. Acknowledgements ...............................................15
   7. Informative References .........................................15
1. Introduction
1. 介绍

The dramatic growth of the Mobile Internet is accelerating the exhaustion of the available IPv4 addresses. It is widely accepted that IPv6 is necessary for the continued operation and growth of the Internet in general and of the Mobile Internet in particular. While IPv6 brings many benefits, certain unique challenges arise when deploying it in mobile networks. This document describes such challenges and outlines the applicability of the existing IPv6 deployment solutions. As such, it can be a useful reference document for service providers as well as network designers. This document does not propose any new protocols or suggest new protocol specification work.


The primary considerations that we address in this document on IPv6 deployment in mobile networks are:


o Public and Private IPv4 address exhaustion and implications to mobile network deployment architecture;

o 公共和私有IPv4地址耗尽及其对移动网络部署架构的影响;

o Placement of Network Address Translation (NAT) functionality and its implications;

o 网络地址转换(NAT)功能的位置及其含义;

o IPv6-only deployment considerations and roaming implications; and

o 仅IPv6部署注意事项和漫游影响;和

o Fixed-Mobile Convergence and implications to overall architecture.

o 固定移动融合和对整体架构的影响。

In the following sections, we discuss each of these in detail.


For the most part, we assume the Third Generation Partnership Project (3GPP) 3G and 4G network architectures specified in [3GPP.3G] and [3GPP.4G]. However, the considerations are general enough for other mobile network architectures as well [3GPP2.EHRPD].


2. Reference Architecture and Terminology
2. 参考体系结构和术语

The following is a reference architecture of a mobile network.


                                +-----+    +-----+
                                | AAA |    | PCRF|
                                +-----+    +-----+
              Home Network         \          /
                                    \        /                       /-
                                     \      /                       / I
  MN     BS                           \    /                       /  n
   |     /\    +-----+ /-----------\ +-----+ /-----------\ +----+ /   t
 +-+    /_ \---| ANG |/ Operator's  \| MNG |/ Operator's  \| BR |/    e
 | |---/    \  +-----+\ IP Network  /+-----+\ IP Network  /+----+\    r
 +-+                   \-----------/    /    \-----------/        \   n
                       ----------------/------                     \  e
                     Visited Network  /                             \ t
                                     /                               \-
         +-----+ /------------------\
         | ANG |/ Visited Operator's \
         +-----+\     IP Network     /
                                +-----+    +-----+
                                | AAA |    | PCRF|
                                +-----+    +-----+
              Home Network         \          /
                                    \        /                       /-
                                     \      /                       / I
  MN     BS                           \    /                       /  n
   |     /\    +-----+ /-----------\ +-----+ /-----------\ +----+ /   t
 +-+    /_ \---| ANG |/ Operator's  \| MNG |/ Operator's  \| BR |/    e
 | |---/    \  +-----+\ IP Network  /+-----+\ IP Network  /+----+\    r
 +-+                   \-----------/    /    \-----------/        \   n
                       ----------------/------                     \  e
                     Visited Network  /                             \ t
                                     /                               \-
         +-----+ /------------------\
         | ANG |/ Visited Operator's \
         +-----+\     IP Network     /

Figure 1: Mobile Network Architecture


A Mobile Node (MN) connects to the mobile network either via its Home Network or via a Visited Network when the user is roaming outside of the Home Network. In the 3GPP network architecture, an MN accesses the network by connecting to an Access Point Name (APN), which maps to a mobile gateway. Roughly speaking, an APN is similar to a Service Set Identifier (SSID) in wireless LAN. An APN is a logical concept that can be used to specify what kinds of services, such as Internet access, high-definition video streaming, content-rich gaming, and so on, that an MN is entitled to. Each APN can specify what type of IP connectivity (i.e., IPv4, IPv6, IPv4v6) is enabled on that particular APN.


While an APN directs an MN to an appropriate gateway, the MN needs an end-to-end "link" to that gateway. In the Long-Term Evolution (LTE) networks, this link is realized through an Evolved Packet System (EPS) bearer. In the 3G Universal Mobile Telecommunications System (UMTS) networks, such a link is realized through a Packet Data Protocol (PDP) context. The end-to-end link traverses multiple nodes, which are defined below:


o Base Station (BS): The radio Base Station provides wireless connectivity to the MN.

o 基站(BS):无线基站向MN提供无线连接。

o Access Network Gateway (ANG): The ANG forwards IP packets to and from the MN. Typically, this is not the MN's default router, and the ANG does not perform IP address allocation and management for the mobile nodes. The ANG is located either in the Home Network or in the Visited Network.

o 接入网网关(ANG):ANG向MN转发IP数据包,并从MN转发IP数据包。通常,这不是MN的默认路由器,并且ANG不为移动节点执行IP地址分配和管理。ANG位于家庭网络或访问网络中。

o The Mobile Network Gateway (MNG): The MNG is the MN's default router, which provides IP address management. The MNG performs functions such as offering Quality of Service (QoS), applying subscriber-specific policy, and enabling billing and accounting; these functions are sometimes collectively referred to as "subscriber-management" operations. The mobile network architecture, as shown in Figure 1, defines the necessary protocol interfaces to enable subscriber-management operations. The MNG is typically located in the Home Network.

o 移动网络网关(MNG):MNG是MN的默认路由器,提供IP地址管理。MNG执行诸如提供服务质量(QoS)、应用特定于用户的策略以及启用计费和记帐等功能;这些功能有时统称为“订户管理”操作。如图1所示,移动网络体系结构定义了必要的协议接口,以支持用户管理操作。MNG通常位于家庭网络中。

o Border Router (BR): As the name implies, a BR borders the Internet for the mobile network. The BR does not perform subscriber management for the mobile network.

