Internet-Draft IPv6 VTN Option May 2023
Dong, et al. Expires 18 November 2023 [Page]
Workgroup:
Network Working Group
Internet-Draft:
draft-ietf-6man-enhanced-vpn-vtn-id-04
Published:
Intended Status:
Standards Track
Expires:
Authors:
J. Dong
Huawei Technologies
Z. Li
Huawei Technologies
C. Xie
China Telecom
C. Ma
China Telecom
G. Mishra
Verizon Inc.

Carrying Virtual Transport Network (VTN) Information in IPv6 Extension Header

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.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 18 November 2023.

Table of Contents

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 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:

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|
          +-+-+-+-+-+-+-+-+

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:

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].

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 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.

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.

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

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, , <https://datatracker.ietf.org/doc/html/draft-ietf-teas-enhanced-vpn-12>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <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, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc4915>.
[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, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc9350>.
[TS23501]
"3GPP TS23.501", , <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
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Chongfeng Xie
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing
102209
China
Chenhao Ma
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing
102209
China
Gyan Mishra
Verizon Inc.