Internet Engineering Task Force S. Floyd, Editor
INTERNET DRAFT
draft-iab-considerations-02.txt August, 2002
General Architectural and Policy Considerations
Status of this Memo
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Abstract
This document suggests general architectural and policy questions
that the IETF community has to address when working on new standards
and protocols. We note that this document contains questions to be
addressed, as opposed to guidelines or architectural principles to be
followed.
Changes from draft-iab-considerations-01.txt:
* Added a discussion on overloading.
* Added a discussion on complexity, robustness, and fragility.
* Added a section on Internationalization.
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1. Introduction
This document suggests general architectural and policy questions to
be addressed in our work in the IETF. This document contains
questions to be addressed, as opposed to guidelines or architectural
principles to be followed. These questions are somewhat similar to
the "Security Considerations" currently required in IETF documents
[RFC2316].
This document is motivated in part by concerns about a growing lack
of coherence in the overall Internet architecture. We have moved
from a world of a single, coherent architecture designed by a small
group of people, to a world of a complex, intricate architecture to
address a wide-spread and heterogeneous environment. Because
individual pieces of the architecture are often designed by sub-
communities, with each sub-community having its own set of interests,
it is necessary to pay increasing attention to how each piece fits
into the larger picture, and to consider how each piece is chosen.
For example, it is unavoidable that each of us is inclined to solve a
problem at the layer of the protocol stack and using the tools that
we understand the best; that does not necessarily mean that this is
the most appropriate layer or set of tools for solving this problem
in the long-term.
2. Relationship to "Architectural Principles of the Internet"
RFC 1958 [RFC1958] outlines some architectural principles of the
Internet, as "guidelines that have been found useful in the past, and
that may be useful to those designing new protocols or evaluating
such designs." An example guideline is that "it is also generally
felt that end-to-end functions can best be realized by end-to-end
protocols." Similarly, an example design issue from [RFC1958] is that
"heterogeneity is inevitable and must be supported by design."
In contrast, this document serves a slightly different purpose, by
suggesting additional architectural questions to be addressed. Thus,
one question suggested in this document is the following: "Is this
proposal the best long-term solution to the problem? If not, what
are the long-term costs of this solution, in terms of restrictions on
future development, if any?" This question could be translated to a
roughly equivalent architectural guideline, as follows: "Identify
whether the proposed protocol is a long-term solution or a short-term
solution, and identify the long-term costs and the exit strategy for
any short-term solutions."
In contrast, other questions are more open-ended, such as the
question about robustness: "How robust is the protocol, not just to
the failure of nodes, but also to compromised or malfunctioning
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nodes, imperfect or defective implementations, etc?" As a community,
we are still learning about the degree of robustness that we are able
to build into our protocols, as well as the tools that are available
to ensure this robustness. Thus, there are not yet clear
architectural guidelines along the lines of "Ensure that your
protocol is robust against X, Y, and Z."
3. Questions.
In this section we list some questions to ask in designing protocols.
Each question is discussed in more depth in the rest of this paper.
We aren't suggesting that all protocol design efforts should be
required to explicitly answer all of these questions; some questions
will be more relevant to one document than to another. We also
aren't suggesting that this is a complete list of architectural
concerns.
Justifying the Solution:
* Why are you proposing this solution, instead of proposing something
else?
Interactions between Layers:
* Why are you proposing a solution at this layer of the protocol
stack, rather than at another layer? Are there solutions at other
layers of the protocol stack as well?
* Is this an appropriate layer in terms of correctness of function,
data integrity, performance, ease of deployment, the diagnosibility
of failures, and other concerns?
* What are the interactions between layers, if any?
Long-term vs. Short-term Solutions:
* Is this proposal the best long-term solution to the problem?
* If not, what are the long-term costs of this solution, in terms of
restrictions on future development, if any? What are the
requirements for the development of longer-term solutions?
Robustness:
* How robust is the protocol, not just to the failure of nodes, but
also to compromised or malfunctioning nodes, imperfect or defective
implementations, etc?
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Tragedy of the Commons:
* Is performance still robust if everyone is using this protocol?
Are there other potential impacts of widespread deployment that need
to be considered?
