DNSEXT Working Group Levon Esibov INTERNET-DRAFT Bernard Aboba Category: Standards Track Dave Thaler
<draft-ietf-dnsext-mdns-04.txt><draft-ietf-dnsext-mdns-05.txt> Microsoft 1314 September 2001 Multicast DNS This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Abstract Today, with the rise of home networking, there are an increasing number of ad-hoc networks operating without a DNS server. In order to allow DNS name resolution in such environments, the use of a multicast DNS is proposed. Table of Contents 1. Introduction .......................................... 3 2. Name resolution using multicast DNS ................... 3 2.1 Behavior of the sender and responder ............ 4 3. Usage model ........................................... 7 3.1 mDNS configuration .............................. 7 4. Sequence of events .................................... 8 5. Conflict resolution ................................... 8 5.1 Considerations for multiple interfaces .......... 10 5.2 API issues ...................................... 12 6. IANA considerations ................................... 12 7. ARPA domain considerations ............................ 12 8. References ............................................ 13 9. Security considerations ............................... 14 ACKNOWLEDGMENTS .............................................. 15 AUTHORS' ADDRESSES ........................................... 15 Intellectual Property Statement .............................. 16 Full Copyright Statement ..................................... 16 1. Introduction Multicast DNS enables DNS name resolution in the scenarios when conventional DNS name resolution is not possible. Namely, when there are no DNS servers available on the network or available DNS servers do not provide name resolution for the names of the hosts on the local network. The latter case, for example, corresponds to a scenario when a network that doesn't have a DNS server is connected to the Internet through an ISP and the network hosts are configured with the ISP's DNS server for the name resolution. The ISP's DNS server provides the name resolution for the names registered on the Internet, but doesn't provide name resolution for the names of the hosts on the network. This document discusses multicast DNS, an extension to the DNS protocol which consists of a single change to the method of use, and no change to the format of DNS packets. Service discovery in general as well as discovery of DNS servers using mDNS in particular is outside of the scope of this document, as is name resolution over non-multicast capable media. In this document, the key words "MAY", "MUST, "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in . 2. Name resolution using Multicast DNS This extension to the DNS protocol consists of a single change to the method of use, and no change to the current format of DNS packets. Namely, this extension allows multicast DNS queries to be sent to and received on port 53. This extension allows multicast DNS queries to be sent to and received on port 53 using a LINKLOCAL address  for IPv4 and the "solicited name" LINKLOCAL multicast addresses for IPv6. LINKLOCAL addresses are used to prevent propagation of multicast DNS traffic across routers, potentially flooding the network. Propagation of multicast DNS packets within the local subnet is considered sufficient to enable DNS name resolution in small adhoc networks. The assumption is that if a network has a router, then the network either has a DNS server or the router can function as a DNS proxy, possibly implementing dynamic DNS. In the future, mDNS may be defined to support greater than LINKLOCAL multicast scope. This would occur if LINKLOCAL mDNS deployment is successful, the assumption that mDNS is not needed in multiple subnets proves incorrect, and multicast routing becomes ubiquitous. For example, it is not clear that this assumption will be valid in large adhoc networking scenarios. Once we have experience in mDNS deployment in terms of administrative issues, usability and impact on the network it will be possible reevaluate which multicast scopes are appropriate for use with mDNS. 2.1. Behavior of the sender and responder For the purpose of this document a host that sends a multicast query is called a "sender", while a host that listens to (but not necessarily responds to) a multicast query is called "responder". A host configured to be a "responder" may also be a "sender". A host configured to not be a "responder" cannot be a "sender". 