draft-ietf-httpbis-proxy-status-08.txt   draft-ietf-httpbis-proxy-status-latest.txt 
HTTP Working Group M. Nottingham HTTP Working Group M. Nottingham
Internet-Draft Fastly Internet-Draft Fastly
Intended status: Standards Track P. Sikora Intended status: Standards Track P. Sikora
Expires: April 16, 2022 Google Expires: December 23, 2022 Google
October 13, 2021 June 21, 2022
The Proxy-Status HTTP Response Header Field The Proxy-Status HTTP Response Header Field
draft-ietf-httpbis-proxy-status-08 draft-ietf-httpbis-proxy-status-latest
Abstract Abstract
This document defines the Proxy-Status HTTP field to convey the This document defines the Proxy-Status HTTP response field to convey
details of intermediary response handling, including generated the details of an intermediary's response handling, including
errors. generated errors.
Note to Readers About This Document
_RFC EDITOR: please remove this section before publication_ This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group Status information for this document may be found at
mailing list (ietf-http-wg@w3.org), which is archived at <https://datatracker.ietf.org/doc/draft-ietf-httpbis-proxy-status/>.
https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].
Working Group information can be found at https://httpwg.org/ [2]; Discussion of this document takes place on the HTTP Working Group
source code and issues list for this draft can be found at mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at
https://github.com/httpwg/http-extensions/labels/proxy-status [3]. <https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group
information can be found at <https://httpwg.org/>.
Source for this draft and an issue tracker can be found at
<https://github.com/httpwg/http-extensions/labels/proxy-status>.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 16, 2022. This Internet-Draft will expire on December 23, 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
1. Introduction 1. Introduction
HTTP intermediaries (see Section 3.7 of [HTTP]) -- including both HTTP intermediaries (see Section 3.7 of [HTTP]) -- including both
forward proxies and gateways (also known as "reverse proxies") -- forward proxies and gateways (also known as "reverse proxies") --
have become an increasingly significant part of HTTP deployments. In have become an increasingly significant part of HTTP deployments. In
particular, reverse proxies and Content Delivery Networks (CDNs) form particular, reverse proxies and content delivery networks (CDNs) form
part of the critical infrastructure of many Web sites. part of the critical infrastructure of many websites.
Typically, HTTP intermediaries forward requests towards the origin Typically, HTTP intermediaries forward requests towards the origin
server (inbound) and then forward their responses back to clients server (inbound) and then forward their responses back to clients
(outbound). However, if an error occurs before a response is (outbound). However, if an error occurs before a response is
obtained from an inbound server, the response is often generated by obtained from an inbound server, the response is often generated by
the intermediary itself. the intermediary itself.
HTTP accommodates these types of errors with a few status codes; for HTTP accommodates these types of errors with a few status codes --
example, 502 Bad Gateway and 504 Gateway Timeout. However, for example, 502 (Bad Gateway) and 504 (Gateway Timeout). However,
experience has shown that more information is necessary to aid experience has shown that more information is necessary to aid
debugging and communicate what's happened to the client. debugging and communicate what's happened to the client.
Additionally, intermediaries sometimes want to convey additional Additionally, intermediaries sometimes want to convey additional
information about their handling of a response, even if they did not information about their handling of a response, even if they did not
generate it. generate it.
To enable these uses, Section 2 defines a new HTTP response field to To enable these uses, Section 2 defines a new HTTP response field to
allow intermediaries to convey details of their handling of a allow intermediaries to convey details of their handling of a
response. Section 2.1 enumerates the information that can be added response. Section 2.1 enumerates the information that can be added
to the field by intermediaries, which can be extended as per to the field by intermediaries, which can be extended per
Section 2.2. Section 2.3 defines a set of error types for use when a Section 2.2. Section 2.3 defines a set of error types for use when a
proxy encounters an issue when obtaining a response for the request; proxy encounters an issue when obtaining a response for the request;
these can likewise be extended as per Section 2.4. these can likewise be extended per Section 2.4.
1.1. Notational Conventions 1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This specification uses Structured Fields [STRUCTURED-FIELDS] to This document uses the following terminology from Section 3 of
specify syntax and parsing, and ABNF [RFC5234] as a shorthand for [STRUCTURED-FIELDS] to specify syntax and parsing: List, String,
that syntax. The terms sf-list, sf-item, sf-string, sf-token, sf- Token, Integer, and Byte Sequence.
integer and key refer to the structured types defined therein.
Note that in this specification, "proxy" is used to indicate both Note that in this specification, "proxy" is used to indicate both
forward and reverse proxies, otherwise known as gateways. "Next hop" forward and reverse proxies, otherwise known as gateways. "Next hop"
indicates the connection in the direction leading to the origin indicates the connection in the direction leading to the origin
server for the request. server for the request.
2. The Proxy-Status HTTP Field 2. The Proxy-Status HTTP Field
The Proxy-Status HTTP response field allows an intermediary to convey The Proxy-Status HTTP response field allows an intermediary to convey
additional information about its handling of a response and its additional information about its handling of a response and its
associated request. The syntax of this header field conforms to associated request.
[STRUCTURED-FIELDS].
It is a List ([STRUCTURED-FIELDS], Section 3.1):
Proxy-Status = sf-list
Each member of the list represents an intermediary that has handled Its value is a List (see Section 3.1 of [STRUCTURED-FIELDS]). Each
the response. The first member of the list represents the member of the List represents an intermediary that has handled the
intermediary closest to the origin server, and the last member of the response. The first member represents the intermediary closest to
list represents the intermediary closest to the user agent. the origin server, and the last member represents the intermediary
closest to the user agent.
