Network Working Group B. Aboba INTERNET-DRAFT D. Thaler Category: Informational Microsoft Corporation 24 February 2007 Principles of Internet Host Configuration 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 becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 August 24, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document describes basic principles of Internet host configuration. It covers issues relating to configuration of parameters that affect the Internet layer, as well as parameters affecting higher layer protocols. Aboba & Thaler Informational [Page 1] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 Table of Contents 1. Introduction.............................................. 3 1.1 Terminology ........................................ 3 2. Principles ............................................... 5 2.1 Minimize Configuration ............................. 5 2.2 Less is More ....................................... 5 2.3 Diversity is Not a Benefit ......................... 6 2.4 Lower Layer Independence ........................... 7 2.5 Configuration is Not Access Control ................ 8 3. Additional Discussion .................................... 9 3.1 General Purpose Mechanisms ......................... 9 3.2 Service Discovery Protocols ........................ 9 3.3 Fate Sharing ....................................... 10 4. Security Considerations .................................. 11 4.1 Configuration Authentication ....................... 12 5. IANA Considerations ...................................... 13 6. References ............................................... 13 6.1 Informative References ............................. 13 Acknowledgments .............................................. 15 Authors' Addresses ........................................... 15 Full Copyright Statement ..................................... 16 Intellectual Property ........................................ 16 Aboba & Thaler Informational [Page 2] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 1. Introduction "Architectural Principles of the Internet" [RFC1958] documents architectural principles of the Internet. This document describes principles of Internet host configuration. It covers issues relating to configuration of parameters that affect the Internet layer, as well as parameters affecting higher layer protocols. In recent years, a number of architectural questions have arisen, for which we provide guidance to protocol developers: o What protocol layers and general approaches are most appropriate for configuration of various parameters. o The relationship between parameter configuration and service discovery. o The relationship between network access authentication and host configuration. o The role of link-layer protocols (including tunneling protocols) in Internet host configuration. The last point above is particularly important to address, since it can directly affect the properties of a link as seen by higher layers (for example, whether privacy extensions [RFC3041] are available to applications). 1.1. Terminology Internet layer configuration is defined as the configuration required to support the operation of the Internet layer. This includes, for example: IP address(es) IP address configuration includes both configuration of link-scope addresses as well as global addresses. Configuration of IP addresses is an important step, since this enables a host to fill in the source address in the packets it sends, as well as to receive packets destined to that address. As a result, the host can now receive unicast IP packets, rather requiring that IP packets be sent to the broadcast or multicast address. Configuration of an IP address also enables the use of IP fragmentation, since packets sent from the unknown address cannot be reliably reassembled (fragments from multiple hosts using the unknown address might be reassembled into a single IP packet). Configuration of an IP address also enables use of security facilities such as IPsec [RFC4301]. Aboba & Thaler Informational [Page 3] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 Subnet prefix(es) Once a subnet prefix is configured, hosts with an IP address can now send and receive unicast IP packets from on-link hosts. Default gateway(s) Once a default gateway is configured, hosts with an IP address can now send and receive unicast IP packets from off-link hosts. Mobility agent(s) While Mobile IPv4 [RFC3344] and Mobile IPv6 [RFC3775] include their own mechanisms for locating home agents, it is also possible for mobile nodes to require dynamic home agent configuration. Other parameters Internet layer parameter configuration also includes configuration of per-host (e.g. IP TTL, enabling/disabling of IP forwarding and source routing) and per-interface parameters (e.g. MTU). Boot service configuration Boot service configuration is defined as the configuration necessary for a host to obtain and perhaps also to verify an appropriate boot image. This is appropriate for diskless hosts looking to obtain a boot image via mechanisms such as TFTP [RFC1350], NFS [RFC3530] and iSCSI [RFC3720,RFC4173]. It also may be useful in situations where it is necessary to update the boot image of a host that supports a disk, such as in the Preboot eXecution Environment (PXE) [PXE][PXEOPT]. While strictly speaking boot services operate above the Internet layer, where boot service is used to obtain the Internet layer code, it may be considered part of Internet layer configuration. Higher-layer configuration is defined as the configuration required to support the operation of other components above the Internet layer. This includes, for example: Name Service Configuration Name service configuration includes the configuration