--- 1/draft-ietf-dnssd-push-16.txt 2019-03-10 17:13:12.427213935 -0700 +++ 2/draft-ietf-dnssd-push-17.txt 2019-03-10 17:13:12.507215873 -0700 @@ -1,19 +1,19 @@ Internet Engineering Task Force T. Pusateri Internet-Draft Unaffiliated Intended status: Standards Track S. Cheshire -Expires: May 9, 2019 Apple Inc. - November 5, 2018 +Expires: September 10, 2019 Apple Inc. + March 9, 2019 DNS Push Notifications - draft-ietf-dnssd-push-16 + draft-ietf-dnssd-push-17 Abstract The Domain Name System (DNS) was designed to return matching records efficiently for queries for data that are relatively static. When those records change frequently, DNS is still efficient at returning the updated results when polled, as long as the polling rate is not too high. But there exists no mechanism for a client to be asynchronously notified when these changes occur. This document defines a mechanism for a client to be notified of such changes to @@ -27,25 +27,25 @@ 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 May 9, 2019. + This Internet-Draft will expire on September 10, 2019. Copyright Notice - Copyright (c) 2018 IETF Trust and the persons identified as the + Copyright (c) 2019 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 @@ -54,64 +54,64 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. State Considerations . . . . . . . . . . . . . . . . . . . . 8 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 9 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 13 - 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 13 - 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 16 - 6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 19 - 6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 19 - 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 22 - 6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22 - 6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 24 - 6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 24 - 6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 26 - 6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 28 - 6.7. Client-Initiated Termination . . . . . . . . . . . . . . 29 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 30 - 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 30 - 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 30 - 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 31 - 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 31 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 - 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 33 - 10.2. Informative References . . . . . . . . . . . . . . . . . 34 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 + 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 14 + 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 14 + 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 17 + 6.3. DNS Push Notification Updates . . . . . . . . . . . . . . 20 + 6.3.1. PUSH Message . . . . . . . . . . . . . . . . . . . . 20 + 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 23 + 6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 23 + 6.5. DNS Push Notification RECONFIRM . . . . . . . . . . . . . 25 + 6.5.1. RECONFIRM Request . . . . . . . . . . . . . . . . . . 25 + 6.5.2. RECONFIRM Response . . . . . . . . . . . . . . . . . 28 + 6.6. DNS Stateful Operations TLV Context Summary . . . . . . . 30 + 6.7. Client-Initiated Termination . . . . . . . . . . . . . . 31 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 + 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 32 + 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 32 + 7.3. TLS Session Resumption . . . . . . . . . . . . . . . . . 33 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 + 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 34 + 10.2. Informative References . . . . . . . . . . . . . . . . . 36 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38 1. Introduction Domain Name System (DNS) records may be updated using DNS Update [RFC2136]. Other mechanisms such as a Discovery Proxy [DisProx] can also generate changes to a DNS zone. This document specifies a protocol for DNS clients to subscribe to receive asynchronous notifications of changes to RRSets of interest. It is immediately relevant in the case of DNS Service Discovery [RFC6763] but is not limited to that use case, and provides a general DNS mechanism for DNS record change notifications. Familiarity with the DNS protocol and DNS packet formats is assumed [RFC1034] [RFC1035] [RFC6895]. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in - "Key words for use in RFCs to Indicate Requirement Levels", when, and - only when, they appear in all capitals, as shown here [RFC2119] - [RFC8174]. + BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all + capitals, as shown here. These words may also appear in this + document in lower case as plain English words, absent their normative + meanings. 2. Motivation As the domain name system continues to adapt to new uses and changes in deployment, polling has the potential to burden DNS servers at many levels throughout the network. Other network protocols have successfully deployed a publish/subscribe model following the Observer design pattern [obs]. XMPP Publish-Subscribe [XEP0060] and Atom [RFC4287] are examples. While DNS servers are generally highly tuned and capable of a high rate of query/response traffic, adding a @@ -124,129 +124,134 @@ multicast group address for all group members to receive. Therefore, Multicast DNS already has asynchronous change notification capability. However, when DNS Service Discovery [RFC6763] is used across a wide area network using Unicast DNS (possibly facilitated via a Discovery Proxy [DisProx]) it would be beneficial to have an equivalent capability for Unicast DNS, to allow clients to learn about DNS record changes in a timely manner without polling. The DNS Long-Lived Queries (LLQ) mechanism [LLQ] is an existing deployed solution to provide asynchronous change notifications, used - by Apple's Back to My Mac Service [RFC6281] introduced in Mac OS X + by Apple's Back to My Mac [RFC6281] service introduced in Mac OS X 10.5 Leopard in 2007. Back to My Mac was designed in an era when the data center operations staff asserted that it was impossible for a server to handle large numbers of mostly-idle TCP connections, so LLQ was defined as a UDP-based protocol, effectively replicating much of TCP's connection state management logic in user space, and creating its own poor imitations of existing TCP features like the three-way handshake, flow control, and reliability. This document builds on experience gained with the LLQ protocol, with an improved design. Instead of using UDP, this specification uses DNS Stateful Operations (DSO) [DSO] running over TLS over TCP, and therefore doesn't need to reinvent existing TCP functionality. Using TCP also gives long-lived low-traffic connections better longevity - through NAT gateways without resorting to excessive keepalive - traffic. Instead of inventing a new vocabulary of messages to - communicate DNS zone changes as LLQ did, this specification borrows - the established syntax and semantics of DNS Update messages - [RFC2136]. + through NAT gateways without depending on the gateway to support NAT + Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control Protocol + (PCP) [RFC6887], or resorting to excessive keepalive traffic. + Instead of inventing a new vocabulary of messages to communicate DNS + zone changes as LLQ did, this specification borrows the established + syntax and semantics of DNS Update messages [RFC2136]. 