Carrying Virtual Transport Network (VTN) Information in IPv6 Extension Header
draft-ietf-6man-enhanced-vpn-vtn-id-04

Network Working Group                                            J. Dong
Internet-Draft                                                     Z. Li
Intended status: Standards Track                     Huawei Technologies
Expires: 18 November 2023                                         C. Xie
                                                                   C. Ma
                                                           China Telecom
                                                               G. Mishra
                                                            Verizon Inc.
                                                             17 May 2023

 Carrying Virtual Transport Network (VTN) Information in IPv6 Extension
                                 Header
                 draft-ietf-6man-enhanced-vpn-vtn-id-04

Abstract

   Virtual Private Networks (VPNs) provide different customers with
   logically separated connectivity over a common network
   infrastructure.  With the introduction and evolvement of 5G and other
   network scenarios, some existing or new customers may require
   connectivity services with advanced characteristics comparing to
   traditional VPNs.  Such kind of network service is called enhanced
   VPNs (VPN+).  VPN+ can be used to deliver IETF network slices, and
   could also be used for other application scenarios.

   A Virtual Transport Network (VTN) is a virtual underlay network which
   consists of a set of dedicated or shared network resources allocated
   from the physical underlay network, and is associated with a
   customized logical network topology.  VPN+ services can be delivered
   by mapping one or a group of overlay VPNs to the appropriate VTNs as
   the virtual underlay.  In packet forwarding, some fields in the data
   packet needs to be used to identify the VTN the packet belongs to, so
   that VTN-specific processing can be performed on each node the packet
   traverses.

   This document proposes a new Hop-by-Hop option of IPv6 extension
   header to carry the VTN related information in data packets, which
   could used to identify the VTN specific processing to be performed on
   the packets.  The procedure of processing 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.

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   Copyright (c) 2023 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  New IPv6 Extension Header Option for VTN  . . . . . . . . . .   4
   3.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Adding VTN Option to Packet . . . . . . . . . . . . . . .   6
     3.2.  VTN based Packet Forwarding . . . . . . . . . . . . . . .   6
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   7
   5.  Considerations about Generalization . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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1.  Introduction

   Virtual Private Networks (VPNs) provide different customers with
   logically isolated connectivity over a common network infrastructure.
   With the introduction and evolvement of 5G and other network
   scenarios, some existing or new customers may require connectivity
   services with advanced characteristics comparing to traditional VPNs,
   such as resource isolation from other services or guaranteed
   performance.  Such kind of network service is called enhanced VPN
   (VPN+).  VPN+ service requires the coordination and integration
   between the overlay VPNs and the capability and resources of the
   underlay network.  VPN+ can be used to deliver IETF network slices
   [I-D.ietf-teas-ietf-network-slices].

   [I-D.ietf-teas-enhanced-vpn] describes a framework and the candidate
   component technologies for providing VPN+ services.  It also
   introduces the concept of Virtual Transport Network (VTN).  A VTN is
   a virtual underlay network which consists of a set of dedicated or
   shared network resources allocated from the physical underlay
   network, and is associated with a logical network topology.  VPN+
   services can be delivered by mapping one or a group of overlay VPNs
   to the appropriate VTNs as the underlay, so as to provide the network
   characteristics required by the customers.  In packet forwarding,
   traffic of different VPN+ services needs to be processed separately
   based on the network resources and the logical topology associated
   with the corresponding VTN.  In the context of network slicing, VTN
   and NRP are considered as similar concepts, and NRP can be seen as an
   instantiation of VTN.

   [I-D.ietf-teas-nrp-scalability] describes the scalability
   considerations and the possible optimizations for providing a
   relatively large number of VTNs for VPN+ services.  One approach to
   improve the data plane scalability of VTN is to introduce a dedicated
   VTN Resource Identifier (VTN Resource ID) in the data packet to
   identify the set of network resources allocated to a VTN, so that
   VTN-specific packet processing can be performed using that set of
   resources, which avoids the possible resource competition with
   services in other VTNs.  This is called Resource Independent (RI)
   VTN.  A VTN Resource ID represents a subset of the resources (e.g.
   bandwidth, buffer and queuing resources) allocated on a given set of
   links and nodes which constitute a logical network topology.  The
   logical topology associated with a VTN could be defined using
   mechanisms such as Multi-Topology [RFC4915], [RFC5120] or Flex-Algo
   [RFC9350], etc.