For example: For example:
Proxy-Status: revproxy1.example.net, ExampleCDN Proxy-Status: revproxy1.example.net, ExampleCDN
indicates that this response was handled first by indicates that this response was handled first by
revproxy1.example.net (a reverse proxy adjacent to the origin server) revproxy1.example.net (a reverse proxy adjacent to the origin server)
and then ExampleCDN. and then ExampleCDN.
Intermediaries determine when it is appropriate to add the Proxy- Intermediaries determine when it is appropriate to add the Proxy-
Status field to a response. Some might decide to append to it to all Status field to a response. Some might decide to append it to all
responses, whereas others might only do so when specifically responses, whereas others might only do so when specifically
configured to, or when the request contains a header field that configured to or when the request contains a header field that
activates a debugging mode. activates a debugging mode.
Each member of the list identifies the intermediary that inserted the Each member of the List identifies the intermediary that inserted the
value, and MUST have a type of either sf-string or sf-token. value and MUST have a type of either String or Token . Depending on
Depending on the deployment, this might be a service name (but not a the deployment, this might be a service name (but not a software or
software or hardware product name; e.g., "Example CDN"is appropriate, hardware product name; e.g., "ExampleCDN" is appropriate, but
but "ExampleProxy" is not, because it doesn't identify the "ExampleProxy" is not because it doesn't identify the deployment), a
deployment), a hostname ("proxy-3.example.com"), an IP address, or a hostname ("proxy-3.example.com"), an IP address, or a generated
generated string. string.
Parameters on each member (as per Section 3.1.2 of Parameters of each member (per Section 3.1.2 of [STRUCTURED-FIELDS])
[STRUCTURED-FIELDS]) convey additional information about that convey additional information about that intermediary's handling of
intermediary's handling of the response and its associated request; the response and its associated request; see Section 2.1. While all
see Section 2.1. While all of these parameters are OPTIONAL, of these parameters are OPTIONAL, intermediaries are encouraged to
intermediaries are encouraged to provide as much information as provide as much information as possible (but see Section 4 for
possible (but see Section 4 for security considerations in doing so). security considerations in doing so).
When adding a value to the Proxy-Status field, intermediaries SHOULD When adding a value to the Proxy-Status field, intermediaries SHOULD
preserve the existing members of the field to allow debugging of the preserve the existing members of the field to allow debugging of the
entire chain of intermediaries handling the request, unless entire chain of intermediaries handling the request unless explicitly
explicitly configured to remove them (e.g., to prevent internal configured to remove them (e.g., to prevent internal network details
network details from leaking; see Section 4). from leaking; see Section 4).
Origin servers MUST NOT generate the Proxy-Status field. Origin servers MUST NOT generate the Proxy-Status field.
Proxy-Status MAY be sent as a HTTP trailer field. For example, if an Proxy-Status MAY be sent as an HTTP trailer field. For example, if
intermediary is streaming a response and the inbound connection an intermediary is streaming a response and the inbound connection
suddenly terminates, Proxy-Status can only be appended to the trailer suddenly terminates, Proxy-Status can only be appended to the trailer
section of the outbound message, since the header section has already section of the outbound message since the header section has already
been sent. However, because it might be silently discarded along the been sent. However, because it might be silently discarded along the
path to the user agent (as is the case for all trailer fields; see path to the user agent (as is the case for all trailer fields; see
Section 6.5 of [HTTP]), Proxy-Status SHOULD NOT be sent as a trailer Section 6.5 of [HTTP]), Proxy-Status SHOULD NOT be sent as a trailer
field unless it is not possible to send it in the header section. field unless it is not possible to send it in the header section.
To allow recipients to reconstruct the relative ordering of Proxy- To allow recipients to reconstruct the relative ordering of Proxy-
Status members conveyed in trailer fields with those conveyed in Status members conveyed in trailer fields with those conveyed in
header fields, an intermediary MUST NOT send Proxy-Status as a header fields, an intermediary MUST NOT send Proxy-Status as a
trailer field unless it has also generated a Proxy-Status header trailer field unless it has also generated a Proxy-Status header
field with the same member (although potentially different field with the same member (although potentially different
skipping to change at page 5, line 4 skipping to change at page 4, line 46
parameters) in that message. parameters) in that message.
For example, a proxy identified as 'ThisProxy' that receives a For example, a proxy identified as 'ThisProxy' that receives a
response bearing a header field: response bearing a header field:
Proxy-Status: SomeOtherProxy Proxy-Status: SomeOtherProxy
would add its own entry to the header field: would add its own entry to the header field:
Proxy-Status: SomeOtherProxy, ThisProxy Proxy-Status: SomeOtherProxy, ThisProxy
thus allowing it to append a trailer field: thus allowing it to append a trailer field:
Proxy-Status: ThisProxy; error=read_timeout Proxy-Status: ThisProxy; error=read_timeout
which would thereby allow a downstream recipient to understand that
... which would thereby allow a downstream recipient to understand processing by 'SomeOtherProxy' occurred before 'ThisProxy'.
that processing by 'SomeOtherProxy' occurred before 'ThisProxy'.
A client MAY promote the Proxy-Status trailer field into a header A client MAY promote the Proxy-Status trailer field into a header
field by following these steps: field by following these steps:
1. For each member trailer_member of the Proxy-Status trailer field 1. For each member trailer_member of the Proxy-Status trailer field
value: value:
1. Let header_member be the first (left-most) value of the 1. Let header_member be the first (leftmost) value of the Proxy-
Proxy-Status header field value, comparing the sf-token or Status header field value, comparing the String or Token
sf-string character-by-character and without consideration of character by character without consideration of parameters.
parameters.
