rfc9209v1.txt   rfc9209.txt 
Internet Engineering Task Force (IETF) M. Nottingham Internet Engineering Task Force (IETF) M. Nottingham
Request for Comments: 9209 Fastly Request for Comments: 9209 Fastly
Category: Standards Track P. Sikora Category: Standards Track P. Sikora
ISSN: 2070-1721 Google ISSN: 2070-1721 Google
February 2022 March 2022
The Proxy-Status HTTP Response Header Field The Proxy-Status HTTP Response Header Field
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.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841. Internet Standards is available in Section 2 of RFC 7841.
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these can likewise be extended 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 "OPTIONAL" in this document are to be interpreted as described in
BCP 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 uses ABNF [RFC5234] as 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 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., "ExampleCDN" 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 (per Section 3.1.2 of [STRUCTURED-FIELDS]) Parameters of each member (per Section 3.1.2 of [STRUCTURED-FIELDS])
convey additional information about that intermediary's handling of convey additional information about that intermediary's handling of
the response and its associated request; see Section 2.1. While all the response and its associated request; see Section 2.1. While all
of these parameters are OPTIONAL, intermediaries are encouraged to of these parameters are OPTIONAL, intermediaries are encouraged to
provide as much information as possible (but see Section 4 for provide as much information as 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 explicitly entire chain of intermediaries handling the request unless explicitly
configured to remove them (e.g., to prevent internal network details configured to remove them (e.g., to prevent internal network details
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which would thereby allow a downstream recipient to understand that which would thereby allow a downstream recipient to understand that
processing by 'SomeOtherProxy' occurred before 'ThisProxy'. 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 (leftmost) value of the Proxy- 1. Let header_member be the first (leftmost) value of the Proxy-
Status header field value, comparing the sf-token or sf- Status header field value, comparing the String or Token
string character by character 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
in 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 a indicates that this 504 response was generated by ExampleCDN due to 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 an HTTP response containing the error, its HTTP status generating an HTTP response containing the error, its HTTP status
code SHOULD be set to the recommended HTTP status code. However, code SHOULD be set to the recommended HTTP status code. However,
there may be circumstances (e.g., for backwards compatibility with there may be circumstances (e.g., for backwards compatibility with
previous behaviours, a status code has already been sent) when previous behaviours, a status code has already been sent) when
another status 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 Application-Layer The next-protocol parameter's value indicates the Application-Layer
Protocol Negotiation (ALPN) protocol identifier [RFC7301] of the Protocol Negotiation (ALPN) protocol identifier [RFC7301] of the
protocol used by the intermediary to connect to the next hop when protocol used by the intermediary to connect to the next hop when
obtaining this response. 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
ALPN Protocol ID (see <https://www.iana.org/assignments/tls- ALPN Protocol ID (see <https://www.iana.org/assignments/tls-
extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol- extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-
ids>). If the protocol identifier is able to be expressed as an sf- ids>). If the protocol identifier is able to be expressed as a Token
token using ASCII encoding, that form MUST be used. using ASCII 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 ALPN 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 code The received-status parameter's value indicates the HTTP status code
that the intermediary received from the next-hop server when 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, per Registration requests are reviewed and approved by Expert Review, per
[RFC8126], Section 4.5. A specification document is appreciated but [RFC8126], Section 4.5. A specification document is appreciated 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:
* Community feedback * Community feedback
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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).
* Parameter names should not conflict with registered extra * Parameter names should not conflict with registered extra
parameters in the "HTTP Proxy Error Types" registry. parameters in the "HTTP Proxy Error Types" registry.
Registration requests should use the following template: Registration requests should use the following template:
Name: [a name for the Proxy-Status Parameter that matches key] Name: [a name for the Proxy-Status parameter that matches key]
Description: [a description of the parameter semantics and value] Description: [a description of the parameter semantics and value]
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-
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 therefore 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
Name: dns_timeout Name: dns_timeout
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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.2. DNS Error 2.3.2. DNS Error
Name: dns_error Name: dns_error
Description: The intermediary encountered a DNS error when trying to Description: The intermediary encountered a DNS error when trying to
find an IP address for the next-hop hostname. find an IP address for the next-hop hostname.
Extra Parameters: Extra Parameters:
rcode: An 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: An 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].
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.3. Destination Not Found 2.3.3. Destination Not Found
Name: destination_not_found Name: destination_not_found
Description: The intermediary cannot determine the appropriate next Description: The intermediary cannot determine the appropriate 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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 500 Recommended HTTP Status Code: 500
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.4. Destination Unavailable 2.3.4. Destination Unavailable
Name: destination_unavailable Name: destination_unavailable
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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 503 Recommended HTTP Status Code: 503
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.5. Destination IP Prohibited 2.3.5. Destination IP Prohibited
Name: destination_ip_prohibited Name: destination_ip_prohibited
Description: The intermediary is configured to prohibit connections Description: The intermediary is configured to prohibit connections
to the next-hop IP address. to the next-hop IP address.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.6. Destination IP Unroutable 2.3.6. Destination IP Unroutable
Name: destination_ip_unroutable Name: destination_ip_unroutable
Description: The intermediary cannot find a route to the next-hop IP Description: The intermediary cannot find a route to the next-hop IP
address. address.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.7. Connection Refused 2.3.7. Connection Refused
Name: connection_refused Name: connection_refused
Description: The intermediary's connection to the next hop was Description: The intermediary's connection to the next hop was
refused. refused.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.8. Connection Terminated 2.3.8. Connection Terminated
Name: connection_terminated Name: connection_terminated
Description: The intermediary's connection to the next hop was Description: The intermediary's connection to the next hop was
closed before a complete response was received. closed before a complete response was received.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.9. Connection Timeout 2.3.9. Connection Timeout
Name: connection_timeout Name: connection_timeout
Description: The intermediary's attempt to open a connection to the Description: The intermediary's attempt to open a connection to the
next hop timed out. next hop timed out.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.10. Connection Read Timeout 2.3.10. Connection Read Timeout
Name: connection_read_timeout Name: connection_read_timeout
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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.11. Connection Write Timeout 2.3.11. Connection Write Timeout
Name: connection_write_timeout Name: connection_write_timeout
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).
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.12. Connection Limit Reached 2.3.12. Connection Limit Reached
Name: connection_limit_reached Name: connection_limit_reached
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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 503 Recommended HTTP Status Code: 503
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.13. TLS Protocol Error 2.3.13. TLS Protocol Error
Name: tls_protocol_error Name: tls_protocol_error
Description: The intermediary encountered a TLS error when Description: The intermediary encountered a TLS error when
communicating with the next hop, either during the handshake or communicating with the next hop, either during the handshake or
afterwards. afterwards.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
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
Name: tls_certificate_error Name: tls_certificate_error
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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.15. TLS Alert Received 2.3.15. TLS Alert Received
Name: tls_alert_received Name: tls_alert_received
Description: The intermediary received a TLS alert from the next Description: The intermediary received a TLS alert from the next
hop. hop.
Extra Parameters: Extra Parameters:
alert-id: An sf-integer containing the applicable value from the alert-id: An Integer containing the applicable value from the
"TLS Alerts" registry. See [RFC8446]. "TLS Alerts" registry. See [RFC8446].
alert-message: An sf-token or sf-string containing the applicable alert-message: A Token or String containing the applicable
description string from the "TLS Alerts" registry. See description string from the "TLS Alerts" registry. See
[RFC8446]. [RFC8446].
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.16. HTTP Request Error 2.3.16. HTTP Request Error
Name: http_request_error Name: http_request_error
Description: The intermediary is generating a client (4xx) response Description: The intermediary is generating a client (4xx) response
on the origin's behalf. Applicable status codes include (but are on the origin's behalf. Applicable status codes include (but are
not limited to) 400, 403, 405, 406, 408, 411, 413, 414, 415, 416, not limited to) 400, 403, 405, 406, 408, 411, 413, 414, 415, 416,
417, and 429. 417, and 429.
Extra Parameters: Extra Parameters:
status-code: An sf-integer containing the generated status code. status-code: An Integer containing the generated status code.
status-phrase: An sf-string containing the generated status status-phrase: A String containing the generated status phrase.
phrase.
Recommended HTTP status code: The applicable 4xx status code Recommended HTTP Status Code: The applicable 4xx status code
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
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
Name: http_request_denied Name: http_request_denied
Description: The intermediary rejected the HTTP request based on its Description: The intermediary rejected the HTTP request based on 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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 403 Recommended HTTP Status Code: 403
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.18. HTTP Incomplete Response 2.3.18. HTTP Incomplete Response
Name: http_response_incomplete Name: http_response_incomplete
Description: The intermediary received an incomplete response to the Description: The intermediary received an incomplete response to the
request from the next hop. request from the next hop.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.19. HTTP Response Header Section Too Large 2.3.19. HTTP Response Header Section Too Large
Name: http_response_header_section_size Name: http_response_header_section_size
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.
Extra Parameters: Extra Parameters:
header-section-size: An sf-integer indicating how large the header-section-size: An Integer indicating how large the received
received headers 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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.20. HTTP Response Header Field Line Too Large 2.3.20. HTTP Response Header Field Line Too Large
Name: http_response_header_size Name: http_response_header_size
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.
Extra Parameters: Extra Parameters:
header-name: An sf-string indicating the name of the header field header-name: A String indicating the name of the header 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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.21. HTTP Response Body Too Large 2.3.21. HTTP Response Body Too Large
Name: http_response_body_size Name: http_response_body_size
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.
Extra Parameters: Extra Parameters:
body-size: An sf-integer indicating how large the received body 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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.22. HTTP Response Trailer Section Too Large 2.3.22. HTTP Response Trailer Section Too Large
Name: http_response_trailer_section_size Name: http_response_trailer_section_size
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.
Extra Parameters: Extra Parameters:
trailer-section-size: An sf-integer indicating how large the trailer-section-size: An Integer indicating how large the
received trailers 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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.23. HTTP Response Trailer Field Line Too Large 2.3.23. HTTP Response Trailer Field Line Too Large
Name: http_response_trailer_size Name: http_response_trailer_size
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.
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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.24. HTTP Response Transfer-Coding Error 2.3.24. HTTP Response Transfer-Coding Error
Name: http_response_transfer_coding Name: http_response_transfer_coding
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.
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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.25. HTTP Response Content-Coding Error 2.3.25. HTTP Response Content-Coding Error
Name: http_response_content_coding Name: http_response_content_coding
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.
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.
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.26. HTTP Response Timeout 2.3.26. HTTP Response Timeout
Name: http_response_timeout Name: http_response_timeout
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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 504 Recommended HTTP Status Code: 504
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.27. HTTP Upgrade Failed 2.3.27. HTTP Upgrade Failed
Name: http_upgrade_failed Name: http_upgrade_failed
Description: The HTTP Upgrade between the intermediary and the next Description: The process of negotiating an upgrade of the HTTP
hop failed. version between the intermediary and the next hop failed.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.28. HTTP Protocol Error 2.3.28. HTTP Protocol Error
Name: http_protocol_error Name: http_protocol_error
Description: The intermediary encountered an 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.
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: false Response Only Generated by Intermediaries: false
Reference: RFC 9209 Reference: RFC 9209
2.3.29. Proxy Internal Response 2.3.29. Proxy Internal Response
Name: proxy_internal_response Name: proxy_internal_response
Description: The intermediary generated the response locally without Description: The intermediary generated the response itself without
attempting to connect to the next hop (e.g., in response to a attempting to connect to the next hop.
request to a debug endpoint terminated at the intermediary).
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: The most appropriate status code for Recommended HTTP Status Code: The most appropriate status code for
the response the response
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.30. Proxy Internal Error 2.3.30. Proxy Internal Error
Name: proxy_internal_error Name: proxy_internal_error
Description: The intermediary encountered an internal error Description: The intermediary encountered an internal error
unrelated to the origin. unrelated to the origin.
Extra Parameters: None Extra Parameters: None
Recommended HTTP status code: 500 Recommended HTTP Status Code: 500
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.31. Proxy Configuration Error 2.3.31. Proxy Configuration Error
Name: proxy_configuration_error Name: proxy_configuration_error
Description: The intermediary encountered an error regarding its Description: The intermediary encountered an error regarding its
configuration. configuration.
