Open Pluggable Edge Services A. Barbir
Internet-Draft Nortel Networks
Expires: December 11, 2003 A. Rousskov
The Measurement Factory
June 12, 2003
OPES Treatment of IAB Considerations
draft-ietf-opes-iab-00
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
IETF Internet Architecture Board (IAB) expressed nine
architecture-level considerations when Open Pluggable Edge Services
(OPES) working group was being chartered at the IETF. The working
group was chartered under the condition that IAB considerations were
addressed by the group. This document describes how OPES addresses
those considerations.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Consideration (2.1) One-party consent . . . . . . . . . . . . 5
4. Consideration (2.2) IP-layer communications . . . . . . . . . 6
5. Notification Considerations . . . . . . . . . . . . . . . . . 8
5.1 Consideration (3.1) Notification . . . . . . . . . . . . . . . 9
5.2 Consideration (3.2) Notification . . . . . . . . . . . . . . . 10
5.3 Consideration (3.3) Non-blocking . . . . . . . . . . . . . . . 11
6. Consideration (4.1) URI resolution . . . . . . . . . . . . . . 12
7. Consideration (4.2) Reference validity . . . . . . . . . . . . 13
8. Consideration (4.3) Addressing extensions . . . . . . . . . . 14
9. Consideration (5.1) Privacy . . . . . . . . . . . . . . . . . 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12. To-do . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
A. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Normative References . . . . . . . . . . . . . . . . . . . . . 20
Informative References . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . 22
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1. Introduction
The Open Pluggable Edge Services (OPES) architecture
[I-D.ietf-opes-architecture], enables cooperative application
services (OPES services) between a data provider, a data consumer,
and zero or more OPES processors. The application services under
consideration analyze and possibly transform application-level
messages exchanged between the data provider and the data consumer.
Following controversy related to chartering OPES, IAB made
recommendations on issues that OPES solutions should be required to
address. These recommendations were formulated in the form of
specific IAB considerations [RFC3238]. IAB emphasized that its
considerations did not recommend specific solutions and did not
mandate specific functional requirements. Addressing an IAB
consideration may involve showing appropriate protocol mechanisms or
demonstrating that the issue does not apply.
The primary goal of this document is to show that all IAB
considerations are addressed by OPES, to the extent those
considerations can be addressed by an IETF working group. We also
explicitly document limitations of our abilities to address certain
aspects of IAB considerations.
There are nine IAB considerations [RFC3238] that OPES has to address.
In the core of this document are the corresponding nine
"Consideration" sections. For each IAB consideration, its section
contains general discussion as well as references to specific OPES
mechanisms relevant to the consideration.
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2. Terminology
This document does not introduce any new terminology but uses
terminology from other OPES documents it quotes.
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3. Consideration (2.1) One-party consent
"An OPES framework standardized in the IETF must require that the use
of any OPES service be explicitly authorized by one of the
application-layer end-hosts (that is, either the content provider or
the client)."[RFC3238]
OPES architecture requires that "OPES processors MUST be consented to
by either the data consumer or data provider application"
[I-D.ietf-opes-architecture]. The requirement alone cannot prevent
consent-less introduction of OPES processors, of course. OPES
enables concerned parties to detect unwanted OPES processors by
examining OPES traces and by checking content signatures.
Tracing is a weak but cheap mechanism that is unable to detect
processors incompliant with OPES specifications on tracing and
operating in stealth mode. Content signatures is a strong but
expensive mechanism that can detect any modifications of signed
content provided the content provider is willing to sign the data and
the client is willing to either check the signature or relay received
content to content provider for signature verification.
OPES adaptations include copying and other forms of non-modifying
access to content. These kinds of adaptations cannot be detected by
the above mentioned mechanisms. Thus, "passive" unwanted OPES
processors cannot be detected. If presence of such processors is a
concern, content encryption can be used. See privacy consideration
for more details.