3. Overview The existing DNS Update protocol [RFC2136] provides a mechanism for clients to add or delete individual resource records (RRs) or entire resource record sets (RRSets) on the zone's server. This specification adopts a simplified subset of these existing syntax and semantics, and uses them for DNS Push Notification messages going in the opposite direction, from server to client, to - communicate changes to a zone. The client subscribes for Push - Notifications by connecting to the server and sending DNS message(s) - indicating the RRSet(s) of interest. When the client loses interest - in receiving further updates to these records, it unsubscribes. + communicate changes to a name's records. The client subscribes for + Push Notifications by connecting to the server and sending DNS + message(s) indicating the RRSet(s) of interest. When the client + loses interest in receiving further updates to these records, it + unsubscribes. The DNS Push Notification server for a zone is any server capable of generating the correct change notifications for a name. It may be a primary, secondary, or stealth name server [RFC7719]. Consequently, the "_dns-push-tls._tcp." SRV record for a zone MAY reference the same target host and port as that zone's "_dns-update-tls._tcp." SRV record. When the same target host and port is offered for both DNS Updates and DNS Push Notifications, a client MAY use a single TCP connection to that server for both DNS Updates and DNS Push Notification Subscriptions. Supporting DNS Updates and DNS Push Notifications on the same server - is OPTIONAL. A DNS Push Notification server does NOT also have to + is OPTIONAL. A DNS Push Notification server is NOT REQUIRED also to support DNS Update. DNS Updates and DNS Push Notifications may be handled on different ports on the same target host, in which case they are not considered to be the "same server" for the purposes of this specification, and communications with these two ports are handled independently. - Standard DNS Queries MAY be sent over a DNS Push Notification - connection. For any zone for which the server is authoritative, it + Standard DNS Queries MAY be sent over a DNS Push Notification (i.e., + DSO) session. For any zone for which the server is authoritative, it MUST respond authoritatively for queries on names falling within that zone (e.g., the in the "_dns-push-tls._tcp." SRV record) - both for DNS Push Notification queries and for normal DNS queries. - For names for which the server is acting as a caching resolver, e.g. - when the server is the local resolver, for any query for which it - supports DNS Push Notifications, it MUST also support standard - queries. + both for normal DNS queries and for DNS Push Notification + subscriptions. For names for which the server is acting as a + recursive resolver, e.g. when the server is the local recursive + resolver, for any query for which it supports DNS Push Notification + subscriptions, it MUST also support standard queries. DNS Push Notification clients are NOT required to implement DNS Update Prerequisite processing. Prerequisites are used to perform tentative atomic test-and-set type operations when a client updates records on a server, and that concept has no applicability when it comes to an authoritative server unilaterally informing a client of changes to DNS records. This DNS Push Notification specification includes support for DNS classes, for completeness. However, in practice, it is anticipated that for the foreseeable future the only DNS class in use will be DNS class "IN", as is the reality today with existing DNS servers and clients. A DNS Push Notification server MAY choose to implement only DNS class "IN". If messages are received for a class other than "IN", and that class is not supported, an error with RCODE NOTIMPL (Not Implemented) should be returned. DNS Push Notifications impose less load on the responding server than rapid polling would, but Push Notifications do still have a cost, so - DNS Push Notification clients must not recklessly create an excessive + DNS Push Notification clients MUST NOT recklessly create an excessive number of Push Notification subscriptions. Specifically: (a) A subscription should only be active when there is a valid reason to need live data (for example, an on-screen display is currently showing the results to the user) and the subscription SHOULD be cancelled as soon as the need for that data ends (for example, when - the user dismisses that display). Implementations may want to - implement idle timeouts, so that if the user ceases interacting with - the device, the subscription is cancelled. + the user dismisses that display). In the case of a device like a + smartphone which, after some period of inactivity, goes to sleep or + otherwise darkens its screen, it should cancel its subscriptions when + darkening the screen (since the user cannot see any changes in the + display anyway) and reinstate its subscriptions when re-awakening + from display sleep. (b) A DNS Push Notification client SHOULD NOT routinely keep a DNS Push Notification subscription active 24 hours a day, 7 days a week, just to keep a list in memory up to date so that if the user does choose to bring up an on-screen display of that data, it can be displayed really fast. DNS Push Notifications are designed to be fast enough that there is no need to pre-load a "warm" list in memory just in case it might be needed later. Generally, as described in the DNS Stateful Operations specification [DSO], a client must not keep a session to a server open indefinitely if it has no subscriptions (or other operations) active on that session. A client MAY close a session as soon as it becomes idle, and then if needed in the future, open a new session when required. Alternatively, a client MAY speculatively keep an idle session open for some time, subject to the constraint that it MUST NOT keep a session open that has been idle for more than the session's idle - timeout (15 seconds by default). + timeout (15 seconds by default) [DSO]. 4. Transport Other DNS operations like DNS Update [RFC2136] MAY use either User Datagram Protocol (UDP) [RFC0768] or Transmission Control Protocol (TCP) [RFC0793] as the transport protocol, in keeping with the historical precedent that DNS queries must first be sent over UDP [RFC1123]. This requirement to use UDP has subsequently been relaxed [RFC7766]. @@ -260,21 +265,21 @@ server by virtue of the TCP three-way handshake. Flooding attacks are possible with any protocol, and a benefit of TCP is that there are already established industry best practices to guard against SYN flooding and similar attacks [SYN] [RFC4953]. Use of TCP also allows DNS Push Notifications to take advantage of current and future developments in TCP, such as Multipath TCP (MPTCP) [RFC6824], TCP Fast Open (TFO) [RFC7413], Tail Loss Probe (TLP) [I-D.dukkipati-tcpm-tcp-loss-probe], and so on. - Transport Layer Security (TLS) [RFC5246] is well understood and + Transport Layer Security (TLS) [RFC8446] is well understood and deployed across many protocols running over TCP. It is designed to prevent eavesdropping, tampering, and message forgery. TLS is REQUIRED for every connection between a client subscriber and server in this protocol specification. Additional security measures such as client authentication during TLS negotiation MAY also be employed to increase the trust relationship between client and server. 5. State Considerations Each DNS Push Notification server is capable of handling some finite @@ -300,75 +305,95 @@ DNS Push Notification clients and servers MUST support DSO. A single server can support DNS Queries, DNS Updates, and DNS Push Notifications (using DSO) on the same TCP port. A DNS Push Notification exchange begins with the client discovering the appropriate server, using the procedure described in Section 6.1, and then making a TLS/TCP connection to it. A typical DNS Push Notification client will immediately issue a DSO - Keepalive operation to request a session timeout or keepalive - interval longer than the the 15-second default, but this is not - required. A DNS Push Notification client MAY issue other requests on - the session first, and only issue a DSO Keepalive operation later if - it determines that to be necessary. However, Push Notification - subscriptions can also be used to establish the DSO session. + Keepalive operation to request a session timeout and/or keepalive + interval longer than the the 15-second default values, but this is + not required. A DNS Push Notification client MAY issue other + requests on the session first, and only issue a DSO Keepalive + operation later if it determines that to be necessary. Sending + either a DSO Keepalive operation or a Push Notification subscription + over the TLS/TCP connection to the server signals the client's + support of DSO and serves to establish a DSO session. In accordance with the current set of active subscriptions, the server sends relevant asynchronous Push Notifications to the client. Note that a client MUST be prepared to receive (and silently ignore) Push Notifications for subscriptions it has previously removed, since there is no way to prevent the situation where a Push Notification is in flight from server to client while the client's UNSUBSCRIBE message cancelling that subscription is simultaneously in flight from client to server. 