required for the host to resolve names. This includes configuration of the addresses of name resolution servers, including IEN 116, DNS, WINS, iSNS and NIS servers, and the setting of name resolution parameters such as the NetBIOS node type, the DNS domain and search list, etc. It may also include the transmission or setting of the host's own name. Once the host has completed name server configuration, it is able to resolve names. This not only allows the host to communicate with other hosts whose IP address is not known, but to the extent that name services are utilized for service discovery, this also Aboba & Thaler Informational [Page 4] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 enables the host to discover services available on the network or elsewhere. Time Service Configuration Time service configuration includes configuration of servers for protocols such as SNTP and NTP. Since accurate determination of the time may be important to operation of the applications running on the host (including security services), configuration of time servers may be a prerequisite for higher layer operation. However, it is typically not a requirement for Internet layer configuration. Other service configuration This can include discovery of additional servers and devices, such as printers, SIP proxies, etc. 2. Principles This Section describes basic principles of Internet host configuration. 2.1. Minimize Configuration Anything that can be configured can be misconfigured. [RFC1958] Section 3.8 states: "Avoid options and parameters whenever possible. Any options and parameters should be configured or negotiated dynamically rather than manually." That is, to minimize the possibility of configuration errors, parameters should be automatically computed (or at least have reasonable defaults) whenever possible. For example, TCP [RFC793] does not require configuration of the Maximum Segment Size, but is able to compute an appropriate value. Sometimes the means by which a parameter is automatically computed by a protocol involves message exchanges by which a protocol configures itself. This is typical for capability negotiation, and often for discovery of other devices that implement the same protocol. 2.2. Less is More The availability of standardized, simple mechanisms for general- purpose Internet host configuration is highly desirable. [RFC1958] states, "Performance and cost must be considered as well as functionality" and "Keep it simple. When in doubt during design, choose the simplest solution." To allow protocol support in more types of devices, it is important to minimize the footprint requirement. For example, Internet hosts Aboba & Thaler Informational [Page 5] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 span a wide range of devices, from embedded devices operating with minimal footprint to supercomputers. Since the resources (memory, code size) available for host configuration may be very small, it is desirable for a host to able to configure itself in as simple a manner as possible. One interesting example is IP support in pre-boot execution environments. Since by definition boot configuration is required in hosts that have not yet fully booted, it is often necessary for pre- boot code to be executed from ROM, with minimal available memory. In PXE, prior to obtaining a boot image, the host is typically only be able to communicate using IP and UDP. This is one reason why Internet layer configuration mechanisms typically depend only on IP and UDP. After obtaining the boot image, the host will have the full facilities of TCP/IP available to it, including support for reliable transport protocols, IPsec, etc. In order to reduce complexity, it is desirable for Internet layer configuration mechanisms to avoid dependencies on higher layers. Since embedded hosts may wish to minimize the code included within a boot ROM, availability of higher layer facilities cannot be guaranteed during Internet layer configuration. In fact, it cannot even be guaranteed that all Internet layer facilities will be available. For example, IP fragmentation and reassembly may not work reliably until a host has obtained an IP address. 2.3. Diversity is Not a Benefit The number of host configuration mechanisms should be minimized. Diversity in Internet host configuration mechanisms presents several problems: Interoperability As configuration diversity increases, it becomes likely that a host will not support the configuration mechanism(s) available on the network to which it has attached, creating interoperability problems. Footprint In order to be able to interoperate, hosts need to implement all configuration mechanisms used on the media they support. This increases the required footprint, a burden for embedded devices. Redundancy To support diversity in host configuration mechanism(s), operators would need to support multiple configuration services to ensure that hosts connecting to their networks could configure themselves. This represents an additional expense for little discernible Aboba & Thaler Informational [Page 6] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 benefit. Latency As configuration diversity increases, hosts supporting multiple configuration mechanisms may spend increasing effort to determine which mechanism(s) are supported. This adds to configuration latency. Conflicts Whenever multiple mechanisms are available, it is possible that multiple configuration(s) will be returned. To handle this, hosts would need to merge potentially conflicting configurations. This would require conflict resolution logic, such as ranking of potential configuration sources, increasing implementation complexity. Additional traffic To limit configuration latency, hosts may simultaneously attempt to obtain configuration by multiple mechanisms, increasing on-the-wire traffic. 