Protecting Competing Interests:
* Does the protocol protect the interests of competing parties (e.g.,
not only end-users, but also ISPs, router vendors, software vendors,
or other parties)? Is the design modularized to allow competing
interests to play out, while also isolating "tussles" and preventing
them from spilling out into unrelated areas?
Designing for Choice vs. Avoiding Unnecessary Complexity:
* Is the protocol designed for choice, to allow different players to
express their preferences where appropriate? At the same time, does
the protocol avoid the "kitchen sink" approach of providing too many
options and too much choice?
Weighing Benefits against Costs:
* How do the architectural benefits of a proposed new protocol
compare against the architectural costs, if any? Have the
architectural costs been carefully considered?
The Whole Picture vs. Building Blocks:
* Have you considered the larger context, while appropriately
restricting your own design efforts to one part of the whole?
* Are there parts of the overall solution that will have to be
provided by other IETF Working Groups or by other standards bodies?
Preserving Evolvability?
* Does the protocol protect the interests of the future, by
preserving the evolvability of the Internet? Does the protocol
enable future developments?
* If an old protocol is overloaded with new functionality, or reused
for new purposes, have the possible complexities introduced been
taken carefully into account?
* For a protocol that introduces new complexity to the Internet
architecture, how does the protocol add robustness and preserve
evolvability, and how does it also introduce new fragilities to the
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system?
Internationalization:
* Where protocols require elements in text format, have the possibly
conflicting requirements of global comprehensibility and the ability
to represent local text content been properly weighed against each
other?
Each of these questions is discussed in more depth in the rest of
this paper.
4. Justifying the Solution.
Question: Why are you proposing this solution, instead of proposing
something else?
4.1. Case study: Integrated and Differentiated Services.
A good part of the work of developing integrated and differentiated
services has been to understand the problem to be solved, and to come
to agreement on the architectural framework of the solution, and on
the nature of specific services. Thus, when integrated services was
being developed, the specification of the Controlled Load [RFC2211]
and Guaranteed [RFC2212] services each required justification of the
need for that particular service, of low loss and bounded delay
respectively.
Later, when RFC 2475 on "An Architecture for Differentiated Services"
proposed a scalable, service differentiation architecture that
differs from the previously-defined architecture for integrated
services, the document also had to clearly justify the requirements
for this new architecture, and compare the proposed architecture to
other possible approaches [RFC2475]. Similarly, when the Assured
Forwarding [RFC2597] and Expedited Forwarding [RFC2598] Per-Hop
Behaviors of differentiated services were proposed, each service
required a justification of the need for that service in the
Internet.
5. Interactions between Layers.
Questions: Why are you proposing a solution at this layer of the
protocol stack, rather than at another layer? Are there solutions at
other layers of the protocol stack as well?
Is this an appropriate layer in terms of correctness of function,
data integrity, performance, ease of deployment, the diagnosibility
of failures, and other concerns?
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What are the interactions between layers, if any?
5.1. Case study: Endpoint Congestion Management.
The goal of the Congestion Manager in Endpoint Congestion Management
is to allow multiple concurrent flows with the same source and
destination address to share congestion control state [RFC3124].
There has been a history of proposals for multiplexing flows at
different levels of the protocol stack; proposals have included
adding multiplexing at the HTTP (WebMux) and TCP (TCP Control Blocks)
layers, as well as below TCP (the Congestion Manager) [Multiplexing].
However, the 1989 article on "Layered Multiplexing Considered
Harmful" suggests that "the extensive duplication of multiplexing
functionality across the middle and upper layers is harmful and
should be avoided" [T89]. Thus, one of the key issues in providing
mechanisms for multiplexing flows is to determine which layer of the
protocol stack is most appropriate for providing this functionality.
The natural tendency of each researcher is generally to add
functionality at the layer that they know the best; this does not
necessarily result in the most appropriate overall architecture.
This is elaborated upon in the section below.
5.2. Discussion: The End-to-End Argument
The classic 1984 paper on "End-To-End Arguments In System Design"
[SRC84] begins a discussion of where to place functions among modules
by suggesting that "functions placed at low levels of a system may be
redundant or of little value when compared with the cost of providing
them at that low level. Examples discussed in the paper include bit
error recovery, security using encryption, duplicate message
suppression, recovery from system crashes, and delivery
acknowledgement. Low level mechanisms to support these functions are
justified only as performance enhancements." The end-to-end
principle is one of the key architectural guidelines to consider in
choosing the appropriate layer for a function.