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4. Consideration (2.2) IP-layer communications
"For an OPES framework standardized in the IETF, the OPES
intermediary must be explicitly addressed at the IP layer by the end
user."[RFC3238]
OPES architecture requires that "OPES processors MUST be addressable
at the IP layer by the end user (data consumer application)"
[I-D.ietf-opes-architecture]. Two caveats are related to this
requirement. First, addressing the first OPES processor in a chain of
processors is sufficient. That is, a chain of OPES processors is
viewed as a single OPES processor at the address of the first chain
element. (XXX: should we move these caveats into a separate section?
they seem to affect many considerations; one the other hand, it is
probably the job of the architecture draft to define these things so
that we can refer to them from here.)
The second caveat is more controversial. Only a very limited subset
of OPES intermediaries are subject to the above requirements. The
situation is examined below, by considering content provider and end
user sides of the architecture.
OPES processors that operate under content provider consent may not
be subject to the above consideration and requirement (XXX the
architecture draft does not reflect this). It is irrational to expect
a content provider to provide access to internal hosts participating
in content generation, whether OPES processors are involved or not.
Moreover, providing such access would serve little practical purpose
because internal OPES processors are not likely to be able to answer
any end user queries, being completely our of content generation
context. For example, an OPES processor adding customer-specific
information to XML pages may not understand or be aware of any final
HTML content that the end user receives and may not be able to map
end user request to any internal user identification.
OPES processors that operate under end user consent may not be
subject to the above consideration and requirement (XXX the
architecture draft does not reflect this). It is irrational to expect
a client-side ISP to provide access to internal hosts participating
in content processing, whether OPES processors are involved or not.
Moreover providing such access would serve little practical purpose
because internal OPES processors are not likely to be able to answer
any end user queries, being completely our of content processing
context. For example, an OPES processor making a client-authorized
XML content translation may not understand or be aware of any final
HTML content that the end user receives and may not be able to map
end user request to any internal user identification.
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IAB consideration 2.2 apparently was not meant to apply to "internal"
OPES intermediaries. It may be better interpreted as "If the first
intermediary on end user's message processing path is an OPES
intermediary, that intermediary must be explicitly addressed at the
IP layer by the end user". In other words, the end user is assured
that the first intermediary that touches her request is explicitly
addressed if it is an OPES intermediary.
(XXX: should we add a picture showing internal and external OPES
intermediaries?)
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5. Notification Considerations
This section discusses how OPES framework addresses IAB Notification
concerns 3.1 and 3.2. OPES framework concentrates on tracing rather
than notification. The tracing specification [XXX] defines "OPES
trace" as "application message information about OPES entities that
adapted that message" and "OPES tracing" as "the process of
including, manipulating, and interpreting an OPES trace" (XXX: keep
these in sync). Thus, OPES trace follows the application message it
traces. It notifies the recipient of the message of what has happened
to that message. Traces are implemented as extensions of application
protocols being adapted and traced.
As opposed to an OPES trace, provider notification (as implied by
IAB) notifies the sender of the message of what had happened to the
message after the message left the sender. Thus, notifications
propagate in the opposite direction of traces. Supporting
notifications directly would require a new protocol. Figure XXX
illustrates the differences between a trace and notification from a
single application message point of view.
sender --[message A]---> OPES --[message A' + trace]--> recipient
^ V
| |
+-<-- [notification] ---+
Figure 1
Since notifications cannot be piggy-backed to application messages,
they create new messages and may at least double the number of
messages the sender has to process (more if several intermediaries on
the message path emit notifications). Moreover, a notification
message may refer to some sender state that has to be kept around
until notification is received, increasing performance overhead of
notifications. These concerns call for optional notification, with a
special protocol to enable notifications when needed.
The level of available details in notifications versus provider
interest in supporting notification is another concern. Experience
shows that content providers often require very detailed information
about user actions to be interested in notifications at all. For
example, Hit Metering protocol [XXX] has been designed to supply
content providers with proxy cache hit counts, in an effort to reduce
cache busting behavior which was caused by content providers desire
to get accurate site "access counts". However, the Hit Metering
protocol is currently not widely deployed because the protocol does
not supply content providers with information such as client IP
addresses, browser versions, or cookies.
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The Hit Metering experience is relevant because Hit Metering protocol
was designed to do for HTTP caching intermediaries what OPES
notifications are meant to do for OPES intermediaries. Performance
requirements call for state reduction via aggregation of
notifications while provider preferences call for state preservation
or duplication. Achieving the right balance when two sides belong to
different organizations and have different optimization priorities is
probably impossible in general.
