| Internet Engineering Task Force | M.M. Mawatari |
| Internet-Draft | Japan Internet Exchange Co.,Ltd. |
| Intended status: Best Current Practice | M.K. Kawashima |
| Expires: October 01, 2012 | NEC AccessTechnica, Ltd. |
| C.B. Byrne | |
| T-Mobile USA | |
| April 2012 |
464XLAT: Combination of Stateful and Stateless Translation
draft-ietf-v6ops-464xlat-02
This document describes an architecture (464XLAT) for providing limited IPv4 connectivity across an IPv6-only network by combining existing and well-known stateful protocol translation RFC 6146 in the core and stateless protocol translation RFC 6145 at the edge. 464XLAT is a simple and scalable technique to quickly deploy limited IPv4 access service to mobile and wireline IPv6-only edge networks without encapsulation.
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This Internet-Draft will expire on October 01, 2012.
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
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The IANA unallocated IPv4 address pool was exhausted on February 3, 2011. Each RIR's unallocated IPv4 address pool will exhaust in the near future. It will be difficult for many networks to assign IPv4 addresses to end users, despite substantial IP connectivity growth required for mobile devices, smart-grid, and cloud nodes.
This document describes an IPv4 over IPv6 solution as one of the techniques for IPv4 service extension and encouragement of IPv6 deployment. 464XLAT is not a one for one replacement of full IPv4 functionality. The 464XLAT IPv4 service is limited to application that function in a client server model and is not fit for IPv4 peer-to-peer communication or inbound IPv4 connections.
The 464XLAT architecture described in this document uses IPv4/IPv6 translation standardized in [RFC6145] and [RFC6146]. It does not require DNS64 [RFC6147] since a host may simply send IPv4 packets, including packets to an IPv4 DNS server, which will be translated on the CLAT to IPv6 and back to IPv4 on the PLAT. 464XLAT networks may use DNS64 to enable single stateful translation [RFC6146] instead of 464XLAT double translation where possible. It is also possible to provide single IPv4/IPv6 translation service, which will be needed in the future case of IPv6-only servers and peers to be reached from legacy IPv4-only hosts. The 464XLAT architecture encourages IPv6 transition by making IPv4 services reachable across IPv6-only networks and providing IPv6 and IPv4 connectivity to single-stack IPv4 or IPv6 servers and peers.
Running a single-stack IPv6-only network has several operational benefits in terms of increasing scalability and decreasing operational complexity. Unfortunately, there are important cases where IPv6-only networks fail to meet subscriber expectations, as described in [I-D.arkko-ipv6-only-experience]. The 464XLAT overcomes the issues described in [I-D.arkko-ipv6-only-experience] to provide subscribers the full IPv6 and limited IPv4 functionality while providing the network operator the benefits of a simple yet highly scalable single-stack IPv6 network.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
In summary, the 464XLAT architecture works today for service providers that require large-scale strategic IPv6 deployments to overcome the challenges of IPv4 address scarcity. Since 464XLAT is stateful, there is no tight coupling or IPv4 address coordination between the PLAT and the CLAT. Unlike other transition architectures associated with tunneling or [I-D.mdt-softwire-mapping-address-and-port], 464XLAT assumes that IPv4 is scarce and IPv6 must work with today's existing systems as much as possible. In the case of tunneling, the tunneling solutions like Dual-Stack Lite [RFC6333] are known to break existing network based deep packet inspection solutions like 3GPP standardized Policy and Charging Control (PCC). 464XLAT does not require much IPv4 address space to enable the stateful translation [RFC6146] function in the PLAT while providing global IPv4 and IPv6 reachability to IPv6-only wireline and wireless subscribers.
464XLAT architecture is shown in the following figure.
----
| v6 |
----
|
---- | .---+---. .------.
| v6 |-----+ / \ / \
---- | ------ / IPv6 \ ------ / IPv4 \
+---| CLAT |---+ Internet +---| PLAT |---+ Internet |
------- | ------ \ / ------ \ /
|v4p/v6 |--+ `---------' `----+----'
------- | |
----- | -----
| v4p |----+ | v4g |
----- | -----
<- v4p -> XLAT <--------- v6 --------> XLAT <- v4g ->
v6 : Global IPv6
v4p : Private IPv4
v4g : Global IPv4
----
| v6 |
----
|
.---+---.