o 边界路由器(BR):顾名思义,BR为移动网络连接互联网。BR不执行移动网络的用户管理。

o Authentication, Authorization, and Accounting (AAA): The general functionality of AAA is used for subscriber authentication and authorization for services as well as for generating billing and accounting information.

o 身份验证、授权和记帐(AAA):AAA的一般功能用于服务的订户身份验证和授权,以及生成计费和记帐信息。

In 3GPP network environments, the subscriber authentication and the subsequent authorization for connectivity and services is provided using the "Home Location Register" (HLR) / "Home Subscriber Server" (HSS) functionality.


o Policy and Charging Rule Function (PCRF): The PCRF enables applying policy and charging rules at the MNG.

o 策略和计费规则功能(PCRF):PCRF允许在MNG应用策略和计费规则。

In the rest of this document, we use the terms "operator", "service provider", and "provider" interchangeably.


3. IPv6 Considerations
3. IPv6注意事项
3.1. IPv4 Address Exhaustion
3.1. IPv4地址耗尽

It is generally agreed that the pool of public IPv4 addresses is nearing its exhaustion. The IANA has exhausted the available '/8' blocks for allocation to the Regional Internet Registries (RIRs). The RIRs themselves have either "run out" of their blocks or are projected to exhaust them in the near future. This has led to a heightened awareness among service providers to consider introducing technologies to keep the Internet operational. For providers, there are two simultaneous approaches to addressing the run-out problem:


delaying the IPv4 address pool exhaustion (i.e., conserving their existing pool) and introducing IPv6 in operational networks. We consider both in the following.


Delaying public IPv4 address exhaustion for providers involves assigning private IPv4 addressing for end-users or extending an IPv4 address with the use of port ranges, which requires tunneling and additional signaling. A mechanism such as the Network Address Translator (NAT) is used at the provider premises (as opposed to customer premises) to manage the private IP address assignment and access to the Internet. In the following, we primarily focus on translation-based mechanisms such as NAT44 (i.e., translation from public IPv4 to private IPv4 and vice versa) and NAT64 (i.e., translation from public IPv6 to public IPv4 and vice versa). We do this because the 3GPP architecture already defines a tunneling infrastructure with the General Packet Radio Service (GPRS) Tunneling Protocol (GTP), and the architecture allows for dual-stack and IPv6-only deployments.


In a mobile network, the IPv4 address assignment for an MN is performed by the MNG. In the 3GPP network architecture, this assignment is performed in conjunction with the Packet Data Network (PDN) connectivity establishment. A PDN connection implies an end-end link (i.e., an EPS bearer in 4G LTE or a PDP context in 3G UMTS) from the MN to the MNG. There can be one or more PDN connections active at any given time for each MN. A PDN connection may support both IPv4 and IPv6 traffic (as in a dual-stack PDN in 4G LTE networks), or it may support only one of the two traffic types (as in the existing 3G UMTS networks). The IPv4 address is assigned at the time of PDN connectivity establishment or is assigned using DHCP after the PDN connectivity is established. In order to delay the exhaustion of public IPv4 addresses, this IP address needs to be a private IPv4 address that is translated into a shared public IPv4 address. Hence, there is a need for a private-public IPv4 translation mechanism in the mobile network.

在移动网络中,MN的IPv4地址分配由MNG执行。在3GPP网络架构中,该分配与分组数据网络(PDN)连接建立一起执行。PDN连接意味着从MN到MNG的终端链路(即,4G LTE中的EPS承载或3G UMTS中的PDP上下文)。对于每个MN,在任何给定时间都可以有一个或多个PDN连接处于活动状态。PDN连接可以同时支持IPv4和IPv6流量(如4G LTE网络中的双栈PDN),也可以仅支持这两种流量类型中的一种(如现有3G UMTS网络)。IPv4地址在建立PDN连接时分配,或在建立PDN连接后使用DHCP分配。为了延迟公共IPv4地址的耗尽,此IP地址需要是转换为共享公共IPv4地址的专用IPv4地址。因此,在移动网络中需要专用的公共IPv4转换机制。

In the Long-Term Evolution (LTE) 4G network, there is a requirement for an always-on PDN connection in order to reliably reach a mobile user in the All-IP network. This requirement is due to the need for supporting Voice over IP service in LTE, which does not have circuit-based infrastructure. If this PDN connection were to use IPv4 addressing, a private IPv4 address is needed for every MN that attaches to the network. This could significantly affect the availability and usage of private IPv4 addresses. One way to address this is by making the always-on PDN (that requires voice service) to be IPv6. The IPv4 PDN is only established when the user needs it.

在长期演进(LTE)4G网络中,为了可靠地到达全IP网络中的移动用户,需要始终在线的PDN连接。这一要求是由于在LTE中需要支持IP语音服务,LTE没有基于电路的基础设施。如果此PDN连接使用IPv4寻址,则连接到网络的每个MN都需要一个专用IPv4地址。这可能会显著影响专用IPv4地址的可用性和使用率。解决这一问题的一种方法是将始终在线的PDN(需要语音服务)设置为IPv6。IPv4 PDN仅在用户需要时建立。

The 3GPP standards also specify a deferred IPv4 address allocation on a dual-stack IPv4v6 PDN at the time of connection establishment. This has the advantage of a single PDN for IPv6 and IPv4 along with deferring IPv4 address allocation until an application needs it. The deferred address allocation requires support for a dynamic configuration protocol such as DHCP as well as appropriate triggers to invoke the protocol. Such a support does not exist today in mobile phones. The newer iterations of smartphones could provide such support. Also, the tethering of smartphones to laptops (which typically support DHCP) could use deferred allocation depending on when a laptop attaches to the smartphone. Until appropriate triggers and host stack support is available, the applicability of the address-deferring option may be limited.

