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 of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 24, 2005. 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. Plonka Expires May 24, 2005 [Page 1] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 2] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 3] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 4] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 5] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 6] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 7] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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 Plonka Expires May 24, 2005 [Page 8] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 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, . 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]. Plonka Expires May 24, 2005 [Page 9] Internet-Draft Embedding IP Addresses Considered HarmfulNovember 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Plonka Expires May 24, 2005 [Page 10]