MASQUE D. Schinazi Internet-Draft Google LLC Intended status: Standards Track 6 July 2024 Expires: 7 January 2025 DNS Configuration for Proxying IP in HTTP draft-schinazi-masque-connect-ip-dns-01 Abstract Proxying IP in HTTP allows building a VPN through HTTP load balancers. However, at the time of writing, that mechanism doesn't offer a mechanism for communicating DNS configuration information inline. In contrast, most existing VPN protocols provide a mechanism to exchange DNS configuration information. This document describes an extension that exchanges this information using HTTP capsules. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://DavidSchinazi.github.io/draft-schinazi-masque-connect-ip-dns/ draft-schinazi-masque-connect-ip-dns.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft- schinazi-masque-connect-ip-dns/. Discussion of this document takes place on the Multiplexed Application Substrate over QUIC Encryption Working Group mailing list (mailto:masque@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/masque/. Subscribe at https://www.ietf.org/mailman/listinfo/masque/. Source for this draft and an issue tracker can be found at https://github.com/DavidSchinazi/draft-schinazi-masque-connect-ip- dns. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Schinazi Expires 7 January 2025 [Page 1] Internet-Draft CONNECT-IP DNS July 2024 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 7 January 2025. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3 2. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. DNS_REQUEST Capsule . . . . . . . . . . . . . . . . . . . 6 2.2. DNS_ASSIGN Capsule . . . . . . . . . . . . . . . . . . . 6 3. Handling . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Full-Tunnel Consumer VPN . . . . . . . . . . . . . . . . 7 4.2. Split-Tunnel Enterprise VPN . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . 10 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction Proxying IP in HTTP ([CONNECT-IP]) allows building a VPN through HTTP load balancers. However, at the time of writing, that mechanism doesn't offer a mechanism for communicating DNS configuration information inline. In contrast, most existing VPN protocols provide a mechanism to exchange DNS configuration information (e.g., [IKEv2]). This document describes an extension that exchanges this Schinazi Expires 7 January 2025 [Page 2] Internet-Draft CONNECT-IP DNS July 2024 information using HTTP capsules ([HTTP-DGRAM]). This document does not define any new ways to convey DNS queries or responses, only a mechanism to exchange DNS configuration information. 1.1. 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. This document uses terminology from [QUIC]. Where this document defines protocol types, the definition format uses the notation from Section 1.3 of [QUIC]. This specification uses the variable-length integer encoding from Section 16 of [QUIC]. Variable-length integer values do not need to be encoded in the minimum number of bytes necessary. 2. Mechanism Similar to how Proxying IP in HTTP exchanges IP address configuration information (Section 4.7 of [CONNECT-IP]), this mechanism leverages capsules to request DNS configuration information and to assign it. Similarly, this mechanism is bidirectional: either endpoint can request DNS configuration information by sending a DNS_REQUEST capsule, and either endpoint can send DNS configuration information in a DNS_ASSIGN capsule. These capsules follow the format defined below. Nameserver { Type (i), Length (i), Value (...), } Figure 1: Nameserver Format Each Nameserver structure contains the following fields: Type: An integer representing the protocol over which DNS queries and responses are sent. See below for possible values. Encoded as a variable-length integer. Length: The length of the following Value field, encoded as a variable-length integer. Value: DNS name server configuration value, depends on the Type. Schinazi Expires 7 January 2025 [Page 3] Internet-Draft CONNECT-IP DNS July 2024 This is commonly an IP address, but for other protocols it can also represent a URI template or a hostname. This document defines the following types: * DNS over port 53. Type = 0. DNS is sent unencrypted over UDP or TCP port 53, as per [DNS]. The Value is an IP address (either IPv4 or IPv6) encoded in network byte order. Length SHALL be either 32 or 128 bits. * DNS over TLS. Type = 1. DNS is sent over TLS, as per [DoT]. The Value is a hostname, optionally followed by a colon and a port. The encoding is the same as an authority without userinfo as defined in Section 3.2 of [URI]. It is encoded as ASCII, and not null-terminated. IPv4 and IPv6 addresses can be encoded using this format, though IPv6 addresses need to be enclosed in square brackets. * DNS over QUIC. Type = 2. DNS is sent over QUIC, as per [DoQ]. The Value is a hostname, encoded the same as for DNS over TLS. * DNS over HTTPS. Type = 3. DNS is sent over HTTPS, as per [DoH]. The Value is a URI Template. It is encoded as ASCII, and not null-terminated. * TODO: properly define an IANA registry with GREASE for future types. Domain { Domain Length (i), Domain Name (..), } Figure 2: Internal Domain Format Each Domain contains the following fields: Domain Length: Length of the following Domain field, encoded as a variable-length integer. Domain Name: Fully Qualified Domain Name in DNS presentation format and using an Internationalized Domain Names for Applications (IDNA) A-label ([IDNA]). Schinazi Expires 7 January 2025 [Page 4] Internet-Draft CONNECT-IP DNS July 2024 DNS Configuration { Request ID (i), Nameserver Count (i), Nameserver (..) ..., Internal Domain Count (i), Internal Domain (..) ..., Search Domain Count (i), Search Domain (..) ..., } Figure 3: Assigned Address Format Each DNS Configuration contains the following fields: Request ID: Request identifier, encoded as a variable-length integer. If this DNS Configuration is part of a request, then this contains a unique request identifier. If this DNS configuration is part of an assignment that is in response to a DNS configuration request then this field SHALL contain the value of the corresponding field in the request. If this DNS configuration is part of an unsolicited assignment, this field SHALL be zero. Nameserver Count: The number of Nameserver structures following this field. Encoded as a variable-length integer. Nameserver: A series of Nameserver structures representing DNS name servers. Internal Domain Count: The number of Domain structures following this field. Encoded as a variable-length integer. Internal Domain: A series of Domain structures representing internal DNS names. Search Domain Count: The number of Domain structures following this field. Encoded as a variable-length integer. Search Domain: A series of Domain structures representing search domains. Schinazi Expires 7 January 2025 [Page 5] Internet-Draft CONNECT-IP DNS July 2024 2.1. DNS_REQUEST Capsule The DNS_REQUEST capsule (see Section 6 for the value of the capsule type) allows an endpoint to request DNS configuration from its peer. The capsule allows the endpoint to optionally indicate a preference for which DNS configuration it would get assigned. The sender can indicate that it has no preference by not sending any name servers or domain names in its request DNS Configuration. DNS_REQUEST Capsule { Type (i) = DNS_REQUEST, Length (i), DNS Configuration (..), } Figure 4: DNS_REQUEST Capsule Format When sending a DNS_REQUEST capsule, the sender MUST generate and send a new non-zero request ID that was not previously used on this IP Proxying stream. Note that this request ID namespace is distinct from the one used by ADDRESS_ASSIGN capsules (see Section 4.7.1 of [CONNECT-IP]). An endpoint that receives a DNS_REQUEST capsule SHALL reply by sending a DNS_ASSIGN capsule with the corresponding request ID. That DNS_ASSIGN capsule MAY be empty, that indicates that its sender has no DNS configuration to share with its peer. 2.2. DNS_ASSIGN Capsule The DNS_ASSIGN capsule (see Section 6 for the value of the capsule type) allows an endpoint to send DNS configuration to its peer. DNS_ASSIGN Capsule { Type (i) = DNS_ASSIGN, Length (i), DNS Configuration (..), } Figure 5: DNS_ASSIGN Capsule Format When sending a DNS_ASSIGN capsule in response to a received DNS_REQUEST capsule, the Request ID field in the DNS_ASSIGN capsule SHALL be set to the value in the received DNS_REQUEST capsule. Otherwise the request ID MUST be set to zero. Schinazi Expires 7 January 2025 [Page 6] Internet-Draft CONNECT-IP DNS July 2024 3. Handling Note that internal domains include subdomains. In other words, if the DNS configuration contains a domain, that indicates that the corresponding domain and all of its subdomains can be resolved by the name servers exchanged in the same DNS configuration. Sending an empty string as an internal