3GPP标准还规定了在建立连接时在双栈IPv4v6 PDN上的延迟IPv4地址分配。这具有IPv6和IPv4的单个PDN的优势,同时可以将IPv4地址分配推迟到应用程序需要时。延迟地址分配需要支持动态配置协议(如DHCP)以及调用协议的适当触发器。这种支持在今天的手机中并不存在。新一代智能手机可以提供这样的支持。此外,智能手机与笔记本电脑的连接(通常支持DHCP)可能会使用延迟分配,具体取决于笔记本电脑与智能手机的连接时间。在适当的触发器和主机堆栈支持可用之前,地址延迟选项的适用性可能会受到限制。

On the other hand, in the existing 3G UMTS networks, there is no requirement for an always-on connection even though many smartphones seldom relinquish an established PDP context. The existing so-called pre-Release-8 deployments do not support the dual-stack PDP connection. Hence, two separate PDP connections are necessary to support IPv4 and IPv6 traffic. Even though some MNs, especially the smartphones, in use today may have IPv6 stack, there are two remaining considerations. First, there is little operational experience and compliance testing with these existing stacks. Hence, it is expected that their use in large deployments may uncover software errors and interoperability problems that inhibit providing services based on IPv6 for such hosts. Second, only a fraction of current phones in use have such a stack. As a result, providers need to test, deploy, and operationalize IPv6 as they introduce new handsets, which also continue to need access to the predominantly IPv4 Internet.

另一方面,在现有的3G UMTS网络中,即使许多智能手机很少放弃已建立的PDP上下文,也不需要始终在线的连接。现有所谓的pre-Release-8部署不支持双堆栈PDP连接。因此,需要两个独立的PDP连接来支持IPv4和IPv6流量。尽管目前使用的一些MN,特别是智能手机,可能有IPv6协议栈,但还有两个需要考虑的问题。首先,对于这些现有堆栈,几乎没有操作经验和法规遵从性测试。因此,预计它们在大型部署中的使用可能会发现软件错误和互操作性问题,这些问题阻碍了为此类主机提供基于IPv6的服务。其次,目前使用的手机中只有一小部分有这样的堆叠。因此,提供商需要在推出新手机时测试、部署和操作IPv6,而新手机也需要继续访问主要为IPv4的互联网。

The considerations from the preceeding paragraphs lead to the following observations. First, there is an increasing need to support private IPv4 addressing in mobile networks because of the public IPv4 address run-out problem. Correspondingly, there is a greater need for private-public IPv4 translation in mobile networks. Second, there is support for IPv6 in both 3G and 4G LTE networks already in the form of PDP context and PDN connections. To begin with, operators can introduce IPv6 for their own applications and services. In other words, the IETF's recommended model of dual-stack IPv6 and IPv4 networks is readily applicable to mobile networks with the support for distinct APNs and the ability to carry IPv6 traffic on PDP/PDN connections. The IETF dual-stack model can be applied using a single IPv4v6 PDN connection in Release-8 and onwards but requires separate PDP contexts in the earlier releases. Finally, operators can make IPv6 the default for always-on mobile connections using either the IPv4v6 PDN or the IPv6 PDN and use IPv4 PDNs as necessary.

上述各段的考虑导致以下意见。首先,由于公共IPv4地址耗尽问题,移动网络中越来越需要支持专用IPv4地址。相应地,移动网络中更需要私有-公共IPv4转换。第二,在3G和4G LTE网络中,已经以PDP上下文和PDN连接的形式支持IPv6。首先,运营商可以为自己的应用程序和服务引入IPv6。换句话说,IETF推荐的双栈IPv6和IPv4网络模型很容易适用于支持不同APN的移动网络,并且能够在PDP/PDN连接上承载IPv6流量。IETF双栈模型可在第8版及以后版本中使用单个IPv4v6 PDN连接应用,但在早期版本中需要单独的PDP上下文。最后,运营商可以使用IPv4v6 PDN或IPv6 PDN将IPv6作为始终在线移动连接的默认设置,并根据需要使用IPv4 PDN。

3.2. NAT Placement in Mobile Networks
3.2. 移动网络中的NAT放置

In the previous section, we observed that NAT44 functionality is needed in order to conserve the available pool and delay public IPv4 address exhaustion. However, the available private IPv4 pool itself is not abundant for large networks such as mobile networks. For instance, the so-called NET10 block [RFC1918] has approximately 16.7 million private IPv4 addresses starting with A large mobile service provider network can easily have more than 16.7 million subscribers attached to the network at a given time. Hence, the private IPv4 address pool management and the placement of NAT44 functionality becomes important.


In addition to the developments cited above, NAT placement is important for other reasons as well. Access networks generally need to produce network and service usage records for billing and accounting. This is true also for mobile networks where "subscriber management" features (i.e., QoS, Policy, and Billing and Accounting) can be fairly detailed. Since a NAT introduces a binding between two addresses, the bindings themselves become necessary information for subscriber management. For instance, the offered QoS on private IPv4 address and the (shared) public IPv4 address may need to be correlated for accounting purposes. As another example, the Application Servers within the provider network may need to treat traffic based on policy provided by the PCRF. If the IP address seen by these Application Servers is not unique, the PCRF needs to be able to inspect the NAT binding to disambiguate among the individual MNs. The subscriber session management information and the service usage information also need to be correlated in order to produce harmonized records. Furthermore, there may be legal requirements for storing the NAT binding records. Indeed, these problems disappear with the transition to IPv6. For now, it suffices to assert that NAT introduces state, which needs to be correlated and possibly stored with other routine subscriber information.