   This document proposes a mechanism to carry the VTN related
   information in a new Hop-by-Hop option called "VTN option" of IPv6
   extension header [RFC8200] of IPv6 packet, so that on each network

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   node along the packet forwarding path, the VTN option in the packet
   is parsed, and the obtained VTN Resource ID is used to instruct the
   network node to use the set of network resources allocated to the
   corresponding VTN to process and forward the packet.  The procedure
   for processing the VTN option is also specified.  This provides a
   scalable solution to support a relatively large number of VTNs in an
   IPv6 network.

   Although the application of the VTN option in this document is to
   carry the resource ID information, the VTN option is considered as a
   generic mechanism to convey network wide VTN identifiers with
   different semantics to meet the possible use cases in the future.

1.1.  Requirements Language

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

2.  New IPv6 Extension Header Option for VTN

   A new Hop-by-Hop option type "VTN" is defined to carry the VTN
   related information in an IPv6 packet.  Its format is shown as below:

        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
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |  Option Type  |  Opt Data Len |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Flags     | Context Type  |            Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                            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 bits of the type field are
   defined as below:

   *  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.

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

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   *  TTTTT To be assigned by IANA.

   Opt Data Len: 8-bit unsigned integer indicates the length of the
   option Data field of this option, in octets.

   Flags: 8-bit flags field.  The most significant bit is defined in
   this document.

                                   0 1 2 3 4 5 6 7
                                  +-+-+-+-+-+-+-+-+
                                  |S|U U U U U U U|
                                  +-+-+-+-+-+-+-+-+

   *  S (Strict Match): The S flag is used to indicate whether the VTN
      ID MUST be strictly matched for the processing of the packet.
      When S flag is set to 1, if the VTN ID in the VTN option does not
      match with any of the VTN ID provisioned on the network node, the
      packet MUST be dropped.  When S flag is set to 0, if the VTN ID
      does not match with any of the VTN ID provisioned on the network
      node, the packet SHOULD be forwarded using the default behavior as
      if the VTN option does not exist.

   *  U (Unused): These flags are reserved for future use.  They SHOULD
      be set to 0 on transmission and MUST be ignored on receipt.

   Context Type (CT): One-octet field used to indicate the semantics and
   length of the VTN ID carried in the option.  The context value
   defined in this document is as follows:

   *  CT=0: The VTN ID is a 4-octet resource ID, which is used to
      identify a subset of network resources on the network nodes and
      links involved in the VTN.

   Reserved: 2-octet field reserved for future use.  They SHOULD be set
   to 0 on transmission and MUST be ignored on receipt.

   VTN ID: The identifier of a Virtual Transport Network, the semantics
   and length of the ID is determined by the Context Type.

   Note that, if a deployment found it useful, the four-octet VTN ID
   field may be derived from the four-octet Single Network Slice
   Selection Assistance Information (S-NSSAI) defined in 3GPP [TS23501].

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3.  Procedures

   As the VTN option needs to be processed by each node along the
   forwarding path, it MUST be carried in IPv6 Hop-by-Hop Options
   header.  This section describes the procedures for VTN option
   processing when the Context Type in the VTN option is set to 0.  The
   processing procedures for VTN option with other Context Types are out
   of the scope of this document and will be specified in separate
   documents which introduce those Context Types.