2.1.1. Behavior of senders A sender sends multicast DNS query for any legal Type of resource record (e.g. A, PTR, etc.) for a name within the ".local.arpa." domain to the LINKLOCAL address. The RD (Recursion Desired) bit MUST NOT be set. If a responder receives a query with the header containing RD set bit, the responder MUST ignore the RD bit. If the multicast query is not positively resolved ("positively resolved" refers in this document to a response with the RCODE set to 0) during a limited amount of time, then a sender MAY repeat the transmission of a query in order to assure themselves that the query has been received by a host capable of responding to the query. Repetition MUST NOT be attempted more than 3 times and SHOULD NOT be repeated more often than once per second to reduce unnecessary network traffic. The delay between attempts should be randomised so as to avoid synchronisation effects. 2.1.2. Behavior of responders A responder listens on port 53 on the LINKLOCAL address. The IPv6 LINKLOCAL address a given responder listens to, and to which a sender sends, is a link-local multicast address formed as follows: The name of the resource record in question is expressed in its canonical form (see RFC 2535 , section 8.1), which is uncompressed with all alphabetic characters in lower case. The first label of the resource record name is then hashed using the MD5 algorithm (see RFC 1321 ). The first 32 bits of the resultant 128-bit hash is then appended to the prefix FF02:0:0:0:0:2::/96 to yield the 128-bit "solicited name multicast address". (Note: this procedure is intended to be the same as that specified in section 3 of ) A responder that listens for queries for multiple names will necessarily listen to multiple of these solicited name multicast addresses. Responders MUST respond to multicast queries to those and only those names for which they are authoritative. As an example, computer "host.example.com.local.arpa." is authoritative for the domain "host.example.com.local.arpa.". On receiving a multicast DNS A record query for the name "host.example.com.local.arpa." such a host responds with A record(s) that contain IP address(es) in the RDATA of the record. In conventional DNS terminology a DNS server authoritative for a zone is authoritative for all the domain names under the zone root except for the branches delegated into separate zones. Contrary to conventional DNS terminology, a responder is authoritative only for the zone root. For example the host "host.example.com.local.arpa." is not authoritative for the name "child.host.example.com.local.arpa." unless the host is configured with multiple names, including "host.example.com.local.arpa." and "child.host.example.com.local.arpa.". The purpose of limiting the name authority scope of a responder is to prevent complications that could be caused by coexistence of two or more hosts with the names representing child and parent (or grandparent) nodes in the DNS tree, for example, "host.example.com.local.arpa." and "child.host.example.com.local.arpa.". In this example (unless this limitation is introduced) a multicast query for an A record for the name "child.host.example.com.local.arpa." would result in two authoritative responses: name error received from "host.example.com.local.arpa.", and a requested A record - from "child.host.example.com.local.arpa.". To prevent this ambiguity, multicast enabled hosts could perform a dynamic update of the parent (or grandparent) zone with a delegation to a child zone. In this example a host "child.host.example.com.local.arpa." would send a dynamic update for the NS and glue A record to "host.example.com.local.arpa.", but this approach significantly complicates implementation of multicast DNS and would not be acceptable for lightweight hosts. A response to a multicast query is composed in exactly the same manner as a response to the unicast DNS query as specified in . Responders MUST never respond using cached data, and the AA (Authoritative Answer) bit MUST be set. The response is sent to the sender via unicast. A response to an mDNS query MUST have RCODE set to zero, since mDNS responders MUST NOT send error replies in response to mDNS queries. If a TC (truncation) bit is set in the response, then the sender MAY use the response if it contains all necessary information, or the sender MAY discard the response and resend the query over TCP or using EDNS0 with larger window using the unicast address of the responder. The RA (Recursion Available) bit in the header of the response MUST NOT be set. Even if the RA bit is set in the response header, the sender MUST ignore it. 2.1.3. mDNS addressing For IPv4 LINKLOCAL addressing, section 2.4 of  lays out the rules with respect to source address selection, TTL settings, and acceptable source/destination address combinations. IPv6 LINKLOCAL addressing is described in . mDNS queries and responses MUST obey the rules laid out in these documents. In composing an mDNS response, the responder MUST set the Hop Limit field in the IPv6 header and the TTL field in IPv4 header of the multicast DNS response to 255. The sender MUST verify that the Hop Limit field in IPv6 header and TTL field in IPv4 header of each response to the multicast DNS query is set to 255. If it is not, then sender MUST ignore the response. Implementation note: In the sockets API for IPv4, the IP_TTL and IP_MULTICAST_TTL socket options are used to specify the TTL of outgoing unicast and multicast packets. The IP_RECVTTL socket option is available on some platforms to receive the IPv4 TTL of received packets with recvmsg(). RFC 2292 specifies similar options for specifying and receiving the IPv6 Hop Limit. 