--- 1/draft-ietf-dnssd-srp-02.txt 2020-07-13 17:13:48.876199176 -0700 +++ 2/draft-ietf-dnssd-srp-03.txt 2020-07-13 17:13:48.924200399 -0700 @@ -1,19 +1,19 @@ -Internet Engineering Task Force S. Cheshire -Internet-Draft Apple Inc. -Intended status: Informational T. Lemon -Expires: January 9, 2020 Nibbhaya Consulting - July 8, 2019 +Internet Engineering Task Force T. Lemon +Internet-Draft Nibbhaya Consulting +Intended status: Informational S. Cheshire +Expires: January 14, 2021 Apple Inc. + July 13, 2020 Service Registration Protocol for DNS-Based Service Discovery - draft-ietf-dnssd-srp-02 + draft-ietf-dnssd-srp-03 Abstract The Service Registration Protocol for DNS-Based Service Discovery uses the standard DNS Update mechanism to enable DNS-Based Service Discovery using only unicast packets. This makes it possible to deploy DNS Service Discovery without multicast, which greatly improves scalability and improves performance on networks where multicast service is not an optimal choice, particularly 802.11 (Wi-Fi) and 802.15.4 (IoT) networks. DNS-SD Service registration @@ -28,25 +28,25 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." - This Internet-Draft will expire on January 9, 2020. + This Internet-Draft will expire on January 14, 2021. Copyright Notice - Copyright (c) 2019 IETF Trust and the persons identified as the + Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as @@ -54,48 +54,49 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Service Registration Protocol . . . . . . . . . . . . . . . . 4 2.1. What to publish . . . . . . . . . . . . . . . . . . . . . 5 2.2. Where to publish it . . . . . . . . . . . . . . . . . . . 6 2.3. How to publish it . . . . . . . . . . . . . . . . . . . . 6 2.3.1. How DNS-SD Service Registration differs from standard RFC2136 DNS Update . . . . . . . . . . . . . . . . . 7 - 2.3.2. Testing using standard RFC2136-compliant servers . . 7 - 2.3.3. How to allow services to update standard - RFC2136-compliant servers . . . . . . . . . . . . . . 8 - 2.4. How to secure it . . . . . . . . . . . . . . . . . . . . 8 - 2.4.1. First-Come First-Served Naming . . . . . . . . . . . 9 - 2.4.2. SRP Server Behavior . . . . . . . . . . . . . . . . . 10 + 2.4. How to secure it . . . . . . . . . . . . . . . . . . . . 7 + 2.4.1. First-Come First-Served Naming . . . . . . . . . . . 8 + 2.4.2. Removing published services . . . . . . . . . . . . . 9 + 2.4.3. SRP Server Behavior . . . . . . . . . . . . . . . . . 9 2.5. TTL Consistency . . . . . . . . . . . . . . . . . . . . . 12 2.6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . 13 2.6.1. Cleaning up stale data . . . . . . . . . . . . . . . 13 2.6.2. Sleep Proxy . . . . . . . . . . . . . . . . . . . . . 14 3. Security Considerations . . . . . . . . . . . . . . . . . . . 15 3.1. Source Validation . . . . . . . . . . . . . . . . . . . . 15 3.2. SIG(0) signature validation . . . . . . . . . . . . . . . 16 3.3. Required Signature Algorithm . . . . . . . . . . . . . . 16 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16 - 5. Delegation of 'service.arpa.' . . . . . . . . . . . . . . . . 17 - 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 + 5. Delegation of 'service.arpa.' . . . . . . . . . . . . . . . . 16 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6.1. Registration and Delegation of 'service.arpa' as a Special-Use Domain Name . . . . . . . . . . . . . . . . . 17 6.2. 'dnssd-srp' Service Name . . . . . . . . . . . . . . . . 17 - 6.3. 'dnssd-srp-tls' Service Name . . . . . . . . . . . . . . 18 - 6.4. Anycast Address . . . . . . . . . . . . . . . . . . . . . 18 + 6.3. 'dnssd-srp-tls' Service Name . . . . . . . . . . . . . . 17 + 6.4. Anycast Address . . . . . . . . . . . . . . . . . . . . . 17 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1. Normative References . . . . . . . . . . . . . . . . . . 18 8.2. Informative References . . . . . . . . . . . . . . . . . 19 - Appendix A. Sample BIND9 configuration for default.service.arpa. 21 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 + Appendix A. Testing using standard RFC2136-compliant servers . . 20 + Appendix B. How to allow services to update standard + RFC2136-compliant servers . . . . . . . . . . . . . 