Internet-Draft | QUIC BDP Tokens | March 2024 |
Misell | Expires 5 September 2024 | [Page] |
This document describes a method to extend QUIC address validation tokens to include structured data that a client can parse and make use of. The initial application envisioned in this document is signalling congestion control parameters for use with Careful Resume.¶
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This document defines a method to extend QUIC address validation tokens to have structure, so that a client can parse them, and optionally make use of additional information within the token, depending on the nature of the extensions in use.¶
The initial application for this is envisioned to be allowing a QUIC server to send calculated Congestion Control parameters to a client for storage and later use on a future connection with Careful Resume [I-D.ietf-tsvwg-careful-resume].¶
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] when, and only when, they appear in all capitals, as shown here.¶
QUIC [RFC9000] defines an address validation token as an opaque blob that the client should not inspect. This document extends this by providing structure to the token, allowing arbitrary fields to be defined on the token by this and future documents.¶
A QUIC client unaware of this document will still be able to make use of extensible tokens without modification, although it will do nothing but pass the entire token back to the server unmodified.¶
The format of an extensible token is defined as follows:¶
BDP Token { Address Validation Length (i), Address Validation (..), Extension ID (i), Extension Data Length (i), Extension Data (..), ... }
The fields are as follows:¶
Extension ID, Extension Data Length, and Extension Data can be repeated as many times as needed to include desired extensions. Extension IDs MUST NOT appear multiple times in a token.¶
The server can send extended tokens to all clients without further negotiation. However a client needs some way to know that there is meaningful structure to a token its received from the server. To this end a new transport parameter is defined.¶
If the server is unable to decode the token received from the client, or vise versa, this MUST be treated as the connection error EX_TOKEN_ERROR (0x4143414213370002).¶
As an extensible token is designed to be presented to clients that may not be aware of what an extensible token is, all extensions defined for extensible tokens MUST be designed such that it can handle its data being echoed back to the server unmodified on a future connection.¶
This document defines the BDP_TOKEN extension, designed to Congestion Control information for use in Careful Resume [I-D.ietf-tsvwg-careful-resume].¶
The format of a token extension containing BDP information is defined as follows:¶
BDP Token { Private Data Length (i), Private Data (..), Capacity (i), RTT (i), Requested Capacity (i), }
The fields are as follows:¶
If the client becomes aware of a change in the available bandwidth of the path, it can use the Requested Capacity field to signal to the server a change it its available bandwidth. The server MUST not accept a value higher than that of the Capacity field, as this could cause an overload of the network path.¶
If the client sets the Requested Bandwidth field to 0 then it is signalling that the server should not attempt to prime its congestion controller from previous state and should instead treat this connection as an entirely new congestion control context.¶
If a server or client is unable to decode the token received as a valid BDP token then this MUST be treated as a connection error BDP_TOKEN_ERROR (0x4143414213370003). A token which is merely expired MUST NOT trigger a connection error, instead it should be silently discarded.¶
Per this document, one new entry has been added to the "QUIC Transport Parameters" registry defined in [RFC9000] section 22.3. This entry is defined below:¶
Value | Status | Specification | Parameter name |
---|---|---|---|
0x41434142 13370002 | Provisional | This document | ex_token |
Per this document, two new entries have been added to the "QUIC Transport Error Codes" registry defined in [RFC9000] section 22.5. This entry is defined below:¶
Value | Status | Code | Description | Specification |
---|---|---|---|---|
0x41434142 13370002 | Provisional | EX_TOKEN_ERROR | The extensible token received is invalid. | This document |
0x41434142 13370003 | Provisional | BDP_TOKEN_ERROR | The BDP token received is invalid. | This document |
Per this document, a new registry for "QUIC Extensible Token Extension IDs" is created under the "QUIC" heading defined in [RFC9000] section 22.¶
In addition to the fields listed in [RFC9000] section 22.1.1, permanent registrations in this registry MUST include the following field:¶
Value | Extension name | Specification |
---|---|---|
0x01 | BDP_TOKEN | Section 3 |
Each value of the form 31 * N + 26 for integer values of N (that is, 26, 57, 88, ...) are reserved for private use; these values are to be treated as opaque blobs meaningful only to the server operator.¶
Each value of the form 31 * N + 27 for integer values of N (that is, 27, 58, 89, ...) are reserved; these values MUST NOT be assigned by IANA and MUST NOT appear in the listing of assigned values.¶
The Congestion Control data MUST be protected against manipulation by malicious or mis-behaving clients. A client that can modify Congestion Control data could cause an overload of the network path.¶
This section is non-normative.¶
Consider the following private data structure:¶
Private Data { IP Address (16 bytes), Expiry Timestamp (8 bytes) }
This structure contains information that could be used to track a client (its previous IP address), and therefore MUST be protected from inspection by wire observers. Additionally the Capacity and RTT fields MUST be protected from modification by a client.¶
To this end this example uses the ChaCha20-Poly1305 [RFC8439] cipher with additional data. The ChaCha20-Poly1305 cipher encrypts data, and protects the encrypted data as well as additional unencrypted data against modification.¶
The additional data has the following structure:¶
Additional Data { Saved Capacity (8 bytes), Saved RTT (16 bytes) }
After encryption the 12 byte nonce is appended to the Private Data structure to allow the encryption to be reversed when the token is later used.¶