2.4. Lower Layer Independence [RFC1958] states, "Modularity is good. If you can keep things separate, do so." It is becoming increasingly common for hosts to support multiple network access mechanisms, including dialup, wireless and wired local area networks, GPRS, CDMA 1X-RTT, etc. As a result, it is desirable for hosts to be able to configure themselves on multiple networks without adding configuration code specific to a new link layer. As a result, it is highly desirable for Internet host configuration mechanisms to be independent of the underlying lower layer. That is, the link layer protocol (whether it be a physical link, or a virtual tunnel link) should only be explicitly aware of link-layer parameters (although it may configure link-layer parameters - see Section 2.1). Introduction of lower layer dependencies increases the likelihood of interoperability problems and adds to the number of Internet layer configuration mechanisms that hosts need to implement. Lower layer dependencies can be best avoided by keeping Internet host configuration above the link layer, thereby enabling configuration to be handled for any link layer that supports IP. In order to provide media independence, Internet host configuration mechanisms should be link-layer protocol independent. While there are examples of IP address assignment within the link Aboba & Thaler Informational [Page 7] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 layer (such PPP IPv4CP [RFC1332]), the disadvantages of this approach have now become apparent. The main disadvantages include the extra complexity of implementing different mechanisms on different link layers, and the difficulty in adding new parameters which would require defining a mechanism in each link layer protocol. For example, PPP IPv4CP and IPCP extensions for name service configuration [RFC1877] were developed at a time when DHCP [RFC2131] had not yet been widely implemented on access devices or in service provider networks. However, in IPv6 where link layer independent mechanisms such as stateless address configuration [RFC2462] and DHCPv6 [RFC2131,RFC3736] are available, PPP IPv6CP [RFC2472] instead simply configures an Interface-Identifier which is similar to a MAC address. In contrast, IKEv2 [RFC4306] repeats the same mistake as PPP IPv4CP by defining a Configuration Payload for Internet host configuration for both IPv4 and IPv6. As a result, extensions to link layer protocols for the purpose of Internet, Transport or Application layer configuration (including server configuration) should be avoided. Such extensions can negatively affect the properties of a link as seen by higher layers. For example, if a link layer protocol (or tunneling protocol) configures individual IPv6 addresses and precludes using any other addresses, then this can break privacy extensions [RFC3041]. Hence applications that desire privacy extensions may not function well. Similar issues may arise for other types of addresses, such as Cryptographically Generated Addresses [RFC3972], as well. Avoidance of lower layer dependencies also applies even where the lower layer in question may be link independent. For example, while Extensible Authentication Protocol (EAP) [RFC3748] may be run over any link satisfying the requirements of [RFC3748] Section 3.1, many link layers do not support EAP and therefore Internet layer configuration mechanisms with EAP dependencies would not usable on all links that support IP. 2.5. Configuration is Not Access Control Network access authentication is a distinct problem from Internet host configuration. Network access authentication is best handled independently of the configuration mechanisms in use for the Internet and higher layers. For example, attempting to control access by requiring authentication in order to obtain configuration parameters (such as an IP address) has little value if the user can manually configure the host. Having an Internet (or higher) layer protocol authenticate clients is appropriate to prevent resource exhaustion of a scarce resource on Aboba & Thaler Informational [Page 8] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 the server, but not for preventing rogue hosts from obtaining access to a link. Note that client authentication is not required for Stateless DHCPv6 [RFC3736] since it does not result in allocation of any limited resources on the server. 3. Additional Discussion 3.1. General Purpose Mechanisms Protocols should either be self-configuring (especially where fate sharing is important), or use general-purpose configuration mechanisms. Given the number of Internet host configuration mechanisms that have already been defined, and the problems resulting from the proliferation of these mechanisms, there is no apparent need for the development of additional general-purpose configuration mechanisms. When defining a new host parameter, protocol designers should first consider whether configuration is indeed necessary (see Section 2.1 for further discussion). If configuration is necessary, protocol designers should next consider: 1. Where the authoritative source of information is. For example, routers are authoritative for default gateway information, DNS servers are authoritative for DNS server information, etc. 2. Which type of administrator would be the source of the information. For example, router administrators and server administrators are often different sets of individuals. 