21 + Appendix C. Sample BIND9 configuration for default.service.arpa. 21 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 1. Introduction DNS-Based Service Discovery [RFC6763] is a component of Zero Configuration Networking [RFC6760] [ZC] [I-D.cheshire-dnssd-roadmap]. This document describes an enhancement to DNS-Based Service Discovery [RFC6763] that allows services to automatically register their services using the DNS protocol rather than using Multicast DNS [RFC6762] (mDNS). There is already a large installed base of DNS-SD @@ -176,52 +177,53 @@ apex of the closest enclosing DNS zone using SOA queries [I-D.ietf-dnssd-push]. Having discovered the enclosing DNS zone, they query for the "_dnssd-srp._tcp" SRV record to discover the server to which they should send DNS updates. Hosts that support SRP updates using TLS use the "_dnssd-srp-tls._tcp" SRV record instead. For devices designed for Constrained-Node Networks [RFC7228] some simplifications are available. Instead of being configured with (or discovering) the service registration domain, the (proposed) special- - use domain name (see [RFC6761]) "default.service.arpa" is used. - Instead of learning the server to which they should send DNS updates, - a fixed IPv6 anycast address is used (value TBD). Anycasts are sent - using UDP unless TCP is required due to the size of the update. It - is the responsibility of a Constrained-Node Network supporting SRP to - provide appropriate anycast routing to deliver the DNS updates to the - appropriate server. It is the responsibility of the SRP server - supporting a Constrained-Node Network to handle the updates - appropriately. In some network environments, updates may be accepted - directly into a local "default.service.arpa" zone, which has only - local visibility. In other network environments, updates for names - ending in "default.service.arpa" may be rewritten internally to names - with broader visibility. + use domain name (see [RFC6761]) "default.service.arpa" is used. The + details of how SRP server(s) are discovered will be specific to the + constrained network, and therefore we do not suggest a specific + mechanism here. - The reason for these different assumptions is that Constrained-Node - Networks generally require special egress support, and Anycast - packets captured at the Constrained-Node Network egress can be - assumed to have originated locally. Low-power devices that typically - use Constrained-Node Networks may have very limited battery power. - The additional DNS lookups required to discover an SRP server and - then communicate with it will increase the power required to - advertise a service; for low-power devices, the additional + SRP clients on constrained networks are expected to receive from the + network a list of SRP servers with which to register. It is the + responsibility of a Constrained-Node Network supporting SRP to + provide one or more SRP server addresses. It is the responsibility + of the SRP server supporting a Constrained-Node Network to handle the + updates appropriately. In some network environments, updates may be + accepted directly into a local "default.service.arpa" zone, which has + only local visibility. In other network environments, updates for + names ending in "default.service.arpa" may be rewritten internally to + names with broader visibility. + + The reason for these different assumptions is that low-power devices + that typically use Constrained-Node Networks may have very limited + battery power. The series of DNS lookups required to discover an SRP + server and then communicate with it will increase the power required + to advertise a service; for low-power devices, the additional flexibility this provides does not justify the additional use of - power. + power. It is also fairly typical of such networks that some network + service information is obtained as part of the process of joining the + network, and so this can be relied upon to provide nodes with the + information they need. - General networks have the potential to have more complicated - topologies at the Internet layer, which makes anycast routing more - difficult. Such networks may or may not have the infrastructure - required to route anycast to a server that can process it. However, - they can be assumed to be able to provide registration domain - discovery and routing. By requiring the use of TCP, the possibility - of off-network spoofing is eliminated. + Networks that are not constrained networks can more complicated + topologies at the Internet layer. Nodes connected to such networks + can be assumed to be able to do DNSSD service registration domain + discovery. Such networks are generally able to provide registration + domain discovery and routing. By requiring the use of TCP, the + possibility of off-network spoofing is eliminated. We will discuss several parts to this process: how to know what to publish, how to know where to publish it (under what name), how to publish it, how to secure its publication, and how to maintain the information once published. 