6.1. Discovery The first step in DNS Push Notification subscription is to discover an appropriate DNS server that supports DNS Push Notifications for the desired zone. The client begins by opening a DSO Session to its normal configured DNS recursive resolver and requesting a Push Notification - subscription. This connection is made to the default DNS-over-TLS - port as defined in DNS over TLS [RFC7858]. If this connection is - successful, then the recursive resolver will make appropriate Push - Notification subscriptions on the client's behalf, and the client - will receive appropriate results. + subscription. This connection is made to TCP port 853, the default + port for DNS-over-TLS DNS over TLS [RFC7858]. If the request for a + Push Notification subscription is successful, then the recursive + resolver will make a corresponding Push Notification subscription on + the client's behalf (if the recursive resolver doesn't already have + an active subscription for that name, type, and class), and pass on + any results it receives back to the client. This is closely + analogous to how a client sends normal DNS queries to its configured + DNS recursive resolver, which issues queries on the client's behalf + (if the recursive resolver doesn't already have appropriate answer(s) + in its cache), and passes on any results it receives back to the + client. - In many contexts, the local recursive resolver will be able to handle - push notifications for all zones that the client may need to follow. - In other cases, the client may require Push Notifications from more - than one zone, and those zones may be served by different servers. - Therefore, it is assumed that the client may need to maintain - connections to more than one DNS Push server. + In many contexts, the recursive resolver will be able to handle Push + Notifications for all names that the client may need to follow. Use + of VPN tunnels and split-view DNS can create some additional + complexity in the client software here; the techniques to handle VPN + tunnels and split-view DNS for DNS Push Notifications are the same as + those already used to handle this for normal DNS queries. - In some cases, the recursive resolver may not be able to get answers - for a particular zone. In this case, rather than returning SERVFAIL, - the resolver returns NOTAUTH. This signals the client that queries - for this zone can't be handled by the local caching resolver. For - that zone, the client SHOULD contact the zone's DNS Push server - itself, even if all other DNS Push queries can be handled by the - local resolver. This may be necessary in cases where the client is - connected to a VPN, for example, or where the client has a pre- - established trust relationship with the owner of the zone that allows - the client, but not the local resolver, to successfully get answers - for queries in that zone. + If the recursive resolver does not support DNS over TLS, or does + support DNS over TLS but is not listening on TCP port 853, or does + support DNS over TLS on TCP port 853 but does not support DSO on that + port, then the DSO Session session establishment will fail [DSO]. - If the recursive resolver does not support Push Notification - subscriptions, then it will return an error code, DSONOTIMPL. This - occurs when the local resolver follows the procedure below and does - not find an SRV record indicating support for DNS Push Notifications. + If the recursive resolver does support DSO but not Push Notification + subscriptions, then it will return the DSO error code, DSOTYPENI + (11). - In case of either failure, the client should proceed to discover the + In some cases, the recursive resolver may support DSO and Push + Notification subscriptions, but may not be able to subscribe for Push + Notifications for a particular name. In this case, the recursive + resolver should return an informative error code to the client so + that the client can make an informed decision how to handle the + error. If the recursive resolver is unable to establish a connection + to the zone's DNS Push Notification server (perhaps because the + required SRV record does not exist) the recursive resolver should + return SERVFAIL. If the recursive resolver is able to establish a + connection to the zone's DNS Push Notification server and some other + error code is then received, the recursive resolver should pass on + this received error code back to the client. In some cases, where + the client has a pre-established trust relationship with the owner of + the zone (that is not handled via the usual mechanisms for VPN + software) the client may handle these failures by contacting the + zone's DNS Push server directly. + + In any of the cases described above where the client fails to + establish a DNS Push Notification subscription via its configured + recursive resolver, the client should proceed to discover the appropriate server for direct communication. The client MUST also determine which TCP port on the server is listening for connections, which need not be (and often is not) the typical TCP port 53 used for conventional DNS, or TCP port 853 used for DNS over TLS. The discovery algorithm described here is an iterative algorithm, which starts with the full name of the record to which the client wishes to subscribe. Successive SOA queries are then issued, trimming one label each time, until the closest enclosing authoritative server is discovered. There is also an optimization to @@ -377,55 +402,59 @@ 1. The client begins the discovery by sending a DNS query to its local resolver, with record type SOA [RFC1035] for the record name to which it wishes to subscribe. As an example, suppose the client wishes to subscribe to PTR records with the name _ipp._tcp.foo.example.com (to discover Internet Printing Protocol (IPP) printers [RFC8010] [RFC8011] being advertised at "foo.example.com"). The client begins by sending an SOA query for _ipp._tcp.foo.example.com to the local recursive resolver. The goal is to determine the server authoritative for the name - _ipp._tcp.foo.example.com. The DNS zone containing the name - _ipp._tcp.foo.example.com could be example.com, or - foo.example.com, or _tcp.foo.example.com, or even + _ipp._tcp.foo.example.com. The closest enclosing DNS zone + containing the name _ipp._tcp.foo.example.com could be + example.com, or foo.example.com, or _tcp.foo.example.com, or even _ipp._tcp.foo.example.com. The client does not know in advance where the closest enclosing zone cut occurs, which is why it uses - the procedure described here to discover this information. + the iterative procedure described here to discover this + information. 2. If the requested SOA record exists, it will be returned in the Answer section with a NOERROR response code, and the client has - succeeded in discovering the information it needs. (This text is - not placing any new requirements on DNS recursive resolvers. It - is merely describing the existing operation of the DNS protocol - [RFC1034] [RFC1035].) + succeeded in discovering the information it needs. + (This language is not placing any new requirements on DNS + recursive resolvers. This text merely describes the existing + operation of the DNS protocol [RFC1034] [RFC1035].) 