]> Apple, Inc.

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Internet-Draft This document defines an HTTP Proxy-Status Parameter that contains the IP address and CNAME chain received over DNS that was used to establish the connection to the next hop. Discussion Venues Source for this draft and an issue tracker can be found at .

Introduction The Proxy-Status HTTP response field allows proxies to convey information about how a proxied request was handled in HTTP responses sent to clients. It defines a set of parameters that provide information, such as the name of the next hop. The Proxy-Status field can be sent by both forward proxies and gateways (or "reverse proxies"). In the case of forward proxies, clients are requesting to establish TCP connections (using the CONNECT method ) and UDP connections (using UDP proxying ) to a target server. This target server can be specified using either a hostname or an IP address. When using a name instead of an IP address, the forward proxy locally performs DNS resolution to resolve the name to an IPv4 or IPv6 address using A or AAAA queries. Clients of forward proxies currently don't have visibility into the DNS resolution that is performed on the proxy. If available, this information could be used by clients to help make various decisions that are influenced by IP addresses and CNAME chains. For example, some clients classify specific names and IP addresses as being used for collecting data to track users (which can be used to influence policies for HTTP cookies), or can recognize them as endpoints that ought to be blocked for features like ad blocking or malware blocking. Without this information, proxying using a forward proxy means that clients lose the ability to fully recognize servers based on IP addresses and CNAME chains. It is possible for clients to perform DNS resolution before using a forward proxy, and proxy using IP addresses, but this has several drawbacks: performing DNS without using the proxy can lead a privacy regression, or a performance regression if the addresses selected are not optimal for connectivity from the proxy; proxying by IP address prevents the proxy from selecting the best address (); and if clients try to resolve via the proxy using DNS over HTTPS (), they can incur a performance hit by requiring an extra round trip before being able to establish a connection. This document allows clients to receive the IP address and CNAME chain received from DNS, without needing to perform DNS on the client, by including the information in a Proxy-Status parameter ().

Requirements 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.

dns-used Parameter The dns-used parameter's value is a String that contains one or more IP addresses and/or DNS names in a comma-separated list. The first item in the list SHOULD be the IP address that was resolved using DNS and was used to open connectivity to the next hop. The remaining items in the list SHOULD include all names received in CNAME records or AliasMode SVCB or HTTPS records during the course of resolving the address. Since DNS names can include comma (,) characters in them, any commas that appear in a DNS names MUST be represented using a percent-encoded %2C value instead. For example: indicates that proxy.example.net, which used target.example.com as the next hop for this request, used the IP address "2001:db8::1" to connect to the target, and encountered the CNAME "tracker.example.com." in DNS resolution chain. Note that while this example includes both the next-hop and dns-used parameters, dns-used can be included without including next-hop. The dns-used parameter only applies when DNS was used to resolve the next hop's name, and does not apply in all situations. Clients can use the information in this parameter to determine how to use the connection established through the proxy, but need to gracefully handle situations in which this parameter is not present.

Security Considerations The dns-used parameter does not include any DNSSEC information or imply that DNSSEC was used. The information included in the parameter can only be trusted to be valid insofar as the client trusts its proxy to provide accurate information. This information is intended to be used as a hint, and SHOULD NOT be used for making security decisions about the identity resource access through the proxy.

IANA Considerations This document registers the "dns-used" parameter in the "HTTP Proxy-Status Parameters" registry <>.

Name:

dns-used

Description:

A string containing the IP address used to establish the proxied connection and the chain of CNAMEs that led to this IP address.

Reference:

This document

References Normative References This document defines the Proxy-Status HTTP response field to convey the details of an intermediary's response handling, including generated errors. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This document describes how to proxy UDP in HTTP, similar to how the HTTP CONNECT method allows proxying TCP in HTTP. More specifically, this document defines a protocol that allows an HTTP client to create a tunnel for UDP communications through an HTTP server that acts as a proxy. 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. This memo describes errors often found in both the operation of Domain Name System (DNS) servers, and in the data that these DNS servers contain. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Google Akamai Technologies Akamai Technologies This document specifies the "SVCB" and "HTTPS" DNS resource record (RR) types to facilitate the lookup of information needed to make connections to network services, such as for HTTP origins. SVCB records allow a service to be provided from multiple alternative endpoints, each with associated parameters (such as transport protocol configuration and keys for encrypting the TLS ClientHello). They also enable aliasing of apex domains, which is not possible with CNAME. The HTTPS RR is a variation of SVCB for use with HTTP [HTTP]. By providing more information to the client before it attempts to establish a connection, these records offer potential benefits to both performance and privacy. TO BE REMOVED: This document is being collaborated on in Github at: https://github.com/MikeBishop/dns-alt-svc (https://github.com/MikeBishop/dns-alt-svc). The most recent working version of the document, open issues, etc. should all be available there. The authors (gratefully) accept pull requests. Informative References Many communication protocols operating over the modern Internet use hostnames. These often resolve to multiple IP addresses, each of which may have different performance and connectivity characteristics. Since specific addresses or address families (IPv4 or IPv6) may be blocked, broken, or sub-optimal on a network, clients that attempt multiple connections in parallel have a chance of establishing a connection more quickly. This document specifies requirements for algorithms that reduce this user-visible delay and provides an example algorithm, referred to as "Happy Eyeballs". This document obsoletes the original algorithm description in RFC 6555. This document defines a protocol for sending DNS queries and getting DNS responses over HTTPS. Each DNS query-response pair is mapped into an HTTP exchange.