2.1. What to publish We refer to the DNS Update message sent by services using SRP as an SRP update. Three types of updates appear in an SRP update: Service @@ -274,32 +276,32 @@ once; this means that it's possible to do all the work of adding a PTR resource record to the PTR RRset on the Service Name, and creating or updating the Service Instance Name and Host Description, in a single transaction. An SRP update takes advantage of this: it is implemented as a single DNS Update message that contains a service's Service Discovery records, Service Description records, and Host Description records. Updates done according to this specification are somewhat different - than regular DNS Updates as defined in RFC2136. RFC2136 uses a - fairly heavyweight process for updating: you might first attempt to + than regular DNS Updates as defined in RFC2136. The RFC2136 update + process can involve many update attempts: you might first attempt to add a name if it doesn't exist; if that fails, then in a second message you might update the name if it does exist but matches certain preconditions. Because the registration protocol uses a single transaction, some of this adaptability is lost. In order to allow updates to happen in a single transaction, SRP - updates do not include update prerequisites. The specified in - Section 2.4.2 are implicit in the processing of SRP updates, and so - there is no need for the service sending the SRP update to put in any - explicit prerequisites. + updates do not include update prerequisites. The requirements + specified in Section 2.4.3 are implicit in the processing of SRP + updates, and so there is no need for the service sending the SRP + update to put in any explicit prerequisites. 2.3.1. How DNS-SD Service Registration differs from standard RFC2136 DNS Update DNS-SD Service Registration is based on standard RFC2136 DNS Update, with some differences: o It implements first-come first-served name allocation, protected using SIG(0) [RFC2931]. @@ -307,88 +309,37 @@ o It optionally performs rewriting of "default.service.arpa" to some other domain. o It optionally performs automatic population of the address-to-name reverse mapping domains. o An SRP server is not required to implement general DNS Update prerequsite processing. - o Simplified clients are allowed to send updates to an anycast - address, for names ending in "default.service.arpa" - -2.3.2. Testing using standard RFC2136-compliant servers - - It may be useful to set up a DNS server for testing that does not - implement SRP. This can be done by configuring the server to listen - on the anycast address, or advertising it in the - _dnssd-srp._tcp. SRV and _dnssd-srp-tls._tcp. record. It - must be configured to be authoritative for "default.service.arpa", - and to accept updates from hosts on local networks for names under - "default.service.arpa" without authentication, since such servers - will not have support for FCFS authentication Section 2.4.1. - - A server configured in this way will be able to successfully accept - and process SRP updates from services that send SRP updates. - However, no prerequisites will be applied, and this means that the - test server will accept internally inconsistent SRP updates, and will - not stop two SRP updates, sent by different services, that claim the - same name(s), from overwriting each other. - - Since SRP updates are signed with keys, validation of the SIG(0) - algorithm used by the client can be done by manually installing the - client public key on the DNS server that will be receiving the - updates. The key can then be used to authenticate the client, and - can be used as a requirement for the update. An example - configuration for testing SRP using BIND 9 is given in Appendix A. - -2.3.3. How to allow services to update standard RFC2136-compliant - servers - - Ordinarily SRP updates will fail when sent to an RFC 2136-compliant - server that does not implement SRP because the zone being updated is - "default.service.arpa", and no DNS server that is not an SRP server - should normally be configured to be authoritative for - "default.service.arpa". Therefore, a service that sends an SRP - update can tell that the receiving server does not support SRP, but - does support RFC2136, because the RCODE will either be NOTZONE, - NOTAUTH or REFUSED, or because there is no response to the update - request (when using the anycast address) - - In this case a service MAY attempt to register itself using regular - RFC2136 DNS updates. To do so, it must discover the default - registration zone and the DNS server