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Versions: 00 01 02 03 04 05 RFC 4085

Global Routing Operations                                      D. Plonka
Internet-Draft                                   University of Wisconsin
Expires: May 24, 2005                                  November 23, 2004


   Embedding Globally Routable Internet Addresses Considered Harmful
                     draft-ietf-grow-embed-addr-05

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
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Copyright Notice

   Copyright (C) The Internet Society (2004).

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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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Problems . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Recommendations  . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1   Disable Unused Features  . . . . . . . . . . . . . . . . .  5
     3.2   Provide User Interface for IP Features . . . . . . . . . .  5
     3.3   Use Domain Names as Service Identifiers  . . . . . . . . .  5
     3.4   Use Special-Purpose, Reserved IP Addresses When
           Available  . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.5   Discover and Utilize Local Services  . . . . . . . . . . .  6
     3.6   Avoid Mentioning the IP Addresses of Services  . . . . . .  7
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   8.1   Normative References . . . . . . . . . . . . . . . . . . . .  8
   8.2   Informative References . . . . . . . . . . . . . . . . . . .  8
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  9
   A.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  9
       Intellectual Property and Copyright Statements . . . . . . . . 10





























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1.  Introduction

   Vendors of consumer electronics and network gear have unfortunately
   chosen to embed, or "hard-code", globally routable Internet Protocol
   addresses within their products' firmware.  These products use these
   embedded IP addresses as service identifiers and direct service
   requests (unsolicited Internet traffic) to them.  One recent example
   was the embedding of the globally routable IP address of a Network
   Time Protocol server in the firmware of hundreds of thousands of
   Internet hosts that are now in operation world-wide.  The hosts are
   primarily, 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.

2.  Problems

   In a number cases, the embedding of IP addresses in products has
   caused an increasing number of Internet hosts 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].  When appropriately
   utilized, DNS permits the service operator to reconfigure the
   resources for maintenance and to load-balance without the



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   participation of the users and without necessitating configuration
   changes in the client hosts.  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 mobility 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 [7] 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
   embedding IP addresses in ways which cause the aforementioned
   problems.

3.  Recommendations

   Internet host and router designers, including network product
   manufacturers, should not assume that their products will be deployed
   and used in only the single global Internet that they happen to
   observe today.  A myriad of private or future internetworks in which
   these products will be used may not allow those hosts to establish
   communications with arbitrary hosts on the global Internet.  Since
   the product failure modes resulting from unknown future states cannot



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   be fully explored, one should avoid assumptions regarding the
   longevity of our current Internet.

   The following recommendations are presented as best practice today:

3.1  Disable Unused Features

   Vendors should, by default, disable unnecessary features in their
   products.  This is especially true of features that generate
   unsolicited Internet 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 known public Simple
   Network Time Protocol (SNTP RFC 2030 [8]) servers, even though only a
   small fraction of the users benefits from these products even having
   some notion of the current date and time.

3.2  Provide User Interface for IP Features

   Vendors should provide an operator interface for every feature that
   generates unsolicited Internet 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 [9].  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.

   RFC 2606 [2] defines the IANA-reserved "example.com", "example.net",
   and "example.org" domains for use in example configurations and
   documentation.  These are candidate examples to be used in user
   interface documentation.

3.3  Use Domain Names as Service Identifiers

   Internet hosts should use the Domain Name System to determine the IP
   addresses associated with the Internet services they require.

   When using domain names as service identifiers in the configurations
   of deployed Internet hosts, designers and vendors are encouraged to
   introduce service names either within a domain which they control or
   have entered into an agreement with its operator to utilize (such as
   for public services provided by the Internet community).  This is
   commonly done by simply introducing a service-specific prefix to the



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   domain name.

   For instance, a vendor named "Example, Inc." with the domain
   "example.com" might configure its product to find its SNTP server by
   the name "sntp-server.config.example.com" or even by a product and
   version-specific name such as
   "sntp-server.v1.widget.config.example.com".  Here, the
   "config.example.com" namespace is dedicated to that vendor's product
   configuration, with sub-domains introduced as deemed necessary.  Such
   special-purpose domain names enable ongoing maintenance and
   reconfiguration of the services for their client hosts and can aid in
   the ongoing measurement of service usage throughout the product's
   lifetime.

   An alternative to inventing vendor-specific domain naming conventions
   for a product's service identifiers is to utilize SRV resource
   records (RR), defined by RFC 2782 [10].  SRV records are a generic
   type of RR which uses a service-specific prefix in combination with a
   base domain name.  For example, an SRV-cognizant SNTP client might
   discover Example, Inc.'s suggested NTP server by performing an
   SRV-type query to lookup for "_ntp._udp.example.com".

   However, note that simply hard-coding DNS name service identifiers
   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.  As such, developers
   and vendors should explore a product's potential failure modes
   resulting from the loss of administrative control of a given domain
   for whatever reason.

3.4  Use Special-Purpose, Reserved IP Addresses When Available

   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]
   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 RFC 3849 [4].  Private Internet Addresses, as defined by RFC
   1918 [5], should not be used for such purposes.

3.5  Discover and Utilize Local Services

   Service providers and enterprise network operators should advertise
   the identities of suitable local services, such as NTP.  Very often
   these services exist, but the advertisement and automated
   configuration of their use is missing.  For instance, the DHCP



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   protocol, as defined by RFC 2132 [9], 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.

3.6  Avoid Mentioning the IP Addresses of Services

   Operators that provide public services on the global Internet, such
   as those in 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 and the
   aforementioned problems.

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 globally 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, its presence
   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.
   As such, remote control mechanisms should be disabled by default to
   be subsequently enabled and disabled by the user.

5.  IANA Considerations

   This document creates no new requirements on IANA namespaces.

6.  Conclusion

   When large numbers of homogenous Internet hosts are deployed, it is
   particularly important that both their designers and other members of



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   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.

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.  Harald
   Alvestrand, Spencer Dawkins, Ted Hardie, and Thomas Narten provided
   valuable feedback during AD and IESG review.

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]  Huston, G., "IPv6 Address Prefix Reserved for Documentation",
        RFC 3849, July 2004.

   [5]  Rekhter, Y., "Address Allocation for Private Internets", RFC
        1918, BCP 5, February 1996.

8.2  Informative References

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

   [7]   Carpenter, B., "IPv4 Address Behaviour Today", RFC 2101,
         February 1997.

   [8]   Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for



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         IPv4, IPv6 and OSI", RFC 2030, October 1996.

   [9]   Alexander, S., "DHCP Options and BOOTP Vendor Extensions", RFC
         2132, March 1997.

   [10]  Gulbrandsen, A., "A DNS RR for specifying the location of
         services (DNS SRV)", RFC 2782, February 2000.

   [11]  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/

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
   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 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 [11].




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Intellectual Property Statement

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Acknowledgment

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   Internet Society.




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