domain indicates the DNS root; i.e., that the corresponding name server can resolve all domain names. As with other IP Proxying capsules, the receiver can decide whether to use or ignore the configuration information. For example, in the consumer VPN scenario, clients will trust the server and apply received DNS configuration, whereas servers will ignore any DNS configuration sent by the client. If the IP proxy sends a DNS_ASSIGN capsule containing a DNS over HTTPS name server, then the client can validate whether the IP proxy is authoritative for the hostname in the URI template. If this validation succeeds, the client SHOULD send its DNS queries to that name server directly as independent HTTPS requests over the same HTTPS connection. 4. Examples 4.1. Full-Tunnel Consumer VPN A full-tunnel consumer VPN hosted at masque.example could configure the client to use DNS over HTTPS to the IP proxy itself by sending the following configuration. DNS Configuration = { Nameservers = [{ Type = 3, // DNS over HTTPS Value = "https://masque.example/dns-query{?dns}", }], Internal Domains = [""], Search Domains = [], } Figure 6: Full Tunnel Example 4.2. Split-Tunnel Enterprise VPN An enterprise switching their preexisting IPsec split-tunnel VPN could use the following configuration. Schinazi Expires 7 January 2025 [Page 7] Internet-Draft CONNECT-IP DNS July 2024 DNS Configuration = { Nameservers = [{ Type = 0, // DNS over 53 Value = 2001:db8::1, }, { Type = 0, // DNS over 53 Value = 192.0.2.33, }], Internal Domains = ["internal.corp.example"], Search Domains = [ "internal.corp.example", "corp.example", ], } Figure 7: Split Tunnel Example 5. Security Considerations Acting on received DNS_ASSIGN capsules can have significant impact on endpoint security. Endpoints MUST ignore DNS_ASSIGN capsules unless it has reason to trust its peer and is expecting DNS configuration from it. The requirement for an endpoint to always send DNS_ASSIGN capsules in response to DNS_REQUEST capsules could lead it to buffer unbounded amounts of memory if the underlying stream is blocked by flow or congestion control. Implementations MUST place an upper bound on that buffering and abort the stream if that limit is reached. 6. IANA Considerations This document, if approved, will request IANA add the following values to the "HTTP Capsule Types" registry maintained at . +============+==============+ | Value | Capsule Type | +============+==============+ | 0x1460B736 | DNS_ASSIGN | +------------+--------------+ | 0x1460B737 | DNS_REQUEST | +------------+--------------+ Table 1: New Capsules Note that, if this document is approved, the values defined above will be replaced by smaller ones before publication. Schinazi Expires 7 January 2025 [Page 8] Internet-Draft CONNECT-IP DNS July 2024 All of these new entries use the following values for these fields: Status: provisional (permanent if this document is approved) Reference: This document Change Controller: IETF Contact: masque@ietf.org Notes: None 7. References 7.1. Normative References [CONNECT-IP] Pauly, T., Ed., Schinazi, D., Chernyakhovsky, A., Kühlewind, M., and M. Westerlund, "Proxying IP in HTTP", RFC 9484, DOI 10.17487/RFC9484, October 2023, . [DNS] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . [DoH] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, . [DoQ] Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, May 2022, . [DoT] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., and P. Hoffman, "Specification for DNS over Transport Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 2016, . [HTTP-DGRAM] Schinazi, D. and L. Pardue, "HTTP Datagrams and the Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August 2022, . [IDNA] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, . Schinazi Expires 7 January 2025 [Page 9] Internet-Draft CONNECT-IP DNS July 2024 [QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . 7.2. Informative References [IKEv2] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, . [IKEv2-DNS] Pauly, T. and P. Wouters, "Split DNS Configuration for the Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 8598, DOI 10.17487/RFC8598, May 2019, . Acknowledgments The mechanism is this document was inspired by [IKEv2] and [IKEv2-DNS]. Author's Address David Schinazi Google LLC 1600 Amphitheatre Parkway Mountain View, CA 94043 United States of America Email: dschinazi.ietf@gmail.com Schinazi Expires 7 January 2025 [Page 10]