--- 1/draft-ietf-dnssd-push-08.txt 2016-10-31 16:17:14.635625206 -0700 +++ 2/draft-ietf-dnssd-push-09.txt 2016-10-31 16:17:14.699626803 -0700 @@ -1,19 +1,19 @@ Internet Engineering Task Force T. Pusateri Internet-Draft Seeking affiliation Intended status: Standards Track S. Cheshire -Expires: January 9, 2017 Apple Inc. - July 8, 2016 +Expires: May 4, 2017 Apple Inc. + October 31, 2016 DNS Push Notifications - draft-ietf-dnssd-push-08 + draft-ietf-dnssd-push-09 Abstract The Domain Name System (DNS) was designed to return matching records efficiently for queries for data that is relatively static. When those records change frequently, DNS is still efficient at returning the updated results when polled. 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 DNS records, called DNS Push Notifications. @@ -26,21 +26,21 @@ 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 http://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, 2017. + This Internet-Draft will expire on May 4, 2017. Copyright Notice Copyright (c) 2016 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -50,123 +50,119 @@ the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 4.1. Client-Initiated Termination . . . . . . . . . . . . . . 7 - 4.2. Server-Initiated Termination . . . . . . . . . . . . . . 9 - 5. State Considerations . . . . . . . . . . . . . . . . . . . . 11 - 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 12 - 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 13 - 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 15 - 6.3. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 20 - 6.4. DNS Push Notification Update Messages . . . . . . . . . . 21 - 6.5. DNS RECONFIRM . . . . . . . . . . . . . . . . . . . . . . 24 - 6.6. DNS Push Notification Termination Message . . . . . . . . 25 + 5. State Considerations . . . . . . . . . . . . . . . . . . . . 6 + 6. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7 + 6.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 8 + 6.2. DNS Push Notification SUBSCRIBE . . . . . . . . . . . . . 10 + 6.2.1. SUBSCRIBE Request . . . . . . . . . . . . . . . . . . 11 + 6.2.2. SUBSCRIBE Response . . . . . . . . . . . . . . . . . 14 + 6.3. DNS Push Notification Update Messages . . . . . . . . . . 18 + 6.3.1. PUSH Message format . . . . . . . . . . . . . . . . . 18 + 6.4. DNS Push Notification UNSUBSCRIBE . . . . . . . . . . . . 21 + 6.4.1. UNSUBSCRIBE Request . . . . . . . . . . . . . . . . . 22 + 6.4.2. UNSUBSCRIBE Response . . . . . . . . . . . . . . . . 24 + 6.5. DNS Session Signaling Push Notification RECONFIRM . . . . 26 + 6.6. Client-Initiated Termination . . . . . . . . . . . . . . 28 7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 - 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 28 - 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 28 - 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 29 - 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 29 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 - 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 30 - 10.2. Informative References . . . . . . . . . . . . . . . . . 31 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 + 7.1. Security Services . . . . . . . . . . . . . . . . . . . . 29 + 7.2. TLS Name Authentication . . . . . . . . . . . . . . . . . 29 + 7.3. TLS Compression . . . . . . . . . . . . . . . . . . . . . 30 + 7.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 30 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 + 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 31 + 10.2. Informative References . . . . . . . . . . . . . . . . . 32 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 1. Introduction - IMPORTANT NOTE: This document currently references the EDNS(0) TCP - Keepalive option [RFC7828]. As a result of discussions about this - document, the community came to the realization that DNS needs - explicit session-level signaling, to complement the current EDNS(0) - per-message signaling. As a result, work on DNS Session Signaling - [I-D.bellis-dnsop-session-signal] is underway, and this document will - be updated shortly to make use of those new Session Signaling - mechanisms once they are agreed. - DNS records may be updated using DNS Update [RFC2136]. Other mechanisms such as a Hybrid Proxy [I-D.ietf-dnssd-hybrid] can also generate changes to a DNS zone. This document specifies a protocol - for Unicast 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]. + 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" [RFC2119]. 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 to state changes - following the Observer design pattern. XMPP Publish-Subscribe + 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 publish/subscribe model for tracking changes to DNS records can result in more timely notification of changes with reduced CPU usage and lower network traffic. Multicast DNS [RFC6762] implementations always listen on a well known link-local IP multicast group, and new services and updates are sent 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 Hybrid Proxy [I-D.ietf-dnssd-hybrid]) 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. DNS Long-Lived Queries (LLQ) [I-D.sekar-dns-llq] is an existing deployed solution to provide asynchronous change notifications. Even though it can be used over TCP, LLQ is defined primarily as a UDP- based protocol, and as such it defines its own equivalents of - existing TCP features like the three-way handshake. This document - builds on experience gained with the LLQ protocol, with an improved - design that uses long-lived TCP connections instead of UDP (and - therefore doesn't need to duplicate existing TCP functionality), and - adopts the syntax and semantics of DNS Update messages [RFC2136] - instead of inventing a new vocabulary of messages to communicate DNS - zone changes. + 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 long-lived TCP connections + [I-D.ietf-dnsop-session-signal], and therefore doesn't need to + reinvent existing TCP functionality. Instead of inventing a new + vocabulary of messages to communicate DNS zone changes, this + specification adopts the syntax and semantics of DNS Update messages + [RFC2136]. - Because DNS Push Notifications impose a certain load on the - responding server (though less load than rapid polling of that - server) DNS Push Notification clients SHOULD exercise restraint in - issuing DNS Push Notification subscriptions. A subscription SHOULD + 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 + number of Push Notification subscriptions. 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 of - that subscription 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 display showing the result of the DNS Push - Notification subscription is automatically dismissed after a certain - period of inactivity. For example, if a user presses the "Print" - button on their phone, and then leaves the phone showing the printer - discovery screen until the phone goes to sleep, then the printer - discovery screen should be automatically dismissed as the device goes - to sleep. If the user does still intend to print, this will require - them to press the "Print" button again when they wake their phone up. + 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 display + showing the result of the DNS Push Notification subscription is + automatically dismissed after a certain period of inactivity. For + example, if a user presses the "Print" button on their smartphone, + and then leaves the phone showing the printer discovery screen until + the phone goes to sleep, then the printer discovery screen should be + automatically dismissed as the device goes to sleep. If the user + does still intend to print, this will require them to press the + "Print" button again when they wake their phone up. A DNS Push Notification client MUST 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 it will be really fast if the user does choose to bring up an on-screen display of that data. 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, a client SHOULD NOT keep a connection to a server open @@ -193,21 +189,21 @@ of generating the correct change notifications for a name. It may be a master, slave, or stealth name server [RFC1996]. 