2. If no matching header_member is found, continue processing 2. If no matching header_member is found, continue processing
the next trailer_member. the next trailer_member.
3. Replace header_member with trailer_member in its entirety, 3. Replace header_member with trailer_member in its entirety,
including any parameters. including any parameters.
2. Remove the Proxy-Status trailer field, if empty. 2. Remove the Proxy-Status trailer field if empty.
2.1. Proxy-Status Parameters 2.1. Proxy-Status Parameters
This section lists parameters that can be used on the members of the This section lists parameters that can be used on the members of the
Proxy-Status field. Unrecognised parameters MUST be ignored. Proxy-Status field. Unrecognised parameters MUST be ignored.
2.1.1. error 2.1.1. error
The "error" parameter's value is an sf-token that is a Proxy Error The "error" parameter's value is a Token that is a proxy error type.
Type. When present, it indicates that the intermediary encountered When present, it indicates that the intermediary encountered an issue
an issue when obtaining this response. when obtaining this response.
The presence of some Proxy Error Types indicates that the response The presence of some proxy error types indicates that the response
was generated by the intermediary itself, rather than being forwarded was generated by the intermediary itself, rather than being forwarded
from the origin server. This is the case when, for example, the from the origin server. This is the case when, for example, the
origin server can't be contacted, so the proxy has to create its own origin server can't be contacted, so the proxy has to create its own
response. response.
Other Proxy Error Types can be added to (potentially partial) Other proxy error types can be added to (potentially partial)
responses that were generated by the origin server or some other responses that were generated by the origin server or some other
inbound server. For example, if the forward connection abruptly inbound server. For example, if the forward connection abruptly
closes, an intermediary might add Proxy-Status with an appropriate closes, an intermediary might add Proxy-Status with an appropriate
error as a trailer field. error as a trailer field.
Proxy Error Types that are registered with a 'Response only generated Proxy error types that are registered with a 'Response only generated
by intermediaries' value of 'true' indicate that they can only occur by intermediaries' value of 'true' indicate that they can only occur
on responses generated by the intermediary. If the value is 'false', in responses generated by the intermediary. If the value is 'false',
the response might be generated by the intermediary or an inbound the response might be generated by the intermediary or an inbound
server. server.
Section 2.3 lists the Proxy Error Types defined in this document; new Section 2.3 lists the proxy error types defined in this document; new
ones can be defined using the procedure outlined in Section 2.4. ones can be defined using the procedure outlined in Section 2.4.
For example: For example:
HTTP/1.1 504 Gateway Timeout HTTP/1.1 504 Gateway Timeout
Proxy-Status: ExampleCDN; error=connection_timeout Proxy-Status: ExampleCDN; error=connection_timeout
indicates that this 504 response was generated by ExampleCDN, due to indicates that this 504 response was generated by ExampleCDN due to a
a connection timeout when going forward. connection timeout when going forward.
Or: Or:
HTTP/1.1 429 Too Many Requests HTTP/1.1 429 Too Many Requests
Proxy-Status: r34.example.net; error=http_request_error, ExampleCDN Proxy-Status: r34.example.net; error=http_request_error, ExampleCDN
indicates that this 429 Too Many Requests response was generated by indicates that this 429 (Too Many Requests) response was generated by
r34.example.net, not the CDN or the origin. r34.example.net, not the CDN or the origin.
When sending the error parameter, the most specific Proxy Error Type When sending the error parameter, the most specific proxy error type
SHOULD be sent, provided that it accurately represents the error SHOULD be sent, provided that it accurately represents the error
condition. If an appropriate Proxy Error Type is not defined, there condition. If an appropriate proxy error type is not defined, there
are a number of generic error types (e.g., proxy_internal_error, are a number of generic error types (e.g., proxy_internal_error,
http_protocol_error) that can be used. If they are not suitable, http_protocol_error) that can be used. If they are not suitable,
consider registering a new Proxy Error Type (see Section 2.4). consider registering a new proxy error type (see Section 2.4).
Each Proxy Error Type has a Recommended HTTP Status Code. When Each proxy error type has a recommended HTTP status code. When
generating a HTTP response containing "error", its HTTP status code generating an HTTP response containing the "error", its HTTP status
SHOULD be set to the Recommended HTTP Status Code. However, there code SHOULD be set to the recommended HTTP status code. However,
may be circumstances (e.g., for backwards compatibility with previous there may be circumstances (e.g., for backwards compatibility with
behaviours, a status code has already been sent) when another status previous behaviours, a status code has already been sent) when
code might be used. another status code might be used.
Proxy Error Types can also define any number of extra parameters for Proxy error types can also define any number of extra parameters for
use with that type. Their use, like all parameters, is optional. As use with that type. Their use, like all parameters, is optional. As
a result, if an extra parameter is used with a Proxy Error Type for a result, if an extra parameter is used with a proxy error type for
which it is not defined, it will be ignored. which it is not defined, it will be ignored.
2.1.2. next-hop 2.1.2. next-hop
The "next-hop" parameter's value is an sf-string or sf-token that The "next-hop" parameter's value is a String or Token that identifies
identifies the intermediary or origin server selected (and used, if the intermediary or origin server selected (and used, if contacted)
contacted) to obtain this response. It might be a hostname, IP to obtain this response. It might be a hostname, IP address, or
address, or alias. alias.
