CID Flow Indicator (CIDFI)

Internet-Draft	CIDFI	August 2023
Wing, et al.	Expires 18 February 2024	[Page]

Abstract

Conveying metadata about network conditions and metadata about individual packets can improve the user experience especially on wireless networks which suffer bandwidth and delay variability.¶

This document describes how clients and servers can cooperate with network elements so their QUIC and DTLS streams can be augmented with information about network conditions and packet importance.¶

Senders rely on ramping up their transmission rate until they encounter packet loss or see [ECN] indicating they should level off or slow down their transmission rate. This feedback takes time and contributes to poor user experience when the sender over- or under-shoots the actual available bandwidth, especially if the sender changes fidelity of the content (e.g., improves video quality which consumes more bandwidth which then gets dropped by the network).¶

Due to network constraints a network element will need to drop or even prioritize a packet ahead of other packets. The decision of which packet to drop or prioritize is improved if the network element knows the importance of the packet. Metadata carried in each packet can influence that decision to improve the user experience.¶

This document defines CIDFI (pronounced "sid fye") which is a system of several protocols that allow communicating about a [QUIC] connection or a DTLS connection [DTLS-CID] from the network to the server and the server to the network. The information exchanged allows the server to know about network conditions and allows the server to signal packet importance.¶

Figure 1 provides a sample network diagram of a CIDFI system showing two bandwidth-constrained networks (or links) depicted by "B" and CIDFI-aware devices immediately upstream of those links, and another bandwidth-constrained link between a smartphone handset and its Radio Access Newwork (RAN). This diagram shows the same protocol and same mechanism can operate with or without 5G, and can operate with different administrative domains such as Wi-Fi, an ISP edge router, and a 5G RAN.¶

Figure 1: Network Diagram

The CIDFI-aware client establishes a TLS connection with the CIDFI-aware network elements (Wi-Fi access point, edge router, and RAN router in the above diagram). Over this connection it receives network performance information and it sends mapping of (QUIC or DTLS) Destination CIDs to packet importance.¶

The design creates new state in the CIDFI-aware network elements for mapping from the QUIC Destination CID or DTLS Destination CID to the packet importance, bandwidth information for that connection towards the client, and for the TLS-encrypted communication with the client.¶

In Section 6.3.2 this document describes network-to-server signaling similar to the use-case described in Section 2 of [I-D.joras-sadcdn], with metadata relaying through the client.¶

In Section 6.3.1 this document describes server-to-network metadata signaling similar to the use-cases described in Section 3 of [I-D.joras-sadcdn]. The server-to-network metadata signaling can also benefit [I-D.ietf-avtcore-rtp-over-quic] and [DTLS-CID].¶

5. Client Operation on Network Attach or Topology Change

On initial network attach topology change (see Section 8), the client learns if the network supports CIDFI (Section 5.1) and authorizes those network elements (Section 5.2).¶

5.1. Client Learns Local Network Supports CIDFI

The client determines if the local network provides CIDFI service by issuing a query to the local DNS server for _cidfi-aware.cidfi.arpa. with the SVCB resource record type (64) [I-D.ietf-dnsop-svcb-https]. If this succeeds, processing skips to Section 5.2.¶

If discovery failed it indicates the local network does not support CIDFI and processing stops.¶

5.2. Client Authorizes CIDFI Network Elements

The SVCB response from the previous step in Section 5.1 will contain one or more CNE.¶

The client authorizes each of the CNE using its local policy. This policy is implementation specific. An example implementation might have the user authorize their ISP's CIDFI server (e.g., allow cidfi.example.net if the user's ISP is configured as example.net). Similarly, if none of the CNE are recognized the client might silently avoid using CIDFI on that network.¶

After authorizing that subset of CNE, the client makes a new HTTPS connection to each of those CNE and performs PKIX validation of their certificates. The client MAY have to authenticate itself to the CIDFI network element.¶

The client then obtains the CIDFI nonce and CIDFI HMAC secret from each network element used later in Section 6.2 to prove the client owns its UDP 4-tuple.¶

For discussion purposes, JSON is shown below to give a flavor of the data the client retrieves from the CIDFI network element. The authors anticipate using a more efficient encoding such as [CBOR].¶

  {"cidfi-path-authentication":[
    {"nonce":"ddqwohxGZysgy0BySNh7sNHV5IH9RbE7rqXmg9wb9Npo",
     "hmac-secret":"jLNsCvuU59mt3F4/ePD9jbZ932TfsLSOP2Nx3XnUqc8v"}]}

