The Applicability Index of Translation
draft-mi-softwire-applicable-index-translation-01

Abstract

The Softwire working group is currently discussing both encapsulation and translation based stateless IPv4/IPv6 solutions in order to be able to provide IPv4 connectivity to customers in an IPv6-Only environment.

The purpose of this document is to describe the basic issues and key elements of the IPv4/IPv6 translation, and presents its applicability index that would help the operators decide on the development scheme for their IPv6 transition.It could lead to significant operational benefits and potential savings for the operators.

Status of This Memo

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This Internet-Draft will expire on June 30, 2016.

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Table of Contents

• 1. Introduction
• 2. The Basic Issues and Key elements of Translation Mechanisms
• 2.1. Basic Issues
• 2.2. Key Elements
• 3. Applicability Index of Translation
• 3.1. Sustainable Index
• 3.2. The Support Degree of Business Application Index
• 3.3. The Preformance Index
• 3.4. The Development Index
• 3.5. The Security Index
• 4. Conclusions
• 5. Acknowledgements
• 6. IANA Considerations
• 7. Security Considerations
• 8. Informative References
• Authors' Addresses

1. Introduction

The Softwire working group is currently discussing both encapsulation and translation based stateless IPv4/IPv6 solutions developed for the purposes of offering IPv4 connectivity to the customers in an IPv6-Only environment.

In the all stages of transition from IPv4 to IPv6, IPv4 networks/hosts and IPv6 networks/hosts are likely to coexist. For the operators, supporting inter-connection is inevitable. One-time translation mechanisms emerged as required.

With the IPv6 development, IPv4 Internet has been gradually replaced. For the low cost, network operators tend to build IPv6 network rather than dual-stack network. In order to ensure the compatibility of legacy IPv4 application, IPv4-IPv6-IPv4 double translation scheme is provided.

Generic mechanism for one-time translation mechanisms are specified in [RFC2765], [RFC6219], [RFC2766], [RFC6146], [RFC6535], and double translation mechanisms are specified in [RFC6877], [I-D.ietf-softwire-map],etc. With the diverse characteristics and transition requirements of practical networks and the lack of overall transition architecture, the selection and deployment of IPv6 transition mechanisms are very difficult.

In an effort to push forward the IPv6 transition process, this document describles the basic issues and key elements of translation mechanisms,and presents the applicability index that would help the operators decide on the development scheme for their IPv6 transition.It could lead to significant operational benefits and potential savings for the operators.

2. The Basic Issues and Key elements of Translation Mechanisms

Translation scheme is used to achieve direct communication between IPv4 and IPv6 networks (or hosts).

2.1. Basic Issues

Its basic operation is to convert the semantics between IPv4 and IPv6, turning IPv4 packet into IPv6 if the packet is destined to IPv6 network, or turning IPv6 packet into IPv4 if the packet is destined to IPv4 network.

1. The basic data operation. IPv4-IPv6 packet translation is the basic data plane operation. It involves network, transport, and application layer. Thus, the basic operations include address and port conversion, IP/TCP/UDP protocol field translation, and application layer translation (address and port conversion when they appear in application protocol). What is more, to overcome further diversities in the protocol definition between IPv4 and IPv6, translation has to take care of issues like fragmentation and reassembling, path MTU (Maximum Transmission Unit) discovery, ICMP, etc.
2. The basic control operation. The basic control plane operation is the address conversion rule: either some special address scheme needs to be deployed in advance, or dynamic address bindings have to be built during the translation. Heterogeneous addressing (learning the in-protocol address of the remote end) and corresponding routing should be performed based on the address conversion rule.
3. The translation model. According to the applicable scenarios, the models of IPv6 translation mechanisms are divided into application-side, network-side and host-side translation. According to the address conversion manner, we can also divide network-side translation mechanisms into stateless translation and stateful translation.