3. If the requested SOA record does not exist, the client will get back a NOERROR/NODATA response or an NXDOMAIN/Name Error response. In either case, the local resolver would normally - include the SOA record for the zone of the requested name in the - Authority Section. If the SOA record is received in the - Authority Section, then the client has succeeded in discovering - the information it needs. (This text is not placing any new - requirements on DNS recursive resolvers. It is merely describing - the existing operation of the DNS protocol regarding negative - responses [RFC2308].) + include the SOA record for the closest enclosing zone of the + requested name in the Authority Section. If the SOA record is + received in the Authority Section, then the client has succeeded + in discovering the information it needs. + (This language is not placing any new requirements on DNS + recursive resolvers. This text merely describes the existing + operation of the DNS protocol regarding negative responses + [RFC2308].) 4. If the client receives a response containing no SOA record, then it proceeds with the iterative approach. The client strips the leading label from the current query name and if the resulting - name has at least one label in it, the client sends a new SOA - query, and processing continues at step 2 above, repeating the - iterative search until either an SOA is received, or the query - name is empty. In the case of an empty name, this is a network - configuration error which should not happen and the client gives - up. The client may retry the operation at a later time, of the - client's choosing, such after a change in network attachment. + name has at least one label in it, the client sends an SOA query + for that new name, and processing continues at step 2 above, + repeating the iterative search until either an SOA is received, + or the query name consists of a single label, i.e., a Top Level + Domain (TLD). In the case of a single-label TLD, this is a + network configuration error which should not happen and the + client gives up. The client may retry the operation at a later + time, of the client's choosing, such after a change in network + attachment. 5. Once the SOA is known (either by virtue of being seen in the Answer Section, or in the Authority Section), the client sends a DNS query with type SRV [RFC2782] for the record name "_dns-push-tls._tcp.", where is the owner name of the discovered SOA record. 6. If the zone in question is set up to offer DNS Push Notifications then this SRV record MUST exist. (If this SRV record does not exist then the zone is not correctly configured for DNS Push @@ -459,89 +488,90 @@ means that, as long as the DNS TTL values on the authoritative records were set to reasonable values, repeated application of this discovery process can be completed nearly instantaneously by the client, using only locally-stored cached data. 6.2. DNS Push Notification SUBSCRIBE After connecting, and requesting a longer idle timeout and/or keepalive interval if necessary, a DNS Push Notification client then indicates its desire to receive DNS Push Notifications for a given - domain name by sending a SUBSCRIBE request over the established DSO - session to the server. A SUBSCRIBE request is encoded in a DSO [DSO] - message. This specification defines a primary DSO TLV for DNS Push - Notification SUBSCRIBE Requests (tentatively DSO Type Code 0x40). + domain name by sending a SUBSCRIBE request to the server. A + SUBSCRIBE request is encoded in a DSO message [DSO]. This + specification defines a primary DSO TLV for DNS Push Notification + SUBSCRIBE Requests (tentatively DSO Type Code 0x40). The entity that initiates a SUBSCRIBE request is by definition the client. A server MUST NOT send a SUBSCRIBE request over an existing session from a client. If a server does send a SUBSCRIBE request over a DSO session initiated by a client, this is a fatal error and the client should immediately abort the connection with a TCP RST (or equivalent for other protocols). 6.2.1. SUBSCRIBE Request A SUBSCRIBE request begins with the standard DSO 12-byte header - [DSO], followed by the SUBSCRIBE TLV. A SUBSCRIBE request message is - illustrated in Figure 1. + [DSO], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE request + message is illustrated in Figure 1. The MESSAGE ID field MUST be set to a unique value, that the client - is not using for any other active operation on this session. For the - purposes here, a MESSAGE ID is in use on this session if the client - has used it in a request for which it has not yet received a + is not using for any other active operation on this DSO session. For + the purposes here, a MESSAGE ID is in use on this session if the + client has used it in a request for which it has not yet received a response, or if the client has used it for a subscription which it has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response the server MUST echo back the MESSAGE ID value unchanged. The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS Opcode is the DSO Opcode. The four - count fields MUST be zero, and the corresponding four sections MUST - be empty (i.e., absent). + specification [DSO]. The DNS OPCODE field contains the OPCODE value + for DNS Stateful Operations (6). The four count fields MUST be zero, + and the corresponding four sections MUST be empty (i.e., absent). - The DSO-TYPE is SUBSCRIBE. The DSO-LENGTH is the length of the DSO- - DATA that follows, which specifies the name, type, and class of the - record(s) being sought. + The DSO-TYPE is SUBSCRIBE (tentatively 0x40). + + The DSO-LENGTH is the length of the DSO-DATA that follows, which + specifies the name, type, and class of the record(s) being sought. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ | MESSAGE ID | \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | - |QR| Opcode | Z | RCODE | | + |QR| OPCODE(6) | Z | RCODE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | QDCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER | ANCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | NSCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | ARCOUNT (MUST BE ZERO) | / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / - | DSO-TYPE = SUBSCRIBE | + | DSO-TYPE = SUBSCRIBE (tentatively 0x40) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | DSO-LENGTH (number of octets in DSO-DATA) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ | | \ \ NAME \ | \ \ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA | TYPE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | CLASS | / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / Figure 1: SUBSCRIBE Request The DSO-DATA for a SUBSCRIBE request MUST contain exactly one NAME, - Type, and CLASS. Since SUBSCRIBE requests are sent over TCP, - multiple SUBSCRIBE request messages can be concatenated in a single - TCP stream and packed efficiently into TCP segments. + TYPE, and CLASS. Since SUBSCRIBE requests are sent over TCP, + multiple SUBSCRIBE DSO request messages can be concatenated in a + single TCP stream and packed efficiently into TCP segments. If accepted, the subscription will stay in effect until the client cancels the subscription using UNSUBSCRIBE or until the DSO session between the client and the server is closed. SUBSCRIBE requests on a given session MUST be unique. A client MUST NOT send a SUBSCRIBE message that duplicates the NAME, TYPE and CLASS of an existing active subscription on that DSO session. For the purpose of this matching, the established DNS case-insensitivity for US-ASCII letters applies (e.g., "example.com" and "Example.com" are @@ -552,22 +582,23 @@ DNS wildcarding is not supported. That is, a wildcard ("*") in a SUBSCRIBE message matches only a literal wildcard character ("*") in the zone, and nothing else. Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message matches only a literal CNAME record in the zone, and nothing else. A client may SUBSCRIBE to records that are unknown to the server at the time of the request (providing that the name falls within one of the zone(s) the server is responsible for) and this is not an error. - The server MUST accept these requests and send Push Notifications if - and when matching records are found in the future. + The server MUST NOT return NXDOMAIN in this case. The server MUST + accept these requests and send Push Notifications if and when + matching records are found in the future. If neither TYPE nor CLASS are ANY (255) then this is a specific subscription to changes for the given NAME, TYPE and CLASS. If one or both of TYPE or CLASS are ANY (255) then this subscription matches any type and/or any class, as appropriate. NOTE: A little-known quirk of DNS is that in DNS QUERY requests, QTYPE and QCLASS 255 mean "ANY" not "ALL". They indicate that the server should respond with ANY matching records of its choosing, not necessarily ALL matching records. This can lead to some surprising @@ -579,23 +610,23 @@ interpreted to mean "ALL", not "ANY". After accepting a subscription where one or both of TYPE or CLASS are 255, the server MUST send Push Notification Updates for ALL record changes that match the subscription, not just some of them. 6.2.2. SUBSCRIBE Response Each SUBSCRIBE request generates exactly one SUBSCRIBE response from the server. - A SUBSCRIBE response message begins with the standard DSO 12-byte - header [DSO], possibly followed by one or more optional TLVs, such as - a Retry Delay TLV. + A SUBSCRIBE response begins with the standard DSO 12-byte header + [DSO], possibly followed by one or more optional TLVs, such as a + Retry Delay TLV. The MESSAGE ID field MUST echo the value given in the ID field of the SUBSCRIBE request. This is how the client knows which request is being responded to. A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. If a client receives a SUBSCRIBE response message containing a SUBSCRIBE TLV then the response message is processed but the SUBSCRIBE TLV MUST be silently ignored. @@ -622,91 +653,95 @@ This document specifies only these RCODE values for SUBSCRIBE Responses. Servers sending SUBSCRIBE Responses SHOULD use one of these values. Note that NXDOMAIN is not a valid RCODE in response to a SUBSCRIBE Request. However, future circumstances may create situations where other RCODE values are appropriate in SUBSCRIBE Responses, so clients MUST be prepared to accept SUBSCRIBE Responses with any other RCODE value. If the server sends a nonzero RCODE in the SUBSCRIBE response, that - means + means: a. the client is (at least partially) misconfigured, b. the server resources are exhausted, or c. there is some other unknown failure on the server. In any case, the client shouldn't retry the subscription to this server right away. If multiple SRV records were returned as - described in discovery Section 6.1, Paragraph 7, a subsequent server - can be tried immediately. + described in Section 6.1, Paragraph 7, a subsequent server can be + tried immediately. If the client has other successful subscriptions to this server, - these subscriptions can remain even though additional subscriptions - may be refused. Neither the client, nor the server are required to - close the connection, although, either end may choose to do so. + these subscriptions remain even though additional subscriptions may + be refused. Neither the client nor the server are required to close + the connection, although, either end may choose to do so. If the server sends a nonzero RCODE then it SHOULD append a Retry Delay TLV [DSO] to the response specifying a delay before the client attempts this operation again. Recommended values for the delay for different RCODE values are given below. These recommended values apply both to the default values a server should place in the Retry Delay TLV, and the default values a client should assume if the server provides no Retry Delay TLV. For RCODE = 1 (FORMERR) the delay may be any value selected by the implementer. A value of five minutes is RECOMMENDED, to reduce the risk of high load from defective clients. For RCODE = 2 (SERVFAIL) the delay should be chosen according to the level of server overload and the anticipated duration of that overload. By default, a value of one minute is RECOMMENDED. If a more serious server failure occurs, the delay may be longer in accordance with the specific problem encountered. For RCODE = 4 (NOTIMP), which occurs on a server that doesn't - implement DSO [DSO], it is unlikely that the server will begin - supporting DSO in the next few minutes, so the retry delay SHOULD - be one hour. Note that in such a case, a server that doesn't - implement DSO is unlikely to place a Retry Delay TLV in its - response, so this recommended value in particular applies to what - a client should assume by default. + implement DNS Stateful Operations [DSO], it is unlikely that the + server will begin supporting DSO in the next few minutes, so the + retry delay SHOULD be one hour. Note that in such a case, a + server that doesn't implement DSO is unlikely to place a Retry + Delay TLV in its response, so this recommended value in particular + applies to what a client should assume by default. For RCODE = 5 (REFUSED), which occurs on a server that implements DNS Push Notifications, but is currently configured to disallow DNS Push Notifications, the retry delay may be any value selected by the implementer and/or configured by the operator. - If the server being queried is not the local resolver, this is a - misconfiguration, since this server is listed in a - "_dns-push-tls._tcp." SRV record, but the server itself is - not currently configured to support DNS Push Notifications for - that zone. Since it is possible that the misconfiguration may be - repaired at any time, the retry delay should not be set too high. - By default, a value of 5 minutes is RECOMMENDED. + If the server being queried is listed in a + "_dns-push-tls._tcp." SRV record for the zone, then this is + a misconfiguration, since this server is being advertised as + supporting DNS Push Notifications for this zone, but the server + itself is not currently configured to perform that task. Since it + is possible that the misconfiguration may be repaired at any time, + the retry delay should not be set too high. By default, a value + of 5 minutes is RECOMMENDED. For RCODE = 9 (NOTAUTH), which occurs on a server that implements DNS Push Notifications, but is not configured to be authoritative for the requested name, the retry delay may be any value selected by the implementer and/or configured by the operator. - This is a misconfiguration, since this server is listed in a - "_dns-push-tls._tcp." SRV record, but the server itself is - not currently configured to support DNS Push Notifications for - that zone. Since it is possible that the misconfiguration may be - repaired at any time, the retry delay should not be set too high. - By default, a value of 5 minutes is RECOMMENDED. + If the server being queried is listed in a + "_dns-push-tls._tcp." SRV record for the zone, then this is + a misconfiguration, since this server is being advertised as + supporting DNS Push Notifications for this zone, but the server + itself is not currently configured to perform that task. Since it + is possible that the misconfiguration may be repaired at any time, + the retry delay should not be set too high. By default, a value + of 5 minutes is RECOMMENDED. - For RCODE = 11 (DSOTYPENI), which occurs on a server that doesn't - implement DNS Push Notifications, it is unlikely that the server - will begin supporting DNS Push Notifications in the next few - minutes, so the retry delay SHOULD be one hour. + For RCODE = 11 (DSOTYPENI), which occurs on a server that + implements DSO but doesn't implement DNS Push Notifications, it is + unlikely that the server will begin supporting DNS Push + Notifications in the next few minutes, so the retry delay SHOULD + be one hour. For other RCODE values, the retry delay should be set by the server as appropriate for that error condition. By default, a value of 5 minutes is RECOMMENDED. For RCODE = 9 (NOTAUTH), the time delay applies to requests for other names falling within the same zone. Requests for names falling within other zones are not subject to the delay. For all other RCODEs the time delay applies to all subsequent requests to this server. @@ -714,42 +749,45 @@ After sending an error response the server MAY allow the session to remain open, or MAY send a DNS Push Notification Retry Delay Operation TLV instructing the client to close the session, as described in the DSO specification [DSO]. Clients MUST correctly handle both cases. 