6. Client Operation on Each Connection to a QUIC Server

When a QUIC client or {DTLS-CID} client connects to a QUIC or {DTLS-CID} server, the client:¶

learns the server supports CIDFI and obtains its mapping of transmitted destinations CID to metadata.¶
proves ownership of its UDP 4-tuple to the on-path network elements.¶
performs initial metadata exchange with the CIDFI network element and server, and server and network element.¶
continually updates the server and the CIDFI network element whenever new information is received from the other party.¶

These steps are described in more detail below.¶

Note: the client is also a sender, and can also perform all these functions in its direction. This functionality will be expanded in later versions of this document. For example, a mobile device connected to Wi-Fi with 5G backhaul might be running an interactive audio/video application and want to indicate to its internal Wi-Fi driver and to the 5G modem its mapping from its transmitted QUIC Destination CID to per-packet metadata and the application can benefit from receiving network performance metrics.¶

6.1. Client Learns Server Supports CIDFI

On initial connection to a QUIC server, the client includes a new QUIC transport parameter CIDFI (Section 12.1) which is remembered for 0-RTT.¶

If the server does not indicate CIDFI support, CIDFI processing stops.¶

If the server indicates CIDFI support, then the server creates a new Server-Initiated, Bidirectional QUIC stream which is dedicated to CIDFI communication. This stream number is communicated in the CIDFI transport response during the QUIC handshake. TODO: specify how CIDFI stream number is communicated to client.¶

The QUIC client and QUIC server exchange CIDFI information over this CIDFI-dedicated stream as described in Section 6.3.¶

6.2. Client Proves Ownership of its UDP 4-Tuple

To ensure the client messages to the CNE pertain only to the client's own UDP 4-tuple, the client sends the CIDFI nonce protected by the HMAC secret it obtained from Section 5.2 over the QUIC UDP 4-tuple it is using with the QUIC server. The ability to transmit that packet on the same UDP 4-tuple as the QUIC connection indicates ownership of that IP address and UDP port. The nonce and HMAC are sent in a [STUN] indication (STUN class of 0b01) containing one or more CIDFI-NONCE attributes (Section 12.5). If there are multiple CNE the single STUN indication contains a CIDFI-NONCE attribute from each of them. This message is discarded by the QUIC server.¶

The figure below shows a summarized message flow obtaining the nonce and HMAC secret from the CNE then later sending the nonce and HMAC in the same UDP 4-tuple towards the QUIC server:¶

Because multiple QUIC clients will use the same incoming Destination CID on their own UDP 4-tuple, the STUN Indication message also allows the CIDFI network element to distinguish which UDP 4-tuple belongs to each CIDFI client.¶

To reduce CIDFI set-up time the client STUN Indication MAY be sent at the same time as the QUIC Initial packet, which is encouraged if the client remembers the server supports CIDFI (0-RTT).¶

To prevent replay attacks, the Nonce is usable only for authenticating one UDP 4-tuple. When the connection is migrated (Section 9 of [QUIC]) the CIDFI network element won't apply any CIDFI behavior to that newly-migrated connection. The client will have to restart CIDFI procedures at the beginning (Section 5).¶

6.2.1. STUN CIDFI-NONCE Attribute

The format of the STUN CIDFI-NONCE attribute is:¶

Figure 2: Format of CIDFI-NONCE Attribute

The nonce is 128 bits obtained from the CIDFI network element. The HMAC-output field is computed per [RFC5869] using the CIDFI network element-provided HMAC secret, and the CIDFI network element-provided Nonce concatenated with the fixed string "cidfi" (without quotes), shown below with "|" denoting concatenation.¶

  HMAC-output = HMAC-SHA256( hmac-secret, nonce | "cidfi" )

6.3. Initial Metadata Exchange

Using its HTTPS channel with each of the CIDFI network elements it previously authorized for CIDFI participation, the client signals the mapping of the server's transmitted short Destination Connection ID and its length to the CNE. As server support of the QUIC CIDFI transport parameter is remembered for 0-RTT, the client can immediately send the nonce.¶

The primary purpose of a second Connection ID is connection migration (Section 9 of [QUIC]). With CIDFI, additional Connection IDs are necessary to: * maintain CIDFI operation when topology remains the same. * use Destination Connection ID to indicate packet importance¶

To maintain CIDFI operation when topology remains the same, the CIDFI client signals the CNEs of that 'next' Destination CID. When QUIC detects a topology change, however, that Destination CID MUST NOT be used by the peer, otherwise it links the communication on the old topology to the new topology (Section 9.5 of [QUIC]). Thus, an additional Connection ID is purposefully not communicated from the CIDFI client to its CNEs, so that Connection ID can be immediately used by the peer during connection migration when the topology changes.¶