Mobile network deployments vary in their allocation of IP address pools. Some network deployments use the "centralized model" where the pool is managed by a common node, such as the PDN's BR, and the pool shared by multiple MNGs all attached to the same BR. This model has served well in the pre-3G deployments where the number of subscribers accessing the Mobile Internet at any given time has not exceeded the available address pool. However, with the advent of 3G networks and the subsequent dramatic growth in the number of users on the Mobile Internet, service providers are increasingly forced to consider their existing network design and choices. Specifically, providers are forced to address private IPv4 pool exhaustion as well as scalable NAT solutions.


In order to tackle the private IPv4 exhaustion in the centralized model, there would be a need to support overlapped private IPv4 addresses in the common NAT functionality as well as in each of the gateways. In other words, the IP addresses used by two or more MNs (which may be attached to the same MNG) are very likely to overlap at the centralized NAT, which needs to be able to differentiate traffic. Tunneling mechanisms such as Generic Routing Encapsulation (GRE) [RFC2784] [RFC2890], MPLS [RFC3031] VPN tunnels, or even IP-in-IP encapsulation [RFC2003] that can provide a unique identifier for a NAT session can be used to separate overlapping private IPv4 traffic as described in [GI-DS-LITE]. An advantage of centralizing the NAT and using the overlapped private IPv4 addressing is conserving the limited private IPv4 pool. It also enables the operator's enterprise network to use IPv6 from the MNG to the BR; this (i.e., the need for an IPv6-routed enterprise network) may be viewed as an additional requirement by some providers. The disadvantages include the need for additional protocols to correlate the NAT state (at the common node) with subscriber session information (at each of the gateways), suboptimal MN-MN communication, absence of subscriber-aware NAT (and policy) function, and, of course, the need for a protocol from the MNG to BR itself. Also, if the NAT function were to experience failure, all the connected gateway service will be affected. These drawbacks are not present in the "distributed" model, which we discuss in the following.


In a distributed model, the private IPv4 address management is performed by the MNG, which also performs the NAT functionality. In this model, each MNG has a block of 16.7 million unique addresses, which is sufficient compared to the number of mobile subscribers active on each MNG. By distributing the NAT functionality to the edge of the network, each MNG is allowed to reuse the available NET10 block, which avoids the problem of overlapped private IPv4 addressing at the network core. In addition, since the MNG is where subscriber management functions are located, the NAT state correlation is readily enabled. Furthermore, an MNG already has existing interfaces to functions such as AAA and PCRF, which allows it to perform subscriber management functions with the unique private IPv4 addresses. Finally, the MNG can also pass-through certain traffic types without performing NAT to the Application Servers located within the service provider's domain, which allows the servers to also identify subscriber sessions with unique private IPv4 addresses. The disadvantages of the "distributed model" include the absence of centralized addressing and centralized management of NAT.


In addition to the two models described above, a hybrid model is to locate NAT in a dedicated device other than the MNG or the BR. Such a model would be similar to the distributed model if the IP pool supports unique private addressing for the mobile nodes, or it would


be similar to the centralized model if it supports overlapped private IP addresses. In any case, the NAT device has to be able to provide the necessary NAT session binding information to an external entity (such as AAA or PCRF), which then needs to be able to correlate those records with the user's session state present at the MNG.


The foregoing discussion can be summarized as follows. First, the management of the available private IPv4 pool has become important given the increase in Mobile Internet users. Mechanisms that enable reuse of the available pool are required. Second, in the context of private IPv4 pool management, the placement of NAT functionality has implications to the network deployment and operations. The centralized models with a common NAT have the advantages of continuing their legacy deployments and the reuse of private IPv4 addressing. However, they need additional functions to enable traffic differentiation and NAT state correlation with subscriber state management at the MNG. The distributed models also achieve private IPv4 address reuse and avoid overlapping private IPv4 traffic in the operator's core, but without the need for additional mechanisms. Since the MNG performs (unique) IPv4 address assignment and has standard interfaces to AAA and PCRF, the distributed model also enables a single point for subscriber and NAT state reporting as well as policy application. In summary, providers interested in readily integrating NAT with other subscriber management functions, as well as conserving and reusing their private IPv4 pool, may find the distributed model compelling. On the other hand, those providers interested in common management of NAT may find the centralized model more compelling.


3.3. IPv6-Only Deployment Considerations
3.3. 仅IPv6部署注意事项

As we observed in the previous section, the presence of NAT functionality in the network brings up multiple issues that would otherwise be absent. NAT should be viewed as an interim solution until IPv6 is widely available, i.e., IPv6 is available for mobile users for all (or most) practical purposes. Whereas NATs at provider premises may slow down the exhaustion of public IPv4 addresses, expeditious and simultaneous introduction of IPv6 in the operational networks is necessary to keep the Internet "going and growing". Towards this goal, it is important to understand the considerations in deploying IPv6-only networks.


   There are three dimensions to IPv6-only deployments: the network
   itself, the mobile nodes, and the applications, represented by the
   3-tuple {nw, mn, ap}.  The goal is to reach the coordinate {IPv6,
   IPv6, IPv6} from {IPv4, IPv4, IPv4}.  However, there are multiple
   paths to arrive at this goal.  The classic dual-stack model would
   traverse the coordinate {IPv4v6, IPv4v6, IPv4v6}, where each
   There are three dimensions to IPv6-only deployments: the network
   itself, the mobile nodes, and the applications, represented by the
   3-tuple {nw, mn, ap}.  The goal is to reach the coordinate {IPv6,
   IPv6, IPv6} from {IPv4, IPv4, IPv4}.  However, there are multiple
   paths to arrive at this goal.  The classic dual-stack model would
   traverse the coordinate {IPv4v6, IPv4v6, IPv4v6}, where each

dimension supports co-existence of IPv4 and IPv6. This appears to be the path of least disruption, although we are faced with the implications of supporting large-scale NAT in the network. There is also the cost of supporting separate PDP contexts in the existing 3G UMTS networks. The other intermediate coordinate of interest is {IPv6, IPv6, IPv4}, where the network and the MN are IPv6-only, and the Internet applications are recognized to be predominantly IPv4. This transition path would, ironically, require interworking between IPv6 and IPv4 in order for the IPv6-only MNs to be able to access IPv4 services and applications on the Internet. In other words, in order to disengage NAT (for IPv4-IPv4), we need to introduce another form of NAT (i.e., IPv6-IPv4) to expedite the adoption of IPv6.

