Global Routing Operations D. Plonka
Internet-Draft University of Wisconsin
Expires: May 1, 2004 November 2003
Embedding Globally Routable Internet Addresses Considered Harmful
draft-ietf-grow-embed-addr-00
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Copyright Notice
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 as identifiers
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 IP addresses as identifiers is temporary and
therefore should not be used in fixed configurations.
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Revision History
The following is the revision history of this document since "-00":
$Log: draft-ietf-grow-embed-addr.xml,v $
Revision 1.11 2003/12/02 22:28:04 plonka
renamed from draft-plonka-embed-addr to draft-ietf-grow-embed-addr
integrated suggestions from Paul Barford
reordered references to match the text
added quote from RFC2101 re: use of IPv4 addresses as identifiers
as mentioned by Brian Carpenter
Revision 1.10 2003/11/03 17:06:54 plonka
added background information in appendix
Revision 1.9 2003/11/03 16:39:30 plonka
various updates based on input from Mike O'Connor:
- indicated that DNS server(s) should be configurable
- clarified DNS round-robin behavior
- clarified "unsolicited traffic" by saying "IP traffic"
added revision history and appendix A
Figure 1
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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 simplify
configuration of IP hosts by preloading them with IP addresses as
service identifiers. Unfortunately, products that 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. This can
result in a service outage 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 Domain Name System, RFC 2219 [1]. DNS permits the service
operator to reconfigure the resources for maintenance and
load-balancing without the participation of the users. For instance,
one common load-balancing technique employs multiple DNS records with
the same name that are then rotated in a round-robin fashion in the
set of answers returned by the Berkeley Internet Name Daemon (BIND)
and other DNS server implementations. Upon receiving such as
response to a query, resolvers typically use the first valid answer
in the set, thus enabling the operator to distribute the user request
load across a set of servers with discrete IP addresses that
generally remain unknown to the user.
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, even after the IP address or block has been reassigned and
no longer hosts the service for which that traffic was meant. Circa
1997, the authors of RFC 2101 [3] made this observation:
Due to dynamic address allocation and increasingly frequent
network renumbering, temporal uniqueness of IPv4 addresses is no
longer globally guaranteed, which puts their use as identifiers
into severe question.
In this way, 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 [2],
encourages Internet Service Providers (ISPs) to treat address
assignments as "loans".
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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
Internet host and router designers, including network product
manufacturers, should not assume that their products will only be
deployed on a single 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 IP 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. A prime example of this that the
Domain Name System resolver should have an interface enabling the
operator to either explicitl set the servers of his choosing or to
enable the use of a standard automated configuration protocol such as
DHCP, defined by RFC 2132 [5]. Within the operator interface, these
features should be disabled by default so that one consequence of
enabling these features is that 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 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 [6], 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
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ask for them. Unless the advertisement of local services is
ubiquitous, designers may resort to ad hoc mechanisms that rely on
central services.
Operators that provide public services on the global Internet, such
as the NTP community, should deprecate the explicit advertisement of
IP addresses of public services. These addresses are ephemeral. As
such, their widespread citations in public service indexes interferes
with the ability to reconfigure the service as necessary to address
unexpected, increased workloads.
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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 numbers of homogenous hosts continue to be deployed, it is
particularly important that both their 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 IP traffic they generate causes problems for the
for those operating the IP addresses to which the traffic is
destined.
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6. Acknowledgements
Thanks go to the following folks for providing input during the
preparation of this document: Paul Barford and Mike O'Connor.
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References
[1] Hamilton, M., "Use of DNS Aliases for Network Services", RFC
2219, BCP 17, October 1997.
[2] Hubbard, K., "INTERNET REGISTRY IP ALLOCATION GUIDELINES", RFC
2050, BCP 12, November 1996.
[3] Carpenter, B., "IPv4 Address Behaviour Today", RFC 2101,
February 1997.
[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.
[6] Rekhter, Y., "Address Allocation for Private Internets", RFC
1918, BCP 5, February 1996.
Author's Address
David J. Plonka
University of Wisconsin - Madison
DoIT, room b116
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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Appendix A. Background
In June 2003, the University of Wisconsin discovered that the network
product vendor named NetGear had manufactured and shipped over
700,000 routers with firmware containing a hard-coded reference to
the IP address of one of the University's NTP servers:
128.105.39.11, which was also known as "ntp1.cs.wisc.edu", a public
stratum-2 NTP server.
Due to that embedded fixed configuration and a bug in the
implementation, the NetGear SNTP client has a failure mode in which
each flawed router produces one query per second destined for the IP
address 128.105.39.11, and hence produces a large-scale flood of
Internet traffic from hundreds-of-thousands of legitimate source
addresses and destined for the University's network resulting in
significant operational problems.
These flawed routers are widely deployed throughout the global
Internet and are likely to remain in use for years to come. As such,
the University of Wisconsin with the cooperation of NetGear will
build a new anycast time service which aims to mitigate the damage
caused by the misbehavior of these flawed routers.
A technical report regarding the details of this situation is
available on the world-wide-web: Flawed Routers Flood University of
Wisconsin Internet Time Server [7]
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