For example: For example:
Proxy-Status: cdn.example.org; next-hop=backend.example.org:8001 Proxy-Status: cdn.example.org; next-hop=backend.example.org:8001
indicates that cdn.example.org used backend.example.org:8001 as the indicates that cdn.example.org used backend.example.org:8001 as the
next hop for this request. next hop for this request.
2.1.3. next-protocol 2.1.3. next-protocol
The "next-protocol" parameter's value indicates the ALPN protocol The "next-protocol" parameter's value indicates the Application-Layer
identifier [RFC7301] of the protocol used by the intermediary to Protocol Negotiation (ALPN) protocol identifier [RFC7301] of the
connect to the next hop when obtaining this response. protocol used by the intermediary to connect to the next hop when
obtaining this response.
The value MUST be either an sf-token or sf-binary, representing a TLS The value MUST be either a Token or Byte Sequence representing a TLS
Application-Layer Protocol Negotiation (ALPN) Protocol ID (see ALPN Protocol ID (see <https://www.iana.org/assignments/tls-
https://www.iana.org/assignments/tls-extensiontype-values/tls- extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-
extensiontype-values.xhtml#alpn-protocol-ids [4]). If the protocol ids>). If the protocol identifier is able to be expressed as a Token
identifier is able to be expressed as an sf-token using ASCII using ASCII encoding, that form MUST be used.
encoding, that form MUST be used.
For example: For example:
Proxy-Status: "proxy.example.org"; next-protocol=h2 Proxy-Status: "proxy.example.org"; next-protocol=h2
Note that the APLN identifier is being used here to identify the Note that the ALPN identifier is being used here to identify the
protocol in use; it may or may not have been actually used in the protocol in use; it may or may not have been actually used in the
protocol negotiation. protocol negotiation.
2.1.4. received-status 2.1.4. received-status
The "received-status" parameter's value indicates the HTTP status The "received-status" parameter's value indicates the HTTP status
code that the intermediary received from the next hop server when code that the intermediary received from the next-hop server when
obtaining this response. obtaining this response.
The value MUST be an sf-integer. The value MUST be an Integer.
For example: For example:
Proxy-Status: ExampleCDN; received-status=200 Proxy-Status: ExampleCDN; received-status=200
2.1.5. details 2.1.5. details
The "details" parameter's value is an sf-string containing additional The "details" parameter's value is a String containing additional
information not captured anywhere else. This can include information not captured anywhere else. This can include
implementation-specific or deployment-specific information. implementation-specific or deployment-specific information.
For example: For example:
Proxy-Status: proxy.example.net; error="http_protocol_error"; Proxy-Status: proxy.example.net; error="http_protocol_error";
details="Malformed response header: space before colon" details="Malformed response header: space before colon"
2.2. Defining New Proxy-Status Parameters 2.2. Defining New Proxy-Status Parameters
New Proxy-Status Parameters can be defined by registering them in the New Proxy-Status parameters can be defined by registering them in the
HTTP Proxy-Status Parameters registry. "HTTP Proxy-Status Parameters" registry.
Registration requests are reviewed and approved by Expert Review, as Registration requests are reviewed and approved by Expert Review, per
per [RFC8126], Section 4.5. A specification document is appreciated, [RFC8126], Section 4.5. A specification document is appreciated but
but not required. not required.
The Expert(s) should consider the following factors when evaluating The expert(s) should consider the following factors when evaluating
requests: requests:
o Community feedback o Community feedback
o If the value is sufficiently well-defined o If the value is sufficiently well defined
o Generic parameters are preferred over vendor-specific, o Generic parameters are preferred over vendor-specific,
application-specific or deployment-specific values. If a generic application-specific, or deployment-specific values. If a generic
value cannot be agreed upon in the community, the parameter's name value cannot be agreed upon in the community, the parameter's name
should be correspondingly specific (e.g., with a prefix that should be correspondingly specific (e.g., with a prefix that
identifies the vendor, application or deployment). identifies the vendor, application, or deployment).
o Parameter names should not conflict with registered extra o Parameter names should not conflict with registered extra
parameters in the Proxy Error Type Registry. parameters in the "HTTP Proxy Error Types" registry.
Registration requests should use the following template: Registration requests should use the following template:
o Name: [a name for the Proxy-Status Parameter that matches key] Name: [a name for the Proxy-Status parameter that matches key]
o Description: [a description of the parameter semantics and value] Description: [a description of the parameter semantics and value]
o Reference: [to a specification defining this parameter; optional] Reference: [to a specification defining this parameter; optional]
See the registry at https://iana.org/assignments/http-proxy-status See the registry at <https://www.iana.org/assignments/http-proxy-
[5] for details on where to send registration requests. status> for details on where to send registration requests.
2.3. Proxy Error Types 2.3. Proxy Error Types
This section lists the Proxy Error Types defined by this document. This section lists the proxy error types defined by this document.
See Section 2.4 for information about defining new Proxy Error Types. See Section 2.4 for information about defining new proxy error types.
Note that implementations might not produce all Proxy Error Types. Note that implementations might not produce all proxy error types.
The set of types below is designed to map to existing states in The set of types below is designed to map to existing states in
implementations, and so may not be applicable to some. implementations and therefore may not be applicable to some.
2.3.1. DNS Timeout 2.3.1. DNS Timeout
o Name: dns_timeout Name: dns_timeout
o Description: The intermediary encountered a timeout when trying to Description: The intermediary encountered a timeout when trying to
find an IP address for the next hop hostname. find an IP address for the next-hop hostname.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.2. DNS Error 2.3.2. DNS Error
o Name: dns_error Name: dns_error
o Description: The intermediary encountered a DNS error when trying Description: The intermediary encountered a DNS error when trying to
to find an IP address for the next hop hostname. find an IP address for the next-hop hostname.
o Extra Parameters: Extra Parameters:
* rcode: A sf-string conveying the DNS RCODE that indicates the rcode: A String conveying the DNS RCODE that indicates the error
error type. See [RFC8499], Section 3. type. See [RFC8499], Section 3.