2.1.4. Use of DNS TTL The responder should use a pre-configured TTL  value in the records returned in the multicast DNS query response. Due to the TTL minimalization necessary when caching an RRset, all TTLs in an RRset MUST be set to the same value. In the additional and authority section of the response the responder includes the same records as a DNS server would insert in the response to the unicast DNS query. 2.1.5. No/multiple responses The sender MUST anticipate receiving no replies to some multicast queries, in the event that no responders are available within the multicast scope, or in the event that no positive non-null responses exist for the transmitted query. If no positive response is received, a resolver treats it as a response that no records of the specified type and class for the specified name exist (NXRRSET). The sender MUST anticipate receiving multiple replies to the same multicast query, in the event that several multicast DNS enabled computers receive the query and respond with valid answers. When this occurs, the responses MAY first be concatenated, and then treated in the same manner that multiple RRs received from the same DNS server would, ordinarily. 3. Usage model A host configured to be an mDNS "responder" MUST also be configured as a "sender". A host not configured as a "responder" MUST NOT be a "sender". Multicast DNS usage is determined by special treatment of the ".local.arpa." namespace. The sender treats queries for ".local.arpa." as a special case. A sender MUST NOT send a unicast query for names ending with the ".local.arpa." suffix except when: a. A sender repeats a query over TCP after it received a response to the previous multicast query with the TC bit set, or b. The sender's cache contains an NS resource record that enables the sender to send a query directly to the hosts authoritative for the name in the query. It is not expected that a host named "host.example.com." will be manually configured to have the additional name "host.example.com.local.arpa." when it is configured to use multicast DNS. Instead, a responder with a name "host.example.com." configured with ".local.arpa." suffix in its domain search configuration is authoritative for the name "host.example.com.local.arpa.". For example, when a responder with the name "host.example.com." receives an A type query for the name "host.example.com.local.arpa." it authoritatively responds to the query. The same host MAY use multicast DNS queries for the resolution of names ending with ".local.arpa.", and unicast DNS queries for resolution of all other names. When a user or application requests a DNS client to resolve a dot-terminated name that contains a ".local.arpa" suffix, the query for such a name MUST be multicast and the name SHOULD NOT be concatenated with any suffix. If a DNS server is running on a host, the host MUST NOT listen for multicast DNS queries, to prevent the host from listening on port 53 and intercepting DNS queries directed to a DNS server. By default, a DNS server MUST NOT listen to multicast DNS queries. 3.1. mDNS configuration Multicast DNS usage can be configured manually or automatically. WhereOn interfaces where no manual or automatic configuration is provided,has been performed, multicast DNS is enabled by default. For IPv6, the stateless DNS discovery mechanisms described in  can be used to discover whether multicast DNS is globally enabled or disabled. Where DHCPv4 or DHCPv6 is implemented, DHCP options can be used to configure multicast DNS.DNS on an interface. The mDNS enable DHCP option, described in , can be used to explicitly enable or disable use of multicast DNS.DNS on an interface. The Name Service Search option, described in RFC 2937 , can be used to globally determine where multicast DNS is used within the name service search order. DHCP option codes are used as RFC 2937 codes signifying name services within the search order. As a result, to specify multicast DNS usage within the name service search order, the option code assigned to the mDNS enable option is used. If a host isan interface has been configured via any automatic configuration mechanisms, either stateful or stateless, and multicast DNSmechanism which is not explicitly enabled,able to supply DNS configuration information, then multicast DNS MUST NOT be used, ensuringused on that interface unless it has been explicitly enabled, whether via that mechanism or any other. This ensures that upgraded hosts do not change their default behavior.behavior, without requiring the source of the configuration information to be simultaneously updated. This implies that on the interface, the host will neither listen on the DNS LINKLOCAL multicast address, nor will it send queries to that address. For a DNS server, automatic configuration mechanisms, either stateful or stateless,mechanisms MUST NOT enable multicast DNS.DNS on any interface. 4. Sequence of events The sequence of events for multicast DNS usage is as follows: 1. If a sender needs to resolve a query for a name "host.example.com.local.arpa", then it sends a multicast query to the LINKLOCAL multicast address. 2. A responder responds to this query only if it is authoritative for the domain name "host.example.com.local.arpa". The responder sends a response to the sender via unicast over UDP. 3. Upon the reception of the response, the sender verifies that the Hop Limit field in IPv6 header or TTL field in IPv4 header (depending on the protocol used) of the response is set to 255. The sender then verifies compliance with the addressing requirements for IPv4  and IPv6 . If these conditions are met, then the sender uses and caches the returned response. If not, then the sender ignores the response and continues waiting for the response. 5. Conflict resolution There are some scenarios when multiple responders MAY respond to the same query. There are other scenarios when only one responder may respond to a query. Resource records for which the latter queries are submitted are referred as UNIQUE throughout this document. The uniqueness of a resource record depends on a nature of the name in the query and type of the query. For example it is expected that: - multiple hosts may respond to a query for a SRV type record - multiple hosts may respond to a query for an A type record for a cluster name (assigned to multiple hosts in the cluster) - only a single host may respond to a query for an A type record for a hostname. Every responder that responds to a multicast DNS query and/or dynamic update request AND includes a UNIQUE record in the response: 1. MUST verify that there is no other host within the scope of the multicast DNS query propagation that can return a DNS record for the same name, type and class. 2. MUST NOT include a UNIQUE resource record in the response without having verified its uniqueness. Where a host is configured to respond to multicast DNS queries on more than one interface, the host MUST verify resource record uniqueness on each interface for each UNIQUE resource record that could be used on that interface. To accomplish this, the host MUST multicast a dynamic DNS update request as specified in RFC 2136  for each new UNIQUE resource record. Uniqueness verification is carried out when the host: - starts up or - is configured to respond to the multicast DNS queries on some interface or - is configured to respond to the multicast DNS queries using additional UNIQUE DNS records. Below we describe the data to be specified in the dynamic update request: Header section contains values according to RFC 2136 . Zone section The zone name in the zone section MUST be set to the name of the UNIQUE record. The zone type in the zone section MUST be set to SOA. The zone class in the zone section MUST be set to the class of the UNIQUE record. Prerequisite section This section MUST contain a record set whose semantics are described in RFC 2136 , Section 2.4.3 "RRset Does Not Exist", requesting that RRs with the NAME and TYPE of the UNIQUE record do not exist. Update section This section MUST be left empty. Additional section This section is set according to RFC 2136. When a host that owns a UNIQUE record receives a dynamic update request that requests that the UNIQUE resource record set does not exist, the host MUST respond via unicast with the YXRRSET error, according to the rules described in Section 3 of RFC 2136 . After client receives an YXRRSET response to its dynamic update request that a UNIQUE resource record does not exist, the host MUST not use the UNIQUE resource record in responses to multicast queries and dynamic update requests. Note that this name conflict detection mechanism doesn't prevent name conflicts when previously partitioned segments are connected by a bridge. In such a situation, name conflicts are detected when a sender receives more than one response to its multicast DNS query. In this case, the sender sends the first response that it received to all responders that responded to this query except the first one, using unicast. A host that receives a query response containing a UNIQUE resource record that it owns, even if it didn't send such a query, MUST verify that no other host within the multicast DNS scope is authoritative for the same name, using the dynamic DNS update request mechanism described above. Based on the result, the host detects whether there is a name conflict and acts as described above. 