Network Working Group J. Klensin
Internet-Draft July 13, 2004
Expires: January 11, 2005
Terminology for Describing Internet Connectivity
draft-klensin-ip-service-terms-04.txt
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Abstract
As the Internet has evolved, many types of arrangements have been
advertised and sold as "Internet connectivity". Because these may
differ significantly in the capabilities they offer, the range of
options, and the lack of any standard terminology, the effort to
distinguish between these services has caused considerable consumer
confusion. This document provides a list of terms and definitions
that may be helpful to providers, consumers, and, potentially,
regulators in clarifying the type and character of services being
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offered.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 The Problem and the Requirement . . . . . . . . . . . . . 3
1.2 Adoption and a Non-pejorative Terminology . . . . . . . . 3
1.3 Definitional Terminology . . . . . . . . . . . . . . . . . 4
2. General Terminology . . . . . . . . . . . . . . . . . . . . . 4
3. Filtering or Security Issues and Terminology . . . . . . . . . 5
4. Additional Terminology . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
7. Disclaimers and Lawyers . . . . . . . . . . . . . . . . . . . 9
8. Informative References . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 11
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1. Introduction
1.1 The Problem and the Requirement
Different ISPs and other providers offer a wide variety of products
that are identified as "Internet" or "Internet access". These
products offer different types of functionality and, as a result,
some may be appropriate for certain users and uses and not others.
For example, a service that offers only access to the Web, but that
does not support any other type of Internet services, may be entirely
appropriate for someone who is exclusively interested in browsing and
in web-based email services, but not for someone who requires access
to download files or make more intense use of email. And it is
likely to be even less appropriate for someone who requires the
ability to operate servers for other users, who needs virtual private
network (VPN) capabilities or other secured access to a remote
office, or who needs to synchronize mail for offline use.
Recent, and rapidly evolving, changes to the Internet's email
environment have led to additional restrictions on sending and
retrieving email. These restrictions, most of them developed as part
of well-intentioned attempts to prevent or fight unsolicited mail of
various types, may be imposed independently of the service types
described below and are discussed separately in Section 3.
Of course, the document describes only the functions provided or
permitted by the service provider. It does not, and cannot, specify
the functions that pass through and are supported by various
user-provided equipment.
[[Note in Draft: This paragraph to be removed by the RFC Editor if
the document progresses that far.]] This document is a first attempt
at establishing some definitions for these various services. It is
hoped that the definitions will evolve into ones that can be
standardized and adopted widely enough to be useful to users and
consumers.
1.2 Adoption and a Non-pejorative Terminology
The definitions proposed here are clearly of little value if service
providers and vendors are not willing to adopt them. Consequently,
the terms proposed are intended to not be pejorative, despite the
belief of some members of the IETF community that some of these
connectively models are simply "broken" or "not really an Internet
service". The mention of a particular service or model in this
document does not imply any endorsement of it, only recognition of
something that exists, or might exist, in the marketplace.
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1.3 Definitional Terminology
When the terms SHOULD, MUST, or MAY are used, and capitalized, in
this document, they are used as defined in [1].
2. General Terminology
The terms listed in this section are the primary "IP Service Terms"
and it is hoped that service providers will adopt them in describing
offerings to potential users or customers.
Terms are listed below more or less in order of ascending (to "full
Internet") capability. In each case, the terminology refers to the
intent of the provider (ISP) as expressed in either technical
measures or terms and conditions of service. It may be possible to
work around particular implementations of these characteristic
connectivity types, but those flexibilities are generally not the
intent of the provider and are unlikely to be supported if the
workarounds stop working.
Web connectivity. This service provides connectivity to the web
only. Other services are generally not supported. In particular,
there may be no access to POP3 or IMAP email, encrypted tunnels or
other VPN mechanisms. The addresses used may be private and/or
not globally reachable. They are generally dynamic and relatively
short-lived (hours or days rather than months or years). These
addresses are often announced as "dynamic" to those who keep lists
of dial-up or dynamic addresses (see Section 3). The provider may
impose a filtering web proxy on the connections; that proxy may
change and redirect URLs to other sites than the one originally
specified by the user or embedded link.
Client connectivity only, without a public address. This service
provides access to the Internet without support for server or most
peer to peer functions. The IP address assigned to the customer
is dynamic and, as a distinguishing feature of this class, is
assigned from non-public address space. Servers and peer-to-peer
functions are generally not supported by the network address
translation (NAT) systems that are required by the use of private
addresses (the more precise categorization of types of NATs given
in [2] are somewhat orthogonal to this document but might be
provided as additional terms as described in Section 4).
Filtering web proxies are common with this type of service, and
the provider SHOULD indicate whether or not one is present.
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Client only, public address. This service provides access to the
Internet without support for server or most peer to peer
functions. The IP address assigned to the customer is in public
address space. It is usually nominally dynamic or otherwise
subject to change, but may not change for months at a time. Most
VPN and similar connections will work with this service. The
provider may prohibit the use of server functions by either legal
(contractual) restrictions or by filtering of incoming connection
attempts. Filtering web proxies are uncommon with this type of
service, and the provider SHOULD indicate if one is present.