Note the source IP address and source UDP port number are not signaled by design. This is because NATs ([NAPT], [NAT]), multiple NATs on the path, IPv6/IPv4 translation, similar technologies, and QUIC connection migration all complicate accurate signaling of the source IP address and source UDP port number.¶

If the CNE receives the HTTPS map request but has not yet seen the STUN nonce message it rejects the mapping request with a 403 and provides a new nonce. The new nonce avoids the problem of an attacker seeing the previous nonce and using that nonce on its own UDP 4-tuple. The client then sends a new STUN message with that new nonce value and send a new HTTPS mapping request(s). This interaction is highlighted in the simplified message flow, below.¶

Figure 3: Client re-transmtting lost nonce

There are two types of metadata exchanged, described in the following sub-sections.¶

6.3.1. Server to Network Elements

The server communicates to network elements via the client which then communicates with the network element(s). While this adds communication delay, it allows the user at the client to authorize the metadata communication about its own incoming (and outgoing) traffic.¶

The communication from the client to the server are using a CIDFI-dedicated QUIC stream over the same QUIC connection as their primary communication.¶

To each of the network elements authorized by the client, the client sends the mappings of the server's transmitted Destination CIDs to packet metadata (see {#packet-metadata}).¶

6.3.2. Network Element to Server

The network element send network performance information to the server which is intended to influence the sender'ss traffic rate (such as improving or reducing fidelity of the audio or video). In the figure below the CNE informs the client of reduced bandwidth and the client informs the server using CIDFI.¶

The communication from the client to the server are using a CIDFI-dedicated QUIC stream over the same QUIC connection as their primary communication.¶

The CNE can update the client with whenever the metadata about the connection changes significantly, but MUST NOT update more frequently than once every second.¶

The metadata exchanged over this channel is described in Section 9.¶

6.4. Ongoing Metadata Exchange

For the duration of the primary QUIC connection between the QUIC client and QUIC server, the client relays network element metadata changes to the server, and server's transmitted QUIC Destination CID to the network elements.¶

9. Details of Metadata Exchanged

This section describes the metadata that can be exchanged from the CNE to the server (generally network performance information) and from the server to the CNE.¶

9.1. Server to CIDFI-aware Network Element

Because there is no direct communications from the server to the network element the communications are relayed through the client.¶

The communication from server to network element do not occur directly, but rather through the client.¶

Two types of mapping metadata are described below: metadata parameters and DSCP code points.¶

9.1.1. Mapping Metadata Parameters to DCIDs

Several of metadata parameters can be mapped to Destination CID:¶

Importance:: Low/Medium/High importance, relative to other CIDs within this same UDP 4-tuple.¶
Delay budget:: Time in milliseconds until this packet is worthless to the receiver. This is counted from when the packet arrives at the CNE to when it is transmitted; other delays may occur before or after that event occurs. The receiver knows its own jitter (playout) buffer length and the client and server can calculate the one-way delay using timestamps. With that information, the client can adjust the server's signaled delay budget with the client's own knowledge. TODO: provide enough details to create interoperable implementations.¶

Over the CIDFI-dedicated QUIC stream, the server sends mapping information to the client when then propagates that information to each of the CNEs.¶

For discussion purposes, JSON is shown below to give a flavor of the data exchanged. The authors anticipate a more efficient encoding such as [CBOR].¶

  {"metadata-parameters":[{"quicversion":1,
    "dcidlength":3,
       "map":[
       {"import":17,"burst":83,"delaybudget":71,"dcids":[551,381]},
       {"import":3,"burst":888,"delaybudget":180,"dcids":[89,983]},
       {"import":7,"burst":37,"delaybudget":55,"dcids":[33]}]}]}

9.1.2. Mapping DiffServ Code Point (DSCP) to DCIDs

A mapping from Destination CID to DiffServ code point [RFC2474] leverages existing DiffServ handling that may already exist in the CIDFI network element. If there are downstream network elements configured with the same DiffServ code point the CIDFI network element could mark the packet with that code point as well.¶

Signaling the DiffServ values for different QUIC Destination CID increases the edge network's confidence the sender's DiffServ intent is preserved into the edge network, even if the DSCP bits were modified en route to the edge network (e.g., [pathologies]).¶

Over the CIDFI-dedicated QUIC stream, the server sends mapping information to the client when then propagates that information to each of the CNEs.¶

For discussion purposes, JSON is shown below to give a flavor of the data exchanged. The authors anticipate using a more efficient encoding such as [CBOR].¶