* info-code: A sf-integer conveying the Extended DNS Error Code info-code: An Integer conveying the Extended DNS Error Code INFO-
info-code. See [RFC8914]. CODE. See [RFC8914].
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.3. Destination Not Found 2.3.3. Destination Not Found
o Name: destination_not_found Name: destination_not_found
o Description: The intermediary cannot determine the appropriate Description: The intermediary cannot determine the appropriate next
next hop to use for this request; for example, it may not be hop to use for this request; for example, it may not be
configured. Note that this error is specific to gateways, which configured. Note that this error is specific to gateways, which
typically require specific configuration to identify the "backend" typically require specific configuration to identify the "backend"
server; forward proxies use in-band information to identify the server; forward proxies use in-band information to identify the
origin server. origin server.
o Extra Parameters: None. Extra Parameters: None
Recommended HTTP Status Code: 500
o Recommended HTTP status code: 500
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.4. Destination Unavailable 2.3.4. Destination Unavailable
o Name: destination_unavailable Name: destination_unavailable
o Description: The intermediary considers the next hop to be Description: The intermediary considers the next hop to be
unavailable; e.g., recent attempts to communicate with it may have unavailable; e.g., recent attempts to communicate with it may have
failed, or a health check may indicate that it is down. failed, or a health check may indicate that it is down.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 503 Recommended HTTP Status Code: 503
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.5. Destination IP Prohibited 2.3.5. Destination IP Prohibited
o Name: destination_ip_prohibited Name: destination_ip_prohibited
o Description: The intermediary is configured to prohibit Description: The intermediary is configured to prohibit connections
connections to the next hop IP address. to the next-hop IP address.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document]
2.3.6. Destination IP Unroutable Reference: RFC 9209
o Name: destination_ip_unroutable 2.3.6. Destination IP Unroutable
o Description: The intermediary cannot find a route to the next hop Name: destination_ip_unroutable
IP address.
o Extra Parameters: None. Description: The intermediary cannot find a route to the next-hop IP
address.
o Recommended HTTP status code: 502 Extra Parameters: None
o Response only generated by intermediaries: true Recommended HTTP Status Code: 502
Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.7. Connection Refused 2.3.7. Connection Refused
o Name: connection_refused Name: connection_refused
o Description: The intermediary's connection to the next hop was Description: The intermediary's connection to the next hop was
refused. refused.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.8. Connection Terminated 2.3.8. Connection Terminated
o Name: connection_terminated Name: connection_terminated
o Description: The intermediary's connection to the next hop was Description: The intermediary's connection to the next hop was
closed before complete response was received. closed before a complete response was received.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.9. Connection Timeout 2.3.9. Connection Timeout
o Name: connection_timeout Name: connection_timeout
o Description: The intermediary's attempt to open a connection to Description: The intermediary's attempt to open a connection to the
the next hop timed out. next hop timed out.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.10. Connection Read Timeout 2.3.10. Connection Read Timeout
o Name: connection_read_timeout Name: connection_read_timeout
o Description: The intermediary was expecting data on a connection Description: The intermediary was expecting data on a connection
(e.g., part of a response), but did not receive any new data in a (e.g., part of a response) but did not receive any new data in a
configured time limit. configured time limit.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.11. Connection Write Timeout 2.3.11. Connection Write Timeout
o Name: connection_write_timeout Name: connection_write_timeout
o Description: The intermediary was attempting to write data to a Description: The intermediary was attempting to write data to a
connection, but was not able to (e.g., because its buffers were connection but was not able to (e.g., because its buffers were
full). full).
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.12. Connection Limit Reached 2.3.12. Connection Limit Reached
o Name: connection_limit_reached Name: connection_limit_reached
o Description: The intermediary is configured to limit the number of Description: The intermediary is configured to limit the number of
connections it has to the next hop, and that limit has been connections it has to the next hop, and that limit has been
passed. exceeded.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 503 Recommended HTTP Status Code: 503
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.13. TLS Protocol Error 2.3.13. TLS Protocol Error
o Name: tls_protocol_error Name: tls_protocol_error
o Description: The intermediary encountered a TLS error when Description: The intermediary encountered a TLS error when
communicating with the next hop, either during handshake or communicating with the next hop, either during the handshake or
afterwards. afterwards.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
o Notes: Not appropriate when a TLS alert is received; see Notes: Not appropriate when a TLS alert is received; see
tls_alert_received tls_alert_received.
2.3.14. TLS Certificate Error 2.3.14. TLS Certificate Error
o Name: tls_certificate_error Name: tls_certificate_error
o Description: The intermediary encountered an error when verifying Description: The intermediary encountered an error when verifying
the certificate presented by the next hop. the certificate presented by the next hop.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document]
Reference: RFC 9209
2.3.15. TLS Alert Received 2.3.15. TLS Alert Received
o Name: tls_alert_received Name: tls_alert_received
o Description: The intermediary received a TLS alert from the next Description: The intermediary received a TLS alert from the next
hop. hop.
o Extra Parameters: Extra Parameters:
* alert-id: an sf-integer containing the applicable value from alert-id: An Integer containing the applicable value from the
the TLS Alerts registry. See {!RFC8446}}. "TLS Alerts" registry. See [RFC8446].