Firewalled Internet Connectivity. This service provides access to
the Internet and supports most server and most peer to peer
functions with one or more (usually more) static public addresses.
It is similar in most respects to "Full Internet Connectivity",
below, and all of the qualifications and restrictions on
limitations described there apply. However, a managed "firewall"
is in place between the customer and the public Internet. This
may result in blocking of some services, and others may be
intercepted by proxies, content-filtering arrangements, or
applications gateways (although the latter three are less common).
The provider SHOULD specify which services are blocked and which
are intercepted or altered in other ways.
In most areas, this service arrangement is offered as an add-on,
extra-cost, option with what would otherwise be Full Internet
Connectivity.
Full Internet Connectivity. This service provides the user full
Internet connectivity, with one or more static public addresses.
Dynamic addresses that are long-lived enough to make operating
servers practical without highly dynamic DNS entries are possible,
provided that they are not characterized as "dynamic" to third
parties. Filtering web proxies, interception proxies, NAT, and
other provider-imposed restrictions on inbound or outbound ports
and traffic are incompatible with this type of service and servers
on a connected customer LAN are typically considered normal. The
only compatible restrictions are bandwidth limitations and
prohibitions against network abuse or illegal activities.
3. Filtering or Security Issues and Terminology
As mentioned in the Introduction, the effort to control or limit
objectionable network traffic including unsolicited mail of various
types (including "spam"); worms, viruses, and their impact; and in
some cases, specific content has led to additional restrictions on
the behavior and capabilities of internet services. In general,
significant restrictions are more likely to be encountered with web
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connectivity and non-public-address services, but some current
recommendations would apply them at all levels. Some of these mail
restrictions may prevent sending outgoing mail except through servers
operated by the ISP for that purpose, may prevent use of return
addresses of the user's choice, and may even prevent access to mail
depositories (other than those supplied by the provider) by
remote-access protocols such as POP3 or IMAP4. Because users may
have legitimate reasons to access remote file services, remote mail
submission servers (or at least to use their preferred email
addresses from multiple locations), and to access remote mail
depositories (again, a near-requirement if a single address is to be
used), it is important that providers disclose the services, filters,
and conditions they are making available or imposing.
Several key issues in email filtering are of particular importance:
Dynamic Addresses. A number of systems, including several
"blacklists", are based on the assumption that most undesired
email originated from systems with dynamic addresses, especially
dialup and home broadband systems. Consequently, they attempt to
prevent the addresses from being used to send mail, or perform
some other services, except through provider systems designated
for that purpose. Different techniques are used to identify
systems with dynamic addresses, including provider advertising of
such addresses to blacklist operators, heuristics that utilize
certain address ranges, and inspection of reverse-mapping domain
names to see if they contain telltale strings such as "dsl" or
"dial". In some cases, the absence of a reverse-mapping DNS
address is taken as an indication that the address is "dynamic"
(prohibition on connections based on the absence of a
reverse-mapping DNS record was a technique developed for FTP
servers many years ago; it was found to have fairly high rates
both of prohibiting legitimate connection attempts and failing to
prevent illegitimate ones). Service providers SHOULD describe
what they are doing in this area for both incoming and outgoing
message traffic, and users should be aware that, if an address is
advertised as "dynamic", it may be impossible to use it to send
mail to an arbitrary system even if Full Internet Connectivity is
otherwise provided.
Non-public addresses and NATs. The NAT systems that are used to map
between private and public address spaces may support connections
to distant mail systems for outbound and inbound mail, but terms
of service often prohibit the use of systems not supplied by the
connectivity provider as well as prohibiting the operation of
"servers" (typically not precisely defined) on the client
connection.
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Outbound port filtering from the provider. Another common technique
involves blocking connections to servers outside the provider's
control by blocking TCP "ports" that are commonly used for
messaging functions. Different providers have different theories
about this. Some prohibit their customers from accessing external
SMTP servers for message submission, but permit the use of the
mail submission protocol ([3]) with sender authentication. Others
try to block all outgoing messaging-related protocols, including
the use of remote mail retrieval protocols (less common with
public-address services than those that are dependent on private
addresses and NATs). If this type of filtering is present,
especially with "Client only, public address" and "Full Internet
Connectivity" services, the provider MUST indicate that fact (see
also Section 4). Still others may divert (reroute) outbound email
traffic to their own servers, on the theory that this eliminates
the need for users of portable machines to reconfigure them as
they connect from different network locations. Again, this MUST
be disclosed, especially since it can have signficant security and
privacy implications.
More generally, filters that block some or all mail being sent to
(or submitted to) remote systems (other than via
provider-supported servers), or that attempt to divert that
traffic to their own servers, are, as discussed above, becoming
common and SHOULD be disclosed.
