The IPv6 Virtual Private Network (VPN) Context Information Option
draft-bonica-6man-vpn-dest-opt-04

Abstract

This document defines a new IPv6 Destination Option that can be used to encode Virtual Private Network (VPN) context information. It is applicable when VPN payload is transported over IPv6.

Status of This Memo

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Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Requirements Language
• 3. VPN Context Information
• 4. The VPN Context Information Option
• 5. Security Considerations
• 6. IANA Considerations
• 7. Acknowledgements
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

Virtual Private Network (VPN) technologies allow network providers to emulate private networks with shared infrastructure. For example, assume that a red sites and blue sites connect to a provider network. The provider network facilitates communication among red sites and facilitates communication among blue sites. However, it prevents communication between red sites and blue sites.

The IETF has standardized many VPN technologies, including:

• Layer 2 VPN (L2VPN).
• Layer 3 VPN (L3VPN).
• Virtual Private LAN Service (VPLS)[RFC4762].
• Ethernet VPN (EVPN).
• Pseudowires.

The above-mentioned technologies include the following components:

• Customer Edge (CE) devices.
• Provider Edge (PE) devices.
• Routing Instances.
• VPN context information.
• Transport tunnels.

CE devices participate in closed communities called VPNs. CEs that participate in one VPN can communicate with one another but cannot communicate with CEs that participate in another VPN.

CE devices connect to provider networks through PE devices. Each PE maintains one Routing Instance for each VPN that it supports. A Routing Instance is a VPN specific Forwarding Information Base (FIB). In EVPN, Routing Instances are called Ethernet Virtual Instances (EVI).

Assume that one CE sends a packet through a provider network to another CE. The packet enters the provider network through an ingress PE and leaves the provider network through an egress PE. The packet may traverse one or more intermediate nodes on route from PE to PE.

When the ingress PE receives the packet, it:

• Identifies the Routing Instance that supports the originating CE's VPN.
• Searches that Routing Instance for the packet's destination.

If the search fails, the ingress PE discards the packet. If the search succeeds, it yields the following:

• VPN context information.
• The egress PE's IP address.

The ingress PE prepends VPN context information and a transport header to the packet, in that order. It then forwards the packet through a transport tunnel to the egress PE.

The egress PE removes the transport header, if it has not already been removed by an upstream device. It then examines and removes the VPN context information. Finally, it uses the VPN context information to forward the packet to its destination (i.e., a directly connected CE).

In the above-mentioned VPN technologies, the ingress PE encodes VPN context information in a Multiprotocol Label Switching (MPLS) label. Depending upon the transport tunnel type, the transport header can be:

• A MPLS label or label stack.
• An IPv4 header.
• An IPv6 header.
• A Generic Routing Encapsulation (GRE) header encapsulated in IPv4 or IPv6.

Some PE devices cannot process MPLS headers. While these devices have several alternatives to MPLS-based transport tunnels, they require an alternative to MPLS-based encoding of VPN context information. This document defines a new IPv6 Destination Option that can be used to encode VPN context information. It is applicable when VPN payload is transported over IPv6.

2. 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 BCP 14 [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. VPN Context Information

VPN context information specifies a forwarding procedure to be executed by the egress PE. However, VPN context information values are not globally mapped to forwarding procedures. Each egress PE maps each forwarding procedure that it supports to a VPN context information value. Therefore, VPN context information values are locally scoped to the egress PE.

PE devices can acquire VPN Context Information:

• From one another, using a distributed, control plane protocol (e.g., BGP [RFC4271] [RFC4760])
• From a controller.

The mechanisms by which PE devices acquire VPN Context Information are beyond the scope of this document.

4. The VPN Context Information Option

       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 |    VPN Context Information ...  
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-      
    

Figure 1

Figure 1 depicts the VPN Context Information Option.

Option fields are as follows:

• Option Type - VPN Context Information option. Value TBD by IANA. See Notes below.
• Opt Data Len - Length of Option Data, measured in bytes.
• VPN Context Information - Specifies a forwarding procedure to be executed by the egress PE.

The VPN Context Information Option MAY appear in a Destination Options header that precedes an upper-layer header. It MUST NOT appear in a Hop-by-hop Options header and SHOULD NOT appear in a Destination Options header that precedes a Routing header. If it appears in a Hop-by-hop Options header, the processing node will discard the packet and send an ICMPv6 Parameter Problem, Code 2, message to the packet's Source Address, pointing to the Option Type. If it appears in a Destination Options header that precedes a Routing header, the processing node will attempt to process the option, because it has not yet encountered the Routing header.

If the VPN Context Information appears in a Destination Options header, it SHOULD be the final option listed in the header. Because the VPN Context Information Option causes the packet to be decapsulated and forwarded, all options listed after the VPN Context Information Option will be ignored.

NOTE 1: The highest-order two bits of the Option Type (i.e., the "act" bits) are 10. These bits specify the action taken by a destination node that does not recognize VPN Context Information option. The required action is to discard the packet and, regardless of whether or not the packet's Destination Address was a multicast address, send an ICMPv6 Parameter Problem, Code 2, message to the packet's Source Address, pointing to the unrecognized Option Type.

NOTE 2: The third highest-order bit of the Option Type (i.e., the "chg" bit) is 0. This indicates that Option Data cannot be modified along the path between the packet's source and its destination.

5. Security Considerations

A VPN can be deployed:

• In a walled-garden environment.
• In an over-the-top environment.

In a walled-garden environment, all PE devices and all devices that connect PEs to one another reside in the same security domain. Therefore, there is no risk that a packet might be modified as it travels from PE to PE.

In an over-the-top environment, all PE devices reside in one security domain while devices that connect PEs to one another can reside in a different security domain. In that case, there is significant risk that a packet might be modified as it travels from PE to PE.

Therefore, the VPN Context Information option MUST be authenticated when used in over-the-top environments. In this scenario, an IPv6 Encapsulating Security Payload (ESP) MUST proceed the Destination Options header that carries the VPN Context Information option. The ESP integrity service MUST be enabled.

6. IANA Considerations

IANA is requested to allocate a codepoint from the Destination Options and Hop-by-hop Options registry (https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml#ipv6-parameters-2). This option is called "VPN Context Information". The "act" bits are 10 and the "chg" bit is 0.

7. Acknowledgements

Thanks to Brian Carpenter, Adrian Farrel, Tom Herbert and John Leddy for their comments.

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses