draft-ietf-httpbis-cdn-loop-00.txt   draft-ietf-httpbis-cdn-loop-01.txt 
HTTP Working Group S. Ludin HTTP Working Group S. Ludin
Internet-Draft Akamai Technologies Internet-Draft Akamai Technologies
Intended status: Standards Track M. Nottingham Intended status: Standards Track M. Nottingham
Expires: February 17, 2019 Fastly Expires: April 27, 2019 Fastly
N. Sullivan N. Sullivan
Cloudflare Cloudflare
August 16, 2018 October 24, 2018
CDN Loop Prevention CDN Loop Prevention
draft-ietf-httpbis-cdn-loop-00 draft-ietf-httpbis-cdn-loop-01
Abstract Abstract
This specification defines the CDN-Loop request header field for This specification defines the CDN-Loop request header field for
HTTP. HTTP.
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.
skipping to change at page 1, line 34 skipping to change at page 1, line 34
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 February 17, 2019. This Internet-Draft will expire on April 27, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 1.1. Relationship to Via . . . . . . . . . . . . . . . . . . . 2
3. The CDN-Loop Request Header Field . . . . . . . . . . . . . . 3 1.2. Conventions and Definitions . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 2. The CDN-Loop Request Header Field . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5 5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
In modern deployments of HTTP servers, it is common to interpose In modern deployments of HTTP servers, it is common to interpose
Content Delivery Networks (CDNs) to improve end-user perceived Content Delivery Networks (CDNs) in front of origin servers to
latency, reduce operational costs, and improve scalability and improve end-user perceived latency, reduce operational costs, and
reliability of services. improve scalability and reliability of services.
Often, more than one CDN is in use by any one server; this happens Often, more than one CDN is in use by a given origin. This happens
for a variety of reasons, such as cost savings, arranging for for a variety of reasons, such as cost savings, arranging for
failover should one CDN have issues, or to directly compare their failover should one CDN have issues, or to directly compare their
services. services.
As a result, it is not unknown for CDNs to be configured in a "loop" As a result, it is not unknown for forwarding CDNs to be configured
accidentally; because routing is achieved through a combination of in a "loop" accidentally; because routing is achieved through a
DNS and forwarding rules, and site configurations are sometimes combination of DNS and forwarding rules, and site configurations are
complex and managed by several parties. sometimes complex and managed by several parties.
When this happens, it is difficult to debug. Additionally, it When this happens, it is difficult to debug. Additionally, it
sometimes isn't accidental; loops between multiple CDNs be used as an sometimes isn't accidental; loops between multiple CDNs be used as an
attack vector (e.g., see [loop-attack]), especially if one CDN attack vector (e.g., see [loop-attack]), especially if one CDN
unintentionally strips the loop detection headers of another. unintentionally strips the loop detection headers of another.
This specification defines the CDN-Loop request header field for HTTP
to enable secure interoperability of forwarding CDNs. Having a
header that is guaranteed not to be modified by other CDNs that are
used by a shared customer helps give each CDN additional confidence
that any purpose (debugging, data gathering, enforcement) that they
use this header for is free from tampering due to how that customer
configured the other CDNs.
1.1. Relationship to Via
HTTP defines the Via header field in [RFC7230], Section 5.7.1 for HTTP defines the Via header field in [RFC7230], Section 5.7.1 for
"tracking message forwards, avoiding request loops, and identifying "tracking message forwards, avoiding request loops, and identifying
the protocol capabilities of senders along the request/response the protocol capabilities of senders along the request/response
chain." chain."
In theory, Via could be used to identify these loops. However, in In theory, Via could be used to identify these loops. However, in
practice it is not used in this fashion, because some HTTP servers practice it is not used in this fashion, because some HTTP servers
use Via for other purposes - in particular, some implementations use Via for other purposes - in particular, some implementations
disable some HTTP/1.1 features when the Via header is present. disable some HTTP/1.1 features when the Via header is present.
This specification defines the CDN-Loop request header field for 1.2. Conventions and Definitions
HTTP, to address this shortcoming.
2. Conventions and Definitions
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with a list extension, defined in Section 7 of notation of [RFC5234] with a list extension, defined in Section 7 of
[RFC7230], that allows for compact definition of comma-separated [RFC7230], that allows for compact definition of comma-separated
lists using a '#' operator (similar to how the '*' operator indicates lists using a '#' operator (similar to how the '*' operator indicates
repetition). Additionally, it uses the OWS rule from [RFC7230] and repetition). Additionally, it uses the OWS rule from [RFC7230] and
the parameter rule from [RFC7231]. the parameter rule from [RFC7231].
