Global Routing Operations                                      D. Plonka
Internet-Draft                                   University of Wisconsin
Expires: May 1, 2004                                       November 2003

   Embedding Globally Routable Internet Addresses Considered Harmful

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   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

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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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   [1]  Hamilton, M., "Use of DNS Aliases for Network Services", RFC
        2219, BCP 17, October 1997.

        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

   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:, 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, 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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   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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