Network Working Group X. Xu
Internet-Draft D. Zhang
Intended status: Standards Track L. Xia
Expires: May 28, 2018 Huawei
November 24, 2017

Encapsulating IPsec ESP in UDP for Load-balancing
draft-xu-ipsecme-esp-in-udp-lb-01

Abstract

IPsec Virtual Private Network (VPN) is widely used by enterprises to interconnect their geographical dispersed branch office locations across IP Wide Area Network (WAN) or the Internet, especially in the Software-Defined-WAN (SD-WAN) era. To fully utilize the bandwidth available in IP WAN or the Internet, load balancing of traffic between different IPsec VPN sites over Equal Cost Multi-Path (ECMP) and/or Link Aggregation Group (LAG) is attractive to those enterprises deploying IPsec VPN solutions. This document defines a method to encapsulate IPsec Encapsulating Security Payload (ESP) packets over UDP tunnels for improving load-balancing of IPsec ESP traffic.

Status of This Memo

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This Internet-Draft will expire on May 28, 2018.

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Table of Contents

1. Introduction

IPsec Virtual Private Network (VPN) is widely used by enterprises to interconnect their geographical dispersed branch office locations across IP Wide Area Network (WAN) or the Internet, especially in the Software-Defined-WAN (SD-WAN) era. To fully utilize the bandwidth available in IP WAN or the Internet, load balancing of traffic between different IPsec VPN sites over Equal Cost Multi-Path (ECMP) and/or Link Aggregation Group (LAG) is much attractive to those enterprises that deploy IPsec VPN solutions. Since most existing core routers within IP WAN or the Internet can already support balancing IP traffic flows based on the hash of the five-tuple of UDP packets, by encapsulating IPsec Encapsulating Security Payload (ESP) packets over UDP tunnels with the UDP source port being used as an entropy field, it will enable existing core routers to perform efficient load-balancing of the IPsec ESP traffic without requiring any change to them. Therefore, this specification defines a method of encapsulating IPsec ESP packets over UDP tunnels for improving load-balancing of IPsec ESP traffic.

Encapsulating ESP in UDP, as defined in this document, can be used in both IPv4 and IPv6 networks. IPv6 flow label has been proposed as an entropy field for load balancing in IPv6 network environment [RFC6438]. However, as stated in [RFC6936], the end-to-end use of flow labels for load balancing is a long-term solution and therefore the use of load balancing using the transport header fields would continue until any widespread deployment is finally achieved. As such, ESP-in-UDP encapsulation would still have a practical application value in the IPv6 networks during this transition timeframe.

Note that the difference between the ESP-in-UDP encapsulation as proposed in this document and the ESP-in-UDP encapsulation as described in [RFC3948] is that the former uses the UDP tunnel for load-balancing improvement purpose and therefore the source port is used as an entropy field while the latter uses the UDP tunnel for NAT traverse purpose and therefore the source port is set to a constant value (i.e., 4500). In addition, this document only discusses about the tunnel mode ESP encapsulation.

1.1. Requirements Language

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 RFC 2119.

2. Terminology

This memo makes use of the terms defined in [RFC2401]and [RFC2406].

3. Encapsulation in UDP

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Source Port = Entropy      |        Dest Port = TBD1       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           UDP Length          |        UDP Checksum           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                           ESP Packet                          ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 1: ESP-in-UDP Encapsulation Format

ESP-in-UDP encapsulation format is shown as follows:

4. Processing Procedures

This ESP-in-UDP encapsulation causes ESP [RFC2406] packets to be forwarded across IP WAN via "UDP tunnels". When performing ESP-in-UDP encapsulation by an IPsec VPN gateway, ordinary ESP encapsulation procedure is performed and then a formatted UDP header is inserted between ESP header and IP header. The Source Port field of the UDP header is filled with an entropy value which is generated by the IPsec VPN gateway. Upon receiving these UDP encapsulated packets, remote IPsec VPN gateway MUST decapsulate these packets by removing the UDP header and then perform ordinary ESP decapsulation procedure consequently.

Similar to all other IP-based tunneling technologies, ESP-in-UDP encapsualtion introduces overheads and reduces the effective Maximum Transmision Unit (MTU) size. ESP-in-UDP encapsulation may also impact Time-to-Live (TTL) or Hop Count (HC) and Differentiated Services (DSCP). Hence, ESP-in-UDP MUST follow the corresponding procedures defined in [RFC2003].

Encapsulators MUST NOT fragment ESP packet, and when the outer IP header is IPv4, encapsulators MUST set the DF bit in the outer IPv4 header. It is strongly RECOMMENDED that IP transit core be configured to carry an MTU at least large enough to accommodate the added encapsulation headers. Meanwhile, it is strongly RECOMMENDED that Path MTU Discovery [RFC1191] [RFC1981] or Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821] is used to prevent or minimize fragmentation.

5. Congestion Considerations

TBD.

6. Applicability Statements

TBD.

7. Acknowledgements

8. IANA Considerations

One UDP destination port number indicating ESP needs to be allocated by IANA:

   Service Name: ESP-in-UDP Transport Protocol(s):UDP 
   Assignee: IESG <iesg@ietf.org> 
   Contact: IETF Chair <chair@ietf.org>. 
   Description: Encapsulate ESP packets in UDP tunnels. 
   Reference: This document. 
   Port Number: TBD1 -- To be assigned by IANA.

9. Security Considerations

TBD.

10. References

10.1. Normative References

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, DOI 10.17487/RFC1191, November 1990.
[RFC1981] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1996.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, DOI 10.17487/RFC2003, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, DOI 10.17487/RFC2401, November 1998.
[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)", RFC 2406, DOI 10.17487/RFC2406, November 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label for Equal Cost Multipath Routing and Link Aggregation in Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011.
[RFC6935] Eubanks, M., Chimento, P. and M. Westerlund, "IPv6 and UDP Checksums for Tunneled Packets", RFC 6935, DOI 10.17487/RFC6935, April 2013.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement for the Use of IPv6 UDP Datagrams with Zero Checksums", RFC 6936, DOI 10.17487/RFC6936, April 2013.

10.2. Informative References

[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L. and M. Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC 3948, DOI 10.17487/RFC3948, January 2005.

Authors' Addresses

Xiaohu Xu Huawei EMail: xuxiaohu@huawei.com
Dacheng Zhang Huawei EMail: dacheng.zhang@huawei.com
Liang Xia Huawei EMail: frank.xialiang@huawei.com