designated to receive updates - for that zone, as described earlier, using the _dns-update._udp SRV - record. It can then make the update using the port and host pointed - to by the SRV record, and should use appropriate prerequisites to - avoid overwriting competing records. Such updates are out of scope - for SRP, and a service that implements SRP MUST first attempt to use - SRP to register itself, and should only attempt to use RFC2136 - backwards compatibility if that fails. Although the owner name for - the SRV record specifies the UDP protocol for updates, it is also - possible to use TCP, and TCP should be required to prevent spoofing. + o Clients are allowed to send updates to the generic domain + "default.service.arpa" 2.4. How to secure it Traditional DNS update is secured using the TSIG protocol, which uses a secret key shared between the client (which issues the update) and the server (which authenticates it). This model does not work for automatic service registration. The goal of securing the DNS-SD Registration Protocol is to provide the best possible security given the constraint that service registration has to be automatic. It is possible to layer more operational security on top of what we describe here, but what we - describe here improves upon the security of mDNS. The goal is not to - provide the level of security of a network managed by a skilled - operator. + describe here is an improvement over the security of mDNS. The goal + is not to provide the level of security of a network managed by a + skilled operator. 2.4.1. First-Come First-Served Naming First-Come First-Serve naming provides a limited degree of security: a service that registers its service using DNS-SD Registration protocol is given ownership of a name for an extended period of time based on the key used to authenticate the DNS Update. As long as the registration service remembers the name and the key used to register that name, no other service can add or update the information associated with that. FCFS naming is used to protect both the @@ -423,109 +374,139 @@ interfaces of devices looking for services of that type for too long. The lifetime of the KEY records is set using the KEY-LEASE field of the Update Lease Option, and should be set to a much longer time, typically 14 days. The result of this is that even though a device may be temporarily unplugged, disappearing from the network for a few days, it makes a claim on its name that lasts much longer. This means that even if a device is unplugged from the network for a few days, and its services are not available for that time, no other - rogue device can come along and immediately claim its name the moment - it disappears from the network. In the event that a device is - unplugged from the network and permanently discarded, then its name - is eventually cleaned up and made available for re-use. + device can come along and claim its name the moment it disappears + from the network. In the event that a device is unplugged from the + network and permanently discarded, then its name is eventually + cleaned up and made available for re-use. -2.4.2. SRP Server Behavior +2.4.2. Removing published services - The SRP server first validates that the SRP update is a syntactically + To remove a service registration, the client retransmits its most + recent update with an Update Lease option that has a LEASE value of + zero. If the registration is to be permanently removed, KEY-LEASE + should also be zero. Otherwise, it should have the same value it had + previously; this holds the name in reserve for when the client is + once again able to provide the service. + + SRP clients are normally expected to remove all service instances + when removing a host. However, in some cases a client may not have + retained sufficient state to know that some service instance is + pointing to a host that it is removing. Nevertheless, removing the + host can be assumed to mean that all service instances pointing to it + are no longer valid. Therefore, SRP servers MAY remove all service + instances pointing to a host when a host is removed, even if the + client doesn't remove them explicitly. + +2.4.3. SRP Server Behavior + +2.4.3.1. Validation of Adds + + The SRP server first validates that the DNS Update is a syntactically and semantically valid DNS Update according to the rules specified in RFC2136. - The SRP server checks each update in the SRP update to see that it - contains a Service Discovery update, a Service Description update, - and a Host Description update. Order matters in DNS updates. + SRP Updates consist of a set of Instructions