Tunneling TCP inside QUIC

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Table of Contents

1. Introduction

The recently proposed QUIC tunnel protocol [I-D.piraux-intarea-quic-tunnel] supports the exchange of IP packets and Ethernet frames over a QUIC connection. Its two existing operating modes transports plain packets inside QUIC frames. Their main advantage is that they support any network-layer protocol. However, this advantage comes with a large per-packet overhead since each packet contains both a network and a transport header. All these headers must be transmitted in addition to the IP/UDP/QUIC headers of the QUIC connection. For TCP connections for instance, the per-packet overhead can be large.¶

In this document, we propose a new operating mode for the QUIC tunnel protocol, called the stream mode. It takes advantage of the QUIC streams to efficiently transport TCP bytestreams over a QUIC connection. Section 3 describes this new mode. Section 5 specifies the format of the messages introduced by this document. Section 6 contains example flows.¶

2. Conventions and Definitions

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 stream mode

Since QUIC supports multiple streams, another possibility to carry the data exchanged over TCP connections between the client and the concentrator is to transport the bytestream of each TCP connection as one of the bidirectional streams of the QUIC connection. For this, we base our approach on the 0-RTT Convert protocol [I-D.ietf-tcpm-converters] that was proposed to ease the deployment of TCP extensions. In a nutshell, it is an application proxy that converts TCP connections, allowing the use of new TCP extensions through an intermediate relay.¶

A similar approach is used in the stream mode. When a client opens a stream, it sends at the beginning of the bytestream one or more TLV messages indicating the IP address and port number of the remote destination of the bytestream. Their format is detailed in section Section 5.1. Upon reception of such a TLV message, the concentrator opens a TCP connection towards the specified destination and connects the incoming bytestream of the QUIC connection to the bytestream of the new TCP connection (and similarly in the opposite direction).¶

Figure 1 summarizes how the new TCP connection is mapped to the QUIC stream. Actions and events of a TCP connection are translated to actions and events of the associated QUIC stream, so that a state transition on one is translated to the other.¶

+------------------+-------------------------+
|        TCP       |      QUIC Stream        |
+------------------+-------------------------+
| SYN received     | Open Stream, send TLVs  |
| FIN received     | Send Stream FIN         |
| RST received     | Send STOP_SENDING       |
|                  | Send RESET_STREAM       |
| Data received    | Send Stream data        |
+------------------+-------------------------+

+-------------------------------+------------+
|         QUIC Stream           |    TCP     |
+-------------------------------+------------+
| Stream opened, TLVs received  | Send SYN   |
| Stream FIN received           | Send FIN   |
| STOP_SENDING received         | Send RST   |
| RESET_STREAM received         | Send RST   |
| Stream data received          | Send data  |
+-------------------------------+------------+

When sending STOP_SENDING or RESET_STREAM frames in response to the receipt of a TCP RST, QUIC tunnel peers MUST use the application protocol error code 0x00 (TCP_CONNECTION_RESET).¶

The QUIC stream-level flow control can be tuned to match the receive window size of the corresponding TCP connection, so that no excessive data needs to be buffered.¶

4. Connection establishment

The support of the stream mode is negotiated during the connection establishment by including the quic_tunnel_stream_mode transport parameter (value TBD). The parameter value has no meaning and SHOULD be null.¶

During the connection establishment, the concentrator can control the number of TCP bytestreams that can be opened initially by setting the initial_max_streams_bidi QUIC transport parameter as defined in [I-D.ietf-quic-transport].¶

5. Messages format

In the following sections, we specify the format of each message introduced in this document. They are encoded using the TLV format described in [I-D.piraux-intarea-quic-tunnel].¶

+------+----------+-----------------------------+
| Type |     Size | Name                        |
+------+----------+-----------------------------+
| 0x00 | 20 bytes | TCP Connect TLV             |
| 0x01 |  2 bytes | TCP Connect OK TLV          |
| 0x02 | Variable | Error TLV                   |
| 0xff |  2 bytes | End TLV                     |
+------+----------+-----------------------------+

      Offset 0         Offset 20   Offset 22
         |                 |         |
Client   v                 v         v
         +-----------------+---------+----------------
Stream 0 | TCP Connect TLV | End TLV | TCP bytestream ...
         +-----------------+---------+----------------

                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Type (8)   |   Length (8)  |     Remote Peer Port (16)     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                  Remote Peer IP Address (128)                 |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Type (8)   |   Length (8)  |        Error Code (16)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     [Error Payload (*)]                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+------+---------------------------+
| Code | Name                      |
+------+---------------------------+
|  0x0 | Protocol Violation        |
|  0x1 | ICMP Packet Received      |
|  0x2 | Malformed TLV             |
|  0x3 | Network Failure           |
+------+---------------------------+

6. Example flows

This section illustrates the different messages described previously and how they are used in a QUIC tunnel connection. For QUIC STREAM frames, we use the following syntax: STREAM[ID, Stream Data [, FIN]]. The first element is the Stream ID, the second is the Stream Data contained in the frame and the last one is optional and indicates that the FIN bit is set.¶

Client                      Concentrator           Final Destination
 | STREAM[0, "TCP Connect, End"] ||                               |
 |------------------------------>||              SYN              |
 |                               ||==============================>|
 |                               ||            SYN+ACK            |
 |STREAM[0,"TCP Connect OK, End"]||<==============================|
 |<------------------------------||                               |
 | STREAM[0, "bytestream data"]  ||                               |
 |------------------------------>||     bytestream data, ACK      |
 |                               ||==============================>|
 |                               ||     bytestream data, ACK      |
 |  STREAM[0, "bytestream data"] ||<==============================|
 |<------------------------------||              FIN              |
 |      STREAM[0, "", FIN]       ||<==============================|
 |<------------------------------||              ACK              |
 |      STREAM[0, "", FIN]       ||==============================>|
 |------------------------------>||              FIN              |
 |                               ||==============================>|
 |                               ||              ACK              |
 |                               ||<==============================|

Legend:
   --- QUIC connection
   === TCP connection

On Figure 7, the client is initiating a TCP connection in stream mode to the Final Destination. A request and a response are exchanged, then the connection is torn down gracefully. A remote-initiated connection accepted by the concentrator on behalf of the client would have the order and the direction of all messages reversed.¶

7. Security Considerations

8. IANA Considerations

+------+-----------------------------+------------+
| Code | Name                        | Reference  |
+------+-----------------------------+------------+
|    0 | TCP Connect TLV             | [This-Doc] |
|    1 | TCP Connect OK TLV          | [This-Doc] |
|    2 | Error TLV                   | [This-Doc] |
|  255 | End TLV                     | [This-Doc] |
+------+-----------------------------+------------+

+------+---------------------------+------------+
| Code | Name                      | Reference  |
+------+---------------------------+------------+
|    0 | Protocol Violation        | [This-Doc] |
|    1 | ICMP packet received      | [This-Doc] |
|    2 | Malformed TLV             | [This-Doc] |
|    3 | Network Failure           | [This-Doc] |
+------+---------------------------+------------+

Appendix A. Change Log

Acknowledgments

This documents draws heavily on the initial version of [I-D.piraux-quic-tunnel]. Their contributors are thanked again here. This work was partially supported by the MQUIC project.¶

Authors' Addresses