6.3. DNS Push Notification Updates Once a subscription has been successfully established, the server generates PUSH messages to send to the client as appropriate. In the - case that the answer set was non-empty at the moment the subscription - was established, an initial PUSH message will be sent immediately - following the SUBSCRIBE Response. Subsequent changes to the answer - set are then communicated to the client in subsequent PUSH messages. + case that the answer set was already non-empty at the moment the + subscription was established, an initial PUSH message will be sent + immediately following the SUBSCRIBE Response. Subsequent changes to + the answer set are then communicated to the client in subsequent PUSH + messages. 6.3.1. PUSH Message - A PUSH message begins with the standard DSO 12-byte header [DSO], - followed by the PUSH TLV. A PUSH message is illustrated in Figure 2. + A PUSH unidirectional message begins with the standard DSO 12-byte + header [DSO], followed by the PUSH primary TLV. A PUSH message is + illustrated in Figure 2. In accordance with the definition of DSO unidirectional messages, the MESSAGE ID field MUST be zero. There is no client response to a PUSH message. - The other header fields MUST also be set as described in the DSO - specification [DSO]. The DNS Opcode is the DSO Opcode. The four - count fields MUST be zero, and the corresponding four sections MUST - be empty (i.e., absent). + The other header fields MUST be set as described in the DSO + specification [DSO]. The DNS OPCODE field contains the OPCODE value + for DNS Stateful Operations (6). The four count fields MUST be zero, + and the corresponding four sections MUST be empty (i.e., absent). - The DSO-TYPE is PUSH (tentatively 0x41). The DSO-LENGTH is the - length of the DSO-DATA that follows, which specifies the changes - being communicated. + The DSO-TYPE is PUSH (tentatively 0x41). + + The DSO-LENGTH is the length of the DSO-DATA that follows, which + specifies the changes being communicated. The DSO-DATA contains one or more Update records. A PUSH Message MUST contain at least one Update record. If a PUSH Message is received that contains zero Update records, this is a fatal error, and the receiver MUST immediately terminate the connection with a TCP RST (or equivalent for other protocols). The Update records are formatted in the customary way for Resource Records in DNS messages. Update records in a PUSH Message are interpreted according to the same rules as for DNS Update [RFC2136] messages, namely: @@ -758,39 +796,38 @@ Delete an RRset from a name: TTL=0, CLASS=ANY, RDLENGTH=0; TYPE specifies the RRset being deleted. Delete an individual RR from a name: TTL=0, CLASS=NONE; TYPE, RDLENGTH and RDATA specifies the RR being deleted. Add to an RRset: - TTL, CLASS, TYPE, RDLENGTH and RDATA specifies the RR being added. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ | MESSAGE ID (MUST BE ZERO) | \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | - |QR| Opcode | Z | RCODE | | + |QR| OPCODE(6) | Z | RCODE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | QDCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER | ANCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | NSCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | ARCOUNT (MUST BE ZERO) | / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / - | DSO-TYPE = PUSH | + | DSO-TYPE = PUSH (tentatively 0x41) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | DSO-LENGTH (number of octets in DSO-DATA) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ \ NAME \ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | TYPE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | CLASS | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | TTL | | @@ -803,21 +840,21 @@ : NAME, TYPE, CLASS, TTL, RDLEN, RDATA : | : Repeated As Necessary : / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / Figure 2: PUSH Message When processing the records received in a PUSH Message, the receiving client MUST validate that the records being added or deleted correspond with at least one currently active subscription on that session. Specifically, the record name MUST match the name given in - the SUBSCRIBE request, subject to the usual established DNS case- + a SUBSCRIBE request, subject to the usual established DNS case- insensitivity for US-ASCII letters. If the TYPE in the SUBSCRIBE request was not ANY (255) then the TYPE of the record must match the TYPE given in the SUBSCRIBE request. If the CLASS in the SUBSCRIBE request was not ANY (255) then the CLASS of the record must match the CLASS given in the SUBSCRIBE request. If a matching active subscription on that session is not found, then that individual record addition/deletion is silently ignored. Processing of other additions and deletions in this message is not affected. The DSO session is not closed. This is to allow for the unavoidable race condition where a client sends an outbound UNSUBSCRIBE while inbound @@ -855,146 +892,168 @@ record is still there. Once a subscription is cancelled (individually, or as a result of the DSO session being closed) record aging for records covered by the subscription resumes and records are removed from the local cache when their TTL reaches zero. 6.4. DNS Push Notification UNSUBSCRIBE To cancel an individual subscription without closing the entire DSO session, the client sends an UNSUBSCRIBE message over the established DSO session to the server. The UNSUBSCRIBE message is encoded as a - DSO [DSO] unidirectional message. This specification defines a + DSO unidirectional message [DSO]. This specification defines a primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE Requests (tentatively DSO Type Code 0x42). A server MUST NOT initiate an UNSUBSCRIBE request. If a server does send an UNSUBSCRIBE request over a DSO session initiated by a client, this is a fatal error and the client should immediately abort the connection with a TCP RST (or equivalent for other protocols). 6.4.1. UNSUBSCRIBE Request An UNSUBSCRIBE request begins with the standard DSO 12-byte header - [DSO], followed by the UNSUBSCRIBE TLV. An UNSUBSCRIBE request - message is illustrated in Figure 3. + [DSO], followed by the UNSUBSCRIBE primary TLV. An UNSUBSCRIBE + request message is illustrated in Figure 3. - The MESSAGE ID field MUST be zero. There is no server response to a + In accordance with the definition of DSO unidirectional messages, the + MESSAGE ID field MUST be zero. There is no server response to a UNSUBSCRIBE message. The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS Opcode is the DSO Opcode. The four - count fields MUST be zero, and the corresponding four sections MUST - be empty (i.e., absent). + specification [DSO]. The DNS OPCODE field contains the OPCODE value + for DNS Stateful Operations (6). The four count fields MUST be zero, + and the corresponding four sections MUST be empty (i.e., absent). - In the UNSUBSCRIBE TLV the DSO-TYPE is UNSUBSCRIBE. The DSO-LENGTH - is 2 octets. + The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42). - The DSO-DATA contains the MESSAGE ID field of the value given in the - ID field of an active SUBSCRIBE request. This is how the server - knows which SUBSCRIBE request is being cancelled. After receipt of - the UNSUBSCRIBE request, the SUBSCRIBE request is no longer active. + The DSO-LENGTH field contains the value 2, the length of the 2-octet + MESSAGE ID contained in the DSO-DATA. + + The DSO-DATA contains the value given in the MESSAGE ID field of an + active SUBSCRIBE request. This is how the server knows which + SUBSCRIBE request is being cancelled. After receipt of the + UNSUBSCRIBE request, the SUBSCRIBE request is no longer active. It is allowable for the client to issue an UNSUBSCRIBE