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 Queries. Supporting DNS Updates and DNS Push Notifications on the same server - is OPTIONAL. A DNS Push Notification server is not REQUIRED to + is OPTIONAL. A DNS Push Notification server does NOT also have 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, provided that these are queries for names falling within the server's zone (the in the "_dns-push-tls._tcp." SRV @@ -216,314 +212,128 @@ 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 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 it is today with existing DNS servers and clients. A - DNS Push Notification server MAY choose to implement only DNS class - "IN". + 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". 4. Transport Implementations of 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]. In keeping with the more recent precedent, DNS Push Notification is defined only for TCP. DNS Push Notification clients MUST use TLS over TCP. Connection setup over TCP ensures return reachability and alleviates concerns of state overload at the server through anonymous subscriptions. All subscribers are guaranteed to be reachable by the - server by virtue of the TCP three-way handshake. Because TCP SYN - flooding attacks are possible with any protocol over TCP, - implementers are encouraged to use industry best practices to guard - against such attacks [IPJ.9-4-TCPSYN] [RFC4953]. + 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 [IPJ.9-4-TCPSYN] [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 deployed across many protocols running over TCP. It is designed to prevent eavesdropping, tampering, or 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. + Additional authentication of the SRV target using DNSSEC verification and DANE TLSA records [RFC7673] is strongly encouraged. See below in Section 7.2 for details. - A DNS Push Notification session begins with a client connecting to a - DNS Push Notification server. Over that connection the client then - issues DNS operation requests, such as SUBSCRIBE. - -4.1. Client-Initiated Termination - - An individual subscription is terminated by sending an UNSUBSCRIBE - message for that specific subscription, or all subscriptions can be - cancelled at once by the client closing the connection. When a - client terminates an individual subscription (via UNSUBSCRIBE) or all - subscriptions on that connection (by closing the connection) it is - signaling to the server that it is longer interested in receiving - those particular updates. It is informing the server that the server - may release any state information it has been keeping with regards to - these particular subscriptions. - - After terminating its last subscription on a connection via - UNSUBSCRIBE, a client MAY close the connection immediately, or it may - keep it open if it anticipates performing further operations on that - connection in the future. If a client wishes to keep an idle - connection open, it MUST continue to meet its keepalive obligations - [RFC7828] or the server is entitled to close the connection (see - below). - - If a client plans to terminate one or more subscriptions on a - connection and doesn't intend to keep that connection open, then as - an efficiency optimization it MAY instead choose to simply close the - connection, which implicitly terminates all subscriptions on that - connection. This may occur because the client computer is being shut - down, is going to sleep, the application requiring the subscriptions - has terminated, or simply because the last active subscription on - that connection has been cancelled. - - When closing a connection, a client will generally do an abortive - disconnect, sending a TCP RST. This immediately discards all - remaining inbound and outbound data, which is appropriate if the - client no longer has any interest in this data. In the BSD sockets - API, sending a TCP RST is achieved by setting the SO_LINGER option - with a time of 0 seconds and then closing the socket. - - If a client has performed operations on this connection that it would - not want lost (like DNS updates) then the client SHOULD do an orderly - disconnect, sending 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. - - In the first SUBSCRIBE response on a connection, the server MUST - include an explicit EDNS(0) TCP Keepalive option. If the first - SUBSCRIBE response does not include an explicit EDNS(0) TCP Keepalive - option this is an error and the client MUST immediately close the TCP - connection and not attempt any further DNS Push Notification requests - to that server until one hour has passed. This situation may occur - if a client connects to a server that doesn't implement DNS Push - Notifications at all, and it is important not to burden such servers - with continuous retries. - - Upon receiving an error response from the server, a client SHOULD NOT - close the connection. An error relating to one particular operation - on a connection does not necessarily imply that all other operations - on that connection have also failed, or that future operations will - fail. The client should assume that the server will make its own - decision about whether or not to close the connection, based on the - server's determination of whether the error condition pertains to - this particular operation, or would also apply to any subsequent - operations. If the server does not close the connection then the - client SHOULD continue to use that connection for subsequent - operations. - - Upon receiving a Termination Message from the server (see below), a - client MUST immediately close the connection. - -4.2. Server-Initiated Termination - - If a client makes a connection and then fails to send any DNS message - that uses EDNS(0) TCP Keepalive [RFC7828] (either SUBSCRIBE, where - Keepalive is implicit, or some other DNS message, with an explicit an - EDNS(0) TCP Keepalive option) then after 30 seconds of inactivity the - server SHOULD close the connection. If no data has been sent on the - connection the server MAY abort the connection with a TCP RST. If - data has been sent on the connection then the server SHOULD close the - connection gracefully with a TCP FIN so that the data is reliably - delivered. - - In the response to the first successful SUBSCRIBE, the included - EDNS(0) TCP Keepalive option specifies the idle timeout so that the - client knows the frequency of traffic it must generate to keep the - connection alive. If the idle timeout for that connection changes, - then the server communicates this by placing an updated EDNS(0) TCP - Keepalive option in a subsequent message to the client. - - At both servers and clients, the generation or reception of any - complete request, response, update, or keepalive message resets the - keepalive timer for that connection. - - In the absence of any requests, responses, or update messages on a - connection, a client MUST generate keepalive traffic before the idle - timeout expires, or the server is entitled to close the connection. - - If a client disconnects from the network abruptly, without closing - its connection, the server learns of this after failing to receive - further traffic from that client. If no requests, responses, update - messages or keepalive traffic occurs on a connection for 1.5 times - the idle timeout, then this indicates that the client is probably no - longer on the network, and the server SHOULD abort the connection - with a TCP RST. The time before the server closes the connection is - intentionally 50% longer than the time before the client is required - to generate keepalive traffic, to allow for differences in clock rate - and network propagation delays. - - [We need to discuss the nature of "the required keepalives". Are - they TCP-layer keepalives? DNS-layer keepalives? There is currently - no DNS-layer keepalive or 'no-op' operation defined. What would that - operation be? A DNS QUERY containing zero questions? A DNS - SUBSCRIBE containing zero questions? An "empty" DNS message over the - TCP connection (just a pair of zero bytes, signifying a zero-length - message)? One benefit of TCP-layer keepalives is that they transmit - fewer bytes, and involve less software overhead for processing those - bytes. Another benefit is that it is more feasible to implement - these in networking offload hardware, which can allow devices to meet - their TCP keepalive obligations while sleeping. This is particularly - important for battery-powered devices like mobile phones and tablets. - On the other hand, using TCP-layer keepalives requires an API for a - client to tell the networking stack at what frequency to perform TCP- - layer keepalives, and an API for a server to request the networking - stack to inform it when TCP-layer keepalives are not received by the - required deadline. TCP-layer keepalives also only verify liveness of - the remote networking stack, whereas DNS-layer keepalives provide - higher assurance of liveness of the remote server application - software -- though this a limited benefit, since there is no reason - to expect that DNS Push Notification server software will routinely - become wedged and unresponsive.] - - After sending an error response to a client, the server MAY close the - connection with a TCP FIN, or may allow the connection to remain - open. For error conditions that only affect the single operation in - question, the server SHOULD return an error response to the client - and leave the connection open for further operations. For error - conditions that are likely to make all operations unsuccessful in the - immediate future, the server SHOULD return an error response to the - client and then close the connection with a TCP FIN. - - If the server is overloaded and needs to shed load, it SHOULD send a - Termination Message to the client and close the connection with a TCP - FIN. - - Apart from the cases described above, a server MUST NOT close a - connection with a DNS Push Notification client, except in - extraordinary error conditions. Closing the connection is the - client's responsibility, to be done at the client's discretion, when - it so chooses. A DNS Push Notification server only closes a DNS Push - Notification connection under exceptional circumstances, such as when - the server application software or underlying operating system is - restarting, the server application terminated unexpectedly (perhaps - due to a bug that makes it crash), or the server is undergoing - maintenance procedures. When possible, a DNS Push Notification - server SHOULD send a Termination Message (Section 6.6 ) informing the - client of the reason for the connection being closed. - - After a connection is closed by the server, the client SHOULD try to - reconnect, to that server, or to another server supporting DNS Push - Notifications for the zone. If reconnecting to the same server, and - there was a Termination Message or error response containing a - EDNS(0) TCP Keepalive option, the client MUST respect the indicated - delay before attempting to reconnect. - 5. State Considerations Each DNS Push Notification server is capable of handling some finite number of Push Notification subscriptions. This number will vary from server to server and is based on physical machine characteristics, network bandwidth, and operating system resource allocation. After a client establishes a connection to a DNS server, each record subscription is individually accepted or rejected. Servers may employ various techniques to limit subscriptions to a manageable level. Correspondingly, the client is free to establish simultaneous connections to alternate DNS servers that support DNS Push Notifications for the zone and distribute record subscriptions at its discretion. In this way, both clients and servers can react to resource constraints. Token bucket rate limiting schemes are also effective in providing fairness by a server across numerous client requests. 6. Protocol Operation + The DNS Push Notification protocol is a session-oriented protocol, + and makes use of DNS Session Signaling + [I-D.ietf-dnsop-session-signal]. + + DNS Push Notification clients and servers MUST support DNS Session + Signaling, but the server must not issue any DNS Session Signaling + operations until after the client has first initiated a DNS Session + Signaling operation of its own. A single server can support DNS + Queries, DNS Updates, and DNS Push Notifications (using DNS Session + Signaling) on the same TCP port, and until the client has sent at + least one DNS Session Signaling operation the server does not know + what kind of client has connected to it. Once the client has + indicated willingness to use DNS Session Signaling operations by + sending one of its own, either side of the connection may then + initiate further Session Signaling operations at any time. + A DNS Push Notification exchange begins with the client discovering - the appropriate server, and then making a TLS/TCP connection to it. - The client may then add and remove Push Notification subscriptions - over this connection. In accordance with the current set of active - subscriptions the server sends relevant asynchronous Push + 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 DNS + Session Signaling Idle Timeout operation to request a session timeout + longer than the the 30-second default, but this is NOT REQUIRED. A + DNS Push Notification client MAY issue other requests on the + connection first, and only issue a DNS Session Signaling Idle Timeout + operation later if it determines that to be necessary. + + Once the connection is made, the client may then add and remove Push + Notification subscriptions. 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. The exchange between client and server terminates when either end closes the TCP connection with a TCP FIN or RST. - A client SHOULD NOT make multiple TLS/TCP connections to the same DNS - Push Notification server. A client SHOULD share a single TLS/TCP - connection for all requests to the same DNS Push Notification server. - This shared connection should be used for all DNS Queries and DNS - Push Notification Queries queries to that server, and for DNS Update - requests too when the "_dns-update-tls._tcp." SRV record - indicates that the same server also handles DNS Update requests. - This is to reduce unnecessary load on the DNS Push Notification - server. - - For the purposes here, the determination of "same server" is made by - inspecting the target hostname and port, regardless of the name being - queried, or what zone if falls within. A given server may support - Push Notifications (and possibly DNS Updates too) for multiple DNS - zones. When a client discovers that the DNS Push Notification server - (and/or DNS Update server) for several different names (including - names that fall within different zones) is the same target hostname - and port, the client SHOULD use a single shared TCP connection for - all relevant operations on those names. A client SHOULD NOT open - multiple TCP connections to the same target host and port just - because the names being queried (or updated) happen to fall within - different zones. - - Note that the "same server" determination described here is made - using the target hostname given in the SRV record, not the IP - address(es) that the hostname resolves to. If two different target - hostnames happen to resolve to the same IP address(es), then the - client SHOULD NOT recognize these as the "same server" for the - purposes of using a single shared connection to that server. If an - administrator wishes to use a single server for multiple zones and/or - multiple roles (e.g., both DNS Push Notifications and DNS Updates), - and wishes to have clients use a single shared connection for - operations on that server, then the administrator MUST use the same - target hostname in the appropriate SRV records. - - However, server implementers and operators should be aware that this - connection sharing may not be possible in all cases. A single client - device may be home to multiple independent client software instances - that don't know about each other, so a DNS Push Notification server - MUST be prepared to accept multiple connections from the same client - IP address. This is undesirable from an efficiency standpoint, but - may be unavoidable in some situations, so a DNS Push Notification - server MUST be prepared to accept multiple connections from the same - client IP address. - - Clients SHOULD silently ignore unrecognized messages (both requests - and responses) over the TLS/TCP connection. For example, UNSUBSCRIBE - and RECONFIRM currently generate no response, but if future versions - of this specification change that, existing clients SHOULD silently - ignore these unexpected responses. This allows for backwards - compatibility with future enhancements. - 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 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 [I-D.ietf-dprive-dns-over-tls]. + port 853 used for DNS over TLS [RFC7858]. 1. The client begins the discovery by sending a DNS query to the local resolver with record type SOA [RFC1035] for the name of the record it wishes to subscribe. 