Additional addresses for QUIC

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Table of Contents

1. Introduction

The QUIC protocol specifies several techniques for network path migration. The client can migrate from one of its local addresses to another at any time after the handshake using connection migration. The server can transfer a connection to one of its other addresses shortly after the handshake by using the preferred_address transport parameter. However, it cannot advertise additional addresses that a client may use.¶

This limitation impacts several scenarios. For instance, a multihomed server that has access to several subnets cannot advertise all its addresses. In entreprise deployments where provider-assigned IPv6 Addresses are used to solve the multihoming problem [RFC8678], announcing several server addresses enables applications using QUIC to recover from provider failures. Also, a dual-stack server cannot advertise its other address so that a client losing the address family used to establish the connection can migrate to the other address family.¶

This document proposes a QUIC frame and a QUIC transport parameter enabling a QUIC server to advertise additional addresses that can be used for a QUIC connection.¶

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. Overview

The ADDITIONAL_ADDRESSES frame proposed in this document enables a QUIC server to securely advertise additional addresses. The Additional Addresses transport parameter enables a QUIC client to indicate support for this frame.¶

These addresses can be used by the client to migrate to a new server address at any time after the handshake. When [MULTIPATH-QUIC] is used over a QUIC connection, the client can use these addresses to establish additional network paths.¶

When sending packets to a new server address, the client validates the address using Path Validation as described in Section 8.2 of [QUIC-TRANSPORT]. When Preferred Adress and Additional Addresses are used together, the client SHOULD NOT migrate to an additional address before acting on the preferred address indicated by the server.¶

Client       Load-balancer @ IP lb        Server @ IP a   Server @ IP b
|                      |                      |               |
|       Initial[0]: CRYPTO(CH(Add.Addr))      |               |
|--------------------->|--------------------->|               |
                             ....
|      Handshake[0]: CRYPTO(EE(Pr.Addr=a),..) |               |
|<---------------------|<---------------------|               |
|         1-RTT[0]: ADDITIONAL_ADDRESSES([b]) |               |
|<---------------------|<---------------------|               |
                             ....
|       Handshake[0]: CRYPTO(Fin)             |               |
|--------------------->|--------------------->|               |
|    /* Migration to Preferred Address a */   |               |
|-------------------------------------------->|               |
                             ....
|                      |                      |
|                      |                      .               |
| 1-RTT[X]: PATH_CHALLENGE  /* Migration to Add. Address b */ |
|------------------------------------------------------------>|
|                                   1-RTT[Y]: PATH_RESPONSE   |
|<------------------------------------------------------------|
|                                                             |

4. Additional Addresses Transport Parameter

The following transport parameter is defined:¶

additional_addresses (TBD - experiments use 0x925addaXX):

Indicates the support of the ADDITIONAL_ADDRESSES frame as defined in the -XX draft version of this document. This transport parameter has a zero-length value. It MUST NOT be sent by a server.¶

5. ADDITIONAL_ADDRESSES Frames

The server uses an ADDITIONAL_ADDRESSES frame (type=TBD - experiments use 0x925addaXX) to advertise the additional addresses that a client can use to reach it. This frame MUST NOT be sent by a client and can only appear in 1-RTT packets.¶

Additional Addresses {
  Type (i) = TBD,
  Sequence Number (i),
  Additional Addresses Count (i),
  Additional Address (..) ...,
}

Sequence Number:

A variable-length integer indicating the sequence of the frame. The number is monotonically increasing within a QUIC connection and is chosen by the sender. It helps the receiver to order ADDITIONAL_ADDRESSES frames by recency. A receiver SHOULD ignore frames with a Sequence Number lower or equal to the highest Sequence Number received.¶

Additional Addresses Count:

A variable-length integer indicating the number of additional addresses in the frame.¶

Additional Address {
  Address Version (8),
  IP Address (..),
  IP Port (16),
}

Address Version:

An 8-bit value identifying the Internet address version of this address. The value 4 indicates IPv4 while 6 indicates IPv6.¶

IP Address:

The address value. Its size depends on its version. IPv4 addresses are 32-bit long while IPv6 addresses are 128-bit long.¶

IP Port:

A 16-bit value representing the port to use with this IP Address.¶

The ADDITIONAL_ADDRESSES frame is ack-eliciting. When a packet containing an ADDITIONAL_ADDRESSES frame is lost and its content is still relevant, the sender MAY retransmit the frame as is. Otherwise, sending a new frame with a new Sequence number is preferred.¶

The server can update the client on its additional addresses at any time by sending an ADDITIONAL_ADDRESSES frame. When a client is using one of these additional addresses and receives an ADDITIONAL_ADDRESSES frame not containing this address, it SHOULD stop using it in favor of another address.¶

6. Security Considerations

This document specifies a mechanism allowing servers to influence the IP addresses towards which clients send QUIC packets. In this case, a malicious server could cause a client to send packets to a victim. A countermeasure similar to Section 21.5.3 of [QUIC-TRANSPORT] is to limit the packets that are sent to a non-validated additional addresses.¶

Given that a server can provide additional addresses at any point in time, a malicious server could overload a client and direct it against many addresses. To alleviate this, a client can choose to limit the number of addresses it keeps track of and the frequency at which it considers them.¶

A client MUST NOT send non-probing frames to an additional address prior to validating that address. The generic measures described in Section 21.5.6 of [QUIC-TRANSPORT] also remain applicable for further mitigation.¶

7. IANA Considerations

This document defines a new transport parameter for indicating support for additional addresses. The draft defines provisional identifiers for experiments. IANA will allocate the final identifiers.¶

The following entry in Table 1 should be added to the "QUIC Transport Parameters" registry under the "QUIC" heading.¶

The last byte of the experimental transport parameter ID is used by implementations to indicate the version of this document they support. For instance, the value 0x925adda01 indicates the support of the -01 version of this document.¶

The following entry in Table 1 should be added to the "QUIC Frame Types" registry under the "QUIC" heading.¶

The last byte of the experimental frame type is used by implementations to indicate the version of this document they support. For instance, the value 0x925adda01 indicates the support of the -01 version of this document.¶

Acknowledgments

We thank Quentin De Coninck and François Michel for their feedback and comments on the first version of this document.¶

We thank Marcel Kempf, Moritz Buhl, Louis Navarre and François Michel for joining the interop during the IETF 118 Hackathon.¶

Authors' Addresses