5.3. Case study: Layering Applications on Top of HTTP.
There has been considerable interest in layering applications on top
of HTTP [RFC3205]. Reasons cited include compatibility with widely-
deployed browsers, the ability to reuse client and server libraries,
the ability to use existing security mechanisms, and the ability to
traverse firewalls. As RFC 3205 discusses, "the recent interest in
layering new protocols over HTTP has raised a number of questions
when such use is appropriate, and the proper way to use HTTP in
contexts where it is appropriate." Thus, RFC 3205 addresses not only
the benefits of layering applications on top of HTTP, but also
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evaluates the additional complexity and overhead of layering an
application on top of HTTP, compared to the costs of introducing a
special-purpose protocol.
The web page on "References on Layering and the Internet
Architecture" has pointers to additional papers discussing general
layering issues in the Internet architecture [Layering].
6. Long-term vs. Short-term Solutions
Questions: Is this proposal the best long-term solution to the
problem?
If not, what are the long-term costs of this solution, in terms of
restrictions on future development, if any? What are the
requirements for the development of longer-term solutions?
6.1. Case study: Traversing NATs.
In order to address problems with NAT middleboxes altering the
external address of endpoints, various proposals have been made for
mechanisms where an originating process attempts to determine the
address (and port) by which it is known on the other side of a NAT.
This would allow an originating process to be able to use address
data in the protocol exchange, or to advertise an external address
from which it will receive connections.
The IAB in [UNSAF] has outlined reasons why these proposals can be
considered at best as short-term fixes to specific problems, and the
specific issues to be carefully evaluated before standardizing such
proposals. These issues include the identification of the limited-
scope problem to be fixed, the description of an exit strategy for
the short-term solution, and the description of the longer-term
problems left unsolved by the short-term solution.
7. General Robustness Questions
Questions: How robust is the protocol, not just to the failure of
nodes, but also to compromised or malfunctioning nodes, imperfect or
defective implementations, etc?
Does the protocol take into account the realistic conditions of the
current or future Internet (e.g., packet drops and packet corruption;
packet reordering; asymmetric routing; etc.)?
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7.1. Discussion: Designing for Robustness.
Robustness has long been cited as one of the overriding goals of the
Internet architecture [Clark88]. The robustness issues discussed in
[Clark88] largely referred to the robustness of packet delivery even
in the presence of failed routers; today robustness concerns have
widened to include a goal of robust performance in the presence of a
wide range of failures, buggy code, and malicious actions.
As [ASSW02] argues, protocols need to be designed somewhat
defensively, to maximize robustness against inconsistencies and
errors. [ASSW02] discusses several approaches for increasing
robustness in protocols, such as verifying information whenever
possible; designing interfaces that are conceptually simple and
therefore less conducive to error; protecting resources against
attack or overuse; and identifying and exposing errors so that they
can be repaired.
Techniques for verifying information range from verifying that
acknowledgements in TCP acknowledge data that was actually sent, to
providing mechanisms for routers to verify information in routing
messages.
Techniques for protecting resources against attack range from
preventing "SYN flood" attacks by designing protocols that don't
allocate resources for a single SYN packet, to partitioning resources
(e.g., preventing one flow or aggregate from using all of the link
bandwidth).
7.2. Case Study: Explicit Congestion Notification (ECN).
The Internet is based on end-to-end congestion control, and
historically the Internet has used packet drops as the only method
for routers to indicate congestion to the end nodes. ECN [RFC3168]
is a recent addition to the IP architecture to allow routers to set a
bit in the IP packet header to inform end-nodes of congestion,
instead of dropping the packet.
The first, Experimental specification of ECN [RFC2481] contained an
extensive discussion of the dangers of a rogue or broken router
"erasing" information from the ECN field in the IP header, thus
preventing indications of congestion from reaching the end-nodes. To
add robustness, the standards-track specification [RFC3168] specified
an additional codepoint in the IP header's ECN field, to use for an
ECN "nonce". The development of the ECN nonce was motivated by
earlier research on specific robustness issues in TCP [SCWA99]. RFC
3168 explains that the addition of the codepoint "is motivated
primarily by the desire to allow mechanisms for the data sender to
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verify that network elements are not erasing the CE codepoint, and
that data receivers are properly reporting to the sender the receipt
of packets with the CE codepoint set, as required by the transport
protocol." Supporting mechanisms for the ECN nonce are needed in the
transport protocol to ensure robustness of delivery of the ECN-based
congestion indication.