维度支持IPv4和IPv6共存。这似乎是中断最少的路径,尽管我们面临着在网络中支持大规模NAT的影响。在现有3G UMTS网络中支持单独的PDP上下文也有成本。另一个感兴趣的中间坐标是{IPv6,IPv6,IPv4},其中网络和MN仅为IPv6,并且因特网应用程序被认为主要是IPv4。具有讽刺意味的是,这种过渡路径需要IPv6和IPv4之间的互通,以便仅IPv6的MN能够访问Internet上的IPv4服务和应用程序。换句话说,为了脱离NAT(对于IPv4-IPv4),我们需要引入另一种形式的NAT(即IPv6-IPv4),以加快IPv6的采用。

It is interesting to consider the preceeding discussion surrounding the placement of NAT for IPv6-IPv4 interworking. There is no overlapping private IPv4 address problem because each IPv6 address is unique and there are plenty of them available. Hence, there is also no requirement for (IPv6) address reuse, which means no protocol is necessary in the centralized model to disambiguate NAT sessions. However, there is an additional requirement of DNS64 [RFC6147] functionality for IPv6-IPv4 translation. This DNS64 functionality must ensure that the synthesized AAAA record correctly maps to the IPv6-IPv4 translator.


IPv6-only deployments in mobile networks need to reckon with the following considerations. First, both the network and the MNs need to be IPv6 capable. Expedited network upgrades as well as rollout of MNs with IPv6 would greatly facilitate this. Fortunately, the 3GPP network design for LTE already requires the network nodes and the mobile nodes to support IPv6. Even though there are no requirements for the transport network to be IPv6, an operational IPv6 connectivity service can be deployed with appropriate existing tunneling mechanisms in the IPv4-only transport network. Hence, a service provider may choose to enforce IPv6-only PDN and address assignment for their own subscribers in their Home Networks (see Figure 1). This is feasible for the newer MNs when the mobile network is able to provide IPv6-only PDN support and IPv6-IPv4 interworking for Internet access. For the existing MNs, however, the provider still needs to be able to support IPv4-only PDP/PDN connectivity.


Migration of applications to IPv6 in MNs with IPv6-only PDN connectivity brings challenges. The applications and services offered by the provider obviously need to be IPv6-capable. However, an MN may host other applications, which also need to be IPv6-capable in IPv6-only deployments. This can be a "long-tail" phenomenon; however, when a few prominent applications start offering IPv6, there can be a strong incentive to provide application-layer (e.g., socket

在具有仅IPv6 PDN连接的MNs中将应用程序迁移到IPv6带来了挑战。提供商提供的应用程序和服务显然需要支持IPv6。但是,MN可能承载其他应用程序,这些应用程序在仅IPv6部署中也需要支持IPv6。这可能是一种“长尾”现象;但是,当一些著名的应用程序开始提供IPv6时,可能会有强烈的动机来提供应用程序层(例如套接字)

interface) upgrades to IPv6. Also, some IPv4-only applications may be able to make use of alternative access such as WiFi when available. A related challenge in the migration of applications is the use of IPv4 literals in application layer protocols (such as XMPP) or content (as in HTML or XML). Some Internet applications expect their clients to supply IPv4 addresses as literals, and this will not be possible with IPv6-only deployments. Some of these experiences and the related considerations in deploying an IPv6-only network are documented in [ARKKO-V6]. In summary, migration of applications to IPv6 needs to be done, and such a migration is not expected to be uniform across all subsets of existing applications.


Voice over LTE (VoLTE) also brings some unique challenges. The signaling for voice is generally expected to be available for free while the actual voice call itself is typically charged on its duration. Such a separation of signaling and the payload is unique to voice, whereas an Internet connection is accounted without specifically considering application signaling and payload traffic. This model is expected to be supported even during roaming. Furthermore, providers and users generally require voice service regardless of roaming, whereas Internet usage is subject to subscriber preferences and roaming agreements. This requirement to ubiquitously support voice service while providing the flexibility for Internet usage exacerbates the addressing problem and may hasten provisioning of VoLTE using the IPv6-only PDN.