2.2. Key Elements

1. Transition equipment. In translation technologies, the translator is the transition equipments. Usually, network-side translation happens on the IPv4-IPv6 border, so the translator would be an AFBR (Address Family Border Router). And host-side translation happens in the TCP/IP stack of the end host, so the translator would be host. They should support address and port conversion, IP/TCP/UDP protocol field translation and also maintain the state. Thus, translator has requirements in the use of bandwidth, computing and finding, storage.
2. Address translation. Using specific address conversion rules, the translator either gets IPv4 address from a specific position of IPv6 address, or builds the IPv6 address using IPv4 address. The address conversion rule includes some special address scheme needs to be deployed in advance, and dynamic address bindings have to be built during the translation.
3. Other fields translation. Except the source address and destination address, there are other fields (fragmentation ID, checksum, ban-fragmentation flag, etc.) in IP/ICMP packets, which carry specific information. In the IPv4-IPv6 translation process, the header information of IPv4 packet cannot be lost. Therefore, translation techniques are required to ensure the integrity of IPv4 information.
4. State maintenance. In IPv6 transition, the state is available to only represent a series of attributes mapping relationship among a communication entity (such as client, server), a communication path (the connection between communication entities), or a communication process (control flow and data flow). The IP address in network layer and ID in transport layer of the communication entities are the core state which need translation techniques to maintain.
5. DNS64 and DNS46. The main function of DNS64 and DNS46 is to realize the bi-directional translation between A and AAAA record. DNS64 translates the AAAA query from IPv6 hosts into A query when receiving one, and DNS46 translates the A response for IPv6 hosts into AAAA response following the IPv4-mapped address rule before sending one out. There are usually two kinds of implementations: static configuration DNS records and dynamic translation.
6. Application layer translation. Those applications whose address and port conversion when they appear in application protocol cannot work in NAT and IPv4/IPv6 translation environments. Such as FTP, SIP, etc. One solution is assist applications to realize translation work by using the application layer gateway.

3. Applicability Index of Translation

There are applicability index which need to be analyzed by the operator when choosing which transition technology option they would like to deploy. The applicability index in terms of sustainable, applications, performance, development and security. This section describes some of those considerations.

3.1. Sustainable Index

Sustainable index would include:

1. The scenarios and function of transition represents whether meet the needs of transitional scenario.
2. Both (a)the coupling degree between IPv4 address and (b) IPv6 address and the reuse rate of IPv4 addresses resource represent whether promote the deployment and usage of IPv6.

3.2. The Support Degree of Business Application Index

The support degree of business application index would include:

1. The support degree of IPv4 application represents the impact on the IPv4 business application.
2. The support degree of IPv6 application represents the impact on the IPv6 business application.

3.3. The Preformance Index

The preformance index would include:

1. The performance requirements of translator can be divided into (a) the routing information announcement and (b) the space and time overhead of state maintenance, which represents the capacity of bandwidth, computing and finding, storage.
2. The routing scalability can be represented by the aggregation of IPv6 addresses, which represents the impact on the scope of deployment.
3. Robustness represents the capacity of redundancy backup.

3.4. The Development Index

The cost of development index would include:

1. Technological and industry maturity represent the support degree of standard.
2. The update cost can be divided into (a) the impact on application layer, (b) the impact on network layerand and (c) the impact on end users layer, which represent the impact on the present network.
3. The cost of operation, management and maintenance represent the impact on the operator.

3.5. The Security Index

The security index includes the security issues and concerns.

4. Conclusions

For the consideration of deployment scenarios and address format, numerous translation mechanisms have been proposed in the past several years. However, due to a wide range of mechanisms and a lot of overlap and similar functions, no one translation mechanism can be used in all transition scenarios.

The applicability index of translation mechanisms described in this document have highlighted the applicability of all translation mechanisms to help the operators decide on the development scheme for their IPv6 transition.

5. Acknowledgements

6. IANA Considerations

This memo includes no request to IANA.

7. Security Considerations

All drafts are required to have a security considerations section.

8. Informative References

Authors' Addresses