3.1.  Adding VTN Option to Packet

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

3.2.  VTN based Packet Forwarding

   On receipt of a packet with the VTN option, each network node which
   can process the VTN option in fast path MUST use the VTN Resource ID
   to determine the set of local network resources which are allocated
   to the VTN.  The packet forwarding behavior is based on both the
   destination IP address and the VTN Resource ID.  More specifically,
   the destination IP address is used to determine the next-hop and the
   outgoing interface, and VTN Resource ID is used to determine the set
   of network resources on the outgoing interface which are allocated to
   the VTN for processing and sending the packet.  If the VTN Resource
   ID does not match with any of the VTN Resource ID provisioned on the
   outgoing interface, the S flag in the VTN option is used to determine
   whether the packet is dropped or forwarded using the default set of
   network resources of the outgoing interface.  The Traffic Class field
   of the outer IPv6 header can be used to provide differentiated
   treatment for packets which belong to the same VTN.  The egress node
   of the IPv6 domain MUST decapsulate the outer IPv6 header and the
   Hop-by-Hop Options header which includes the VTN option.

   In the forwarding plane, there can be different approaches of
   partitioning the local network resources and allocating them to
   different VTNs.  For example, on one physical interface, a subset of
   the forwarding plane resources (e.g. bandwidth and the associated
   buffer and queuing resources) can be allocated to a particular VTN
   and represented as a virtual sub-interface or a data channel with
   reserved bandwidth resource.  In packet forwarding, the IPv6
   destination address of the received packet is used to identify the

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   next-hop and the outgoing layer-3 interface, and the VTN Resource ID
   is used to further identify the virtual sub-interface or the data
   channel on the outgoing interface which is associated with the VTN.

   Network nodes which do not support the processing of Hop-by-Hop
   Options header SHOULD ignore the Hop-by-Hop options header and
   forward the packet only based on the destination IP address.  Network
   nodes which support Hop-by-Hop Options header, but do not support the
   VTN option SHOULD ignore the VTN option and forward the packet only
   based on the destination IP address.  The network node MAY process
   the rest of the Hop-by-Hop options in the Hop-by-Hop Options header.

4.  Operational Considerations

   As described in [RFC8200], network nodes may be configured to ignore
   the Hop-by-Hop Options header, drop packets containing a Hop-by-Hop
   Options header, or assign packets containing a Hop-by-Hop Options
   header to a slow processing path.  In networks with such network
   nodes, it is important that packets of a VTN are not dropped due to
   the existence of the Hop-by-Hop Options header.  Operators need to
   make sure that all the network nodes involved in a VTN can either
   process the Hop-by-Hop Options header in the fast path, or ignore the
   Hop-by-Hop Options header.  Since a VTN is associated with a logical
   network topology, one practical approach is to ensure that all the
   network nodes involved in that logical topology support the
   processing of the Hop-by-Hop Options header and the VTN option in the
   fast path, and constrain the packet forwarding path to the logical
   topology of the VTN.

   [I-D.ietf-6man-hbh-processing] specifies the modified procedures for
   the processing of IPv6 Hop-by-Hop Options header, with the purpose of
   making the Hop-by-Hop Options header useful.  Network nodes complying
   with [I-D.ietf-6man-hbh-processing] will not drop packets with Hop-
   by-Hop Options header and the VTN option.

5.  Considerations about Generalization

   During the discussion of this document in the 6MAN WG, one of the
   suggestions received is to make the VTN option more generic in terms
   of semantics and encoding.  This section gives some analysis about to
   what extent the semantics of VTN could be generalized, and how the
   generalization could be achieved with the proposed encoding.

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   Based on the VTN definition in [I-D.ietf-teas-enhanced-vpn], the
   concept of VTN could be extended as: a virtual transport network
   which is associated with a set of network-wide attributes and states
   maintained on each participating network node.  The attributes
   associated with an VTN may include but not limited to: network
   resource attributes, network topology attributes, and network
   function attributes etc.

   *  The network resource can refer to various type of data plane
      resources, including link bandwidth, bufferage and queueing
      resources.

   *  The network topology can be multipoint-to-multipoint, point-to-
      point, point-to-multipoint or multipoint-to-point.

   *  The network functions may include both data forwarding actions and
      other types network functions which can be executed on data
      packets mapped to a VTN.