that together add one or + more services. Each instruction consists either of a single add, or + a delete followed by an add. When an instruction contains a delete + and an add, the delete MUST precede the add. + + The SRP server checks each Instruction in the SRP update to see that + it is either a Service Discovery update, a Service Description + update, or a Host Description update. Order matters in DNS updates. Specifically, deletes must precede adds for records that the deletes would affect; otherwise the add will have no effect. This is the only ordering constraint; aside from this constraint, updates may appear in whatever order is convenient when constructing the update. Because the SRP update is a DNS update, it MUST contain a single question that indicates the zone to be updated. Every delete and update in an SRP update MUST be within the zone that is specified for the SRP Update. - An update is a Service Discovery update if it contains + An Instruction is a Service Discovery Instruction if it contains - o exactly one RRset update, - o which is for a PTR RR, + o exactly one "Add to an RRSet" ([RFC2136] Section 2.5.1) RR, + o which is a PTR RR, o which points to a Service Instance Name - o for which an update is present in the SRP update. - o Service Discovery updates do not contain any deletes, and do not - contain any other updates. + o for which a Service Description Instruction is present in the SRP + Update. + o Service Discovery Instructions do not contain any deletes, and do + not contain any other adds. - An update is a Service Description update if, for the appropriate - Service Instance Name, it contains + An Instruction is a Service Description Instruction if, for the + appropriate Service Instance Name, it contains - o exactly one "Delete all RRsets from a name" update, - o exactly one SRV RRset update, - o zero or one KEY RR update that adds a KEY RR that contains the - public key corresponding to the private key that was used to sign - the message (if present, the KEY MUST match the KEY RR given in - the Host Description), - o one or more TXT RRset updates, - o and the target of the SRV record update references a hostname for - which there is a Host Description update in the SRP update. - o Service Descriptions do not update any other records. + o exactly one "Delete all RRsets from a name" update for the service + instance name [RFC2136] Section 2.5.3, + o exactly one "Add to an RRset" SRV RR, + o zero or one "Add to an RRset" KEY RR that contains the public key + corresponding to the private key that was used to sign the message + (if present, the KEY MUST match the KEY RR given in the Host + Description), + o one or more "Add to an RRset" TXT RRs, + o and the target of the SRV RR Add points to a hostname for which + there is a Host Description Instruction in the SRP Update. + o Service Descriptions Instructions do not modify any other RRs. - An update is a Host Description update if, for the appropriate - hostname, it contains + An Instruction is a Host Description Instruction if, for the + appropriate hostname, it contains - o exactly one "Delete all RRsets from a name" update, - o one or more A or AAAA RR update(s) - o exactly one KEY RR update that adds a KEY RR that contains the - public key corresponding to the private key that was used to sign - the message, - o there is a Service Instance Name update in the SRP update that - updates an SRV RR so that it points to the hostname being updated - by this update. - o Host Description updates do not update any other records. + o exactly one "Delete all RRsets from a name" RR, + o one or more "Add to an RRset" RRs of type A and/or AAAA, + o exactly one "Add to an RRset" RR that adds a KEY RR that contains + the public key corresponding to the private key that was used to + sign the message, + o there is a Service Instance Name Instruction in the SRP update for + which the SRV RR that is added points to the hostname being + updated by this update. + o Host Description updates do not modify any other records. - An SRP update MUST include at least one Service Discovery update, at - least one Service Description update, and exactly one Host - Description update. An update message that does not is not an SRP - update. An update message that contains any other updates, any other - deletes, or any update prerequisites, is not an SRP update. Such + An SRP Update MUST include at least one Service Discovery + Instruction, at least one Service Description Instruction, and + exactly one Host Description Instruction. A DNS Update that does not + is not an SRP update. A DNS Update that contains