Global Routing Operations                                      D. Plonka
Internet-Draft                                   University of Wisconsin
Expires: December 7, 2004                                   June 8, 2004

   Embedding Globally Routable Internet Addresses Considered Harmful

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on December 7, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.


   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

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Revision History

   following is the revision history of this document

   $Log: draft-ietf-grow-embed-addr.xml,v $
   Revision 1.17  2004/06/08 20:27:02  plonka
   minor edits

   renamed from "-02" to "-03"

   Revision 1.16  2004/06/08 20:15:03  plonka
   minor edits, fixed some typos

   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 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

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   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

   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.  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
   address 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 fix problems
   if and when they arise.  As such, a significant responsibility lies
   with the manufacturer or vendor of the Internet host to avoid

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   embedding IP addresses in ways which cause the aforementioned

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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 "", "", and "" domains
   for use in example configurations and documentation.

   Default configurations, documentation, and example configurations for
   Internet hosts should use Internet addresses that reside within
   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 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, such as NTP.  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 including NTP 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

   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 decision 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

        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,

Author's Address

   David Plonka
   University of Wisconsin - Madison

   EMail: plonka AT doit DOT wisc DOT edu

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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:, which was also known as "", a public
   stratum-2 NTP server.

   Due to that embedded fixed configuration and an unrelated bug in the
   SNTP client, the affected products occasionally exhibit 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
   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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