  {"dscp":[{"quicversion":1,
    "dcidlength":3,
    "map":[
      {"dscp":10,"dcids":[123,456]},
      {"dscp":46,"dcids":[998,183]}]}]}

Figure 4: Example JSON for DSCP Mapping

9.2. CIDFI-aware Network Element to Server

The CIDFI-aware client informs the network element of the client's received Destination CIDs. As bandwidth availability to that client changes, the CNE updates the client with new metadata.¶

For discussion purposes, JSON is shown below to give a flavor of the data sent from the CNE to the client. The authors anticipate using a more efficient encoding such as [CBOR].¶

  {"dcid":123,
   "bandwidth":"1Mbps"}

The client then sends that information to the server in the CIDFI-dedicated QUIC stream associated with that same Connection ID.¶

10. Discussion Points

This section discusses known issues that would benefit from wider discussion.¶

10.1. Client versus Server Signaling CID-to-importance Mapping

Need to evaluate number of round trips (and other overhead) of client signaling CID-to-importance mapping or server signaling CID-to-importance mapping.¶

10.2. Overhead of QUIC DCID Packet Examination

If CID-to-importance metadata was signaled by the server as described in Section 6.3.1, the CNE have to examine the UDP payload of each packet for a matching Destination CID for the lifetime of the connection. This is somewhat assuaged by the STUN nonce transmitted which may well be an easier signal to identify.¶

10.3. Interaction with Wi-Fi Packet Aggregation

Per-packet metadata influences transmission of that packet but may well conflict with some Wi-Fi optimizations (e.g., [wifi-aggregation]) and similar 5G optimizations.¶

This impact needs further study.¶

10.4. Overhead of Mapping CID to packet metadata

Network Elements have to maintain a mapping between each UDP 4-tuple and QUIC CID and its DSCP code point. This also needs updating whenever sender changes its CID. This is awkward.¶

An alternative is a fixed mapping of QUIC CIDs to their meanings, as proposed in [I-D.zmlk-quic-te]. However, this will ossify the meaning of those QUIC CIDs. It also requires all networks to agree on the meaning of those QUIC CIDs.¶

10.5. Improve CIDFI Initialization time

Find approaches to further reduce network communications to start CIDFI.¶

10.6. Primary QUIC Channel CID Change {#primary-cid-change}:

Because the CIDFI network element, QUIC server, and QUIC client all cooperate to share the primary QUIC connection's Destination CID, when a new CIDFI network element is involved (e.g., due to client attaching to a different network), a new Destination CID SHOULD be used for the reasons discussed in Section 9.5 of [QUIC]}.¶

We need clear way to signal which DCIDs can be used for 'this' network attach and which DCIDs are for a migrated connection. Probably belongs in the QUIC transport parameter signaling?¶

11. Security Considerations

Because the sender's QUIC Destination Connection ID is mapped to packet importance, and the DCID remains the same for many packets, an attacker could determine which DCIDs are important by causing interference on the bandwidth-constrained link (by creating other legitimate traffic or creating radio interference) and observing which DCIDs are transmitted versus which DCIDs are dropped. This is a side- effect of using fixed identifier (DCIDs) rather than encrypting the packet importance. This was a design trade-off to reduce the CPU effort on the CNEs. A mitigation is using several DCIDs for every packet importance.¶

Communications are relayed through the client because only the client and server knows the identity of the server and can validate its certificate. The protocol in this specification does not disclose the server's identity to the CIDFI network element.¶

For an attacker to succeed with the nonce challenge against a victim's UDP 4-tuple the attacker has to send a STUN CIDFI-NONCE packet using the victim's source IP address and a valid HMAC. A valid HMAC can only be obtained by the attacker making its own connection to the CIDFI server and spoofing the source IP address and UDP port of the victim. Such spoofing of a victim's IP address is prevented by the network using network ingress filtering ([RFC2827], [RFC7513], [RFC6105], and/or [RFC6620]). In the event network ingress filtering is not configured or configured improperly, the CIDFI network element can detect an attack if the client implements CIDFI. The CIDFI network element receive two HTTPS connections describing the same DCID (one connection from the attacker, another from the victim). The CIDFI network element will issue unique Nonces and HMACs to both the attacker and victim, and the attacker and victim will both send the STUN indication on that same UDP 4-tuple. This should never normally occur and should generate an alarm on the CIDFI network element. In this situation, it is recommended both attack and victim be denied CIDFI access.¶

Table 1: New QUIC Transport Parameter
Value	Parameter Name	Reference
TBD1	CIDFI	This-Document