LTE语音(VoLTE)也带来了一些独特的挑战。语音信号通常是免费的,而实际的语音呼叫本身通常根据其持续时间收费。信令和有效负载的这种分离对于语音来说是唯一的,而互联网连接是在没有特别考虑应用信令和有效负载流量的情况下进行的。即使在漫游期间,也应支持此模型。此外,无论漫游情况如何,提供商和用户通常都需要语音服务,而互联网的使用取决于用户偏好和漫游协议。这种在提供互联网使用灵活性的同时普遍支持语音服务的要求加剧了寻址问题,并可能加快使用仅IPv6 PDN的VoLTE的供应。

As seen earlier, roaming is unique to mobile networks, and it introduces new challenges. Service providers can control their own network design but not their peers' networks, which they rely on for roaming. Users expect uniformity in experience even when they are roaming. This imposes a constraint on providers interested in IPv6-only deployments to also support IPv4 addressing when their own (outbound) subscribers roam to networks that do not offer IPv6. For instance, when an LTE deployment is IPv6-only, a roamed 3G network may not offer IPv6 PDN connectivity. Since a PDN connection involves the radio base station, the ANG, and the MNG (see Figure 1), it would not be possible to enable IPv6 PDN connectivity without roamed network support. These considerations also apply when the visited network is used for offering services such as VoLTE in the so-called Local Breakout model; the roaming MN's capability as well as the roamed network capability to support VoLTE using IPv6 determine whether fallback to IPv4 would be necessary. Similarly, there are inbound roamers to an IPv6-ready provider network whose MNs are not capable of IPv6. The IPv6-ready provider network has to be able to support IPv4 PDN connectivity for such inbound roamers. There are encouraging signs that the existing deployed network nodes in the 3GPP architecture already provide support for IPv6 PDP context. It

如前所述,漫游是移动网络所独有的,它带来了新的挑战。服务提供商可以控制自己的网络设计,但不能控制对等方的网络,因为它们依赖于对等方的网络进行漫游。用户即使在漫游时也希望体验一致。这就限制了对仅IPv6部署感兴趣的提供商在其自身(出站)订户漫游到不提供IPv6的网络时也支持IPv4寻址。例如,当LTE部署仅为IPv6时,漫游3G网络可能不提供IPv6 PDN连接。由于PDN连接涉及无线基站、ANG和MNG(见图1),因此如果没有漫游网络支持,就不可能启用IPv6 PDN连接。当访问的网络用于提供服务时,这些考虑也适用,例如所谓的本地分支模型中的VoLTE;漫游MN的能力以及支持使用IPv6的VoLTE的漫游网络能力决定是否需要回退到IPv4。类似地,也有到IPv6就绪提供商网络的入站漫游者,其MN不支持IPv6。IPv6就绪提供商网络必须能够支持此类入站漫游者的IPv4 PDN连接。有令人鼓舞的迹象表明,3GPP体系结构中现有部署的网络节点已经提供了对IPv6-PDP上下文的支持。信息技术

would be necessary to scale this support for a (very) large number of mobile users and offer it as a ubiquitous service that can be accounted for.


In summary, IPv6-only deployments should be encouraged alongside the dual-stack model, which is the recommended IETF approach. This is relatively straightforward for an operator's own services and applications, provisioned through an appropriate APN and the corresponding IPv6-only PDP or EPS bearer. Some providers may consider IPv6-only deployment for Internet access as well, and this would require IPv6-IPv4 interworking. When the IPv6-IPv4 translation mechanisms are used in IPv6-only deployments, the protocols and the associated considerations specified in [RFC6146] and [RFC6145] apply. Finally, such IPv6-only deployments can be phased-in for newer mobile nodes, while the existing ones continue to demand IPv4-only connectivity.

总之,应鼓励在双栈模型的基础上进行仅IPv6的部署,这是推荐的IETF方法。这对于运营商自己的服务和应用程序来说相对简单,通过适当的APN和相应的仅IPv6的PDP或EPS承载提供。一些提供商可以考虑IPv6仅用于Internet接入,这将需要IPv6 IPv4互通。当IPv6-IPv4转换机制用于仅限IPv6的部署时,[RFC6146]和[RFC6145]中指定的协议和相关注意事项适用。最后,这种仅限IPv6的部署可以分阶段用于较新的移动节点,而现有的移动节点仍然需要仅限IPv4的连接。

Roaming is important in mobile networks, and roaming introduces diversity in network deployments. Until IPv6 connectivity is available in all mobile networks, IPv6-only mobile network deployments need to be prepared to support IPv4 connectivity (and NAT44) for their own outbound roaming users as well as for inbound roaming users. However, by taking the initiative to introduce IPv6- only for the newer MNs, the mobile networks can significantly reduce the demand for private IPv4 addresses.


3.4. Fixed-Mobile Convergence
3.4. 固定移动融合

Many service providers have both fixed broadband and mobile networks. Access networks are generally disparate, with some common characteristics but with enough differences to make it challenging to achieve "convergence". For instance, roaming is not a consideration in fixed access networks. An All-IP mobile network service provider is required to provide voice service, whereas this is not required for a fixed network provider. A "link" in fixed networks is generally capable of carrying IPv6 and IPv4 traffic, whereas not all mobile networks have "links" (i.e., PDP/PDN connections) capable of supporting IPv6 and IPv4. Indeed, roaming makes this problem worse when a portion of the link (i.e., the Home Network in Figure 1) is capable of supporting IPv6 and the other portion of the link (i.e., the Visited Network in Figure 1) is not. Such architectural differences, as well as policy and business model differences make convergence challenging.


Nevertheless, within the same provider's space, some common considerations may apply. For instance, IPv4 address management is a common concern for both of the access networks. This implies that the same mechanisms discussed earlier, i.e., delaying IPv4 address


exhaustion and introducing IPv6 in operational networks, apply for the converged networks as well. However, the exact solutions deployed for each access network can vary for a variety of reasons, such as:


o Tunneling of private IPv4 packets within IPv6 is feasible in fixed networks where the endpoint is often a cable or DSL modem. This is not the case in mobile networks where the endpoint is an MN itself.

o 在固定网络中,IPv6内的专用IPv4数据包隧道是可行的,在固定网络中,端点通常是电缆或DSL调制解调器。在移动网络中,端点本身就是MN,但情况并非如此。

o Encapsulation-based mechanisms such as 6rd [RFC5969] are useful where the operator is unable to provide native or direct IPv6 connectivity and a residential gateway can become a tunnel endpoint for providing this service. In mobile networks, the operator could provide IPv6 connectivity using the existing mobile network tunneling mechanisms without introducing an additional layer of tunneling.