2. If the SOA record exists, it MUST be returned in the Answer Section of the response. If not, the local resolver SHOULD include the SOA record for the zone of the requested name in the Authority Section. @@ -563,236 +373,234 @@ "weight" indicates the weighted probability that the client should contact that server. Higher weights have higher probabilities of being selected. If a server is not reachable or is not willing to accept a subscription request, then a subsequent server is to be contacted. Each time a client makes a new DNS Push Notification subscription connection, it SHOULD repeat the discovery process in order to determine the preferred DNS server for subscriptions at that time. + Note that this repeated discovery step is typically very fast and + typically results in no queries on the network. The client device + MUST respect the DNS TTL values on records it receives, and store + them in its local cache with this lifetime. This 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 data. + 6.2. DNS Push Notification SUBSCRIBE - A DNS Push Notification client indicates its desire to receive DNS - Push Notifications for a given domain name by sending a SUBSCRIBE - request over the established TCP connection to the server. A - SUBSCRIBE request is formatted identically to a conventional DNS - QUERY request [RFC1035], except that the opcode is SUBSCRIBE (6) - instead of QUERY (0). If neither QTYPE nor QCLASS are ANY (255) then - this is a specific subscription to changes for the given name, type - and class. If one or both of QTYPE or QCLASS are ANY (255) then this - subscription matches any type and/or any class, as appropriate. + After connecting, and requesting a longer idle timeout 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 TLS connection to the server. A + SUBSCRIBE request is encoded in a DNS Session Signaling + [I-D.ietf-dnsop-session-signal] message. This specification defines + a new DNS Session Signaling TLV for DNS Push Notification SUBSCRIBE + Requests/Responses (tentatively Session Signaling Type Code 64). - 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 - and unexpected results, were a query returns some valid answers but - not all of them, and makes QTYPE=ANY queries less useful than people - sometimes imagine. + A server may not initiate a SUBSCRIBE request. - When used in conjunction with DNS SUBSCRIBE, QTYPE and QCLASS 255 - should be interpreted to mean "ALL", not "ANY". After accepting a - subscription where one or both of QTYPE or QCLASS are 255, the server - MUST send Push Notification Updates for ALL record changes that match - the subscription, not just some of them. +6.2.1. SUBSCRIBE Request - In a SUBSCRIBE request the DNS Header QR bit MUST be zero. - If the QR bit is not zero the message is not a SUBSCRIBE request. + A SUBSCRIBE request message begins with the standard DNS Session + Signaling 4-byte header [I-D.ietf-dnsop-session-signal], followed by + the SUBSCRIBE TLV. - The AA, TC, RD, RA, Z, AD, and CD bits, and the RCODE field, MUST be - zero on transmission, and MUST be silently ignored on reception. + 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 | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | SSOP-TYPE (SUBSCRIBE) | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | SSOP-LENGTH | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | | + \ QNAME \ + \ \ + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QTYPE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QCLASS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - The ID field may be set to any value of the client's choosing, and - the server MUST echo this value back in the response message. The - client is not required to select unique ID values; it is permissible - to use the same value (e.g., zero) for all operations. Since the - name, qtype, and qclass are sufficient to uniquely identify a - SUBSCRIBE operation on a connection, the name, qtype, and qclass in a - SUBSCRIBE response are sufficient to correlate a response with its - corresponding request. However, for convenience, the client may put - any value it chooses in the ID field of the SUBSCRIBE request, and - the server MUST echo that value back unchanged in the SUBSCRIBE - response. Note that the ID field of Push Notification Update - Messages is always zero, since a Push Notification Update Message - could potentially match more than one subscription, or could relate - to a subscription that the client has just cancelled with an - UNSUBSCRIBE message. + Figure 1 - Like a DNS QUERY request, a SUBSCRIBE request MUST contain exactly - one question. Since SUBSCRIBE requests are sent over TCP, multiple - SUBSCRIBE requests can be concatenated in a single TCP stream and - packed efficiently into TCP segments, so the ability to pack multiple - SUBSCRIBE operations into a single DNS message within that TCP stream - would add extra complexity for little benefit. + The MESSAGE ID field MUST be set to a unique value, that the client + is not using for any other active operation on this connection. For + the purposes here, a MESSAGE ID is in use on this connection if the + client has used it in a request for which it has not yet received a + response, or if 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. - ANCOUNT MUST be zero, and the Answer Section MUST be empty. - Any records in the Answer Section MUST be silently ignored. + In a request the DNS Header QR bit MUST be zero. - NSCOUNT MUST be zero, and the Authority Section MUST be empty. - Any records in the Authority Section MUST be silently ignored. + The DNS Header Opcode field holds the Session Signaling Opcode value + (tentatively 6). - ARCOUNT specifies the number of records in the Additional Data - Section. Typically this is zero, but it may be nonzero in some - cases, such as when the request includes an EDNS(0) OPT record. + The Z bits MUST be zero on transmission, and MUST be silently ignored + on reception. + + The return code (RCODE) field MUST be set to 0 in a request. + + In the SUBSCRIBE TLV the SSOP-TYPE is SUBSCRIBE (tentatively 64). + The SSOP-LENGTH is the length of the data that follows, which + specifies the name, type, and class of the record(s) being sought. + + A SUBSCRIBE request MUST contain exactly one question. There is no + QCOUNT field to specify more than one question. Since SUBSCRIBE + requests are sent over TCP, multiple SUBSCRIBE requests 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 - revokes the subscription or until the connection between the client - and the server is closed. + cancels the subscription using UNSUBSCRIBE or until the connection + between the client and the server is closed. SUBSCRIBE requests on a given connection 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 TLS/TCP connection. - For the purpose of this matching, the established DNS case- - insensitivity for US-ASCII letters applies (e.g., "foo.com" and + MUST NOT send a SUBSCRIBE message that duplicates the QNAME, QTYPE + and QCLASS of an existing active subscription on that TLS/TCP + connection. For the purpose of this matching, the established DNS + case-insensitivity for US-ASCII letters applies (e.g., "foo.com" and "Foo.com" are the same). If a server receives such a duplicate SUBSCRIBE message this is an error and the server MUST immediately close the TCP connection. 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 matches are found in the future. + and when matching records are found in the future. - Since all SUBSCRIBE operations are implicitly long-lived operations, - the server MUST interpret a SUBSCRIBE request as if it contained an - EDNS(0) TCP Keepalive option [RFC7828]. A client MUST NOT include an - actual EDNS(0) TCP Keepalive option in the request, since it is - automatic, and implied by the semantics of SUBSCRIBE. If a server - receives a SUBSCRIBE request that does contain an actual EDNS(0) TCP - Keepalive option this is an error and the server MUST immediately - close the TCP connection. + If neither QTYPE nor QCLASS are ANY (255) then this is a specific + subscription to changes for the given QNAME, QTYPE and QCLASS. If + one or both of QTYPE or QCLASS are ANY (255) then this subscription + matches any type and/or any class, as appropriate. - A SUBSCRIBE operation MAY include an explicit EDNS(0) [RFC6891] OPT - record where necessary to carry additional EDNS(0) information other - than a TCP Keepalive option. + 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 + and unexpected results, were a query returns some valid answers but + not all of them, and makes QTYPE=ANY queries less useful than people + sometimes imagine. - The presence of a SUBSCRIBE operation on a connection indicates to - the server that the client fully implements EDNS(0) [RFC6891], and - can correctly understand any response that conforms to that - specification. After receiving a SUBSCRIBE request, the server MAY - include OPT record in