3. Whether the parameter is a per-interface parameter or a global parameter. For example, most standard general purpose configuration protocols run on a per-interface basis and hence are more appropriate for per-interface parameters. Finally, protocol designers should choose to either make the protocol that needs the parameter be self-configuring, or use the most appropriate general purpose configuration mechanism (generally DHCP, but possibly a service discovery protocol as noted below in Section 3.2). The choice should be made taking into account all of the principles discussed in Section 2. 3.2. Service Discovery Protocols Higher-layer configuration often includes configuring addresses of servers. Hence the question arises as to how this differs from "service discovery" as provided by Service Discovery protocols such as SLPv2 [RFC2608]. Aboba & Thaler Informational [Page 9] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 In general-purpose configuration mechanisms such as DHCP, hosts on the same link are typically considered equivalent, and server instances are likewise considered equivalent. In service discovery protocols, on the other hand, a host desires to find a server satisfying a particular set of criteria, where the set of criteria may vary by request. In addition, service discovery protocols such as SLPv2 can support discovery of servers on the Internet [RFC3832], not just those within the local network. General-purpose configuration mechanisms such as DHCP, on the other hand, typically assume the server(s) in the local network contain the authoritative set of information. For the service discovery problem (i.e., where the criteria varies on a per-request basis, even from the same host), protocols should either be self-discovering (if fate sharing is critical), or use general purpose service discovery mechanisms. In order to avoid a dependency on multicast routing, it is necessary for a host to either restrict discovery to services on the local link or to discover the location of the Directory Agent (DA). Therefore the use of service discovery protocols beyond the local link is typically dependent on a parameter configuration mechanism. As a result, service discovery protocols are typically not appropriate for use in obtaining basic Internet layer configuration, although they can be used to obtain higher-layer configuration for parameters that don't meet the assumptions above made by general-purpose configuration mechanisms. 3.3. Fate Sharing If a server (or set of servers) is needed to get a set of configuration parameters, "fate sharing" ([RFC1958] Section 2.3) is preserved if the servers are ones without which the parameters could not be used, even if they were obtained via other means. For example, learning the default gateways from the gateways themselves via Router Advertisements provides perfect fate sharing. That is, the parameters can be obtained if and only if they can actually be used. Furthermore, the possibility of incorrect information being configured is minimized if there is only one machine which is authoritative for the information (i.e., there is no need to keep multiple authoritative servers in sync). While fate sharing is a desirable property of a configuration mechanism, existing configuration schemes typically only provide for fate sharing in limited circumstances. When utilized to discover services on the local link, service discovery protocols typically provide for fate sharing, since hosts providing service information Aboba & Thaler Informational [Page 10] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 typically also provide the services. However, where service discovery is assisted by a DA, fate sharing is typically not supported. The ability to discover services is dependent on whether the DA is operational, even though the DA is typically not involved in the delivery of the service. Since the DA and service agents (SAs) can be out of synchronization, it is possible for the DA to provide service information that is no longer current. For example, service descriptions provided to the DA by SAs might be included in response to service discovery queries even after the SAs were no longer operational. Similarly, recently introduced services might not yet have been registered by the DA. Similar limitations exist for other server-based configuration mechanisms such as DHCP. For example, typically DHCP servers do not check for the liveness of the configuration information they provide, or discover new configuration information automatically. As a result, there is no guarantee that configuration information will be current. "IPv6 Host configuration of DNS Server Information Approaches" [RFC4339] Section 3.3 discusses the use of well-known anycast addresses for discovery of DNS servers. The use of anycast addresses enables fate sharing, even where the anycast address is provided by an unrelated server. However, in order to be universally useful, this approach would require allocation of a well-known anycast address for each service. 4. Security Considerations Today IP configuration is typically not secured. For example, PPP IPv4CP [RFC1332] does not support secure negotiation, enabling an attacker with access to the link to subvert the negotiation. DHCPv4 [RFC2131] initially did not include support for security; this was added in [RFC3118]. DHCPv6 [RFC3736] does include security support. However, DHCP authentication is not yet widely implemented for either DHCPv4 or DHCPv6. A number of issues exist with various classes of parameters, as discussed in Section 2.6, [RFC3756] Section 4.2.7, [RFC3118] Section 1.1, and [RFC3315] Section 23. Given the potential vulnerabilities resulting from implementation of these options, it is currently common for hosts to restrict support for DHCP options to the minimum set required to provide basic TCP/IP configuration. Securing Internet layer configuration requires securing the protocol used to obtain it: Secure Neighbor Discovery (SEND) [RFC3971] for