o 当运营商无法提供本机或直接IPv6连接,并且住宅网关可以成为提供此服务的隧道端点时,基于封装的机制(如6rd[RFC5969])非常有用。在移动网络中,运营商可以使用现有的移动网络隧道机制提供IPv6连接,而无需引入额外的隧道层。

o A mobile network provider may have Application Servers (e.g., an email server) in its network that require unique private IPv4 addresses for MN identification, whereas a fixed network provider may not have such a requirement or the service itself.

o 移动网络提供商可能在其网络中具有需要用于MN标识的唯一专用IPv4地址的应用服务器(例如,电子邮件服务器),而固定网络提供商可能没有这样的要求或服务本身。

These examples illustrate that the actual solutions used in an access network are largely determined by the requirements specific to that access network. Nevertheless, some sharing between an access and core network may be possible depending on the nature of the requirement and the functionality itself. For example, when a fixed network does not require a subscriber-aware feature such as NAT, the functionality may be provided at a core router while the mobile access network continues to provide the NAT functionality at the mobile gateway. If a provider chooses to offer common subscriber management at the MNG for both fixed and wireless networks, the MNG itself becomes a convergence node that needs to support the applicable transition mechanisms for both fixed and wireless access networks.


Different access networks of a provider are more likely to share a common core network. Hence, common solutions can be more easily applied in the core network. For instance, configured tunnels or MPLS VPNs from the gateways from both mobile and fixed networks can be used to carry traffic to the core routers until the entire core network is IPv6-enabled.

提供商的不同接入网络更可能共享一个共同的核心网络。因此,通用解决方案可以更容易地应用于核心网络。例如,来自移动和固定网络网关的配置隧道或MPLS VPN可用于将流量传输到核心路由器,直到整个核心网络启用IPv6。

There can also be considerations due to the use of NAT in access networks. Solutions such as Femto Networks rely on a fixed Internet connection being available for the Femto Base Station to communicate with its peer on the mobile network, typically via an IPsec tunnel.


When the Femto Base Station needs to use a private IPv4 address, the mobile network access through the Femto Base Station will be subject to NAT policy administration including periodic cleanup and purge of NAT state. Such policies affect the usability of the Femto Network and have implications to the mobile network provider. Using IPv6 for the Femto (or any other access technology) could alleviate some of these concerns if the IPv6 communication could bypass the NAT.


In summary, there is interest in Fixed-Mobile Convergence, at least among some providers. While there are benefits to harmonizing the network as much as possible, there are also idiosyncrasies of disparate access networks that influence the convergence. Perhaps greater harmonization is feasible at the higher service layers, e.g., in terms of offering unified user experience for services and applications. Some harmonization of functions across access networks into the core network may be feasible. A provider's core network appears to be the place where most convergence is feasible.


4. Summary and Conclusion
4. 总结与结论

IPv6 deployment in mobile networks is crucial for the Mobile Internet. In this document, we discussed the considerations in deploying IPv6 in mobile networks. We summarize the discussion in the following:


o IPv4 address exhaustion and its implications to mobile networks: As mobile service providers begin to deploy IPv6, conserving their available IPv4 pool implies the need for network address translation in mobile networks. At the same time, providers can make use of the 3GPP architecture constructs such as APN and PDN connectivity to introduce IPv6 without affecting the predominantly IPv4 Internet access. The IETF dual-stack model [RFC4213] can be applied to the mobile networks readily.

o IPv4地址耗尽及其对移动网络的影响:随着移动服务提供商开始部署IPv6,保护其可用IPv4池意味着需要在移动网络中进行网络地址转换。同时,提供商可以利用3GPP架构构造(如APN和PDN连接)来引入IPv6,而不影响主要的IPv4互联网接入。IETF双栈模型[RFC4213]可以很容易地应用于移动网络。

o The placement of NAT functionality in mobile networks: Both the centralized and distributed models of private IPv4 address pool management have their relative merits. By enabling each MNG to manage its own NET10 pool, the distributed model achieves reuse of the available private IPv4 pool and avoids the problems associated with the non-unique private IPv4 addresses for the MNs without additional protocol mechanisms. The distributed model also augments the "subscriber management" functions at an MNG, such as readily enabling NAT session correlation with the rest of the subscriber session state. On the other hand, existing deployments that have used the centralized IP address management can continue their legacy architecture by placing the NAT at a common node. The centralized model also achieves private IPv4 address reuse but

o NAT功能在移动网络中的位置:私有IPv4地址池管理的集中式和分布式模型都有各自的优点。通过使每个MNG能够管理其自己的NET10池,分布式模型实现了对可用专用IPv4池的重用,并避免了与MNs的非唯一专用IPv4地址相关的问题,而无需额外的协议机制。分布式模型还增强了MNG上的“订户管理”功能,例如容易地启用NAT会话与订户会话状态的其余部分的关联。另一方面,使用集中式IP地址管理的现有部署可以通过将NAT放置在公共节点来继续其传统体系结构。集中式模型还实现了私有IPv4地址重用,但

needs additional protocol extensions to differentiate overlapping addresses at the common NAT as well as to integrate with policy and billing infrastructure.


o IPv6-only mobile network deployments: This deployment model is feasible in the LTE architecture for an operator's own services and applications. The existing MNs still expect IPv4 address assignment. Furthermore, roaming, which is unique to mobile networks, requires that a provider support IPv4 connectivity when its (outbound) users roam into a mobile network that is not IPv6- enabled. Similarly, a provider needs to support IPv4 connectivity for (inbound) users whose MNs are not IPv6-capable. The IPv6-IPv4 interworking is necessary for IPv6-only MNs to access the IPv4 Internet.