any of its responses, as needed. + When used in conjunction with SUBSCRIBE, QTYPE and QCLASS 255 should + be interpreted to mean "ALL", not "ANY". After accepting a + subscription where one or both of QTYPE or QCLASS 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. - In a SUBSCRIBE response the DNS Header QR bit MUST be one. - If the QR bit is not one the message is not a SUBSCRIBE response. + A SUBSCRIBE response message begins with the standard DNS Session + Signaling 4-byte header [I-D.ietf-dnsop-session-signal], possibly + followed by one or more optional modifier TLVs such as a Terminate + modifier TLV [I-D.ietf-dnsop-session-signal]. - The AA, TC, RD, RA, Z, AD, and CD bits, MUST be zero on transmission, - and MUST be silently ignored on reception. + 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 | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - The ID field MUST echo the value given in the ID field of the - SUBSCRIBE request. + Figure 2 - The Question Section MUST echo back the values provided by the client - in the SUBSCRIBE request that generated this SUBSCRIBE response. + 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. - ANCOUNT MUST be zero, and the Answer Section MUST be empty. - Any records in the Answer Section MUST be silently ignored. - If the subscription was accepted and there are positive answers for - the requested name, type and class, then these positive answers MUST - be communicated to the client in an immediately following Push - Notification Update, not in the Answer Section of the SUBSCRIBE - response. This simplifying requirement is made so that there is only - a single way that information is communicated to a DNS Push - Notification client. Since a DNS Push Notification client has to - parse information received via Push Notification Updates anyway, it - is simpler if it does not also have to parse information received via - the Answer Section of a SUBSCRIBE response. + In a response the DNS Header QR bit MUST be one. + If the QR bit is not one the message is not a response. - NSCOUNT MUST be zero, and the Authority Section MUST be empty. - Any records in the Authority Section MUST be silently ignored. + The DNS Header Opcode field holds the Session Signaling Opcode value + (tentatively 6). - ARCOUNT specifies the number of records in the Additional Data - Section, e.g., the EDNS(0) OPT record. + The Z bits MUST be zero on transmission, and MUST be silently ignored + on reception. In the SUBSCRIBE response the RCODE indicates whether or not the subscription was accepted. Supported RCODEs are as follows: - +----------+-------+------------------------------------------------+ + +------------+-------+----------------------------------------------+ | Mnemonic | Value | Description | - +----------+-------+------------------------------------------------+ + +------------+-------+----------------------------------------------+ | NOERROR | 0 | SUBSCRIBE successful. | | FORMERR | 1 | Server failed to process request due to a | | | | malformed request. | | SERVFAIL | 2 | Server failed to process request due to | | | | resource exhaustion. | - | NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification MUST NOT | - | | | return NXDOMAIN errors in response to | - | | | SUBSCRIBE requests. | - | NOTIMP | 4 | Server does not implement DNS Push | - | | | Notifications. | + | NXDOMAIN | 3 | NOT APPLICABLE. DNS Push Notification | + | | | servers MUST NOT return NXDOMAIN errors in | + | | | response to SUBSCRIBE requests. | + | NOTIMP | 4 | Server does not recognize DNS Session | + | | | Signaling Opcode. | | REFUSED | 5 | Server refuses to process request for policy | | | | or security reasons. | - | NOTAUTH | 9 | Server is not authoritative for the requested | - | | | name. | - +----------+-------+------------------------------------------------+ + | NOTAUTH | 9 | Server is not authoritative for the | + | | | requested name. | + | SSOPNOTIMP | 11 | SUBSCRIBE operation not supported. | + +------------+-------+----------------------------------------------+ SUBSCRIBE Response codes This document specifies only these RCODE values for SUBSCRIBE Responses. Servers sending SUBSCRIBE Responses SHOULD use one of these values. 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 RCODE value. - In the first SUBSCRIBE response on a connection, the server MUST - include an explicit EDNS(0) TCP Keepalive option. If the first - SUBSCRIBE response does not include an explicit EDNS(0) TCP Keepalive - option this is an error and the client MUST immediately close the TCP - connection. In this case the client should act as if the response - contained an EDNS(0) TCP Keepalive option with a value of one hour, - and not attempt any further DNS Push Notification requests to that - server until one hour has passed. This situation may occur if a - client connects to a server that doesn't implement DNS Push - Notifications at all, and it is important not to burden such servers - with continuous retries. - - The server MAY include EDNS(0) TCP Keepalive options in subsequent - messages, if the idle timeout changes. If the client receives - subsequent messages that do not contain an explicit EDNS(0) TCP - Keepalive option then the idle timeout for that connection remains - unchanged at that time. - - In an error response, with nonzero RCODE, the server MUST contain an - EDNS(0) TCP Keepalive option specifying the delay before the client - submits further requests to this server: + If the server sends a nonzero RCODE in the SUBSCRIBE response, either + the client is (at least partially) misconfigured or the server + resources are exhausted. In either case, the client shouldn't retry + the subscription right away. Either end can terminate the + connection, but the client may want to try this subscription again or + it may have other successful subscriptions that it doesn't want to + abandon. If the server sends a nonzero RCODE then it SHOULD append a + Terminate modifier TLV [I-D.ietf-dnsop-session-signal] 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: For RCODE = 1 (FORMERR) the delay may be any value selected by the - implementer. A value of one minute is RECOMMENDED, to avoid high - load from defective clients. + implementer. A value of five minutes is RECOMMENDED, to avoid + high load from defective clients. For RCODE = 2 (SERVFAIL), which occurs due to resource exhaustion, 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. For RCODE = 4 (NOTIMP), 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. Note that a - server that doesn't implement DNS Push Notifications will most - likely not implement this retry delay mechanism using the EDNS(0) - TCP Keepalive option either, and in this case the client will fall - back to the case described above specifying how to handle - SUBSCRIBE responses that do not contain an EDNS(0) TCP Keepalive - option. + implement DNS Session Signaling [I-D.ietf-dnsop-session-signal], + it is unlikely that the server will begin supporting DNS Session + Signaling in the next few minutes, so the retry delay SHOULD be + one hour. 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. 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. 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 @@ -802,366 +610,431 @@ 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. + For RCODE = 11 (DNS Push SUBSCRIBE operation not supported), 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 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. - After sending an error response the server MAY close the TCP - connection with a FIN, or MAY allow it to remain open, depending on - the nature of the error. Clients MUST correctly handle both cases. - -6.3. DNS Push Notification UNSUBSCRIBE - - To cancel an individual subscription without closing the entire - connection, the client sends an UNSUBSCRIBE message over the - established TCP connection to the server. The UNSUBSCRIBE message is - formatted identically to the SUBSCRIBE message which created the - subscription, with the exact same name, type and class, except that - the opcode is UNSUBSCRIBE (7) instead of SUBSCRIBE (6). - - A client MUST NOT send an UNSUBSCRIBE message that does not exactly - match the name, type and class of an existing active subscription on - that TLS/TCP connection. If a server receives such an UNSUBSCRIBE - message this is an error and the server MUST immediately close the - connection. - - No response message is generated as a result of processing an - UNSUBSCRIBE message. - - Having being successfully revoked with a correctly-formatted - UNSUBSCRIBE