In contrast, a more difficult and less clear-cut robustness issue for
ECN concerns the differential treatment of packets in the network by
middleboxes, based on the TCP header's ECN flags in a TCP SYN packet
[RFC3360]. The issue concerns "ECN-setup" SYN packets, that is, SYN
packets with ECN flags set in the TCP header to negotiate the use of
ECN between the two TCP end-hosts. There exist firewalls in the
network that drop "ECN-setup" SYN packets, others that send TCP Reset
messages, and yet others that zero ECN flags in TCP headers. None of
this was anticipated by the designers of ECN, and RFC 3168 added
optional mechanisms to permit the robust operation of TCP in the
presence of firewalls that drop "ECN-setup" SYN packets. However,
ECN is still not robust to all possible scenarios of middleboxes
zeroing ECN flags in the TCP header. Up until now, transport
protocols have been standardized independently from the mechanisms
used by middleboxes to control the use of these protocols, and it is
still not clear what degree of robustness is required from transport
protocols in the presence of the unauthorized modification of
transport headers in the network. These and similar issues are
discussed in more detail in [RFC3360].
8. Avoiding Tragedy of the Commons.
Question: Is performance still robust if everyone is using the new
protocol? Are there other potential impacts of widespread deployment
that need to be considered?
8.1. Case Study: End-to-end Congestion Control.
[RFC2914] discusses the potential for congestion collapse if flows
are not using end-to-end congestion control in a time of high
congestion. For example, if a new transport protocol was proposed
that did not use end-to-end congestion control, it might be easy to
show that a flow using the new transport protocol would perform quite
well as long as all of the competing flows in the network were using
end-to-end congestion control. To fully evaluate the new transport
protocol, it is necessary to look at performance when many flows are
competing, all using the new transport protocol. If all of the
competing flows were using the more aggressive transport protocol in
a time of high congestion, the result could be a tragedy of the
commons, with many links busy carrying packets that will only be
dropped downstream.
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9. Balancing Competing Interests
Question: Does the protocol protect the interests of competing
parties (e.g., not only end-users, but also ISPs, router vendors,
software vendors, or other parties)? Is the design modularized to
allow competing interests to play out, while also isolating "tussles"
and preventing them from spilling out into unrelated areas?
9.1. Discussion: balancing competing interests
[CWSB02] discusses the role that competition between competing
interests plays in the evolution of the Internet, and takes the
position that the role of Internet protocols is to design the playing
field in this competition, rather than to pick the outcome. The IETF
has long taken the position that it can only design the protocols,
and that often two competing approaches will be developed, with the
marketplace left to decide between them [A02]. (It has also been
suggested that "the marketplace" left entirely to itself does not
always make the best decisions, and that working to identify and
adopt the technically best solution is sometimes helpful.)
An example cited in [CWSB02] of modularization in support of
competing interests is the decision to use codepoints in the IP
header to select QoS, rather than binding QoS to other properties
such as port numbers. This separates the structural and economic
issues related to QoS from technical issues of protocols and port
numbers, and allows space for a wide range of structural and pricing
solutions to emerge.
It has also been suggested that companies in some cases have an
incentive to add complexity to protocol design in order to make the
protocol more difficult to implement, as a way of increasing the
barrier for competition. Clearly if this were to occur, such a
protocol would not be protecting the interests of competing parties.
10. Designing for Choice vs. Avoiding Unnecessary Complexity:
Is the protocol designed for choice, to allow different players to
express their preferences where appropriate? At the same time, does
the protocol avoid the "kitchen sink" approach of providing too many
options and too much choice?
10.1. Discussion: the importance of choice
[CWSB02] suggests that "the fundamental design goal of the Internet
is to hook computers together, and since computers are used for
unpredictable and evolving purposes, making sure that the users are
not constrained in what they can do is doing nothing more than
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preserving the core design tenet of the Internet. In this context,
user empowerment is a basic building block, and should be embedded
into all mechanism whenever possible."