o 仅限IPv6的移动网络部署:这种部署模式在LTE架构中对于运营商自己的服务和应用是可行的。现有MN仍然需要IPv4地址分配。此外,移动网络特有的漫游要求提供商在其(出站)用户漫游到未启用IPv6的移动网络时支持IPv4连接。类似地,提供商需要支持MNs不支持IPv6的(入站)用户的IPv4连接。IPv6-IPv4互通对于仅IPv6的MNs访问IPv4 Internet是必要的。

o Fixed-Mobile Convergence: The examples discussed illustrate the differences in the requirements of fixed and mobile networks. While some harmonization of functions may be possible across the access networks, the service provider's core network is perhaps better-suited for converged network architecture. Similar gains in convergence are feasible in the service and application layers.

o 固定-移动融合:讨论的示例说明了固定网络和移动网络需求的差异。虽然可以跨接入网络实现功能的某种协调,但服务提供商的核心网络可能更适合于融合网络体系结构。在服务层和应用层中,类似的收敛收益也是可行的。

5. Security Considerations
5. 安全考虑

This document does not introduce any new security vulnerabilities.


6. Acknowledgements
6. 致谢

This document has benefitted from discussions with and reviews from Cameron Byrne, David Crowe, Hui Deng, Remi Despres, Fredrik Garneij, Jouni Korhonen, Teemu Savolainen, and Dan Wing. Thanks to all of them. Many thanks to Mohamed Boucadair for providing an extensive review of a draft version of this document. Cameron Byrne, Kent Leung, Kathleen Moriarty, and Jari Arkko provided reviews that helped improve this document. Thanks to Nick Heatley for providing valuable review and input on VoLTE.

本文件得益于与卡梅隆·伯恩、大卫·克罗、惠登、雷米·德斯普雷斯、弗雷德里克·加内伊、朱尼·科霍宁、蒂姆·萨沃莱宁和丹·温的讨论和评论。感谢他们所有人。非常感谢Mohamed Boucadair对本文件草案进行了广泛审查。Cameron Byrne、Kent Leung、Kathleen Moriarty和Jari Arkko提供了有助于改进本文件的评论。感谢Nick Heatley为VoLTE提供了宝贵的评论和意见。

7. Informative References
7. 资料性引用

[3GPP.3G] "General Packet Radio Service (GPRS); Service description; Stage 2, 3GPP TS 23.060, December 2006".

[3GPP.3G]“通用分组无线业务(GPRS);业务描述;第2阶段,3GPP TS 23.06012006年12月”。

[3GPP.4G] "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access", 3GPP TS 23.401 8.8.0, December 2009.

[3GPP.4G]“通用分组无线业务(GPRS)对演进型通用地面无线接入网(E-UTRAN)接入的增强”,3GPP TS 23.401 8.8.02009年12月。

[3GPP2.EHRPD] "E-UTRAN - eHRPD Connectivity and Interworking: Core Network Aspects", Specs/X.S0057-0_v1.0_090406.pdf.

[3GPP2.EHRPD]“E-UTRAN-EHRPD连接和互通:核心网络方面”, 规范/X.S0057-0_v1.0_090406.pdf。

[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996.

[RFC1918]Rekhter,Y.,Moskowitz,B.,Karrenberg,D.,de Groot,G.,和E.Lear,“私人互联网地址分配”,BCP 5,RFC 1918,1996年2月。

[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, October 1996.

[RFC2003]Perkins,C.,“IP内的IP封装”,RFC 2003,1996年10月。

[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.

[RFC2784]Farinaci,D.,Li,T.,Hanks,S.,Meyer,D.,和P.Traina,“通用路由封装(GRE)”,RFC 27842000年3月。

[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", RFC 2890, September 2000.

[RFC2890]Dommety,G.“GRE的密钥和序列号扩展”,RFC 28902000年9月。

[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001.

[RFC3031]Rosen,E.,Viswanathan,A.,和R.Callon,“多协议标签交换体系结构”,RFC 30312001年1月。

[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for IPv6 Hosts and Routers", RFC 4213, October 2005.

[RFC4213]Nordmark,E.和R.Gilligan,“IPv6主机和路由器的基本转换机制”,RFC 4213,2005年10月。

[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) -- Protocol Specification", RFC 5969, August 2010.

[RFC5969]Townsley,W.和O.Troan,“IPv4基础设施上的IPv6快速部署(第6条)——协议规范”,RFC 5969,2010年8月。

[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation Algorithm", RFC 6145, April 2011.

[RFC6145]Li,X.,Bao,C.,和F.Baker,“IP/ICMP翻译算法”,RFC 61452011年4月。

[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, April 2011.

[RFC6146]Bagnulo,M.,Matthews,P.,和I.van Beijnum,“有状态NAT64:从IPv6客户端到IPv4服务器的网络地址和协议转换”,RFC 61462011年4月。

[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van Beijnum, "DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to IPv4 Servers", RFC 6147, April 2011.

[RFC6147]Bagnulo,M.,Sullivan,A.,Matthews,P.,和I.van Beijnum,“DNS64:用于从IPv6客户端到IPv4服务器的网络地址转换的DNS扩展”,RFC 61472011年4月。

[ARKKO-V6] Arkko, J. and A. Keranen, "Experiences from an IPv6-Only Network", Work in Progress, April 2011.


[GI-DS-LITE] Brockners, F., Gundavelli, S., Speicher, S., and D. Ward, "Gateway Initiated Dual-Stack Lite Deployment", Work in Progress, July 2011.


Author's Address


Rajeev Koodli Cisco Systems USA