Network Working Group D. Plonka
Internet-Draft University of Wisconsin
Expires: April 18, 2004 October 19, 2003
Embedding Globally Routable Internet Addresses Considered Harmful
draft-plonka-embed-addr-00
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
Vendors of consumer electronics and network gear have produced and
sold hundreds of thousands of Internet hosts with globally routable
Internet Protocol addresses embedded within their products' firmware.
These products are now in operation world-wide and primarily include,
but are not necessarily limited to, low-cost routers and middleboxes
for personal or residential use.
This "hard-coding" of globally routable IP addresses within the
host's firmware presents significant problems to the operation of the
Internet and to the management of its address space.
This document means to clarify best current practices in the Internet
community. It denouces the practice of embedding references to
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unique, globally routable IP addresses in Internet hosts, describes
some of the resulting problems, and considers selected alternatives.
It is also intended to remind the Internet community of the ephemeral
nature of unique, globally routable IP addresses and that the
assignment and use of such addresses is temporary and therefore
should not be used in fixed configurations.
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1. Introduction
Internet hosts should not contain globally routable Internet Protocol
addresses embedded within firmware or elsewhere as part of their
default configuration influencing their run-time behavior.
Ostensibly, this practice arose as an attempt to implement of "zero
configuration" with neither peer review nor the use of a proposed or
standard Internet protocol to do so. Unfortunately, products which
rely on such embedded IP addresses initially may appear convenient to
both the product's designer and its operator or user, but this
dubious benefit comes at the expense of others in the Internet
community.
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2. Problems
In a number cases, the embedding of IP addresses has caused Internet
products to rely on a single central Internet service, which can
result in a collapse when the aggregate workload overwhelms that
service. When fixed addresses are embedded in an ever-increasing
number of client IP hosts, this practice runs directly counter to the
design intent of hierarchically deployed services that would
otherwise be robust solutions.
The reliability, scalability, and performance of many Internet
services require that the pool of users not directly access a service
by IP address. Instead they rely on a level of indirection provided
by the DNS, RFC 2219 [2]. DNS permits the service operator to
reconfigure the resources for maintenance and load-balancing without
the participation of the users. For instance, a load-balancing
technique in common use today employs multiple DNS records with the
same name which are then doled out in a round-robin fashion by the
Berkeley Internet Name Daemon (BIND) and other DNS server
implementations. This enables the operator to distribute the user
request load across a set of servers with discrete IP addresses,
which generally remain unknown to the user.
Furthermore, embedding globally unique IP addresses taints the IP
address blocks in which they reside, lessening the usefulness and
portability of those IP address blocks and increasing the cost of
operation. Unsolicited traffic may continue to be delivered to the
embedded addresses for historical reasons, even after the IP address
or block has been reassigned. IP address blocks containing addresses
that have been embedded into the configuration of many Internet hosts
become encumbered by their historical use. This may interfere with
the ability of the Internet Assigned Numbers Authority (IANA) and the
Internet Registry (IR) hierarchy to usefully reallocate IP address
blocks. This is of particular concern as the IPv4 address space nears
exhaustion. Note that, to facilitate IP address reuse, RFC 2050 [3],
encourages Internet Service Providers (ISPs) to treat address
assignments as "loans".
Because consumers are not necessarily capable, experienced operators
of Internet hosts, they are not able to be relied upon to implement a
fix if and when problems arise. As such, a significant
responsibility lies with the manufacturer or vendor of the Internet
host to avoid embedding IP addresses.
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3. Recommendations
Network product manufacturers should not assume that their products
will only be deployed on a single (mythical) global Internet, that
they happen to observe today. A myriad of private internets in which
these products will be used will often not allow these hosts to
establish end-to-end communications with arbitrary hosts on the
global Internet.
Vendors should, by default, disable unnecessary features in their
products. This is especially true of features that generate
unsolicited traffic. In this way these hosts will be conservative
regarding the unsolicited Internet traffic they produce. For
instance, one of the most common uses of embedded IP addresses has
been the hard-coding of addresses of well know public Simple Network
Time Protocol (SNTP RFC 2030 [4]) servers, even though only a small
fraction of the users benefits from these products even having some
notion of the current date and time.
Vendors should provide an operator interface for every feature that
generates unsolicited IP traffic. Non-default configuration should
be required to enable these features so that, as a consequence, the
operator becomes aware that the feature exists. This will mean that
it is more likely that the product's owner or operator can
participate in problem determination and mitigation if and when
problems arise.
Internet hosts should use the Domain Name System to determine the
routable IP addresses associated with the Internet services they
require. However, note that simply hard-coding DNS names rather than
IP addresses is not a panacea. Entries in the domain name space are
also ephemeral and can change owners for various reasons including
such as acquisitions and litigation. A given vendor ought not assume
that it will retain control of a given zone indefinitely.
Whenever possible, default configurations, documentation, and example
configurations for Internet hosts should use Private Internet
Addresses, as defined by RFC 1918 [1], rather than unique, globally
routable IP addresses.
Service providers and enterprise network operators should advertise
the identities of suitable local services. For instance, the DHCP
protocol, as defined by RFC 2132 [5], enables one to configure a
server to answer queries regarding available servers to clients that
ask for them. Unless the advertisement of local services is
ubiquitous, designers may resort to ad hoc mechanisms which rely on
central services.
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Operators that provide public services on the global Internet, such
as the the NTP community, should deprecate the advertisement of the
explicit IP addresses of public services. These addresses are
ephemeral, and their widespread citations in indexes of public
services interferes with these services to be reconfigured to scale
with unexpected, increased load.
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4. Security Considerations
Embedding or "hard-coding" IP addresses within a host's configuration
almost always means that some sort of host-based trust model is being
employed, and that the Internet host with the given address is
trusted in some way. Due to the ephemeral roles of routable IP
addresses, the practice of embedding them within products' firmware
or default configurations presents a security risk.
An Internet host designer may be tempted to implement some sort of
remote control mechanism within a product, by which its Internet host
configuration can be changed without reliance on, interaction with,
or even the knowledge of its operator or user. This raises security
issues of its own. If such a scheme is implemented, this should be
fully disclosed to the customer, operator, and user so that an
informed decision can be made, in accordance with local security or
privacy policy. Furthermore, the significant possibility of
malicious parties exploiting such a remote control mechanism may
completely negate any potential benefit of the remote control scheme.
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5. Conclusion
As larger number of homogenous hosts continue to be deployed, it is
particularly important that both designers and other members of the
Internet community are diligent in assessing host implementation
quality and reconfigurability. Unique, globally routable IP
addresses should not be embedded within a host's fixed configuration
because doing so excludes the ability to remotely influence hosts
when the unsolicited traffic they generate causes problems for the
for those operating the IP addresses to which the traffic is
destined.
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References
[1] Rekhter, Y., "Address Allocation for Private Internets", RFC
1918, BCP 5, February 1996.
[2] Hamilton, M., "Use of DNS Aliases for Network Services", RFC
2219, BCP 17, October 1997.
[3] Hubbard, K., "INTERNET REGISTRY IP ALLOCATION GUIDELINES", RFC
2050, BCP 12, November 1996.
[4] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for
IPv4, IPv6 and OSI", RFC 2030, October 1996.
[5] Alexander, S., "DHCP Options and BOOTP Vendor Extensions", RFC
2132, March 1997.
Author's Address
David J. Plonka
University of Wisconsin - Madison
DoIT, room b263
1210 W. Dayton Street
Madison, WI 53705
US
Phone: +1 608 265 5184
EMail: plonka@doit.wisc.edu
URI: http://net.doit.wisc.edu/~plonka/
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