5.1. Considerations for Multiple Interfaces A multi-homed host may elect to configure multicast DNS on only one of its active interfaces. In many situations this will be adequate. However, should a host wish to configure multicast DNS on more than one of its active interfaces, there are some additional precautions it MUST take. Implementers who are not planning to support multicast DNS on multiple interfaces simultaneously may skip this section. A multi-homed host checks the uniqueness of UNIQUE records as described in Section 5. The situation is illustrated in figure 1 below: ---------- ---------- | | | | [A] [myhost] [myhost] Figure 1. LINKLOCAL name conflict In this situation, the multi-homed myhost will probe for, and defend, its host name on both interfaces. A conflict will be detected on one interface, but not the other, and as a result, the multi-homed myhost will not be able to respond with a host RR for "myhost". Since names are only unique per-link, hosts on different links could be using the same name. If an mDNS client sends requests over multiple interfaces, and receives replies from more than one, the result returned to the client is defined by the implementation. The situation is illustrated in figure 2 below. ---------- ---------- | | | | [A] [myhost] [A] Figure 2. Off-segment name conflict If host myhost is configured to use mDNS on both interfaces, it will send mDNS queries on both interfaces. When host myhost sends a query for the host RR for name "A" it will receive a response from hosts on both interfaces. Host myhost will then forward a response from the first responder to the second responder, who will attempt to verify the uniqueness of host RR for its name, but will not discover a conflict, since the conflicting host resides on a different subnet. Therefore it will continue using its name. Indeed, host myhost cannot distinguish between the situation shown in Figure 2, and that shown in Figure 3 where no conflict exists: [A] | | ----- ----- | | [myhost] Figure 3. Multiple paths to same host This illustrates that the proposed name conflict resolution mechanism does not support detection or resolution of conflicts between hosts on different subnets. This problem can also occur with unicast DNS when a multi-homed host is connected to two different networks with separated name spaces. It is not the intent of this document to address the issue of uniqueness of names within DNS. 5.2. API issues RFC 2553  provides an API which can partially solve the name ambiguity problem for applications written to use this API, since the sockaddr_in6 structure exposes the scope within which each scoped address exists, and this structure can be used for both IPv4 (using v4-mapped IPv6 addresses) and IPv6 addresses. Following the example in Figure 2, an application on 'myhost' issues the request getaddrinfo("A", ...) with ai_family=AF_INET6 and ai_flags=AI_ALL|AI_V4MAPPED. mDNS requests will be sent from both interfaces and the resolver library will return a list containing multiple addrinfo structures, each with an associated sockaddr_in6 structure. This list will thus contain the IPv4 and IPv6 addresses of both hosts responding to the name 'A'. Link-local addresses will have a sin6_scope_id value that disambiguates which interface is used to reach the address. Of course, to the application, Figures 2 and 3 are still indistinguishable, but this API allows the application to communicate successfully with any address in the list. 6. IANA Considerations Authors will contact IANA to reserve LINKLOCAL IPv4 and IPv6 addresses. 7. ARPA domain considerations This document specifies the use of a new sub-domain of the "ARPA" domain. According to Section 2.1 of the ARPA Guidelines , this specification requires description and justification. The 'local.arpa' domain is used to distinguish a local namespace. This namespace differs from others in the following respects: - Name servers responding to requests for names in this domain have different rules concerning authority. As explained in Section 2.1, mDNS servers have limited scope of authority, not extending to sub-domains of domain they are authoritative for. - DNS servers SHOULD NOT forward queries for domain names in the local.arpa domain - if the server cannot answer the query from its own database, it should reply with a non-authoritative NXDOMAIN. - Hosts may derive their own names in this namespace, independent of centralized authorization and registration (as defined in section 3 and section 5). - There is no delegation or administrative structure to sub-domains of '.local.arpa'. How protocol objects are mapped into lookup keys: Names are associated with resources which can be requested according to the DNS protocol. However, recursive lookup is impossible. Further, mDNS specifies only the use of multicast to transmit these requests. 