Thus, instead of explicitly supporting notifications on a protocol
level, OPES concentrates on tracing facilities and supports
notifications indirectly, using those tracing facilities. In other
words, the IAB choice of "Notification" label is interpreted as
"Notification assistance" (i.e. making notifications meaningful) and
is not interpreted as a "Notification protocol".
5.1 Consideration (3.1) Notification
"The overall OPES framework needs to assist content providers in
detecting and responding to client-centric actions by OPES
intermediaries that are deemed inappropriate by the content
provider."[RFC3238]
OPES tracing mechanisms assist content providers in detecting
client-centric actions by OPES intermediaries. Specifically, a
compliant OPES intermediary or system notifies a content provider of
its presence by including its tracing information in the application
protocol requests. An OPES intermediary MUST leave its trace (XXX
quote tracing draft). Detection assistance has its limitations. Some
OPES intermediaries may work exclusively on responses and may not
have a chance to trace the request. Moreover, some application
protocols may not have explicit requests (e.g., a content push
service).
OPES tracing mechanisms assist content providers in responding to
client-centric actions by OPES intermediaries. Specifically, OPES
traces MUST include identification of OPES systems and SHOULD include
a list of adaptation actions performed on provider's content. This
tracing information may be included in the application request.
Usually, however, this information will be included in the
application response, an adapted version of which does not reach the
content provider. If OPES end points cooperate, then notification can
be assisted with traces. Content providers that suspect or experience
difficulties can do any of the following:
Check whether requests they receive pass through OPES
intermediaries. Presence of OPES tracing info will determine that.
This check is only possible for request/response protocols. For
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other protocols (e.g., broadcast or push), the provider would have
to assume that OPES intermediaries are involved until proven
otherwise.
If OPES intermediaries are suspected, request OPES traces from
potentially affected user(s). The trace will be a part of the
application message received by the user software. If users
cooperate, the provider(s) have all the information they need. If
users do not cooperate, the provider(s) cannot do much about it
(they might be able to deny service to uncooperative users in some
cases).
Some traces may indicate that more information is available by
accessing certain resources on the specified OPES intermediary or
elsewhere. Content providers may query for more information in
that case.
If everything else fails, providers can enforce no-adaptation
policy using appropriate OPES bypass mechanisms and/or end-to-end
encryption mechanisms.
OPES detection and response assistance is limited to application
protocols with support for tracing extensions. For example, HTTP
[RFC2616] has such support while DNS over UDP does not.
(XXX: should we prohibit adaptation of application protocols that do
not allow for tracing?)
5.2 Consideration (3.2) Notification
"The overall OPES framework should assist end users in detecting the
behavior of OPES intermediaries, potentially allowing them to
identify imperfect or compromised intermediaries."[RFC3238]
OPES tracing mechanisms assist end users in detecting OPES
intermediaries. Specifically, a compliant OPES intermediary or system
notifies an end user of its presence by including its tracing
information in the application protocol messages sent to the client.
An OPES intermediary MUST leave its trace (XXX quote tracing draft).
Detection assistance has its limitations. Some OPES intermediaries
may work exclusively on requests and may not have a chance to trace
the response. Moreover, some application protocols may not have
explicit responses (e.g., event logging service).
OPES detection assistance is limited to application protocols with
support for tracing extensions. For example, HTTP [RFC2616] has such
support while DNS over UDP does not.
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(XXX: should we prohibit adaptation of application protocols that do
not allow for tracing?)
5.3 Consideration (3.3) Non-blocking
"If there exists a "non-OPES" version of content available from the
content provider, the OPES architecture must not prevent users from
retrieving this "non-OPES" version from the content
provider."[RFC3238]
OPES intermediaries MUST support a bypass feature (XXX quote bypass
draft). If an application message includes bypass instructions, the
matching OPES intermediary will not process the message. Bypass may
generate content errors since some OPES services may be essential.
(Should there be a way to bypass non-essential services only?)
Bypass support has limitations similar to the two
notification-related considerations above.