Extra Parameters: None Extra Parameters: None
Recommended HTTP status code: 500 Recommended HTTP Status Code: 500
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 Reference: RFC 9209
2.3.32. Proxy Loop Detected 2.3.32. Proxy Loop Detected
Name: proxy_loop_detected Name: proxy_loop_detected
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]).
Extra Parameters: None. Extra Parameters: None
Recommended HTTP status code: 502 Recommended HTTP Status Code: 502
Response only generated by intermediaries: true Response Only Generated by Intermediaries: true
Reference: RFC 9209 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, per Registration requests are reviewed and approved by Expert Review, per
[RFC8126], Section 4.5. A specification document is appreciated but [RFC8126], Section 4.5. A specification document is appreciated 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:
* Community feedback * Community feedback
* If the value is sufficiently well-defined * If the value is sufficiently well-defined
* Generic types are preferred over vendor-specific, application- * Generic types are preferred over vendor-specific, application-
specific, or deployment-specific values. If a generic value specific, or deployment-specific values. If a generic value
cannot be agreed upon in the community, the type'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).
* Extra Parameters should not conflict with registered Proxy-Status * 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:
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 Description: [a description of the conditions that generate the
Proxy Error Type] proxy error type]
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)]
Recommended HTTP status code: [the appropriate HTTP status code for Recommended HTTP Status Code: [the appropriate HTTP status code for
this entry] this entry]
Response only generated by intermediaries: ['true' or 'false'] Response Only Generated by Intermediaries: ['true' or 'false']
Reference: [to a specification defining this error type; optional] Reference: [to a specification defining this error type; optional]
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-
for details on where to send registration requests. status> for details on where to send registration requests.
3. IANA Considerations 3. IANA Considerations
IANA has created the "HTTP Proxy-Status Parameters" registry and the IANA has created the "HTTP Proxy-Status Parameters" registry and the
"HTTP Proxy Error Types" registry at <https://iana.org/assignments/ "HTTP Proxy Error Types" registry at
http-proxy-status> and has populated them with the types defined in <https://www.iana.org/assignments/http-proxy-status> and has
Sections 2.1 and 2.3, respectively; see Sections 2.2 and 2.4 for populated them with the types defined in Sections 2.1 and 2.3
their associated procedures. respectively; see Sections 2.2 and 2.4 for their associated
procedures.
Additionally, the following entry has been added to the "Hypertext Additionally, the following entry has been added to the "Hypertext
Transfer Protocol (HTTP) Field Name Registry": Transfer Protocol (HTTP) Field Name Registry":
Field name: Proxy-Status Field name: Proxy-Status
Status: permanent Status: permanent
Specification document(s): RFC 9209 Specification document(s): RFC 9209
Comments: Comments:
4. Security Considerations 4. Security Considerations
skipping to change at line 1072 skipping to change at line 1064
generation of the field itself. Also, the field's content is not generation of the field itself. Also, the field's content is not
verified; an intermediary can claim certain actions (e.g., sending a verified; an intermediary can claim certain actions (e.g., sending a
request over 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., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", RFC 9110, DOI 10.17487/RFC9110, Ed., "HTTP Semantics", RFC 9110, DOI 10.17487/RFC9110,
February 2022, <https://www.rfc-editor.org/info/rfc9110>. March 2022, <https://www.rfc-editor.org/info/rfc9110>.
[STRUCTURED-FIELDS]
Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/info/rfc8941>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
"Transport Layer Security (TLS) Application-Layer Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, <https://www.rfc-editor.org/info/rfc8446>.
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D. [RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914, Lawrence, "Extended DNS Errors", RFC 8914,
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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [STRUCTURED-FIELDS]
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Nottingham, M. and P-H. Kamp, "Structured Field Values for
<https://www.rfc-editor.org/info/rfc8446>. HTTP", RFC 8941, DOI 10.17487/RFC8941, March 2021,
<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>.
Authors' Addresses Authors' Addresses
Mark Nottingham Mark Nottingham
Fastly Fastly
Prahran Prahran
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