Network Working Group                                            J. Dong
Internet-Draft                                                     Z. Li
Intended status: Standards Track                     Huawei Technologies
Expires: May 6, 2021                                              C. Xie
                                                                   C. Ma
                                                           China Telecom
                                                        November 2, 2020

 Carrying Virtual Transport Network Identifier in IPv6 Extension Header


   A Virtual Transport Network (VTN) is a virtual network which has a
   customized network topology and a set of dedicated or shared network
   resources allocated from the network infrastructure.  A VTN can be
   used as the underlay for one or a group of VPNs to provide enhanced
   VPN (VPN+) services.  In packet forwarding, some fields in data
   packet needs to be used to identify the VTN the packet belongs to, so
   that the VTN-specific processing can be performed.

   This document proposes a new option type to carry VTN ID in an IPv6
   extension headers to identify the Virtual Transport Network (VTN) the
   packet belongs to.  The procedure for processing of the VTN option is
   also specified.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on May 6, 2021.

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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  New IPv6 Extension Header Option for VTN  . . . . . . . . . .   3
   4.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  VTN Option Insertion  . . . . . . . . . . . . . . . . . .   4
     4.2.  VTN based Packet Forwarding . . . . . . . . . . . . . . .   4
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Virtual Private Networks (VPNs) provide different groups of users
   with logically isolated connectivity over a common shared network
   infrastructure.  With the introduction of 5G, new service types may
   require connectivity services with advanced characteristics comparing
   to traditional VPNs, such as strict isolation from other services or
   guaranteed performance.  These services are refered to as "enhanced
   VPNs" (VPN+).  [I-D.ietf-teas-enhanced-vpn] describes a framework and
   candidate component technologies for providing VPN+ services.

   The enhanced properties of VPN+ require tighter coordination and
   integration between the underlay network resources and the overlay
   network.  VPN+ service can be built on a Virtual Transport Network
   (VTN) which has a customized network topology and a set of dedicated

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   or shared network resources allocated from the underlay network.  The
   overlay VPN together with the corresponding VTN in the underlay
   provide the VPN+ service.  In the network, traffic of different VPN+
   services need to be processed separately based on the topology and
   the network resources associated with the corresponding VTN.

   [I-D.dong-teas-enhanced-vpn-vtn-scalability] describes the
   scalability considerations for VPN+, one of which is to improve the
   data plane scalability through the introduction of a dedicated
   identifier in data packets that is used to identify the VTN the
   packets belong to, so that VTN-specific packet processing can be
   performed.  This is called Resource Independent (RI) VTN.

   This document proposes a mechanism to carry the VTN ID in an IPv6
   extension header [RFC8200] of a packet, so that the packet will be
   processed by network nodes using the network resources allocated to
   the corresponding VTN.  The procedure for processing the VTN ID is
   also specified.  This provides a scalable solution for enhanced VPN
   data plane, so that it may be used to support a large number of VTNs
   in an IPv6 network.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

3.  New IPv6 Extension Header Option for VTN

   A new option type "VTN" is defined to carry the Virtual Transport
   Network Identifier (VTN ID) in an IPv6 packet header.  Its format is
   shown as below:

                         Option   Option       Option
                          Type   Data Len       Data
                       |BBCTTTTT|00000100|  4-octet VTN ID |
                        Figure 1. The format of VTN Option

   Option Type: 8-bit identifier of the type of option.  The type of VTN
   option is to be assigned by IANA.  The highest-order bits of the type
   field are defined as below:

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   o  BB 00 The highest-order 2 bits are set to 00 to indicate that a
      node which does not recognize this type will skip over it and
      continue processing the header.

   o  C 0 The third highest-order bit are set to 0 to indicate this
      option does not change en route.

   Opt Data Len: 8-bit unsigned integer indicates the length of the
   option Data field of this option, in octets.  The value of Opt Data
   Len of VTN option SHOULD be set to 4.

   Option Data: 4-octet identifier which uniquely identifies a VTN.

