The IPv6 Tunnel Payload Forwarding (TPF) Option

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Table of Contents

1. Introduction

This document explains how IPv6 options [RFC8200] can be used in IPv6 tunnels. It also defines the IPv6 Tunnel Payload Forwarding (TPF) option.¶

An IPv6 tunnel [RFC2473] connects two nodes, called the entry-point and the exit-point. The entry-point receives a packet and encapsulates it in a Tunnel IPv6 Header. Figure 1 depicts the encapsulation.¶

                            +----------------------------------//-----+
                            | Original |                              |
                            |          |   Original Packet Payload    |
                            | Header   |                              |
                            +----------------------------------//-----+
                             <            Original Packet            >
                                              |
                                              v
       <Tunnel IPv6 Headers> <       Original Packet                 >

      +---------+ - - - - - +-------------------------//--------------+
      | IPv6    | IPv6      |                                         |
      |         | Extension |        Original Packet                  |
      | Header  | Headers   |                                         |
      +---------+ - - - - - +-------------------------//--------------+
       <                          Tunnel IPv6 Packet                 >

The original packet can be any layer-2 or layer-3 packet (e.g., Ethernet, IPv4, IPv6). The Tunnel Header is an IPv6 header followed by zero or more extension headers. The resulting packet is a Tunnel IPv6 Packet.¶

The entry-point sends the Tunnel IPv6 Packet to the exit-point which then executes the following procedure:¶

• Process the Tunnel IPv6 Header.¶
• Remove the Tunnel IPv6 Header, exposing the original packet.¶
• Submit the original packet to the next-protocol engine.¶

The exit-point node processes the Tunnel IPv6 Header in strict left-to-right order. It processes the IPv6 header first and then processes extension headers in the order that they appear in the packet. The IPv6 header, and each extension header, includes a Next Header field. The last Next Header field processed identifies the next-protocol engine.¶

Entry-point nodes can send optional information to the next-protocol engine on the exit-point node. For example, the entry-point can indicate:¶

• The interface through which the next-protocol engine should send the packet.¶
• The routing table that the next-protocol engine should use to process the packet.¶

To send this information, the entry-point node includes an IPv6 Destination Option header in the Tunnel IPv6 Header. The IPv6 Destination Options header includes an IPv6 TPF option and the IPv6 TPF option includes TPF information. The next-protocol engine on the exit-point node uses TPF information when it forwards the original packet.¶

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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. The IPv6 Tunnel Payload Forwarding (TPF) Option

The TPF Option contains the following fields:¶

• Option Type: 8-bit selector. TPF option. Value TBD by IANA. (Suggested value: 0x41). See Note below.¶
• Opt Data Len - 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Option Length fields. This field MUST be set to 4.¶
• Option Data - 32-bits. Tunnel Payload Forwarding (TPF) Information.¶

The TPF 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 or in a Destination Options header that precedes a Routing header.¶

NOTE : The highest-order two bits of the Option Type (i.e., the "act" bits) are 01. These bits specify the action taken by a destination node that does not recognize the option. The required action is to discard the packet. 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.¶

9. Acknowledgements

Thanks to Dr. Vanessa Ameen, Brian Carpenter, Adrian Farrel, Ishaan Gandhi, Tom Herbert, John Leddy, Srihari Sangli and Tony Li for their comments.¶

Authors' Addresses