   This shows the semantics of VTN can be quite generic.  Although
   generalization is something good to have, it would be important to
   understand and identify the boundary of generalization.  In this
   document, It is anticipated that for one network attribute to be
   included in VTN, it needs to be a network-wide attribute rather than
   a node-specific attribute.  Thus whether a network-wide view can be
   provided or not could be considered as one prerequisite of making one
   attribute part of the VTN option.

   The format of the VTN option contains the Flags field, the Context
   Type field and the Reserved field, which provide the capability for
   future extensions.  That said, since the VTN option needs to be
   processed by network nodes in the fast path, the capability of
   network devices need to be considered when new semantics and encoding
   are introduced.

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
      ---------------------------------------------
       TBA           VTN Option       this document

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   This document requests IANA to create a new registry for the "VTN
   Option Context Type" under the "Internet Protocol Version 6 (IPv6)
   Parameters" registry.  The allocation policy of this registry is
   "Standards Action".  The initial codepoints are assigned by this
   document as follows:

      Value          Description       Reference
      ---------------------------------------------
        0            Resource ID      this document
      1-254          Unassigned
       255           Reserved

7.  Security Considerations

   The security considerations with IPv6 Hop-by-Hop Options header are
   described in [RFC8200], [RFC7045], [RFC9098] [RFC9099] and
   [I-D.ietf-6man-hbh-processing].  This document introduces a new IPv6
   Hop-by-Hop option which is either processed in the fast path or
   ignored by network nodes, thus it does not introduce additional
   security issues.

8.  Contributors

      Zhibo Hu
      Email: huzhibo@huawei.com

      Lei Bao
      Email: baolei7@huawei.com

9.  Acknowledgements

   The authors would like to thank Juhua Xu, James Guichard, Joel
   Halpern, Tom Petch, Aijun Wang, Zhenqiang Li, Tom Herbert, Adrian
   Farrel, Eric Vyncke and Erik Kline for their review and valuable
   comments.

10.  References

10.1.  Normative References

   [I-D.ietf-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Network (VPN+)",
              Work in Progress, Internet-Draft, draft-ietf-teas-
              enhanced-vpn-12, 23 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              enhanced-vpn-12>.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

10.2.  Informative References

   [I-D.ietf-6man-hbh-processing]
              Hinden, R. M. and G. Fairhurst, "IPv6 Hop-by-Hop Options
              Processing Procedures", Work in Progress, Internet-Draft,
              draft-ietf-6man-hbh-processing-08, 30 April 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-6man-
              hbh-processing-08>.

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "A Framework for
              IETF Network Slices", Work in Progress, Internet-Draft,
              draft-ietf-teas-ietf-network-slices-19, 21 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slices-19>.

   [I-D.ietf-teas-nrp-scalability]
              Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J.,
              Mishra, G. S., Qin, F., Saad, T., and V. P. Beeram,
              "Scalability Considerations for Network Resource
              Partition", Work in Progress, Internet-Draft, draft-ietf-
              teas-nrp-scalability-01, 24 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              nrp-scalability-01>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

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   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,
              <https://www.rfc-editor.org/info/rfc7045>.

   [RFC9098]  Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
              G., and W. Liu, "Operational Implications of IPv6 Packets
              with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,
              September 2021, <https://www.rfc-editor.org/info/rfc9098>.

   [RFC9099]  Vyncke, É., Chittimaneni, K., Kaeo, M., and E. Rey,
              "Operational Security Considerations for IPv6 Networks",
              RFC 9099, DOI 10.17487/RFC9099, August 2021,
              <https://www.rfc-editor.org/info/rfc9099>.

   [RFC9350]  Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
              and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
              DOI 10.17487/RFC9350, February 2023,
              <https://www.rfc-editor.org/info/rfc9350>.

   [TS23501]  "3GPP TS23.501", 2016,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3144>.

Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing
   100095
   China
   Email: jie.dong@huawei.com

   Zhenbin Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing
   100095
   China
   Email: lizhenbin@huawei.com

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   Chongfeng Xie
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing
   102209
   China
   Email: xiechf@chinatelecom.cn

   Chenhao Ma
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing
   102209
   China
   Email: machh@chinatelecom.cn

   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com

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