As an example of choice, "the design of the mail system allows the
user to select his SMTP server and his POP server" [CWSB02]. More
open-ended questions about choice concern the design of mechanisms
that would enable the user to choose the path at the level of
providers, or to allow users to choose third-party intermediaries
such as web caches, or providers for Open Pluggable Edge Services
(OPES). [CWSB02] also notes that the issue of choice itself reflects
competing interests. For example, ISPs would generally like to lock
in customers, while customers would like to preserve their ability to
change among providers.
At the same time, we note that excessive choice can lead to "kitchen
sink" protocols that are inefficient and hard to understand, have too
much negotiation, or have unanticipated interactions between options.
These dangers are discussed in [BMMWRO02], which gives guidelines for
responding to the "continuous flood" of suggestions for modifications
and extensions to SIP (Session Initiation Protocol). In particular,
the SIP Working Group is concerned that proposed extensions have
general use, and do not provide efficiency at the expense of
simplicity or robustness. [BMMWRO02] suggests that other highly
extensible protocols developed in the IETF might also benefit from
more coordination of extensions.
11. Weighing architectural benefits against architectural costs.
Questions: How do the architectural benefits of a proposed new
protocol compare against the architectural costs, if any? Have the
architectural costs been carefully considered?
11.1. Case Study: Performance-enhancing proxies (PEPs)
RFC 3135 [RFC3135] considers the relative costs and benefits of
placing performance-enhancing proxies (PEPs) in the middle of a
network to address link-related degradations. In the case of PEPs,
the potential costs include disabling the end-to-end use of IP layer
security mechanisms; introducing a new possible point of failure that
is not under the control of the end systems; adding increased
difficulty in diagnosing and dealing with failures; and introducing
possible complications with asymmetric routing or mobile hosts. RFC
3135 carefully considers these possible costs, the mitigations that
can be introduced, and the cases when the benefits of performance-
enhancing proxies to the user are likely to outweight the costs.
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11.2. Case Study: Open Pluggable Edge Services (OPES)
One of the issues raised by middleboxes in the Internet involves the
end-to-end integrity of data. This is illustrated in the recent
question of chartering the Open Pluggable Edge Services (OPES)
Working Group. Open Pluggable Edge Services are services that would
be deployed as application-level intermediaries in the network, for
example, at a web proxy cache between the origin server and the
client. These intermediaries would transform or filter content, with
the explicit consent of either the content provider or the end user.
One of the architectural issues that arose in the process of
chartering the OPES Working Group concerned the end-to-end integrity
of data. As an example, it was suggested that ``OPES would reduce
both the integrity, and the perception of integrity, of
communications over the Internet, and would significantly increase
uncertainly about what might have been done to content as it moved
through the network'', and that therefore the risks of OPES
outweighed the benefits [CDT01].
As one consequence of this debate, the IAB wrote a document on "IAB
Architectural and Policy Considerations for OPES", considering both
the potential architectural benefits and costs of OPES [RFC3238].
This document did not recommend specific solutions or mandate
specific functional requirements, but instead included
recommendations of issues such as concerns about data integrity that
OPES solutions standardized in the IETF should be required to
address.
11.3. Case Study: Stresses on DNS.
As an example, over and over again, we find people wanting to
overload the DNS with new services and functions. In each case, we
may ask whether or not it is feasible to add a particular feature,
and often the answer is yes. What we rarely ask is the impact of all
this added functionality on the provision of the original service.
[K02] considers many of the newer demands being placed upon the DNS.
12. Looking at the whole picture vs. making a building block.
For a complex protocol which interacts with protocols from other
standards bodies as well as from other IETF working groups, it can be
necessary to keep in mind the overall picture while, at the same
time, breaking out specific parts of the problem to be standardized
in particular working groups.
Question: Have you considered the larger context, while restricting
your own design efforts to one part of the whole?
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Question: Are there parts of the overall solution that will have to
be provided by other IETF Working Groups or by other standards
bodies?
12.1. Case Study: The Session Initiation Protocol (SIP)
The Session Initiation Protocol (SIP) [RFC2543], for managing
connected, multimedia sessions, is an example of a complex protocol
that has been broken into pieces for standardization in other working
groups. SIP has also involved interaction with other standardization
bodies.
