An IPv4 Service Continuity Solution for Smooth IPv6 Transition
IPv4 address exhaustion is a reality. The IETF has been investigating several tunnel-based solutions1 to ease the introduction of IPv6, while continuously offering IPv4 services during the transition period. Dual-Stack Lite2 (DS-Lite), which defines a model for providing IPv4 access over an IPv6 network,3 aims to better align the costs and benefits of deploying IPv6 in operator’s networks. The DS-Lite model proposes a network address and port translation (NAPT) function in the operator’s network to dynamically assign public IPv4 addresses and ports to internal IPv4 packets.
Lightweight 4over64 (Lw4o6) is an optimization of DS-Lite designed to reduce NAPT states in the operator’s network. The underlying idea of Lw4o6 is to relocate the NAPT function from the tunnel concentrator (lwAFTR) to the initiators (lwB4s). The lwB4 element is provisioned with a public IP address and a port set.
Public 4over65 describes a model for assigning full-public IP addresses to initiators (4over6 CE). Lightweight 4over6 can be regarded as an address-sharing mode of Public 4over6.
There are three main components in the Lightweight 4over6 architecture (see figure 1):
- lwB4. Performs the NAPT function and encapsulation/decapsulation of IPv4/IPv6. It is provisioned with a public IPv4 address and a port set, which is used to restrict the external ports used by the NAPT function to source packets. The NAPT function is colocated in the lwB4.
- lwAFTR. Performs the encapsulation/decapsulation of IPv4/IPv6. It is also responsible for forwarding incoming packets to the appropriate lwB4, and outgoing packets to the IPv4 network.
- Provisioning system. Configures the lwB4 with the Public IPv4 address and port set.
Lightweight 4over6 decouples IPv4 and IPv6 address architectures, which means that it doesn’t require IPv4 address information to be embedded in the IPv6 address. As a result, flexible and independent IPv4/IPv6 addressing schemes can be used, enabling operators to efficiently utilize public IPv4 addresses without affecting existing IPv6 address schema. The solution simplifies address planning and increases the lwAFTR scalability.
Currently, the Lightweight 4over6 design team includes seven operators, including China Telecom, France Telecom, Deutsche Telekom, and Comcast; and eight vendors, including Huawei, GreenNet, and FiberHome.
Two interoperability tests have been carried out with the participation of Huawei, GreenNet, Fiberhome, Yamaha, BII, Tsinghua, and China Telecom. The first test was conducted at Tsinghua University from 22–29 October 2012; the second test was conducted by the CNGI committee in Beijing University of Posts and Telecommunications from 12–15 November 2012. This test consisted of seven lwB4s and four lwAFTRs. More than 1,400 test cases have been run between them. See figure 2.
Inspired by the IETF mantra of “rough consensus and running code” to expose IETF technologies to real operator requirements and scenarios, the Lightweight 4over6 design team demonstrated their prototypes during IETF 85 with the hope of gaining community feedback.
Figure 3 shows the topology of the demonstration, which included:
• five hosts, including one Android host with built-in lwB4 function and a Windows 7 host with built-in lwB4 function,
• four CPEs embedded the lwB4 function,
• three lwAFTRs,
• one DHCPv4 server, and
• one Ethernet switch connecting all the devices together and connected to the IETF dual-stack router for external connectivity.
The demonstration illustrated three scenarios, which are labeled as 1, 2, and 3 in figure 3.
Scenario 1 comprised two CPEs with built-in lwB4. CPEs were provided by Huawei and Tsinghua. Also in this scenario, was an lwAFTR (also acting as a DHCP relay) and a DHCPv4 server, both provided by Huawei. The IPv4 provisioning method was DHCPv4-over-IPv6;6 and the lwB4s were provisioned with the same public IPv4 address from DHCPv4 server with different port sets.7 Port set allocation policy was statically configured in the DHCPv4 server.
Scenario 2 comprised two lwB4s—one CPE based and one Android mobile host based, both provided by Huawei and Tsinghua. The lwAFTR (acting as a DHCP server) was provided by Tsinghua; the DHCP server embedded in the lwAFTR provisioned a second public IPv4 address with different port sets to the two lwB4s. Port-set allocation was dynamically managed by the DHCP server.