8. References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Meyer, D., "Administratively Scoped IP Multicast", BCP 23, RFC 2365, July 1998.  Smith, C., "The Name Service Search Option for DHCP", RFC 2937, September 2000.  Mockapetris, P., "Domain Names - Implementation and Specification", RFC 1035, November 1987.  Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", RFC 1034, November, 1987.  Guttman, E., "DHCP mDNS Enable Option", Internet draft (work in progress), draft-guttman-mdns-enable-01.txt, July 2001.  Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.  Hinden, R., Deering, S., "IP Version 6 Addressing Architecture", RFC 2373, July 1998.  Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE Std. 802.11-1997, 1997.  Vixie, P., Thomson, S., Rekhter, Y., Bound, J., "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997.  Huston, G., "Management Guidelines & Operational Requirements for the Internet Infrastructure Domain ("ARPA")", Internet draft (work in progress), draft-iab-arpa-03.txt, July 2001.  Gilligan, R., Thomson, S., Bound, J., Stevens, W., "Basic Socket Interface Extensions for IPv6", RFC 2553, March 1999.  Crawford, Matt, "IPv6 Node Information Queries", Internet draft (work in progress), draft-ietf-ipn-gwg-icmp-name-lookups-07.txt, August 2000.  Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999.  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992.  Aboba, B., "DHCP Domain Search Option", Internet draft (work in progress), draft-aboba-dhc-domsearch-06.txt, August 2001.  Cheshire, S., Aboba, B., "Dynamic Configuration of IPv4 Link-Local Addresses", Internet draft (work in progress), draft-ietf-zeroconf- ipv4-linklocal-05.txt, September 2001.  Thaler, D., Hagino, I., "IPv6 Stateless DNS Discovery", Internet draft (work in progress), draft-ietf-ipngwg-dns-discovery-02.txt, July 2001. 9. Security Considerations This draft does not prescribe a means of securing the multicast DNS mechanism. It is possible that hosts will allocate conflicting names for a period of time, or that non-conforming hosts will attempt to deny service to other hosts by allocating the same name. Such attacks also allow nodes to receive packets destined for other nodes. The protocol reduces the exposure to such threats in the absence of authentication by ignoring multicast DNS query response packets received from off-link senders. In all received responses, the Hop Limit field in IPv6 and the TTL field in IPv4 are verified to contain 255, the maximum legal value. Since routers decrement the Hop Limit on all packets they forward, received packets containing a Hop Limit of 255 must have originated from a neighbor. These threats are most serious in wireless networks such as 802.11, since attackers on a wired network will require physical access to the home network, while wireless attackers may reside outside the home. Link-layer security will serve to secure mDNS against the above threats if it is available. For example, where 802.11 "Wired Equivalency Privacy" (WEP)  is implemented, a casual attacker is likely to be deterred from gaining access to the home network. The mechanism specified in this draft does not require use of the DNSSEC, which means that the responses to the multicast DNS queries may not be authenticated. If a network contains a "signed key distribution center" for all (or at least some) of the DNS zones that the responders are authoritative for, then hosts on such a network are configured with the key for the top zone, "local.arpa." (hosted by "signed keys distribution center") and may use DNSSEC for authentication of the responders using DNSSEC. Acknowledgments This work builds upon original work done on multicast DNS by Bill Manning and Bill Woodcock. Bill Manning's work was funded under DARPA grant #F30602-99-1-0523. The authors gratefully acknowledge their contribution to the current specification. Constructive input has also been received from Mark Andrews, Stuart Cheshire, Robert Elz, James Gilroy, Olafur Gudmundsson, Erik Guttman, Myron Hattig, Thomas Narten, Erik Nordmark, Sander Van-Valkenburg and Tomohide Nagashima. Authors' Addresses Levon Esibov Microsoft Corporation One Microsoft Way Redmond, WA 98052 EMail: firstname.lastname@example.org Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: +1 (425) 936-6605 EMail: email@example.com Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: +1 (425) 703-8835 EMail: firstname.lastname@example.org Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards- related documentation can be found in BCP-11. 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