/ \
/ IPv6 \
| Internet |
\ /
UE / Mobile Phone `---------'
+----------------------+ |
| ---- | | .---+---. .------.
| | v6 |----+ | / \ / \
| ---- | ------| / IPv6 PDP \ ------ / IPv4 \
| +---| CLAT |---+ Mobile Core +---| PLAT |--+ Internet |
| | ------| \ GGSN / ------ \ /
| | | \ ' `----+---'
| ------ | | `-------' |
| | v4p |---+ | -----
| ------ | | | v4g |
+----------------------+ -----
<- v4p -> XLAT <--------- v6 --------> XLAT <- v4g ->
v6 : Global IPv6
v4p : Private IPv4
v4g : Global IPv4
When an ISP has IPv6 access network infrastructure and 464XLAT, the ISP can provide IPv4 service to end users across an IPv6 access network. The result is that edge network growth is no longer tightly coupled to the availability of scarce IPv4 addresses.
If the IXP or another provider operates the PLAT, the ISP is only required to deploy an IPv6 access network. All ISPs do not need IPv4 access networks. They can migrate their access network to a simple and highly scalable IPv6-only environment. Incidentally, Japan Internet Exchange(JPIX) is providing 464XLAT trial service since July 2010. In addition to this, the effectiveness of 464XLAT was confirmed in the WIDE camp Spring 2012. The result is described in [I-D.hazeyama-widecamp-ipv6-only-experience].
The vast majority of mobile wireless networks are compliant to Pre-Release 9 3GPP standards. In Pre-Release 9 3GPP networks, GSM and UMTS networks must signal and support both IPv4 and IPv6 PDP attachments to access IPv4 and IPv6 network destinations. Since there are 2 PDPs required to support 2 address families, this is double the number of PDPs required to support the status quo of 1 address family, which is IPv4. Doubling the PDP count to support IPv4 and IPv6 is generally not operationally viable since a large portion of the network cost is derived from the number of PDP attachments, both in terms of licenses from the network hardware vendors and in terms of actual hardware resources required to support and maintain the PDP signaling and mobility events. Doubling the number of PDP attachments has been one of the major barriers to introducing IPv6 in mobile networks. Dual-stack IPv4 and IPv6 simply costs more from the network provider perspective and does not result in any new revenues. In 3GPP Release 9 and forward, 2 PDPs are no longer required but the scarcity of IPv4 addresses remain.
Now that both global and private IPv4 addresses are scarce to the extent that it is a substantial business risk and limiting growth in many areas, the mobile network providers must support IPv6 to solve the IP address scarcity issue. It is not feasible to simply turn on additional IPv6 PDP network attachments since that does not solve the near-term IPv4 scarcity issues and it increases cost in most cases. The most logical path forward is to replace IPv4 with IPv6 and replace the common NAT44 with stateful translation [RFC6146] and DNS64 [RFC6147]. Extensive live network testing with hundreds of friendly-users has shown that IPv6-only network attachments for mobile devices supports over 85% of the common applications on the Android mobile operating systems. The remaining 15% of applications do not work because the application requires an IPv4 socket or the application does an IPv4-referral. These findings are consistent with the mobile IPv6-only user experience in [I-D.arkko-ipv6-only-experience].
464XLAT in combination with stateful translation [RFC6146] and DNS64 [RFC6147] allows 85% of the Android applications to continue to work with single translation or native IPv6 access. For the remaining 15% of applications that require IPv4 connectivity, the CLAT function on the UE provides a private IPv4 address and IPv4 default-route on the host for the applications to reference and bind to. Connections sourced from the IPv4 interface are immediately routed to the CLAT function and passed to the IPv6-only mobile network, destine to the PLAT. In summary, the UE has the CLAT function that does a stateless translation [RFC6145], but only when required. The mobile network has a PLAT that does stateful translation [RFC6146].
IPv6 address format in 464XLAT is defined in Section 2.2 of [RFC6052].
IPv4/IPv6 address translation chart is shown in the following figure.
Source IPv4 address
+----------------------------+
| Global IPv4 address |
| assigned to IPv4 pool@PLAT |
+--------+ +----------------------------+
| IPv4 | Destination IPv4 address
| server | +----------------------------+
+--------+ | Global IPv4 address |
^ | assigned to IPv4 server |
| +----------------------------+
+--------+
| PLAT | Stateful XLATE(IPv4:IPv6=1:n)
+--------+
^
|
Source IPv6 address (IPv6 cloud)
+--------------------------------------------------------------+
| IPv4-Embedded IPv6 address |
| defined in Section 2.2 of RFC6052 |
+--------------------------------------------------------------+
Destination IPv6 address
+--------------------------------------------------------------+
| IPv4-Embedded IPv6 address |
| defined in Section 2.2 of RFC6052 |
+--------------------------------------------------------------+
(IPv6 cloud)
^
|
|
|
+--------+
| | Case 1: CLAT will have a
| | dedicated IPv6 prefix
| | -> Stateless XLATE
| | (IPv4:IPv6=1:1)
| CLAT |
| | Case 2: CLAT will not have a
| | dedicated IPv6 prefix
| | -> NAT44 -> Stateless XLATE
| | (IPv4:IPv6=1:1)
+--------+
^ Source IPv4 address
| +----------------------------+
+--------+ | Private IPv4 address |
| IPv4 | | assigned to IPv4 client |
| client | +----------------------------+
+--------+ Destination IPv4 address
+----------------------------+
| Global IPv4 address |
| assigned to IPv4 server |
+----------------------------+
+--------+-------------+-----------------------+-------------+
| Server | Application | Traffic Treatment | Location of |
| | and Host | | Translation |
+--------+-------------+-----------------------+-------------+
| IPv6 | IPv6 | End-to-end IPv6 | None |
+--------+-------------+-----------------------+-------------+
| IPv4 | IPv6 | Stateful Translation | PLAT |
+--------+-------------+-----------------------+-------------+
| IPv4 | IPv4 | 464XLAT | PLAT/CLAT |
+--------+-------------+-----------------------+-------------+
| IPv6 | IPv4 | Stateless Translation | CLAT |
+--------+-------------+-----------------------+-------------+
The above chart shows most common traffic types and traffic treatment.