* alert-message: an sf-token or sf-string containing the alert-message: A Token or String containing the applicable
applicable description string from the TLS Alerts registry. description string from the "TLS Alerts" registry. See
See [RFC8446]. [RFC8446].
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.16. HTTP Request Error 2.3.16. HTTP Request Error
o Name: http_request_error Name: http_request_error
o Description: The intermediary is generating a client (4xx) Description: The intermediary is generating a client (4xx) response
response on the origin's behalf. Applicable status codes include on the origin's behalf. Applicable status codes include (but are
(but are not limited to) 400, 403, 405, 406, 408, 411, 413, 414, not limited to) 400, 403, 405, 406, 408, 411, 413, 414, 415, 416,
415, 416, 417, 429. 417, and 429.
o Extra Parameters: Extra Parameters:
* status-code: an sf-integer containing the generated status status-code: An Integer containing the generated status code.
code.
* status-phrase: an sf-string containing the generated status status-phrase: A String containing the generated status phrase.
phrase.
o Recommended HTTP status code: The applicable 4xx status code Recommended HTTP Status Code: The applicable 4xx status code
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
o Notes: This type helps distinguish between responses generated by
Notes: This type helps distinguish between responses generated by
intermediaries from those generated by the origin. intermediaries from those generated by the origin.
2.3.17. HTTP Request Denied 2.3.17. HTTP Request Denied
o Name: http_request_denied Name: http_request_denied
o Description: The intermediary rejected the HTTP request based on Description: The intermediary rejected the HTTP request based on its
its configuration and/or policy settings. The request wasn't configuration and/or policy settings. The request wasn't
forwarded to the next hop. forwarded to the next hop.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 403
o Response only generated by intermediaries: true Recommended HTTP Status Code: 403
o Reference: [this document] Response Only Generated by Intermediaries: true
Reference: RFC 9209
2.3.18. HTTP Incomplete Response 2.3.18. HTTP Incomplete Response
o Name: http_response_incomplete Name: http_response_incomplete
o Description: The intermediary received an incomplete response to Description: The intermediary received an incomplete response to the
the request from the next hop. request from the next hop.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.19. HTTP Response Header Section Too Large 2.3.19. HTTP Response Header Section Too Large
o Name: http_response_header_section_size Name: http_response_header_section_size
o Description: The intermediary received a response to the request Description: The intermediary received a response to the request
whose header section was considered too large. whose header section was considered too large.
o Extra Parameters: Extra Parameters:
* header-section-size: an sf-integer indicating how large the header-section-size: An Integer indicating how large the received
headers received were. Note that they might not be complete; headers were. Note that they might not be complete; i.e., the
i.e., the intermediary may have discarded or refused additional intermediary may have discarded or refused additional data.
data.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.20. HTTP Response Header Field Line Too Large 2.3.20. HTTP Response Header Field Line Too Large
o Name: http_response_header_size Name: http_response_header_size
o Description: The intermediary received a response to the request Description: The intermediary received a response to the request
containing an individual header field line that was considered too containing an individual header field line that was considered too
large. large.
o Extra Parameters: Extra Parameters:
* header-name: an sf-string indicating the name of the header header-name: A String indicating the name of the header field
field that triggered the error. that triggered the error.
* header-size: an sf-integer indicating the size of the header header-size: An Integer indicating the size of the header field
field that triggered the error. that triggered the error.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.21. HTTP Response Body Too Large 2.3.21. HTTP Response Body Too Large
o Name: http_response_body_size Name: http_response_body_size
o Description: The intermediary received a response to the request Description: The intermediary received a response to the request
whose body was considered too large. whose body was considered too large.
o Extra Parameters: Extra Parameters:
* body-size: an sf-integer indicating how large the body received body-size: An Integer indicating how large the received body was.
was. Note that it may not have been complete; i.e., the Note that it may not have been complete; i.e., the intermediary
intermediary may have discarded or refused additional data. may have discarded or refused additional data.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.22. HTTP Response Trailer Section Too Large 2.3.22. HTTP Response Trailer Section Too Large
o Name: http_response_trailer_section_size Name: http_response_trailer_section_size
o Description: The intermediary received a response to the request Description: The intermediary received a response to the request
whose trailer section was considered too large. whose trailer section was considered too large.
o Extra Parameters: Extra Parameters:
* trailer-section-size: an sf-integer indicating how large the trailer-section-size: An Integer indicating how large the
trailers received were. Note that they might not be complete; received trailers were. Note that they might not be complete;
i.e., the intermediary may have discarded or refused additional i.e., the intermediary may have discarded or refused additional
data. data.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.23. HTTP Response Trailer Field Line Too Large 2.3.23. HTTP Response Trailer Field Line Too Large
o Name: http_response_trailer_size Name: http_response_trailer_size
o Description: The intermediary received a response to the request Description: The intermediary received a response to the request
containing an individual trailer field line that was considered containing an individual trailer field line that was considered
too large. too large.
o Extra Parameters: Extra Parameters:
* trailer-name: an sf-string indicating the name of the trailer trailer-name: A String indicating the name of the trailer field
field that triggered the error. that triggered the error.