request for a previous SUBSCRIBE request for which the client has not yet received a SUBSCRIBE response. This is to allow for the case where a client starts and stops a subscription in less than the round-trip time to the server. The client is NOT required to wait for the SUBSCRIBE response before issuing the UNSUBSCRIBE request. + Consequently, it is possible for a server to receive an UNSUBSCRIBE + request that does not match any currently active subscription. This + can occur when a client sends a SUBSCRIBE request, which subsequently + fails and returns an error code, but the client sent an UNSUBSCRIBE + request before it became aware that the SUBSCRIBE request had failed. + Because of this, servers MUST silently ignore UNSUBSCRIBE requests + that do not match any currently active subscription. + 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ | MESSAGE ID (MUST BE ZERO) | \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | - |QR| Opcode | Z | RCODE | | + |QR| OPCODE(6) | Z | RCODE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | QDCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER | ANCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | NSCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | ARCOUNT (MUST BE ZERO) | / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / - | DSO-TYPE = UNSUBSCRIBE | + | DSO-TYPE = UNSUBSCRIBE (tentatively 0x42) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | DSO-LENGTH (2 octets) | + | DSO-LENGTH (2) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ | SUBSCRIBE MESSAGE ID | > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / Figure 3: UNSUBSCRIBE Request 6.5. DNS Push Notification RECONFIRM Sometimes, particularly when used with a Discovery Proxy [DisProx], a DNS Zone may contain stale data. When a client encounters data that - it believe may be stale (e.g., an SRV record referencing a target + it believes may be stale (e.g., an SRV record referencing a target host+port that is not responding to connection requests) the client can send a RECONFIRM request to ask the server to re-verify that the data is still valid. For a Discovery Proxy, this causes it to issue new Multicast DNS requests to ascertain whether the target device is - still present. For other types of DNS server, the RECONFIRM - operation is currently undefined, and SHOULD result in a NOERROR - response, but otherwise need not cause any action to occur. Frequent - RECONFIRM operations may be a sign of network unreliability, or some - kind of misconfiguration, so RECONFIRM operations MAY be logged or - otherwise communicated to a human administrator to assist in - detecting, and remedying, such network problems. + still present. How the Discovery Proxy causes these new Multicast + DNS requests to be issued depends on the details of the underlying + Multicast DNS being used. For example, a Discovery Proxy built on + Apple's dns_sd.h API responds to a DNS Push Notification RECONFIRM + message by calling the underlying API's DNSServiceReconfirmRecord() + routine. + + For other types of DNS server, the RECONFIRM operation is currently + undefined, and SHOULD result in a NOERROR response, but otherwise + need not cause any action to occur. + + Frequent use of RECONFIRM operations may be a sign of network + unreliability, or some kind of misconfiguration, so RECONFIRM + operations MAY be logged or otherwise communicated to a human + administrator to assist in detecting, and remedying, such network + problems. If, after receiving a valid RECONFIRM request, the server determines that the disputed records are in fact no longer valid, then subsequent DNS PUSH Messages will be generated to inform interested clients. Thus, one client discovering that a previously-advertised device (like a network printer) is no longer present has the side effect of informing all other interested clients that the device in question is now gone. 6.5.1. RECONFIRM Request A RECONFIRM request begins with the standard DSO 12-byte header - [DSO], followed by the primary DSO RECONFIRM TLV. A RECONFIRM - request message is illustrated in Figure 4. + [DSO], followed by the RECONFIRM primary TLV. A RECONFIRM request + message is illustrated in Figure 4. The MESSAGE ID field MUST be set to a unique value, that the client is not using for any other active operation on this DSO session. For the purposes here, a MESSAGE ID is in use on this session if the client has used it in a request for which it has not yet received a response, or if the client has used it for a subscription which it has not yet cancelled using UNSUBSCRIBE. In the RECONFIRM response the server MUST echo back the MESSAGE ID value unchanged. The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS Opcode is the DSO Opcode. The four - count fields MUST be zero, and the corresponding four sections MUST - be empty (i.e., absent). + specification [DSO]. The DNS OPCODE field contains the OPCODE value + for DNS Stateful Operations (6). The four count fields MUST be zero, + and the corresponding four sections MUST be empty (i.e., absent). - The DSO-TYPE is RECONFIRM (tentatively 0x43). The DSO-LENGTH is the - length of the data that follows, which specifies the name, type, - class, and content of the record being disputed. + The DSO-TYPE is RECONFIRM (tentatively 0x43). + + The DSO-LENGTH is the length of the data that follows, which + specifies the name, type, class, and content of the record being + disputed. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ | MESSAGE ID | \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | - |QR| Opcode | Z | RCODE | | + |QR| OPCODE(6) | Z | RCODE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | QDCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER | ANCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | NSCOUNT (MUST BE ZERO) | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | ARCOUNT (MUST BE ZERO) | / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / - | DSO-TYPE = RECONFIRM | + | DSO-TYPE = RECONFIRM (tentatively 0x43) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | DSO-LENGTH (number of octets in DSO-DATA) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ \ NAME \ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | TYPE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA | CLASS | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | \ RDATA \ / @@ -1016,23 +1075,23 @@ the zone, and nothing else. Aliasing is not supported. That is, a CNAME in a RECONFIRM message matches only a literal CNAME record in the zone, and nothing else. 6.5.2. RECONFIRM Response Each RECONFIRM request generates exactly one RECONFIRM response from the server. - A RECONFIRM response message begins with the standard DSO 12-byte - header [DSO], possibly followed by one or more optional TLVs, such as - a Retry Delay TLV. For suggested values for the Retry Delay TLV, see + A RECONFIRM response begins with the standard DSO 12-byte header + [DSO], possibly followed by one or more optional TLVs, such as a + Retry Delay TLV. For suggested values for the Retry Delay TLV, see Section 6.2.2. The MESSAGE ID field MUST echo the value given in the ID field of the RECONFIRM request. This is how the client knows which request is being responded to. A RECONFIRM response message MUST NOT include a DSO RECONFIRM TLV. If a client receives a RECONFIRM response message containing a RECONFIRM TLV then the response message is processed but the RECONFIRM TLV MUST be silently ignored. @@ -1094,50 +1153,50 @@ the client's point of view. The client may log them to aid in debugging, but otherwise they require no special action. Nonzero RCODE values other than these three indicate a serious problem with the client. After sending an error response other than one of these three, the server SHOULD send a DSO Retry Delay TLV to end the DSO session, as described in the DSO specification [DSO]. 