3. The CDN-Loop Request Header Field 2. The CDN-Loop Request Header Field
The CDN-Loop request header field is intended to help a Content The CDN-Loop request header field is intended to help a Content
Delivery Network identify when an incoming request has already passed Delivery Network identify when an incoming request has already passed
through that CDN's servers, to prevent loops. through that CDN's servers, to prevent loops.
CDN-Loop = #cdn-id CDN-Loop = #cdn-id
cdn-id = token *( OWS ";" OWS parameter ) cdn-id = token *( OWS ";" OWS parameter )
Conforming Content Delivery Networks SHOULD add a value to this Conforming Content Delivery Networks SHOULD add a value to this
header field to all requests they generate or forward (creating the header field to all requests they generate or forward (creating the
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Note that the token syntax does not allow whitespace, DQUOTE or any Note that the token syntax does not allow whitespace, DQUOTE or any
of the characters "(),/:;<=>?@[]{}". See [RFC7230], Section 3.2.6. of the characters "(),/:;<=>?@[]{}". See [RFC7230], Section 3.2.6.
Likewise, note the rules for when parameter values need to be quoted Likewise, note the rules for when parameter values need to be quoted
in [RFC7231], Section 3.1.1. in [RFC7231], Section 3.1.1.
To be effective, intermediaries - including Content Delivery Networks To be effective, intermediaries - including Content Delivery Networks
- MUST NOT remove this header field, or allow it to be removed (e.g., - MUST NOT remove this header field, or allow it to be removed (e.g.,
through configuration) and servers (including intermediaries) SHOULD through configuration) and servers (including intermediaries) SHOULD
NOT use it for other purposes. NOT use it for other purposes.
4. Security Considerations 3. Security Considerations
The threat model that the CDN-Loop header field addresses is a
customer who is attempting to attack a service provider by
configuring a forwarding loop by accident or malice. For it to
function, CDNs cannot allow it to be modified by customers (see
Section 2).
The CDN-Loop header field can be generated by any client, and The CDN-Loop header field can be generated by any client, and
therefore its contents cannot be trusted. CDNs who modify their therefore its contents cannot be trusted. CDNs who modify their
behaviour based upon its contents should assure that this does not behaviour based upon its contents should assure that this does not
become an attack vector (e.g., for Denial-of-Service). become an attack vector (e.g., for Denial-of-Service).
It is possible to sign the contents of the header (either by putting It is possible to sign the contents of the header (either by putting
the signature directly into the field's content, or using another the signature directly into the field's content, or using another
header field), but such use is not defined (or required) by this header field), but such use is not defined (or required) by this
specification. specification.
5. IANA Considerations 4. IANA Considerations
This document registers the "CDN-Loop" header field in the Permanent This document registers the "CDN-Loop" header field in the Permanent
Message Header Field Names registry. Message Header Field Names registry.
o Header Field Name: CDN-Loop o Header Field Name: CDN-Loop
o Protocol: http o Protocol: http
o Status: standard o Status: standard
o Reference: (this document) o Reference: (this document)
6. References 5. References
6.1. Normative References 5.1. Normative References
[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>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
skipping to change at page 5, line 14 skipping to change at page 5, line 33
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[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>.
6.2. Informative References 5.2. Informative References
[loop-attack] [loop-attack]
Chen, J., Jiang, J., Zheng, X., Duan, H., Liang, J., Li, Chen, J., Jiang, J., Zheng, X., Duan, H., Liang, J., Li,
K., Wan, T., and V. Paxson, "Forwarding-Loop Attacks in K., Wan, T., and V. Paxson, "Forwarding-Loop Attacks in
Content Delivery Networks", ISBN 1-891562-41-X, Content Delivery Networks", ISBN 1-891562-41-X,
DOI 10.14722/ndss.2016.23442, February 2016, DOI 10.14722/ndss.2016.23442, February 2016,
<http://www.icir.org/vern/papers/cdn-loops.NDSS16.pdf>. <http://www.icir.org/vern/papers/cdn-loops.NDSS16.pdf>.
Authors' Addresses Authors' Addresses
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