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6. Consideration (4.1) URI resolution
"OPES documentation must be clear in describing these services as
being applied to the result of URI resolution, not as URI resolution
itself."[RFC3238]
"OPES Scenarios and Use Cases" specification
[I-D.ietf-opes-scenarios] documents content adaptations that are in
scope of the OPES framework (XXX provide a quote). These adaptations
do not include URI resolution (XXX check). In some environments, it
is technically possible to adapt URIs (and other kinds of identifiers
or addresses) using documented OPES mechanisms.
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7. Consideration (4.2) Reference validity
"All proposed services must define their impact on inter- and
intra-document reference validity."[RFC3238]
OPES working group does not propose adaptation services. However,
OPES tracing requirements include identification of OPES
intermediaries and services (for details, see "Notification"
consideration sections in this document). It is required that
provided identification can be used to locate information about the
OPES intermediaries, including the description of impact on reference
validity (XXX quote tracing draft).
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8. Consideration (4.3) Addressing extensions
"Any services that cannot be achieved while respecting the above two
considerations may be reviewed as potential requirements for Internet
application addressing architecture extensions, but must not be
undertaken as ad hoc fixes."[RFC3238]
OPES framework does not contain ad hoc services. This and other OPES
documents should be sufficient to inform service creators of IAB
considerations. If a service does URI resolution or silently affects
document reference validity, the authors are requested to review
service impact on Internet application addressing architecture and
work within IETF on potential extension requirements.
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9. Consideration (5.1) Privacy
"The overall OPES framework must provide for mechanisms for end users
to determine the privacy policies of OPES intermediaries."[RFC3238]
OPES tracing mechanisms allow end users to identify OPES
intermediaries (for details, see "Notification" consideration
sections in this document). It is required that provided
identification can be used to locate information about the OPES
intermediaries, including their privacy policies.
The terms "privacy" and "privacy policy" are not defined in this
context (by IAB or OPES working group). OPES tracing mechanisms allow
end users and content providers to identify OPES intermediaries. It
is believed that once an intermediary is identified, it would be
possible to locate relevant information about that intermediary,
including information relevant to requesters perception of privacy
policy or reference validity. (XXX: should we move this paragraph
into a separate section and expand it? one the other hand, it is
probably the job of the architecture draft to define these things so
that we can refer to them from here.)
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10. Security Considerations
XXX.
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11. Compliance
This document may be perceived as a proof of OPES compliance with IAB
implied recommendations. However, this document does not introduce
any compliance subjects. Compliance of OPES implementations is
defined in other OPES documents discussed above.
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12. To-do
security section: Does this document have any original security
matters worth documenting?
normative IDs: To be normative, OPES Internet-Drafts must be replaced
with corresponding RFCs when the latter are published.
architecture draft: Should architecture draft talk about external/
internal OPES intermediaries and about privacy policies? Should
this document be limited to a compilation of references from other
OPES drafts, or should we introduce/discuss new concepts here?
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Appendix A. Change Log
Internal WG revision control ID: $Id: iab-cons.xml,v 1.13 2003/06/12
15:38:48 rousskov Exp $
head-sid9
* Polished to meet new xml2rfc sctrict requirements.
head-sid8
* Added unpolished meat for all nine considerations.
* Added Abbie Barbir as an author.
head-sid7
* Initial revision
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Normative References
[I-D.ietf-opes-architecture]
Barbir, A., "An Architecture for Open Pluggable Edge
Services (OPES)", draft-ietf-opes-architecture-04 (work in
progress), December 2002.
[I-D.ietf-opes-scenarios]
Barbir, A., "OPES Use Cases and Deployment Scenarios",
draft-ietf-opes-scenarios-01 (work in progress), August
2002.
[RFC3238] Floyd, S. and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC
3238, January 2002.
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Informative References
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
Authors' Addresses
Abbie Barbir
Nortel Networks
3500 Carling Avenue
Nepean, Ontario
CA
Phone: +1 613 763 5229
EMail: abbieb@nortelnetworks.com
Alex Rousskov
The Measurement Factory
EMail: rousskov@measurement-factory.com
URI: http://www.measurement-factory.com/
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