any other adds, any + other deletes, or any prerequisites, is not an SRP update. Such messages should either be processed as regular RFC2136 updates, including access control checks and constraint checks, if supported, or else rejected with RCODE=REFUSED. Note that if the definitions of each of these update types are followed carefully, this means that many things that look very much like SRP updates nevertheless are not. For example, a DNS update - that contains an update to a Service Name and an update to a Service - Instance Name, where the Service Name does not reference the Service - Instance Name, is not a valid SRP update message, but may be a valid - RFC2136 update. + that contains an RRset Add to a Service Name and an RRset Add to a + Service Instance Name, where the Service Name does not reference the + Service Instance Name, is not a valid SRP update message, but may be + a valid RFC2136 update. - Assuming that an update message has been validated with these - conditions and is a valid SRP update, the server checks that the name - in the Host Description update exists. If so, then the server checks - to see if the KEY record on the name is the same as the KEY record in - the update. The server performs the same check for the KEY records - in any Service Description update. For KEY records that were - omitted, the KEY from the Host Description update is used. If any - existing KEY record corresponding to a KEY record in the SRP update - does not match the KEY record in the SRP update, then the server MUST - reject the SRP update with the YXDOMAIN RCODE. + Assuming that a DNS Update message has been validated with these + conditions and is a valid SRP Update, the server checks that the name + in the Host Description Instruction exists. If so, then the server + checks to see if the KEY record on that name is the same as the KEY + record in the Host Description Instruction. The server performs the + same check for the KEY records in any Service Description + Instrructions. For KEY records that were omitted from Service + Description Instructions, the KEY from the Host Description + Instruction is used. If any existing KEY record corresponding to a + KEY record in the SRP Update does not match the KEY same record in + the SRP Update (whether provided or taken from the Host Description + Instruction), then the server MUST reject the SRP Update with the + YXDOMAIN RCODE. - Otherwise, the server validates the SRP update using SIG(0) on the + Otherwise, the server validates the SRP Update using SIG(0) on the public key in the KEY record of the Host Description update. If the validation fails, the server MUST reject the SRP Update with the REFUSED RCODE. Otherwise, the SRP update is considered valid and authentic, and is processed according to the method described in RFC2136. KEY record updates omitted from Service Description update are processed as if they had been explicitly present: every Service Description that is updated MUST, after the update, have a KEY RR, and it must be the same KEY RR that is present in the Host @@ -875,24 +855,20 @@ [SUDN] "Special-Use Domain Names Registry", July 2012, . [LSDZ] "Locally-Served DNS Zones Registry", July 2011, . 8.2. Informative References - [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", - STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, - . - [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, DOI 10.17487/RFC2131, March 1997, . [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", @@ -904,24 +880,20 @@ . [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September 2000, . [RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update", RFC 3007, DOI 10.17487/RFC3007, November 2000, . - [RFC3152] Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152, - DOI 10.17487/RFC3152, August 2001, - . - [RFC6760] Cheshire, S. and M. Krochmal, "Requirements for a Protocol to Replace the AppleTalk Name Binding Protocol (NBP)", RFC 6760, DOI 10.17487/RFC6760, February 2013, . [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", RFC 6761, DOI 10.17487/RFC6761, February 2013, . [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, @@ -943,49 +915,101 @@ DOI 10.17487/RFC8310, March 2018, . [I-D.ietf-dnssd-hybrid] Cheshire, S., "Discovery Proxy for Multicast DNS-Based Service Discovery", draft-ietf-dnssd-hybrid-10 (work in progress), March 2019. [I-D.ietf-dnssd-push] Pusateri, T. and S. Cheshire, "DNS Push Notifications", - draft-ietf-dnssd-push-21 (work in progress), July 2019. + draft-ietf-dnssd-push-25 (work in progress), October 2019. [I-D.cheshire-dnssd-roadmap] Cheshire, S., "Service