Global Routing Operations D. Plonka
Internet-Draft University of Wisconsin
Expires: December 7, 2004 June 8, 2004
Embedding Globally Routable Internet Addresses Considered Harmful
draft-ietf-grow-embed-addr-02
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document means to clarify best current practices in the Internet
community. Internet hosts should not contain globally routable
Internet Protocol addresses embedded within firmware or elsewhere as
part of their default configuration such that it influences run-time
behavior.
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Revision History
RFC-EDITOR: PLEASE REMOVE REVISION HISTORY BEFORE PUBLICATION. The
following is the revision history of this document
$Log: draft-ietf-grow-embed-addr.xml,v $
Revision 1.15 2004/06/08 14:16:45 plonka
revised conclusion based on input from Geoff Huston
added netgear-sntp technical report to list of informative references
Revision 1.14 2004/06/07 18:16:27 plonka
split references into normative and informative sections
Revision 1.13 2004/06/07 16:32:10 plonka
Set category to BCP.
Rewrote/resized abstract and introduction as suggested by Pekka Savola.
Improved section about using DNS names, re; hard-coding caveats, as
suggested by Pekka Savola.
Encouraged use of IPv4 documentation/example prefix 192.0.2.0/24 rather
than private addresses, as noted by Pekka Savola.
Mentioned IPv6 2001:DB8::/32 documentation prefix, as noted by Tom Petch.
Added note for RFC-editor requesting that revision history be removed.
Reworded various portions.
Renamed from "-00" to "-01" and updated date.
Revision 1.12 2003/12/05 15:51:23 plonka
typo fixes and updates from Michael Patton
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
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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
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.
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.
This document denounces the practice of embedding references to
unique, globally routable IP addresses in Internet hosts, describes
some of the resulting problems, and considers selected alternatives.
It also reminds 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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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 typically rely on a level of indirection
provided by the Domain Name System, RFC 2219 [6]. DNS permits the
service operator to reconfigure the resources for maintenance and to
load-balance 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 many DNS server implementations. Upon
receiving such a response to a query, resolvers typically will try
the answers in order, until one succeeds, 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 well after the IP address or block has been reassigned and
no longer hosts the service for which that traffic was intended.
Circa 1997, the authors of RFC 2101 [5] 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.
When IP addresses are used as service identifiers in the
configuration of many Internet hosts, the IP address blocks 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. Likewise, to facilitate IP address reuse, RFC 2050 [1],
encourages Internet Service Providers (ISPs) to treat address
assignments as "loans".
Because consumers are not necessarily experienced in the operation 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
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host to avoid embedding IP addresses in ways which cause the
aforementioned problems.
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3. Recommendations
Internet host and router designers, including network product
manufacturers, should not assume that their products will be deployed
and used in only a single global Internet, that they happen to
observe today. A myriad of private or future internets in which
these products will be used may not allow those hosts to establish
end-to-end communications with arbitrary hosts on the global
Internet. Since the product failure modes resulting from unknown
future states cannot be fully explored, one should avoid assumptions
regarding the longevity of our current 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 [7]) 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 is that
the Domain Name System resolver should have an interface enabling the
operator to either explicitly set the servers of his choosing or to
enable the use of a standard automated configuration protocol such as
DHCP, defined by RFC 2132 [8]. Within the operator interface, these
features should originally be disabled so that one consequence of
subsequently 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 IP
addresses associated with the Internet services they require.
However, 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 acquisitions and
litigation. A given vendor ought not assume that anyone will retain
control of a given zone indefinitely. RFC 2606 [2] defines the
IANA-reserved "example.com", "example.net", and "example.org" domains
for use in example configurations and documentation.
Default configurations, documentation, and example configurations for
Internet hosts should use Internet addresses that reside with special
blocks that have been reserved for these purposes, rather than
unique, globally routable IP addresses. For IPv4, RFC 3330 [3]
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states that the 192.0.2.0/24 block has been assigned for use in
documentation and example code. The IPv6 global unicast address
prefix 2001:DB8::/32 has been similarly reserved for documentation
purposes. Private Internet Addresses, as defined by RFC 1918 [4],
should not be used for such purposes.
Service providers and enterprise network operators should advertise
the identities of suitable local services. For instance, the DHCP
protocol, as defined by RFC 2132 [8], enables one to configure a
server to answer queries for service identitifiers to clients that
ask for them. When local services are available but not pervasively
advertised using such common protocols, designers are more likely
deploy ad hoc initialization mechanisms that unnecessarily rely on
central services.
Operators that provide public services on the global Internet, such
as the NTP community, should deprecate the explicit advertisement of
the IP addresses of public services. These addresses are ephemeral.
As such, their widespread citation in public service indexes
interferes with the ability to reconfigure the service as necessary
to address unexpected, increased traffic.
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4. Security Considerations
Embedding or "hard-coding" IP addresses within a host's configuration
often means that a 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 in that unknown parties may inadvertently be
trusted.
Internet host designers 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 decisions can be made, perhaps 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. IANA Considerations
This document creates no new requirements on IANA namespaces.
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6. Conclusion
When large numbers of homogenous Internet hosts are deployed, it is
particularly important that both their designers and other members of
the Internet community diligently assess host implementation quality
and reconfigurability.
Implementors of host services should avoid any kind of use of unique
globally routable IP addresses within a fixed configuration part of
the service implementation. If there is a requirement for
pre-configured state then care should be taken to use an appropriate
service identifier and use standard resolution mechanisms to
dynamically resolve the identifier into an IP address. Also, any
such identifiers should be alterable in the field through a
conventional command and control interface for the service.
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7. Acknowledgements
The author thanks the following reviewers for their contributions to
this document: Paul Barford, Geoff Huston, David Meyer, Mike
O'Connor, Michael Patton, Tom Petch, and Pekka Savola.
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8. References
8.1 Normative References
[1] Hubbard, K., "INTERNET REGISTRY IP ALLOCATION GUIDELINES", RFC
2050, BCP 12, November 1996.
[2] Eastlake, D., "Reserved Top Level DNS Names", RFC 2606, BCP 32,
June 1999.
[3] Internet Assigned Numbers Authority, "Special-Use IPv4
Addresses", RFC 3330, September 2002.
[4] Rekhter, Y., "Address Allocation for Private Internets", RFC
1918, BCP 5, February 1996.
8.2 Informative References
[5] Carpenter, B., "IPv4 Address Behaviour Today", RFC 2101,
February 1997.
[6] Hamilton, M., "Use of DNS Aliases for Network Services", RFC
2219, BCP 17, October 1997.
[7] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for
IPv4, IPv6 and OSI", RFC 2030, October 1996.
[8] Alexander, S., "DHCP Options and BOOTP Vendor Extensions", RFC
2132, March 1997.
[9] Plonka, D., "Flawed Routers Flood University of Wisconsin
Internet Time Server", August 2003,
<http://www.cs.wisc.edu/~plonka/netgear-sntp/>.
Author's Address
David Plonka
University of Wisconsin - Madison
EMail: plonka AT doit DOT wisc DOT edu
URI: http://net.doit.wisc.edu/~plonka/
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Appendix A. Background
In June 2003, the University of Wisconsin discovered that a 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 an unrelated bug in the
SNMP client, the affected products occasionally exhibit 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
source addresses, 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 [9].
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