The basic SIP framework is being standardized by the SIP working
group. This working group has focused on the core functional
features of setting up, managing, and tearing down multimedia
sessions. Extensions are considered if they relate to these core
features.
The task of setting up a multimedia session also requires a
description of the desired multimedia session. This is provided by
the Session Description Protocol (SDP). SDP is a building block that
is supplied by the Multiparty Multimedia Session Control (MMUSIC)
working group. It is not standardized within the SIP working group.
Other working groups are involved in standardizing extensions to SIP
that fall outside of core functional features or applications. The
SIPPING working group is analyzing the requirements for SIP applied
to different tasks, and the SIMPLE working group is examining the
application of SIP to instant messaging and presence. The IPTEL
working group is defining a call processing language (CPL) that
interacts with SIP in various ways. These working groups occasionally
feed requirements back into the main SIP working group.
Finally, outside standardization groups have been very active in
providing the SIP working group with requirements. The Distributed
Call Signaling (DCS) group from the PacketCable Consortium, 3GPP, and
3GPP2 are all using SIP for various telephony-related applications,
and members of these groups have been involved in drafting
requirements for SIP. In addition, there are extensions of SIP which
are under consideration in these standardization bodies that are not
appropriate material for IETF, because they are not generally
applicable but only relate to the particular application of SIP being
developed by the standardization bodies. An example is particular
interactions with accounting and billing for mobile telephony.
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13. Preserving evolvability?
Does the protocol protect the interests of the future, by preserving
the evolvability of the Internet? Does the protocol enable future
developments?
If an old protocol is overloaded with new functionality, or reused
for new purposes, have the possible complexities introduced been
taken into account?
For a protocol that introduces new complexity to the Internet
architecture, does the protocol add robustness and preserve
evolvability? Does it also introduce unwanted new fragilities to the
system?
13.1. Discussion: evolvability.
There is an extensive literature and an ongoing discussion about the
evolvability, or lack of evolvability, of the Internet
infrastructure; the web page on "Papers on the Evolvability of the
Internet Infrastructure" has pointers to some of this literature
[Evolvability]. Issues range from the evolvability and overloading
of the DNS; the difficulties of the Internet in evolving to
incorporate multicast, QoS, or IPv6; the difficulties of routing in
meeting the demands of a changing and expanding Internet; and the
role of firewalls and other middleboxes in limiting evolvability.
[CWSB02] suggests that among all of the issues of evolvability,
"keeping the net open and transparent for new applications is the
most important goal." In the beginning, the relative transparency of
the infrastructure in transmitting packets from one end-node to
another was sufficient to ensure evolvability. However, this
transparency has become more murky over time, as cataloged in
[RFC3234]. [CWSB02] also realistically suggests the following
guideline: "Failures of transparency will occur - design what happens
then." Thus, maintaining evolvability also requires mechanisms for
allowing evolution in the face of a lack of transparency of the
infrastructure itself.
13.2. Discussion: overloading.
There has been a strong tendency in the last few years to overload
some designs with new functionality, with resulting operational
complexities. Extensible protocols could be seen as one of the tools
for providing evolvability. However, if protocols and systems are
stretched beyond their reasonable design parameters, then scaling,
reliability, or security isssues could be introduced. Examples of
protocols that could be seen as either productively extended, or as
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dangerously overloaded, include DNS [K02], MPLS, and BGP. In some
cases, overloading or extending a protocol may reduce total
complexity by avoiding the creation of a new protocol; in other cases
a new protocol might be the simpler solution.
We have a number of re-useable technologies, including component
technologies specifically designed for re-use. Examples include SASL,
BEEP and APEX. On the other hand, re-use should not go so far as to
turn a protocol into a Trojan Horse, as has happened with HTTP
[RFC3205].
13.3. Discussion: complexity, robustness, and fragility.
[WD02] gives a historical account of the evolution of the Internet as
a complex system, with particular attention to the tradeoffs between
complexity, robustness, and fragility. [WD02] describes the
robustness that follows from the simplicity of a connectionless,
layered, datagram infrastructure and a universal logical addressing
scheme, and, as case studies, describes the increasing complexity of
TCP and of BGP. The paper describes a complexity/robustness spiral
of an initially robust design and the appearance of fragilities,
followed by modifications for more robustness that themselves
introduce new fragilities. [WD02] conjectures that "the Internet is
only now beginning to experience an acceleration of this
complexity/robustness spiral and, if left unattended, can be fully
expected to experience arcane, irreconcilable, and far-reaching
robustness problems in the not-too-distant future." Citing [WD02],
[BFM02] views complexity as the primary mechanism that impedes
efficient scaling, and discusses the ways that complexity increases
capital and operational expenditures in carrier IP networks.