* trailer-size: an sf-integer indicating the size of the trailer trailer-size: An Integer indicating the size of the trailer field
field that triggered the error. that triggered the error.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.24. HTTP Response Transfer-Coding Error 2.3.24. HTTP Response Transfer-Coding Error
o Name: http_response_transfer_coding Name: http_response_transfer_coding
o Description: The intermediary encountered an error decoding the Description: The intermediary encountered an error decoding the
transfer-coding of the response. transfer coding of the response.
o Extra Parameters: Extra Parameters:
* coding: an sf-token containing the specific coding (from the coding: A Token containing the specific coding (from the "HTTP
HTTP Transfer Coding Registry) that caused the error. Transfer Coding Registry") that caused the error.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.25. HTTP Response Content-Coding Error 2.3.25. HTTP Response Content-Coding Error
o Name: http_response_content_coding Name: http_response_content_coding
o Description: The intermediary encountered an error decoding the Description: The intermediary encountered an error decoding the
content-coding of the response. content coding of the response.
o Extra Parameters: Extra Parameters:
* coding: an sf-token containing the specific coding (from the coding: A Token containing the specific coding (from the "HTTP
HTTP Content Coding Registry) that caused the error. Content Coding Registry") that caused the error.
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.26. HTTP Response Timeout 2.3.26. HTTP Response Timeout
o Name: http_response_timeout Name: http_response_timeout
o Description: The intermediary reached a configured time limit Description: The intermediary reached a configured time limit
waiting for the complete response. waiting for the complete response.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.27. HTTP Upgrade Failed 2.3.27. HTTP Upgrade Failed
o Name: http_upgrade_failed Name: http_upgrade_failed
o Description: The HTTP Upgrade between the intermediary and the Description: The process of negotiating an upgrade of the HTTP
next hop failed. version between the intermediary and the next hop failed.
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.28. HTTP Protocol Error 2.3.28. HTTP Protocol Error
o Name: http_protocol_error Name: http_protocol_error
o Description: The intermediary encountered a HTTP protocol error Description: The intermediary encountered an HTTP protocol error
when communicating with the next hop. This error should only be when communicating with the next hop. This error should only be
used when a more specific one is not defined. used when a more specific one is not defined.
o Extra Parameters: None. Extra Parameters: None
Recommended HTTP Status Code: 502
o Recommended HTTP status code: 502
o Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
o Reference: [this document] Reference: RFC 9209
2.3.29. Proxy Internal Response 2.3.29. Proxy Internal Response
o Name: proxy_internal_response Name: proxy_internal_response
o Description: The intermediary generated the response locally, Description: The intermediary generated the response itself without
without attempting to connect to the next hop (e.g. in response to attempting to connect to the next hop.
a request to a debug endpoint terminated at the intermediary).
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: The most appropriate status code for Recommended HTTP Status Code: The most appropriate status code for
the response the response
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.30. Proxy Internal Error 2.3.30. Proxy Internal Error
o Name: proxy_internal_error Name: proxy_internal_error
o Description: The intermediary encountered an internal error Description: The intermediary encountered an internal error
unrelated to the origin. unrelated to the origin.
o Extra Parameters: None Extra Parameters: None
o Recommended HTTP status code: 500 Recommended HTTP Status Code: 500
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.31. Proxy Configuration Error 2.3.31. Proxy Configuration Error
o Name: proxy_configuration_error Name: proxy_configuration_error
o Description: The intermediary encountered an error regarding its Description: The intermediary encountered an error regarding its
configuration. configuration.
o Extra Parameters: None Extra Parameters: None
o Recommended HTTP status code: 500
o Response only generated by intermediaries: true Recommended HTTP Status Code: 500
Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.3.32. Proxy Loop Detected 2.3.32. Proxy Loop Detected
o Name: proxy_loop_detected Name: proxy_loop_detected
o Description: The intermediary tried to forward the request to Description: The intermediary tried to forward the request to
itself, or a loop has been detected using different means (e.g. itself, or a loop has been detected using different means (e.g.,
[RFC8586]). [RFC8586]).
o Extra Parameters: None. Extra Parameters: None
o Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
o Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
o Reference: [this document] Reference: RFC 9209
2.4. Defining New Proxy Error Types 2.4. Defining New Proxy Error Types
New Proxy Error Types can be defined by registering them in the HTTP New proxy error types can be defined by registering them in the "HTTP
Proxy Error Types registry. Proxy Error Types" registry.
Registration requests are reviewed and approved by Expert Review, as Registration requests are reviewed and approved by Expert Review, per
per [RFC8126], Section 4.5. A specification document is appreciated, [RFC8126], Section 4.5. A specification document is appreciated but
but not required. not required.
The Expert(s) should consider the following factors when evaluating The expert(s) should consider the following factors when evaluating
requests: requests:
o Community feedback o Community feedback
o If the value is sufficiently well-defined o If the value is sufficiently well-defined
o Generic types are preferred over vendor-specific, application- o Generic types are preferred over vendor-specific, application-
specific or deployment-specific values. If a generic value cannot specific, or deployment-specific values. If a generic value
be agreed upon in the community, the types's name should be cannot be agreed upon in the community, the type's name should be
correspondingly specific (e.g., with a prefix that identifies the correspondingly specific (e.g., with a prefix that identifies the
vendor, application or deployment). vendor, application, or deployment).
o Extra Parameters should not conflict with registered Proxy-Status o Extra parameters should not conflict with registered Proxy-Status
parameters. parameters.