The CLAT SHOULD implement a DNS proxy as defined in [RFC5625]. The case of an IPv4-only node behind CLAT querying an IPv4 DNS server is undesirable since it requires both stateful and stateless translation for each DNS lookup. The CLAT SHOULD set itself as the DNS server via DHCP or other means and proxy DNS queries for IPv4 and IPv6 clients. Using the CLAT enabled home router or UE as a DNS proxy is a normal consume gateway function and simplifies the traffic flow so that only IPv6 native queries are made across the access network. The CLAT SHOULD allow for a client to query any DNS server of its choice and bypass the proxy.
There are two approaches. In one of the cases, the CLAT will have a dedicated /64 via DHCPv6 prefix delegation [RFC3633] or other means to source and receive IPv6 packets associated with the [RFC6145] stateless translation of IPv4 packets to the local clients. If the CLAT choose one /64 prefix for translation from delegated prefix, then it SHOULD NOT be used for anything else.
In another cases where the access network does not allow for a dedicated translation prefix, the CLAT will do NAT44 such that all private IPv4 sourced LAN packets appears from one private IPv4 address which is statelessly translated to one IPv6 address.
The CLAT MAY discover the Pref64::/n of the PLAT via some method such as DHCPv6 option, TR-069, DNS APL RR [RFC3123] or [I-D.ietf-behave-nat64-discovery-heuristic].
The CLAT is a stateless translation feature which can be implemented in a common home router or mobile phone that has a mobile router feature. The router with CLAT function SHOULD provide common router services such as DHCP of [RFC1918] addresses, DHCPv6, and DNS service. The router SHOULD set itself as the DNS server advertised via DHCP or other means to the clients so that it may implement the DNS proxy function to avoid double translation of DNS request.
While CLAT to CLAT IPv4 communication may work when the client IPv4 subnets do not overlap, this traffic flow is out of scope. 464XLAT is a hub and spoke architecture focused on enabling IPv4-only services over IPv6-only access networks.
Even if the Internet access provider for consumers is different from the PLAT provider (another Internet access provider or Internet exchange provider, etc.), it can implement traffic engineering independently from the PLAT provider. Detailed reasons are below:
This 464XLAT architecture has two capabilities. One is a IPv4 -> IPv6 -> IPv4 translation for sharing global IPv4 addresses, another is a IPv4 -> IPv6 translation for reaching IPv6-only servers from IPv4-only clients that can not support IPv6. IPv4-only clients must be support through the long period of global transition to IPv6.
To implement a PLAT, see security considerations presented in Section 5 of [RFC6146].
To implement a CLAT, see security considerations presented in Section 7 of [RFC6145]. The CLAT MAY comply with [RFC6092].
This document has no actions for IANA.
The authors would like to thank JPIX NOC members, JPIX 464XLAT trial service members, Seiichi Kawamura, Dan Drown, Brian Carpenter, Rajiv Asati, Washam Fan, Behcet Sarikaya, Jan Zorz, Remi Despres, Tatsuya Oishi, Lorenzo Colitti, Erik Kline, and Ole Troan for their helpful comments. We also would like to thank Fred Baker and Joel Jaeggli for their support.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC6052] | Bao, C., Huitema, C., Bagnulo, M., Boucadair, M. and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, October 2010. |
| [RFC6144] | Baker, F., Li, X., Bao, C. and K. Yin, "Framework for IPv4/IPv6 Translation", RFC 6144, April 2011. |
| [RFC6145] | Li, X., Bao, C. and F. Baker, "IP/ICMP Translation Algorithm", RFC 6145, April 2011. |
| [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. |