14. Internationalization.
Where protocols require elements in text format, have the possibly
conflicting requirements of global comprehensibility and the ability
to represent local text content been properly weighed against each
other?
14.1. Discussion: internationalization.
RFC 1958 [RFC1958] included a simple statement of the need for a
common language:
"Public (i.e. widely visible) names should be in case-independent
ASCII. Specifically, this refers to DNS names, and to protocol
elements that are transmitted in text format."
The IETF has studied character set issues in general [RFC 2130] and
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made specific recommendations for the use of a standardised approach
[RFC 2277]. The situation is complicated by the fact that some uses
of text are hidden entirely in protocol elements and need only be
read by machines, while other uses are intended entirely for human
consumption. Many uses lie between these two extremes, which leads to
conflicting implementation requirements.
For the specific case of DNS, the Internationalized Domain Name
working group is considering these issues. As stated in the charter
of that working group, "A fundamental requirement in this work is to
not disturb the current use and operation of the domain name system,
and for the DNS to continue to allow any system anywhere to resolve
any domain name." This leads to some very strong requirements for
backwards compatibility with the existing ASCII-only DNS. Yet since
the DNS has come to be used as if it was a directory service, domain
names are also expected to be presented to users in local character
sets.
This document does not attempt to resolve these complex and difficult
issues, but simply states this as an issue to be addressed in our
work. The requirement that names encoded in a text format within
protocol elements be universally decodable (i.e. encoded in a
globally standard format with no intrinsic ambiguity) does not seem
likely to change. However, at some point, it is possible that this
format will no longer be case-independent ASCII.
15. Conclusions
This document, in progress, suggests general architectural and policy
questions to be addressed when working on new protocols and standards
in the IETF.
We would welcome feedback on this document. Feedback could be send
to the editor, Sally Floyd, at floyd@icir.org.
16. Acknowledgements
This document has borrowed text freely from other IETF RFCs, and has
drawn on ideas from [ASSW02], [CWSB02], [M01] and elsewhere. This
document has developed from discussions in the IAB, and has drawn
from suggestions made at IAB Plenary sessions and on the ietf general
discussion mailing list. The case study on SIP was contributed by
James Kempf, and the case study on Stresses on DNS was contributed by
Karen Sollins. The discussions on Internationization and on
Overloading were based on an earlier document by Brian Carpenter and
Rob Austein. We have also benefited from discussions with Noel
Chiappa, Karen Sollins, John Wroclawski, and others, and from helpful
feedback from members of the IESG.
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17. Normative References
18. Informative References
[A02] Harald Alvestrand, "Re: How many standards or protocols...",
email to the ietf discussion mailing list, Message-id:
<598204031.1018942481@localhost>, April 16, 2002.
[ASSW02] T. Anderson, S. Shenker, I. Stoica, and D. Wetherall,
"Towards More Robust Internet Protocols", February 2002. [No public
URL yet.]
[BFM02] Randy Bush, Tim Griffin, and David Meyer, "Some Internet
Architectural Guidelines and Philosophy", internet draft, work in
progress, July 2002.
[BMMWRO02] S. Bradner, A. Mankin, R. Mahy, D. Willis, B. Rosen, J.
Ott, "Change Process for the Session Initiation Protocol (SIP)",
draft-tsvarea-sipchange-02.txt, internet draft, work in progress, May
2002.
[CDT01] Policy Concerns Raised by Proposed OPES Working Group
Efforts, email to the IESG, from the Center for Democracy &
Technology, August 3, 2001. URL "http://www.imc.org/ietf-
openproxy/mail-archive/msg00828.html".
[Clark88] David D. Clark, The Design Philosophy of the DARPA Internet
Protocols, SIGCOMM 1988.
[CWSB02] Clark, D., Wroslawski, J., Sollins, K., and Braden, R.,
"Tussle in Cyberspace: Defining Tomorrow's Internet", SIGCOMM 2002.