13. References

13.1. Normative References

[CBOR]: Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, <https://www.rfc-editor.org/rfc/rfc8949>.
[DTLS-CID]: Rescorla, E., Ed., Tschofenig, H., Ed., Fossati, T., and A. Kraus, "Connection Identifier for DTLS 1.2", RFC 9146, DOI 10.17487/RFC9146, March 2022, <https://www.rfc-editor.org/rfc/rfc9146>.
[I-D.ietf-dnsop-svcb-https]: Schwartz, B. M., Bishop, M., and E. Nygren, "Service binding and parameter specification via the DNS (DNS SVCB and HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf-dnsop-svcb-https-12, 11 March 2023, <https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-svcb-https-12>.
[QUIC]: Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, <https://www.rfc-editor.org/rfc/rfc9000>.
[RFC2119]: Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC2474]: Nichols, K., Blake, S., Baker, F., and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 10.17487/RFC2474, December 1998, <https://www.rfc-editor.org/rfc/rfc2474>.
[RFC5869]: Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/RFC5869, May 2010, <https://www.rfc-editor.org/rfc/rfc5869>.
[RFC8174]: Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[STUN]: Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, DOI 10.17487/RFC5389, October 2008, <https://www.rfc-editor.org/rfc/rfc5389>.

13.2. Informative References

[ECN]: Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 10.17487/RFC3168, September 2001, <https://www.rfc-editor.org/rfc/rfc3168>.
[I-D.ietf-avtcore-rtp-over-quic]: Ott, J., Engelbart, M., and S. Dawkins, "RTP over QUIC (RoQ)", Work in Progress, Internet-Draft, draft-ietf-avtcore-rtp-over-quic-05, 26 July 2023, <https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-rtp-over-quic-05>.
[I-D.joras-sadcdn]: Joras, M., "Securing Ancillary Data for Communicating with Devices in the Network", Work in Progress, Internet-Draft, draft-joras-sadcdn-01, 10 July 2023, <https://datatracker.ietf.org/doc/html/draft-joras-sadcdn-01>.
[I-D.zmlk-quic-te]: Zheng, Z., Ma, Y., Liu, Y., and M. Kühlewind, "QUIC-enabled Service Differentiation for Traffic Engineering", Work in Progress, Internet-Draft, draft-zmlk-quic-te-00, 5 May 2023, <https://datatracker.ietf.org/doc/html/draft-zmlk-quic-te-00>.
[IANA-QUIC]: "QUIC", 26 July 2023, <https://www.iana.org/assignments/quic/quic.xhtml>.
[IANA-STUN]: "STUN Attributes", 20 March 2023, <https://www.iana.org/assignments/stun-parameters/stun-parameters.xhtml>.
[IANA-SVCB]: "DNS Service Bindings (SVCB)", 13 June 2023, <https://www.iana.org/assignments/dns-svcb/dns-svcb.xhtml>.
[IANA-WKU]: "Well-known URIs", 20 June 2023, <https://www.iana.org/assignments/well-known-uris/well-known-uris.xhtml>.
[NAPT]: Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, DOI 10.17487/RFC3022, January 2001, <https://www.rfc-editor.org/rfc/rfc3022>.
[NAT]: Srisuresh, P. and M. Holdrege, "IP Network Address Translator (NAT) Terminology and Considerations", RFC 2663, DOI 10.17487/RFC2663, August 1999, <https://www.rfc-editor.org/rfc/rfc2663>.
[pathologies]: Custura, A., Secchi, R., and G. Fairhurst, "Exploring DSCP modification pathologies in the Internet", May 2018, <https://www.sciencedirect.com/science/article/pii/S0140366417312835>.
[RFC2827]: Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827, May 2000, <https://www.rfc-editor.org/rfc/rfc2827>.
[RFC6105]: Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, DOI 10.17487/RFC6105, February 2011, <https://www.rfc-editor.org/rfc/rfc6105>.
[RFC6620]: Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS SAVI: First-Come, First-Served Source Address Validation Improvement for Locally Assigned IPv6 Addresses", RFC 6620, DOI 10.17487/RFC6620, May 2012, <https://www.rfc-editor.org/rfc/rfc6620>.
[RFC7513]: Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address Validation Improvement (SAVI) Solution for DHCP", RFC 7513, DOI 10.17487/RFC7513, May 2015, <https://www.rfc-editor.org/rfc/rfc7513>.
[wifi-aggregation]: Høiland-Jørgensen, T., Kazior, M., Täht, D., Hurtig, P., and A. Brunstrom, "Ending the Anomaly: Achieving Low Latency and Airtime Fairness in WiFi", 22 May 2017, <https://www.usenix.org/conference/atc17/technical-sessions/presentation/hoilan-jorgesen>.