For both scenarios 1 and 2, the team set up two WiFi APs, which were broadcasting SSID lw4o6-1 and lw4o6-2, thereby enabling the audience to experience Lightweight 4over6 on their own devices.
Scenario 3 comprised a lwB4 connecting to an lwAFTR, both provided by GreenNet. The lwB4 requested the IPv4 address and available port set from the lwAFTR using PCP protocol.8
The team demonstrated Lightweight 4over6 via a variety of IPv4 applications, including web browsing, video streaming, VoIP (e.g., Skype), and peer-to-peer multimedia (e.g., PPLive), running on a range of devices, including smart phones, laptops, and tablets. Audience participants could not detect that they were actually connected to an IPv6-only network.
Spectators—including operators and vendors—offered many valuable comments and raised many good questions, including one about Lightweight 4over6 deployment scenarios. Lightweight 4over6 can be deployed in IPv6-only access network and continue to provide IPv4 connectivity for IPv4 services. The deployment scenarios of Lightweight4over6 are similar to that of DS-Lite.
Testing and deployment of this mechanism is happening around the globe. China Telecom has been running a Lightweight 4over6 field trial in Hunan Province, China, since early 2012 that includes lwAFTR deployed at the entrance to the metropolitan area network (MAN), and the lwB4 function deployed in subscribers’ customer-premises equipment (CPE).9 China Telecom plans a larger-scale deployment in the year 2013. Germany’s Deutsche Telekom (DT) is presently testing Lightweight 4over6, and has completed lab testing on the functionality of the lwB4 and lwAFTR. So far, their implementation has been proved to be simple and stable.10
Spectators also inquired about the relationship between Lightweight 4over6 and DS-Lite. Lightweight 4over6 puts the NAPT function in the lwB4. The lwB4 is then given a public IPv4 address and a restricted port-set., and the lwB4 uses this information to perform a NAPT function for IPv4 connections. DS-lite puts the NAPT function in the address-family transition router (AFTR) and provides more dynamic NAPT functions among hundreds of B4s. For NAPT-state management, Lightweight 4over6 requires per-subscriber state in the AFTR. In contrast, DS-lite requires per-session state in the AFTR. Despite these differences, DS-Lite and Lightweight 4over6 are compatible and can be deployed together to provide different user services based on a service agreement.
1. Cui Y., Dong J., Wu P., et al., “Tunnel-based IPv6 Transition,” IEEE Internet Computing, April 2012.
2. Durand A., Droms R., et al, Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion, IETF RFC 6333, August 2011.
3. Cui Y., Wu P., Xu M., et al., “4over6: Network Layer Virtualization for IPv4-IPv6 Coexistence,” IEEE Network, October 2012.
4. Cui Y., Sun Q., Boucadair M., Tsou T., Lee Y., and Farrer I., Lightweight 4over6: An Extension to the DS-Lite Architecture, draft-cui-softwire-b4-translated-ds-lite-09, October 2012.
5. Cui Y., Wu J., Wu P., Vautrin O., Lee Y., Public IPv4 over IPv6 Access Network, draft-ietf-softwire-public-4over6-04, October 2012.
6. Cui Y., Wu P., Wu J., Lemon T., DHCPv4 over IPv6 Transport, draft-ietf-dhc- dhcpv4-over-ipv6-05, September 2012.
7. Sun Q., Lee Y., Sun Q., Bajko G., Boucadair M., Dynamic Host Configuration Protocol (DHCP) Option for Port Set Assignment, draft-sun-dhc-port-set-option-00, October 2012.
8. Sun Q., Boucadair M., Deng X., Zhou C., Tsou T., Perreault S., Using PCP to Coordinate Between the CGN and Home Gateway, draft-tsou-pcp-natcoord-09, November 2012.
9. Sun Q., Xie C., Lee Y., Chen M., Deployment Considerations for Lightweight 4over6, draft-sun-softwire-lightweight-4over6-deployment-02, July 2012.
10. Farrer I., Durand A., lw4over6 Deterministic Architecture, draft-farrer-softwire-lw4o6- deterministic-arch-01, October 2012.