URL "http://www.acm.org/sigcomm/sigcomm2002/adprog.html".
[Evolvability] Floyd, S., "Papers on the Evolvability of the Internet
Infrastructure". Web Page, URL
"http://www.icir.org/floyd/evolution.html".
[K02] John C. Klensin, "Role of the Domain Name System", draft-
klensin-dns-role-03.txt, internet-draft, work in progress, June 2002.
[Layering] Floyd, S., "References on Layering and the Internet
Architecture", Web Page, URL "http://www.icir.org/floyd/layers.html".
[Multiplexing] S. Floyd, "Multiplexing, TCP, and UDP: Pointers to the
Discussion", Web Page, URL "http://www.icir.org/floyd/tcp_mux.html".
[M01] Tim Moors, A Critical Review of End-to-end Arguments in System
Design, 2001. URL "http://uluru.poly.edu/~tmoors/".
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[RFC1958] B. Carpenter, "Architectural Principles of the Internet",
RFC 1958, June 1996.
[RFC2211] Wroclawski, J., "Specification of the Controlled Load
Quality of Service", RFC 2211, September 1997.
[RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212, September 1997.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
and W. Weiss, "An Architecture for Differentiated Services", RFC
2475, December 1998.
[RFC2481] K. K. Ramakrishnan and S. Floyd, A Proposal to add Explicit
Congestion Notification (ECN) to IP, RFC 2481, January 1999.
[RFC2543] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg,
"SIP: Session Initiation Protocol", RFC 25434, March 1999.
[RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597. June 1999.
[RFC2598] Jacobson, V., Nichols, K. and K. Poduri, "An Expedited
Forwarding PHB", RFC 2598, June 1999.
[RFC2316] Bellovin, S., "Report of the IAB Security Architecture
Workshop", RFC 2316, April 1998.
[RFC3124] H. Balakrishnan and S. Seshan, "The Congestion Manager",
RFC 3124, June 2001.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z.
Shelby, "Performance Enhancing Proxies Intended to Mitigate Link-
Related Degradations", RFC 3135, June 2001.
[RFC3168] K.K. Ramakrishnan, S. Floyd, and D. Black, The Addition of
Explicit Congestion Notification (ECN) to IP, RFC 3168, Proposed
Standard, September 2001.
[RFC3205] K. Moore, "On the use of HTTP as a Substrate", RFC 3205,
February 2002.
[RFC3234] B. Carpenter and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, February 2002.
[RFC3238] S. Floyd and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC 3238,
Informational, January 2002.
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[RFC3360] Floyd, S., "Inappropriate TCP Resets Considered Harmful",
RFC 3360, August 2002.
[SCWA99] Stefan Savage, Neal Cardwell, David Wetherall, Tom Anderson,
"TCP Congestion Control with a Misbehaving Receiver", ACM Computer
Communications Review, October 1999.
[SRC84] J. Saltzer, D. Reed, and D. D. Clark, "End-To-End Arguments
In System Design", ACM Transactions on Computer Systems, V.2, N.4, p.
277-88. 1984.
[T89] D. Tennenhouse, "Layered Multiplexing Considered Harmful",
Protocols for High-Speed Networks, 1989.
[UNSAF] L. Daigle, "IAB Considerations for UNilateral Self-Address
Fixing (UNSAF)", draft-iab-unsaf-considerations-02.txt, internet-
draft, work in progress, June 2002.
[WD02] Walter Willinger and John Doyle, "Robustness and the Internet:
Design and Evolution", draft, March 2002, URL
"http://netlab.caltech.edu/internet/".
19. Security Considerations
This document does not propose any new protocols, and therefore does
not involve any security considerations in that sense. However,
throughout this document there are discussions of the privacy and
integrity issues and the architectural requirements created by those
issues.
20. IANA Considerations
There are no IANA considerations regarding this document.
AUTHORS' ADDRESSES
Internet Architecture Board
EMail: iab@iab.org
IAB Membership at time this document was completed:
Harald Alvestrand
Ran Atkinson
Rob Austein
Fred Baker
Leslie Daigle
Steve Deering
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Sally Floyd
Ted Hardie
Geoff Huston
Charlie Kaufman
James Kempf
Eric Rescorla
Mike St. Johns
This draft was created in August 2002.
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