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Private Octopus Inc.

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Transport QUIC QUIC STUN Address Discovery Unless they have out-of-band knowledge, QUIC endpoints have no information about their network situation. They neither know their external IP address and port, nor do they know if they are directly connected to the internet or if they are behind a NAT. This QUIC extension allows nodes to determine their reflexive IP address and port for any QUIC path. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the QUIC Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction STUN () allows nodes to discover their reflexive transport address by asking a remote server to report the observed source address. While the QUIC () packet header was designed to allow demultiplexing from STUN packets, moving address discovery into the QUIC layer has a number of advantages:

1. STUN encryption relies on shared keys, which have to be provisioned. Absent such provisioning, STUN traffic is unencrypted QUIC provides encryption by default, using TLS 1.3.
2. When unencrypted, STUN traffic can be observed and modified by on-path observers. By moving address discovery into QUIC's encrypted envelope it becomes invisible to observers.
3. STUN packet format is designed to facilitate multiplexing STUN and other protocols on the same IP address and port number (see ). That property can be used by observers to detect use of STUN and infer use of peer-to-peer communications. In contrast, address discovery using QUIC does not "stick out".
4. When located behind a load balancer, QUIC packets may be routed based on the QUIC connection ID. Depending on the architecture, not using STUN might simplify the routing logic.
5. If QUIC traffic doesn't need to be demultiplexed from STUN traffic, implementations can enable QUIC bit greasing ().

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 when, and only when, they appear in all capitals, as shown here.

Negotiating Extension Use Endpoints advertise their support of the extension by sending the address_discovery (0x9f81a176) transport parameter () with a variable-length integer value. The value determines the behavior with respect to address discovery:

• 0: The node is willing to provide address observations to its peer, but is not interested in receiving address observations itself.
• 1: The node is interested in receiving address observations, but it is not willing to provide address observations.
• 2: The node is interested in receiving address observations, and it is willing to provide address observations.

Implementations that understand this transport parameter MUST treat the receipt of any other value than these as a connection error of type TRANSPORT_PARAMETER_ERROR. When using 0-RTT, both endpoints MUST remember the value of this transport parameter. This allows sending the frame defined by this extension in 0-RTT packets. If 0-RTT data is accepted by the server, the server MUST NOT disable this extension or change the value on the resumed connection.

Frames This extension defines the OBSERVED_ADDRESS frame.

OBSERVED_ADDRESS The OBSERVED_ADDRESS frame contains the following fields:

Sequence Number:

A variable-length integer specifying the sequence number assigned for this OBSERVED_ADDRESS frame. The sequence number MUST be monotonically increasing for OBSERVED_ADDRESS frames in the same connection. Frames may be received out of order. A peer SHOULD ignore an incoming OBSERVED_ADDRESS frame if it previously received another OBSERVED_ADDRESS frame for the same path with a Sequence Number equal to or higher than the sequence number of the incoming frame.

IPv4:

The IPv4 address. Only present if the least significant bit of the frame type is 0.

IPv6:

The IPv6 address. Only present if the least significant bit of the frame type is 1.

Port:

The port number, in network byte order.

This frame MUST only appear in the application data packet number space. It is a "probing frame" as defined in . OBSERVED_ADDRESS frames are ack-eliciting, and SHOULD be retransmitted if lost. Retransmissions MUST happen on the same path as the original frame was sent on. An endpoint MUST NOT send an OBSERVED_ADDRESS frame to a node that did not request the receipt of address observations as described in . A node that did not request the receipt of address observations MUST close the connection with a PROTOCOL_VIOLATION error if it receives an OBSERVED_ADDRESS frame.

Address Discovery An endpoint that negotiated (see ) this extension and offered to provide address observations to the peer MUST send an OBSERVED_ADDRESS frame on every new path. This also applies to the path used for the QUIC handshake. The OBSERVED_ADDRESS frame SHOULD be sent as early as possible. For paths used after completion of the handshake, endpoints SHOULD bundle the OBSERVED_ADDRESS frame with probing packets. This is possible, since the frame is defined to be a probing frame (). Additionally, the sender SHOULD send an OBSERVED_ADDRESS frame when it detects a change in the remote address on an existing path. This could be indicative of a NAT rebinding. However, the sender MAY limit the rate at which OBSERVED_ADDRESS frames are produced, to mitigate the spoofed packets attack described in .

Security Considerations

On the Requester Side In general, nodes cannot be trusted to report the correct address in OBSERVED_ADDRESS frames. If possible, endpoints might decide to only request address observations when connecting to trusted peers, or if that is not possible, define some validation logic (e.g. by asking multiple untrusted peers and observing if the responses are consistent). This logic is out of scope for this document.

On the Responder Side Depending on the routing setup, a node might not be able to observe the peer's reflexive transport address, and attempts to do so might reveal details about the internal network. In these cases, the node SHOULD NOT offer to provide address observations. On-path attackers could capture packets sent from the requester to the responder, and resend them from a spoofed source address. If done repeatedly, these spoofed packets could trigger the sending of a large number of OBSERVED_ADDRESS frames. The recommendation to only include OBSERVED_ADDRESS frames in packets sent on the same path over which the address was observed ensures that the peer will not receive the OBSERVED_ADDRESS frames if the addresses are not valid, but this does not reduce the number of packets sent over the network. The attack also has the effect of causing spurious detection of NAT rebinding, and is a variant of the replacement of addresses of packets mentioned in . QUIC implementations are expected to have sufficient protection against spurious NAT rebinding to limit the incidental traffic caused by such attacks. The same protection logic SHOULD be used to prevent sending of a large number of spurious OBSERVED_ADDRESS frames.

IANA Considerations TODO: fill out registration request for the transport parameter and frame types

References Normative References Session Traversal Utilities for NAT (STUN) is a protocol that serves as a tool for other protocols in dealing with NAT traversal. It can be used by an endpoint to determine the IP address and port allocated to it by a NAT. It can also be used to check connectivity between two endpoints and as a keep-alive protocol to maintain NAT bindings. STUN works with many existing NATs and does not require any special behavior from them. STUN is not a NAT traversal solution by itself. Rather, it is a tool to be used in the context of a NAT traversal solution. This document obsoletes RFC 5389. This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References This document defines how Datagram Transport Layer Security (DTLS), Real-time Transport Protocol (RTP), RTP Control Protocol (RTCP), Session Traversal Utilities for NAT (STUN), Traversal Using Relays around NAT (TURN), and ZRTP packets are multiplexed on a single receiving socket. It overrides the guidance from RFC 5764 ("SRTP Extension for DTLS"), which suffered from four issues described and fixed in this document. This document updates RFC 5764. This document describes a method for negotiating the ability to send an arbitrary value for the second-most significant bit in QUIC packets. Apple Inc. Apple Inc. Apple Inc. This document defines an extension to the QUIC transport protocol that adds support for requesting and receiving the public network address of an endpoint from its peer.

Acknowledgments Unbeknownst to the authors, the idea of moving address discovery into QUIC was conceived of before in .