4. Additional Terminology
These additional terms, while not as basic to understanding a service
offering as the ones identified above, as listed as additional
information that a service provider might choose to provide to
complement those general definitions. Or a potential customer might
use those that are relevant by, for example, constructing a list of
specific questions to ask.
Version support. Does the service include IPv4 support only, both
IPv4 and IPv6 support, or IPv6 support only?
Authentication support. Which technical mechanism(s) are used by the
service to establish and possibly authenticate connections?
Examples might include unauthenticated DHCP, PPP, RADIUS, or HTTP
interception.
VPNs and Tunnels. Is IPSec blocked or permitted? Are other
tunneling techniques at the IP layer or below, such as L2TP,
permitted? Is there any attempt to block applications-layer
tunnel mechanisms such as SSH?
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DNS support. Are users required to utilize DNS servers provided by
the service provider, or are DNS queries permitted to reach
arbitrary servers?
IP-related services. Are ICMP messages to and from end user sites
generally blocked or permitted? Are specific functions such as
ping and traceroute blocked and, if so, at what point in the
network?
Roaming support. Does the service intentionally include support for
IP roaming and, if so, how is this defined?
For "broadband" connections, is some dialup arrangement provided
for either backup or customer travel? If present, does that
arrangement have full access to mailboxes, etc.
Applications services provided. Are email services and/or web
hosting provided as part of the service, and on what basis? An
email services listing should identify whether POP3, IMAP, or web
access are provided and in what combinations and what types of
authentication and privacy services are supported or required for
each.
Use and Blocking of Outbound Applications Services. Does the service
block use of SMTP or mail submission to other than its own servers
or intercept such submissions and route them to its servers? Do
its servers restrict the user to use of its domain names on
outbound email? (For email specifically, also see Section 3
above.) Is FTP PASV supported or blocked? Are blocks or
intercepts imposed on other file sharing or file transfer
mechanisms, on conferencing applications, or on private
applications services? More generally, the provider should
identify any actions of the service to block, restrict, or alter
the destination of, the outbound use (i.e., the use of services
not supplied by the provider or on the provider's network) of
applications services.
Use and Blocking of Inbound Applications Services. In addition to
any issues raised by dynamic or private address space (when
present), does the service take any other measures to specifically
restrict the connections that can be made to equipment operated by
the customer? Specifically, are inbound SMTP, HTTP or HTTPS, FTP,
or various peer-to-peer or other connections (possibly including
applications not specifically recognized by the provider)
prohibited and, if so, which ones?
Application Content Filtering. The service should declare whether it
provides filtering or protection against worms or denial of
service attacks against its customers, virus and UCE filtering for
its mail services (if any), non-discretionary or "parental
control" filtering of content, and so on.
Wiretapping and interception. The service should indicate whether
traffic passing through it is subject to lawful intercept with or
without notice? Is traffic data stored for possible use by law
enforcement with or without notice?
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5. Security Considerations
This document is about terminology, not protocols, and does not raise
any particular security issues. However, if the type of terminology
that is proposed is widely adopted, it may become easier to identify
security-related expectations of particular hosts, LANs, and types of
connections.
6. Acknowledgements
This document was inspired by an email conversation with Vernon
Schryver, Paul Vixie, and Nathaniel Bornstein. While there have been
proposals to produce definitions like the ones above for many years,
that conversation convinced the author that it was finally time to
get a strawman on the table to see if the IETF could actually carry
it forward. Harald Alvestrand, Brian Carpenter, George Michaelson,
Vernon Schryver, and others made several suggestions on the initial
draft that resulted in clarifications to the second one and Stephane
Bortzmeyer, Brian Carpenter, Tony Finch, Susan Harris, Pekka Savola,
and Vernon Schryver made very useful suggestions that were
incorporated into subsequent versions. Susan Harris also gave the
penultimate version an exceptional careful reading, which is greatly
appreciated.
7. Disclaimers and Lawyers
[[Note to the IESG and in Draft: several of the people who have
contributed to, or commented on, this document have observed that, if
it is considered successful, sections of it could well end up in
national or local regulations, other types of consumer protection
provisions, or contractual terms and conditions. Given that concern,
the IESG is requested, to consult legal counsel as to whether the
normal disclaimers, which were designed somewhat more for protocol
specifications, are adequate to prevent creating (quoting from one
contributor), "the smallest atom of liability for the author, the
IETF, the RFC Editor, ISOC, or anyone else within 10000 km" from
liability. This section should then be removed and, if needed,
replaced by text here or elsewhere in the document as appropriate.]]
8 Informative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Srisuresh, P. and M. Holdrege, "IP Network Address Translator
(NAT) Terminology and Considerations", RFC 2663, August 1999.
[3] Gellens, R. and J. Klensin, "Message Submission", RFC 2476,
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December 1998.
Author's Address
John C Klensin
1770 Massachusetts Ave, #322
Cambridge, MA 02140
USA
Phone: +1 617 491 5735
EMail: john-ietf@jck.com
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