Discovery Road Map", draft- cheshire-dnssd-roadmap-03 (work in progress), October 2018. [I-D.cheshire-edns0-owner-option] Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft- cheshire-edns0-owner-option-01 (work in progress), July 2017. [ZC] Cheshire, S. and D. Steinberg, "Zero Configuration Networking: The Definitive Guide", O'Reilly Media, Inc. , ISBN 0-596-10100-7, December 2005. -Appendix A. Sample BIND9 configuration for default.service.arpa. +Appendix A. Testing using standard RFC2136-compliant servers + + It may be useful to set up a DNS server for testing that does not + implement SRP. This can be done by configuring the server to listen + on the anycast address, or advertising it in the + _dnssd-srp._tcp. SRV and _dnssd-srp-tls._tcp. record. It + must be configured to be authoritative for "default.service.arpa", + and to accept updates from hosts on local networks for names under + "default.service.arpa" without authentication, since such servers + will not have support for FCFS authentication Section 2.4.1. + + A server configured in this way will be able to successfully accept + and process SRP updates from services that send SRP updates. + However, no prerequisites will be applied, and this means that the + test server will accept internally inconsistent SRP updates, and will + not stop two SRP updates, sent by different services, that claim the + same name(s), from overwriting each other. + + Since SRP updates are signed with keys, validation of the SIG(0) + algorithm used by the client can be done by manually installing the + client public key on the DNS server that will be receiving the + updates. The key can then be used to authenticate the client, and + can be used as a requirement for the update. An example + configuration for testing SRP using BIND 9 is given in Appendix C. + +Appendix B. How to allow services to update standard RFC2136-compliant + servers + + Ordinarily SRP updates will fail when sent to an RFC 2136-compliant + server that does not implement SRP because the zone being updated is + "default.service.arpa", and no DNS server that is not an SRP server + should normally be configured to be authoritative for + "default.service.arpa". Therefore, a service that sends an SRP + update can tell that the receiving server does not support SRP, but + does support RFC2136, because the RCODE will either be NOTZONE, + NOTAUTH or REFUSED, or because there is no response to the update + request (when using the anycast address) + + In this case a service MAY attempt to register itself using regular + RFC2136 DNS updates. To do so, it must discover the default + registration zone and the DNS server designated to receive updates + for that zone, as described earlier, using the _dns-update._udp SRV + record. It can then make the update using the port and host pointed + to by the SRV record, and should use appropriate prerequisites to + avoid overwriting competing records. Such updates are out of scope + for SRP, and a service that implements SRP MUST first attempt to use + SRP to register itself, and should only attempt to use RFC2136 + backwards compatibility if that fails. Although the owner name for + the SRV record specifies the UDP protocol for updates, it is also + possible to use TCP, and TCP should be required to prevent spoofing. + +Appendix C. Sample BIND9 configuration for default.service.arpa. zone "default.service.arpa." { type master; file "/etc/bind/master/service.db"; allow-update { key demo.default.service.arpa.; }; }; Zone Configuration in named.conf $ORIGIN . $TTL 57600 ; 16 hours -default.service.arpa IN SOA ns3.default.service.arpa. postmaster.default.service.arpa. ( + default.service.arpa IN SOA ns3.default.service.arpa. + postmaster.default.service.arpa. ( 2951053287 ; serial 3600 ; refresh (1 hour) 1800 ; retry (30 minutes) 604800 ; expire (1 week) 3600 ; minimum (1 hour) ) NS ns3.default.service.arpa. SRV 0 0 53 ns3.default.service.arpa. $ORIGIN default.service.arpa. $TTL 3600 ; 1 hour @@ -1006,25 +1030,26 @@ KEY 513 3 13 ( qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU 9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg== ); alg = ECDSAP256SHA256 ; key id = 15008 AAAA ::1 Example Zone file Authors' Addresses + Ted Lemon + Nibbhaya Consulting + P.O. Box 958 + Brattleboro, Vermont 05302 + United States of America + + Email: mellon@fugue.com + Stuart Cheshire Apple Inc. One Apple Park Way Cupertino, California 95014 USA Phone: +1 408 974 3207 Email: cheshire@apple.com - Ted Lemon - Nibbhaya Consulting - P.O. Box 958 - Brattleboro, Vermont 05302 - United States of America - - Email: mellon@fugue.com