6.6. DNS Stateful Operations TLV Context Summary - This document defines four new DSO TLVs. As suggested in [DSO], - Section 8.2, the valid contexts of these new TLV types are summarized - below. + This document defines four new DSO TLVs. As suggested in Section 8.2 + of the DNS Stateful Operations specification [DSO], the valid + contexts of these new TLV types are summarized below. The client TLV contexts are: - C-P: Client primary TLV - C-U: Client primary unidirectional TLV - C-A: Client additional TLV - CRP: Client response primary TLV - CRA: Client response additional TLV + C-P: Client request message, primary TLV + C-U: Client unidirectional message, primary TLV + C-A: Client request or unidirectional message, additional TLV + CRP: Response back to client, primary TLV + CRA: Response back to client, additional TLV +-------------+-----+-----+-----+-----+-----+ | TLV Type | C-P | C-U | C-A | CRP | CRA | +-------------+-----+-----+-----+-----+-----+ | SUBSCRIBE | X | | | | | | PUSH | | | | | | | UNSUBSCRIBE | | X | | | | | RECONFIRM | X | | | | | +-------------+-----+-----+-----+-----+-----+ Table 3: DSO TLV Client Context Summary The server TLV contexts are: - S-P: Server primary TLV - S-U: Server primary unidirectional TLV - S-A: Server additional TLV - SRP: Server response primary TLV - SRA: Server response additional TLV + S-P: Server request message, primary TLV + S-U: Server unidirectional message, primary TLV + S-A: Server request or unidirectional message, additional TLV + SRP: Response back to server, primary TLV + SRA: Response back to server, additional TLV +-------------+-----+-----+-----+-----+-----+ | TLV Type | S-P | S-U | S-A | SRP | SRA | +-------------+-----+-----+-----+-----+-----+ | SUBSCRIBE | | | | | | | PUSH | | X | | | | | UNSUBSCRIBE | | | | | | | RECONFIRM | | | | | | +-------------+-----+-----+-----+-----+-----+ @@ -1180,25 +1239,28 @@ If a client has performed operations on this session that it would not want lost (like DNS updates) then the client SHOULD do an orderly disconnect, sending a TLS close_notify followed by a TCP FIN. (In the BSD Sockets API, sending a TCP FIN is achieved by calling "shutdown(s,SHUT_WR)" and keeping the socket open until all remaining data has been read from it.) 7. Security Considerations The Strict Privacy Usage Profile for DNS over TLS is REQUIRED for DNS - Push Notifications as defined in "Usage Profiles for DNS over TLS and - DNS over DTLS" [RFC8310]. Cleartext connections for DNS Push + Push Notifications [RFC8310]. Cleartext connections for DNS Push Notifications are not permissible. Since this is a new protocol, transition mechanisms from the Opportunistic Privacy profile are - deemed unnecessary. + unnecessary. + + Also, see Section 9 of the DNS over (D)TLS Usage Profiles document + [RFC8310] for additional recommendations for various versions of TLS + usage. DNSSEC is RECOMMENDED for the authentication of DNS Push Notification servers. TLS alone does not provide complete security. TLS certificate verification can provide reasonable assurance that the client is really talking to the server associated with the desired host name, but since the desired host name is learned via a DNS SRV query, if the SRV query is subverted then the client may have a secure connection to a rogue server. DNSSEC can provided added confidence that the SRV query has not been subverted. @@ -1232,40 +1294,27 @@ then be authenticated using DANE TLSA records for the associated SRV record. This associates the target's name and port number with a trusted TLS certificate [RFC7673]. This procedure uses the TLS Sever Name Indication (SNI) extension [RFC6066] to inform the server of the name the client has authenticated through the use of TLSA records. Therefore, if the SRV record passes DNSSEC validation and a TLSA record matching the target name is useable, an SNI extension must be used for the target name to ensure the client is connecting to the server it has authenticated. If the target name does not have a usable TLSA record, then the use of the SNI extension is optional. - See Usage Profiles for DNS over TLS and DNS over DTLS [RFC8310] for - more information on authenticating domain names. Also note that a - DNS Push server is an authoritative server and a DNS Push client is a - standard DNS client. While the terminology in Usage Profiles for DNS - over TLS and DNS over DTLS [RFC8310] explicitly states it does not - apply to authoritative servers, it does in this case apply to DNS - Push Notification clients and servers. - -7.3. TLS Compression - - In order to reduce the chances of compression-related attacks, TLS- - level compression SHOULD be disabled when using TLS versions 1.2 and - earlier. In TLS 1.3 [RFC8446], TLS-level compression has been - removed completely. + more information on authenticating domain names. -7.4. TLS Session Resumption +7.3. TLS Session Resumption TLS Session Resumption is permissible on DNS Push Notification - servers. The server may keep TLS state with Session IDs [RFC5246] or + servers. The server may keep TLS state with Session IDs [RFC8446] or operate in stateless mode by sending a Session Ticket [RFC5077] to the client for it to store. However, closing the TLS connection terminates the DSO session. When the TLS session is resumed, the DNS Push Notification server will not have any subscription state and will proceed as with any other new DSO session. Use of TLS Session Resumption may allow a TLS connection to be set up more quickly, but the client will still have to recreate any desired subscriptions. 8. IANA Considerations @@ -1278,28 +1327,28 @@ +-----------------------+------+----------------------+-------------+ | DNS Push Notification | None | "_dns-push-tls._tcp" | Section 6.1 | | Service Type | | | | +-----------------------+------+----------------------+-------------+ Table 5: IANA Service Type Assignments This document also defines four new DNS Stateful Operation TLV types to be recorded in the IANA DSO Type Code Registry. - +-------------+------------------------+---------------+ + +-------------+------------------------+-------------+ | Name | Value | Definition | - +-------------+------------------------+---------------+ + +-------------+------------------------+-------------+ | SUBSCRIBE | TBA (tentatively 0x40) | Section 6.2 | - | PUSH | TBA (tentatively 0x41) | Section 6.3.1 | + | PUSH | TBA (tentatively 0x41) | Section 6.3 | | UNSUBSCRIBE | TBA (tentatively 0x42) | Section 6.4 | - | RECONFIRM | TBA (tentatively 0x43) | Section 6.5.1 | - +-------------+------------------------+---------------+ + | RECONFIRM | TBA (tentatively 0x43) | Section 6.5 | + +-------------+------------------------+-------------+ Table 6: IANA DSO TLV Type Code Assignments 9. Acknowledgements The authors would like to thank Kiren Sekar and Marc Krochmal for previous work completed in this field. This draft has been improved due to comments from Ran Atkinson, Tim Chown, Mark Delany, Ralph Droms, Bernie Volz, Jan Komissar, Manju @@ -1345,25 +1394,20 @@ [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, DOI 10.17487/RFC2136, April 1997, . [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, DOI 10.17487/RFC2782, February 2000, . - [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security - (TLS) Protocol Version 1.2", RFC 5246, - DOI 10.17487/RFC5246, August 2008, - . - [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, . [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, DOI 10.17487/RFC6335, August 2011, @@ -1441,20 +1485,29 @@ [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, . [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013, . + [RFC6886] Cheshire, S. and M. Krochmal, "NAT Port Mapping Protocol + (NAT-PMP)", RFC 6886, DOI 10.17487/RFC6886, April 2013, + . + + [RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and + P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, + DOI 10.17487/RFC6887, April 2013, + . + [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, . [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, . @@ -1494,16 +1547,16 @@ Tom Pusateri Unaffiliated Raleigh, NC 27608 USA Phone: +1 919 867 1330 Email: pusateri@bangj.com Stuart Cheshire Apple Inc. - 1 Infinite Loop + One Apple Park Way Cupertino, CA 95014 USA - Phone: +1 408 974 3207 + Phone: +1 (408) 996-1010 Email: cheshire@apple.com