stateless address autoconfiguration, or DHCP authentication for stateful address configuration. Aboba & Thaler Informational [Page 11] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 4.1. Configuration Authentication While most threats against configuration mechanisms result in denial- of-service, some parameters are more critical. For example, since boot configuration determines the boot image to be run by the host, a successful attack on boot configuration could result in an attacker gaining complete control over a host. As a result, it is particularly important that boot configuration be secured. Internet host configuration parameters fall into two categories: those that are necessary for basic IP unicast connectivity (Internet layer configuration), and those that aren't (Higher layer configuration). The techniques available for securing Internet layer configuration are inherently limited, since classic security protocols such as IPsec [RFC4301] or TLS [RFC4346] cannot be used since an IP address is not yet available. Use of lower layer security mechanisms are limited by the "lower layer independence" principle. As a result, security mechanisms have typically been implemented within the configuration protocols themselves. For example, IPv6 supports SEcure Neighbor Discovery (SEND) [RFC3971], DHCPv4 supports DHCP authentication [RFC3118], and DHCPv6 supports an equivalent facility [RFC3315]. Higher layer configuration parameters, however, typically do not have this problem. When stateful DHCPv6 uses authentication for Internet layer configuration, higher-layer configuration parameters can be similarly secured. However, even if a host does not support DHCPv6 authentication, higher-layer configuration via Stateless DHCPv6 [RFC2462] can still be secured with IPsec. Possible exceptions to this may exist where security facilities may not yet be available until later in the boot process. For example, it may be difficult to secure boot configuration even once the Internet layer has been configured, because security code may not become available until after boot configuration has been completed. For example, Kerberos, IPsec or TLS may not yet be available. Finally, where public key cryptography is used to authenticate and integrity protect configuration, hosts need to be configured with trust anchors in order to validate received configuration messages. For a node which visits multiple administrative domains, acquiring the required trust anchors may be difficult. This is left as an area for future work. Aboba & Thaler Informational [Page 12] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 5. IANA Considerations This document has no actions for IANA. 6. References 6.1. Informative References [PXE] Henry, M. and M. Johnston, "Preboot Execution Environment (PXE) Specification", September 1999, http://www.pix.net/software/pxeboot/archive/pxespec.pdf [PXEOPT] Johnston, M., "DHCP Options for the Intel Preboot eXecution Environment (PXE)", draft-ietf-dhc-pxe-options-03.txt, Internet draft (work in progress), March 2006. [RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC1332] McGregor, G., "PPP Internet Control Protocol", RFC 1332, Merit, May 1992. [RFC1350] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC 1350, July 1992. [RFC1877] Cobb, S., "PPP Internet Protocol Control Protocol Extensions for Name Server Addresses", RFC 1877, December 1995. [RFC1958] Carpenter, B., "Architectural Principles of the Internet", RFC 1958, June 1996. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC2472] Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC 2472, December 1998. [RFC2608] Guttman, E., et al., "Service Location Protocol, Version 2", RFC 2608, June 1999. [RFC3041] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001. Aboba & Thaler Informational [Page 13] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 [RFC3315] Droms, R., Ed., Bound, J., Volz,, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002. [RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M. and D. Noveck, "Network File System (NFS) version 4 Protocol", RFC 3530, April 2003. [RFC3720] Satran, J., Meth, K., Sapuntzakis, C. Chadalapaka, M. and E. Zeidner, "Internet Small Computer Systems Interface (iSCSI)", RFC 3720, April 2004. [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC3756] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor Discovery (ND) Trust Models and Threats", RFC 3756, May 2004. [RFC3775] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [RFC3832] Zhao, W., Schulzrinne, H., Guttman, E., Bisdikian, C. and W. Jerome, "Remote Service Discovery in the Service Location Protocol (SLP) via DNS SRV", RFC 3832, July 2004. [RFC3971] Arkko, J., Kempf, J., Sommerfeld, B., Zill, B. and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005. [RFC4173] Sarkar, P., Missimer, D. and C. Sapuntzakis, "Bootstrapping Clients using the iSCSI Protocol", RFC 4173, September 2005. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. Aboba & Thaler Informational [Page 14] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 [RFC4339] Jeong, J., "IPv6 Host Configuration of DNS Server Information Approaches", RFC 4339, February 2006. [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006. Acknowledgments Bob Hinden and James Kempf provided valuable input on this document. Authors' Addresses Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 EMail: bernarda@microsoft.com Phone: +1 425 706 6605 Fax: +1 425 936 7329 Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052 EMail: dthaler@microsoft.com Aboba & Thaler Informational [Page 15] INTERNET-DRAFT Principles of Host Configuration 24 February 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Aboba & Thaler Informational [Page 16]