Registration requests should use the following template: Registration requests should use the following template:
o Name: [a name for the Proxy Error Type that matches sf-token] Name: [a name for the proxy error type that is of type Token ]
Description: [a description of the conditions that generate the
o Description: [a description of the conditions that generate the proxy error type]
Proxy Error Type]
o Extra Parameters: [zero or more optional parameters, along with Extra Parameters: [zero or more optional parameters, along with
their allowable type(s)] their allowable Structured Type(s)]
o Recommended HTTP status code: [the appropriate HTTP status code Recommended HTTP Status Code: [the appropriate HTTP status code for
for this entry] this entry]
o Response only generated by intermediaries: ['true' or 'false'] Response Only Generated by Intermediaries: ['true' or 'false']
o Reference: [to a specification defining this error type; optional] Reference: [to a specification defining this error type; optional]
o Notes: [optional] Notes: [optional]
If the Proxy Error Type might occur in responses that are not If the proxy error type might occur in responses that are not
generated by the intermediary -- for example, when an error is generated by the intermediary -- for example, when an error is
detected as the response is streamed from a forward connection, detected as the response is streamed from a forward connection,
causing a Proxy-Status trailer field to be appended -- the 'Response causing a Proxy-Status trailer field to be appended -- the 'Response
only generated by intermediaries' should be 'false'. If the Proxy only generated by intermediaries' should be 'false'. If the proxy
Error Type only occurs in responses that are generated by the error type only occurs in responses that are generated by the
intermediary, it should be 'true'. intermediary, it should be 'true'.
See the registry at https://iana.org/assignments/http-proxy-status See the registry at <https://www.iana.org/assignments/http-proxy-
[6] for details on where to send registration requests. status> for details on where to send registration requests.
3. IANA Considerations 3. IANA Considerations
Upon publication, please create the HTTP Proxy-Status Parameters IANA has created the "HTTP Proxy-Status Parameters" registry and the
registry and the HTTP Proxy Error Types registry at "HTTP Proxy Error Types" registry at
https://iana.org/assignments/http-proxy-status [7] and populate them <https://www.iana.org/assignments/http-proxy-status> and has
with the types defined in Section 2.1 and Section 2.3 respectively; populated them with the types defined in Sections 2.1 and 2.3
see Section 2.2 and Section 2.4 for its associated procedures. respectively; see Sections 2.2 and 2.4 for their associated
procedures.
Additionally, please register the following entry in the Hypertext
Transfer Protocol (HTTP) Field Name Registry:
o Field name: Proxy-Status Additionally, the following entry has been added to the "Hypertext
Transfer Protocol (HTTP) Field Name Registry":
o Status: permanent Field name: Proxy-Status
o Specification document(s): [this document] Status: permanent
o Comments: Specification document(s): RFC 9209
4. Security Considerations 4. Security Considerations
One of the primary security concerns when using Proxy-Status is One of the primary security concerns when using Proxy-Status is
leaking information that might aid an attacker. For example, leaking information that might aid an attacker. For example,
information about the intermediary's configuration and back-end information about the intermediary's configuration and backend
topology can be exposed, allowing attackers to directly target back- topology can be exposed, allowing attackers to directly target
end services that are not prepared for high traffic volume or backend services that are not prepared for high traffic volume or
malformed inputs. Some information might only be suitable to reveal malformed inputs. Some information might only be suitable to reveal
to authorized parties. to authorized parties.
As a result, care needs to be taken when deciding to generate a As a result, care needs to be taken when deciding to generate a
Proxy-Status field and what information to include in it. Note that Proxy-Status field and what information to include in it. Note that
intermediaries are not required to generate a Proxy-Status field in intermediaries are not required to generate a Proxy-Status field in
any response, and can conditionally generate them based upon request any response and can conditionally generate them based upon request
attributes (e.g., authentication tokens, IP address). attributes (e.g., authentication tokens, IP address).
Likewise, generation of all parameters is optional, as is generation Likewise, generation of all parameters is optional, as is the
of the field itself. Also, the field's content is not verified; an generation of the field itself. Also, the field's content is not
intermediary can claim certain actions (e.g., sending a request over verified; an intermediary can claim certain actions (e.g., sending a
an encrypted channel) but fail to actually do that. request over an encrypted channel) but fail to actually do that.
5. References 5. References
5.1. Normative References 5.1. Normative References
[HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP [HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", draft-ietf-httpbis-semantics-19 (work in Semantics", draft-ietf-httpbis-semantics-19 (work in
progress), September 2021. progress), September 2021.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 24, line 7 skipping to change at page 23, line 25
DOI 10.17487/RFC8914, October 2020, DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/info/rfc8914>. <https://www.rfc-editor.org/info/rfc8914>.
[STRUCTURED-FIELDS] [STRUCTURED-FIELDS]
Nottingham, M. and P-H. Kamp, "Structured Field Values for Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/info/rfc8941>. <https://www.rfc-editor.org/info/rfc8941>.
5.2. Informative References 5.2. Informative References
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop [RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop
Detection in Content Delivery Networks (CDNs)", RFC 8586, Detection in Content Delivery Networks (CDNs)", RFC 8586,
DOI 10.17487/RFC8586, April 2019, DOI 10.17487/RFC8586, April 2019,
<https://www.rfc-editor.org/info/rfc8586>. <https://www.rfc-editor.org/info/rfc8586>.
5.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] https://httpwg.org/
[3] https://github.com/httpwg/http-extensions/labels/proxy-status
[4] https://www.iana.org/assignments/tls-extensiontype-values/tls-
extensiontype-values.xhtml#alpn-protocol-ids
[5] https://iana.org/assignments/http-proxy-status
[6] https://iana.org/assignments/http-proxy-status
[7] https://iana.org/assignments/http-proxy-status
Authors' Addresses Authors' Addresses
Mark Nottingham Mark Nottingham
Fastly Fastly
Prahran Prahran
Australia Australia
Email: mnot@mnot.net Email: mnot@mnot.net
URI: https://www.mnot.net/ URI: https://www.mnot.net/
 End of changes. 292 change blocks. 
449 lines changed or deleted 416 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/