   Editor's note: The length of the VTN ID is defined as 4-octet for the
   matching with the 4-octet Single Network Slice Selection Assistance
   Information (S-NSSAI) defined in 3GPP [TS23501].

                          8-bit              24-bit
                     |    SST     |   Slice Differentiator  |
                         Figure 2. The format of S-NSSAI

4.  Procedures

   As the VTN option needs to be processed by each node along the path
   for VTN-specific forwarding, it SHOULD be carried in IPv6 Hop-by-Hop
   options header when the Hop-by-Hop options header can be processed in
   forwarding plane by all the nodes along the path.

4.1.  VTN Option Insertion

   When an ingress node of an IPv6 domain receives a packet, according
   to traffic classification or mapping policy, the packet is steered
   into one of the VTNs in the network, then packet SHOULD be
   encapsulated in an outer IPv6 header, and the VTN-ID of the VTN which
   the packet is mapped to SHOULD be carried in the Hop-by-Hop options
   header associated with the outer IPv6 header.

4.2.  VTN based Packet Forwarding

   On receipt of a packet with the VTN option, each network node which
   can parse the VTN option SHOULD use the VTN ID to identify the VTN
   the packet belongs to.  This means the forwarding behavior is based
   on both the destination IP address and the VTN option.  The
   destination IP address is used for the lookup of the next-hop node,
   and VTN-ID can be used to determine the set of network resources
   reserved for processing and sending the packet to the next-hop node.

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   The egress node of the IPv6 domain SHOULD decapsulate the outer IPv6

   There can be different implementations for reserving local network
   resources to the VTNs.  For example, on one interface, a subset of
   forwarding plane resource allocated to a particular VTN can be
   considered as a virtual sub-interface with dedicated bandwidth and
   other associated resources.  In packet forwarding, the IPv6
   destination address of the received packet is used to identify the
   next-hop and the outgoing interface, and the VTN ID is used to
   further identify the virtual sub-interface which is associated with
   the VTN on the outgoing interface.

   Routers which do not support Hop-by-Hop options header SHOULD ignore
   the Hop-by-Hop options header and forward the packet only based on
   the destination IP address.  Routers which support Hop-by-Hop Options
   header, but do not support the VTN option SHOULD ignore the Hop-by-
   Hop option and continue to forward the packet only based on the
   destination IP address.

5.  Operational Considerations

   As described in [RFC8200], nodes may be configured to ignore the Hop-
   by-Hop Options header, and in some implementations a packet
   containing a Hop-by-Hop Options header may be dropped or assigned to
   a slow processing path.  This needs to be taken into consideration
   when VTN option is introduced to a network.  The operator needs to
   make sure that all the network nodes in a VTN can either process Hop-
   by-Hop Options header in packet forwarding, or ignore the Hop-by-Hop
   Option header.  In other word, packets steered into a VTN MUST NOT be
   dropped due to the existence of the Hop-by-Hop Options header.  It is
   RECOMMENDED to configure all the nodes in a VTN to process the Hop-
   by-Hop Options header if there is a nob for this.

6.  IANA Considerations

   This document requests IANA to assign a new option type from
   "Destination Options and Hop-by-Hop Options" registry.

      Value   Description     Reference
      TBD     VTN Option      this document

7.  Security Considerations


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8.  Contributors

      Zhibo Hu

      Lei Bao

9.  Acknowledgements

   The authors would like to thank Juhua Xu and James Guichard for their
   review and valuable comments.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

10.2.  Informative References

              Dong, J., Li, Z., and F. Qin, "Virtual Transport Network
              (VTN) Scalability Considerations for Enhanced VPN", draft-
              dong-teas-enhanced-vpn-vtn-scalability-00 (work in
              progress), February 2020.

              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Service", draft-ietf-teas-enhanced-vpn-06 (work in
              progress), July 2020.

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   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,

   [TS23501]  "3GPP TS23.501", 2016,

Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing  100095


   Zhenbin Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing  100095


   Chongfeng Xie
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing  102209


   Chenhao Ma
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing  102209


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