message, the previously referenced subscription is no - longer active and the server MAY discard the state associated with it - immediately, or later, at the server's discretion. + After sending an error response the server MAY allow the connection + to remain open, or MAY send a DNS Push Notification Terminate Session + operation TLV and then close the TCP connection, as described in the + DNS Session Signaling specification [I-D.ietf-dnsop-session-signal]. + Clients MUST correctly handle both cases. -6.4. DNS Push Notification Update Messages +6.3. DNS Push Notification Update Messages Once a subscription has been successfully established, the server - generates Push Notification Updates to send to the client as - appropriate. An initial Push Notification Update will be sent - immediately in the case that the answer set was non-empty at the - moment the subscription was established. Subsequent changes to the - answer set are then communicated to the client in subsequent Push - Notification Updates. + generates PUSH messages to send to the client as appropriate. An + initial PUSH message will be sent immediately in the case that the + answer set was non-empty at the moment the subscription was + established. Subsequent changes to the answer set are then + communicated to the client in subsequent PUSH messages. - The format of Push Notification Updates borrows from the existing DNS - Update [RFC2136] protocol, with some simplifications. +6.3.1. PUSH Message format - The following figure shows the existing DNS Update header format: + A PUSH message begins with the standard DNS Session Signaling 4-byte + header [I-D.ietf-dnsop-session-signal], followed by the PUSH TLV. + + The format of PUSH messages borrows from the existing DNS Update + [RFC2136] protocol, with some simplifications. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | ID | + | MESSAGE ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode | Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | ZOCOUNT | + | SSOP-TYPE (PUSH) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | PRCOUNT | + | SSOP-LENGTH | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | UPCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | ADCOUNT | + | | + \ Resource Records... \ + \ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - Figure 1 + Figure 3 - For DNS Push Notifications the following rules apply: + The MESSAGE ID field MUST be set to zero on transmission, and + silently ignored on reception. A PUSH message could potentially + match more than one subscription, or could relate to a subscription + that the client has just cancelled with an UNSUBSCRIBE message, so + the MESSAGE ID field serves no useful purpose. - The QR bit MUST be zero, and the Opcode MUST be UPDATE (5). - Messages received where this is not true are not Push Notification - Update Messages and should be silently ignored for the purposes of - Push Notification Update Message handling. + In a PUSH message the DNS Header QR bit MUST be zero. - ID, the Z bits, and RCODE MUST be zero on transmission, - and MUST be silently ignored on reception. + The DNS Header Opcode field holds the Session Signaling Opcode value + (tentatively 6). - ZOCOUNT MUST be zero, and the Zone Section MUST be empty. - Any records in the Zone Section MUST be silently ignored. + The Z bits MUST be zero on transmission, and MUST be silently ignored + on reception. - PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. - Any records in the Prerequisite Section MUST be silently ignored. + The return code (RCODE) field MUST be set to 0 in a request. - UPCOUNT specifies the number of records in the Update Section. + In the PUSH message TLV the SSOP-TYPE is PUSH (tentatively 65). The + SSOP-LENGTH is the length of the SSOP-DATA that follows. - ADCOUNT specifies the number of records in the Additional Data - Section. Typically this is zero, but it may be nonzero in some - cases, such as when the message includes an EDNS(0) OPT record. + The SSOP-DATA contains a two-byte count of the number of records that + follow, followed by the records, in customary Resource Record format + (as used in DNS Update [RFC2136] messages). - The Update Section contains the relevant change information for the + The SSOP-DATA contains the relevant change information for the client, formatted identically to a DNS Update [RFC2136]. To recap: Delete all RRsets from a name: TTL=0, CLASS=ANY, RDLENGTH=0, TYPE=ANY. 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. - When processing the records received in a Push Notification Update - Message, the receiving client MUST validate that the records being - added or deleted correspond with at least one currently active - subscription on that connection. Specifically, the record name MUST - match the name given in the SUBSCRIBE request, subject to the usual - established DNS case-insensitivity for US-ASCII letters. If the - QTYPE in the SUBSCRIBE request was not ANY (255) then the TYPE of the - record must match the QTYPE given in the SUBSCRIBE request. If the - QCLASS in the SUBSCRIBE request was not ANY (255) then the CLASS of - the record must match the QCLASS given in the SUBSCRIBE request. If - a matching active subscription on that connection 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 TCP connection is not closed. This is to allow for - the race condition where a client sends an outbound UNSUBSCRIBE while - inbound Push Notification Updates for that subscription from the - server are still in flight. + 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 + connection. Specifically, the record name MUST match the name given + in the SUBSCRIBE request, subject to the usual established DNS case- + insensitivity for US-ASCII letters. If the QTYPE in the SUBSCRIBE + request was not ANY (255) then the TYPE of the record must match the + QTYPE given in the SUBSCRIBE request. If the QCLASS in the SUBSCRIBE + request was not ANY (255) then the CLASS of the record must match the + QCLASS given in the SUBSCRIBE request. If a matching active + subscription on that connection 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 TCP + connection is not closed. This is to allow for the unavoidable race + condition where a client sends an outbound UNSUBSCRIBE while inbound + PUSH messages for that subscription from the server are still in + flight. In the case where a single change affects more than one active - subscription, only one update is sent. For example, an update adding - a given record may match both a SUBSCRIBE request with the same QTYPE - and a different SUBSCRIBE request with QTYPE=ANY. It is not the case - that two updates are sent because the new record matches two active - subscriptions. + subscription, only one PUSH message is sent. For example, a PUSH + message adding a given record may match both a SUBSCRIBE request with + the same QTYPE and a different SUBSCRIBE request with QTYPE=ANY. It + is not the case that two PUSH messages are sent because the new + record matches two active subscriptions. The server SHOULD encode change notifications in the most efficient manner possible. For example, when three AAAA records are deleted from a given name, and no other AAAA records exist for that name, the - server SHOULD send a "delete an RRset from a name" update, not three - separate "delete an individual RR from a name" updates. Similarly, - when both an SRV and a TXT record are deleted from a given name, and - no other records of any kind exist for that name, the server SHOULD - send a "delete all RRsets from a name" update, not two separate - "delete an RRset from a name" updates. + server SHOULD send a "delete an RRset from a name" PUSH message, not + three separate "delete an individual RR from a name" PUSH messages. + Similarly, when both an SRV and a TXT record are deleted from a given + name, and no other records of any kind exist for that name, the + server SHOULD send a "delete all RRsets from a name" PUSH message, + not two separate "delete an RRset from a name" PUSH messages. A server SHOULD combine multiple change notifications in a single - Update Message when possible, even if those change notifications - apply to different subscriptions. Conceptually, a Push Notification - Update Message is a connection-level concept, not a subscription- - level concept. - - Push Notification Update Messages MAY contain an EDNS(0) TCP - Keepalive option [RFC7828] if the idle timeout has changed since the - last time the server sent an EDNS(0) TCP Keepalive option on this - connection. - - In the event that the server wishes to inform a client of a new idle - timeout for the connection, the server MAY combine that with the next - message it sends to the client, or the server MAY send an empty Push - Notification Update Message (zero records in the Update Section) to - carry the EDNS(0) TCP Keepalive option. Clients MUST correctly - receive and process the EDNS(0) TCP Keepalive option in both cases. + PUSH message when possible, even if those change notifications apply + to different subscriptions. Conceptually, a PUSH messages is a + connection-level concept, not a subscription-level concept. - Reception of a Push Notification Update Message does not directly - generate a response back to the server. (Updates may indirectly - generate other operations; e.g., a Push Notification Update Message - declaring the appearance of a PTR record could lead to a query for - the SRV record named in the rdata of that PTR record[RFC6763]. + Reception of a PUSH message does not directly generate a response + back to the server. (Updates may indirectly generate other + operations; e.g., a Push Notification Update Message declaring the + appearance of a PTR record could lead to a query for the SRV record + named in the rdata of that PTR record [RFC6763].) The TTL of an added record is stored by the client and decremented as time passes, with the caveat that for as long as a relevant subscription is active, the TTL does not decrement below 1 second. For as long as a relevant subscription remains active, the client SHOULD assume that when a record goes away the server will notify it of that fact. Consequently, a client does not have to poll to verify that the record is still there. Once a subscription is cancelled (individually, or as a result of the TCP connection being closed) - record aging resumes and records are removed from the local cache + record ageing resumes and records are removed from the local cache when their TTL reaches zero. -6.5. DNS RECONFIRM +6.4. DNS Push Notification UNSUBSCRIBE - Sometimes, particularly when used with a Hybrid Proxy - [I-D.ietf-dnssd-hybrid], 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 host+port that is not responding to - connection requests) the client sends a DNS RECONFIRM message to - request that the server re-verify that the data is still valid. For - a Hybrid Proxy, this causes it to issue new Multicast DNS requests to - ascertain whether the target device is still present. For other - kinds of DNS server the RECONFIRM operation is currently undefined - and SHOULD be silently ignored. + To cancel an individual subscription without closing the entire + connection, the client sends an UNSUBSCRIBE message over the + established TCP connection to the server. The UNSUBSCRIBE message is + encoded in a DNS Session Signaling [I-D.ietf-dnsop-session-signal] + message. This specification defines a new DNS Session Signaling TLV + for DNS Push Notification UNSUBSCRIBE Requests/Responses (tentatively + Session Signaling Type Code 66). - A RECONFIRM request is formatted similarly to a conventional DNS - QUERY request [RFC1035], except that the opcode is RECONFIRM (8) - instead of QUERY (0). QTYPE MUST NOT be the value ANY (255). QCLASS - MUST NOT be the value ANY (255). + A server may not initiate an UNSUBSCRIBE request. - In a RECONFIRM request the DNS Header QR bit MUST be zero. - If the QR bit is not zero the message is not a RECONFIRM request. +6.4.1. UNSUBSCRIBE Request - The AA, TC, RD, RA, Z, AD, and CD bits, the ID field, and the RCODE - field, MUST be zero on transmission, and MUST be silently ignored on - reception. + An UNSUBSCRIBE request message begins with the standard DNS Session + Signaling 4-byte header [I-D.ietf-dnsop-session-signal], followed by + the UNSUBSCRIBE TLV. - Like a DNS QUERY request, a RECONFIRM request MUST contain exactly - one question. Since RECONFIRM requests are sent over TCP, multiple - RECONFIRM requests can be concatenated in a single TCP stream and - packed efficiently into TCP segments, so the ability to pack multiple - RECONFIRM operations into a single DNS message within that TCP stream - would add extra complexity for little benefit. + 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 | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | SSOP-TYPE (UNSUBSCRIBE) | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | SSOP-LENGTH (0) | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - ANCOUNT MUST be nonzero, and the Answer Section MUST contain the - rdata for the record(s) that the client believes to be in doubt. + Figure 4 - NSCOUNT MUST be zero, and the Authority Section MUST be empty. - Any records in the Authority Section MUST be silently ignored. + The MESSAGE ID field MUST match 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. If a + server receives an UNSUBSCRIBE message where the MESSAGE ID does not + match the ID of an active SUBSCRIBE request this is an error and the + the server MUST return a response containing RCODE = 1 (FORMERR). In + the UNSUBSCRIBE response the server MUST echo back the MESSAGE ID + value unchanged. 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. - ARCOUNT specifies the number of records in the Additional Data - Section. Typically this is zero, but it may be nonzero in some - cases, such as when the request includes an EDNS(0) OPT record. + In a request the DNS Header QR bit MUST be zero. - DNS wildcarding is not supported. That is, a wildcard ("*") in a - SUBSCRIBE message matches only a wildcard ("*") in the zone, and - nothing else. + The DNS Header Opcode field holds the Session Signaling Opcode value + (tentatively 6). - Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message - matches only a CNAME in the zone, and nothing else. + The Z bits MUST be zero on transmission, and MUST be silently ignored + on reception. - No response message is generated as a result of processing a - RECONFIRM message. + The return code (RCODE) field MUST be set to 0 in a request. - If the server receiving the RECONFIRM request determines that the - records are in fact no longer valid, then subsequent DNS Push - Notification Update Messages will be generated to inform interested - clients. Thus, one client discovering that a previously-advertised - printer is no longer present has the side effect of informing all - other interested clients that the printer in question is now gone. + In the UNSUBSCRIBE TLV the SSOP-TYPE is UNSUBSCRIBE (tentatively 66). -6.6. DNS Push Notification Termination Message + The SSOP-LENGTH is zero. - If a server is low on resources it MAY simply terminate a client - connection with a TCP RST. However, the likely behaviour of the - client may be simply to reconnect immediately, putting more burden on - the server. Therefore, a server SHOULD instead choose to shed client - load by (a) sending a DNS Push Notification Termination Message and - then (b) immediately closing the client connection with a TCP FIN - instead of RST, thereby facilitating reliable delivery of the - Termination Message. Upon successful reception of the Termination - Message the client is expected to close the connection. The server - SHOULD set a timer and, if the client has not closed the connection - within a reasonable time, the server SHOULD then terminate the TCP - connection with a TCP RST. The RECOMMENDED time the server should - wait before terminating the TCP connection with a TCP RST is ten - seconds. +6.4.2. UNSUBSCRIBE Response - The format of a Termination Message is similar to a Push Notification - Update. + Each UNSUBSCRIBE request generates exactly one UNSUBSCRIBE response + from the server. - The following figure shows the existing DNS Update header format: + An UNSUBSCRIBE response message contains with the standard DNS + Session Signaling 4-byte header [I-D.ietf-dnsop-session-signal]. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | ID | + | MESSAGE ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode | Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | ZOCOUNT | - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | PRCOUNT | - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | UPCOUNT | - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | ADCOUNT | - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - Figure 2 + Figure 5 - For Termination Messages the following rules apply: + The MESSAGE ID field MUST echo the value given in the ID field of the + UNSUBSCRIBE request. This is how the client knows which request is + being responded to. - The QR bit MUST be zero, and the Opcode MUST be UPDATE (5). - Messages received where this is not true are not Termination Messages - and should be silently ignored. + In a response the DNS Header QR bit MUST be one. + If the QR bit is not one the message is not a response. - ID and the Z bits MUST be zero on transmission, - and MUST be silently ignored on reception. + The DNS Header Opcode field holds the Session Signaling Opcode value + (tentatively 6). - ZOCOUNT MUST be zero, and the Zone Section MUST be empty. - Any records in the Zone Section MUST be silently ignored. + The Z bits MUST be zero on transmission, and MUST be silently ignored + on reception. - PRCOUNT MUST be zero, and the Prerequisite Section MUST be empty. - Any records in the Prerequisite Section MUST be silently ignored. + In the UNSUBSCRIBE response the RCODE indicates whether or not the + unsubscribe request was successful. Supported RCODEs are as follows: - UPCOUNT MUST be zero, and the Update Section MUST be empty. - Any records in the Update Section MUST be silently ignored. + +------------+-------+----------------------------------------------+ + | Mnemonic | Value | Description | + +------------+-------+----------------------------------------------+ + | NOERROR | 0 | UNSUBSCRIBE successful. | + | FORMERR | 1 | Server failed to process request due to a | + | | | malformed request. | + | NOTIMP | 4 | Server does not recognize DNS Session | + | | | Signaling Opcode. | + | SSOPNOTIMP | 11 | UNSUBSCRIBE operation not supported. | + +------------+-------+----------------------------------------------+ - ADCOUNT specifies the number of records in the Additional Data - Section, e.g., the EDNS(0) OPT record.. + UNSUBSCRIBE Response codes - The RCODE MUST contain a nonzero code giving the reason for - termination, as indicated below: + This document specifies only these RCODE values for UNSUBSCRIBE + Responses. Servers sending UNSUBSCRIBE Responses SHOULD use one of + these values. However, future circumstances may create situations + where other RCODE values are appropriate in UNSUBSCRIBE Responses, so + clients MUST be prepared to accept UNSUBSCRIBE Responses with any + RCODE value. - +----------+-------+------------------------------------------------+ + Having being successfully revoked with a correctly-formatted + UNSUBSCRIBE message (resulting in a response with RCODE NOERROR) the + previously referenced subscription is no longer active and the server + MAY discard the state associated with it immediately, or later, at + the server's discretion. + + Nonzero RCODE values signal some kind of error. + + RCODE value FORMERR indicates an incorrect MESSAGE ID or other + message format error. + + RCODE values NOTIMP and SSOPNOTIMP should not occur in practice. + + A server would only generate NOTIMP if it did not support Session + Signaling, and if the server does not support Session Signaling then + it should not be possible for a client to have an active subscription + to cancel. + + Similarly, a server would only generate SSOPNOTIMP if it did not + support Push Notifications, and if the server does not support Push + Notifications then it should not be possible for a client to have an + active subscription to cancel. + + All nonzero RCODE values indicate a serious problem with the client. + After sending an error response, the server SHOULD send a DNS Push + Notification Terminate Session operation TLV and then close the TCP + connection, as described in the DNS Session Signaling specification + [I-D.ietf-dnsop-session-signal]. + +6.5. DNS Session Signaling Push Notification RECONFIRM + + Sometimes, particularly when used with a Hybrid Proxy + [I-D.ietf-dnssd-hybrid], 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 host+port that is not responding to + connection requests) the client can send a RECONFIRM message to + request that the server re-verify that the data is still valid. For + a Hybrid 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 be silently ignored. + + A RECONFIRM request is formatted identically to a SUBSCRIBE request, + except that the TLV type is RECONFIRM (tentatively 67) instead of + SUBSCRIBE. Additionally, QTYPE MUST NOT be the value ANY (255) and + QCLASS MUST NOT be the value ANY (255). + + Like all DNS Session Signaling [I-D.ietf-dnsop-session-signal] + requests, a RECONFIRM request MUST contain a unique MESSAGE ID, not + currently in use in this session. + + A RECONFIRM request generates exactly one RECONFIRM response from the + server, formatted identically to a SUBSCRIBE response, which echoes + back the unique MESSAGE ID from the RECONFIRM request. + + In the RECONFIRM response the RCODE indicates whether or not the + request was successful. Supported RCODEs are as follows: + + +------------+-------+----------------------------------------------+ | Mnemonic | Value | Description | - +----------+-------+------------------------------------------------+ - | SERVFAIL | 2 | The server is overloaded due to resource | - | | | exhaustion. | - | REFUSED | 5 | The server has been reconfigured and is no | - | | | longer accepting DNS Push Notification | - | | | requests for one or more of the currently | - | | | subscribed names. | - +----------+-------+------------------------------------------------+ + +------------+-------+----------------------------------------------+ + | NOERROR | 0 | RECONFIRM successful. | + | FORMERR | 1 | Server failed to process request due to a | + | | | malformed request. | + | NOTIMP | 4 | Server does not recognize DNS Session | + | | | Signaling Opcode. | + | SSOPNOTIMP | 11 | RECONFIRM operation not supported. | + +------------+-------+----------------------------------------------+ - Termination Response codes + RECONFIRM Response codes - This document specifies only these two RCODE values for Termination - Messages. Servers sending Termination Messages SHOULD use one of - these two values. However, future circumstances may create - situations where other RCODE values are appropriate in Termination - Messages, so clients MUST be prepared to accept Termination Messages - with any RCODE value. In particular, a Termination Message with - RCODE value zero (NOERROR) is still a Termination Message and should - be treated as such. + This document specifies only these RCODE values for RECONFIRM + Responses. Servers sending RECONFIRM Responses SHOULD use one of + these values. However, future circumstances may create situations + where other RCODE values are appropriate in RECONFIRM Responses, so + clients MUST be prepared to accept RECONFIRM Responses with any RCODE + value. - The Termination Message MUST contain an EDNS(0) TCP Keepalive option - [RFC7828]. The client MUST wait for the time indicated in the - EDNS(0) TCP Keepalive option's idle timeout before attempting any new - connections to this server. A client that receives a Termination - Message without an EDNS(0) TCP Keepalive option SHOULD treat it as - equivalent to a TCP Keepalive option with a zero timeout value. + A correctly-formatted RECONFIRM message results in a response with + RCODE NOERROR. - In the case where the server is rejecting some, but not all, of the - existing subscriptions (perhaps because it has been reconfigured and - is no longer authoritative for those names) with a REFUSED (5) RCODE, - the EDNS(0) TCP Keepalive option's idle timeout MAY be zero, - indicating that the client SHOULD attempt to re-establish its - subscriptions immediately. + Nonzero RCODE values signal some kind of error. If the server sends + a nonzero RCODE then it SHOULD append a Terminate modifier TLV + [I-D.ietf-dnsop-session-signal] to the response specifying a delay + before the client attempts this operation again. The RECOMMENDED + value for the delay is five minutes. For serious errors, after + sending the error response, the server SHOULD send a DNS Push + Notification Terminate Session operation TLV and then close the TCP + connection, as described in the DNS Session Signaling specification + [I-D.ietf-dnsop-session-signal]. - In the case where a server is terminating a large number of - connections at once (e.g., if the system is restarting) and the - server doesn't want to be inundated with a flood of simultaneous - retries, it SHOULD send different EDNS(0) TCP Keepalive values to - each client. These adjustments MAY be selected randomly, - pseudorandomly, or deterministically (e.g., incrementing the time - value by one tenth of a second for each successive client, yielding a - post-restart reconnection rate of ten clients per second). + If, after receiving a valid RECONFIRM request, the server determines + that the 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 printer is no + longer present has the side effect of informing all other interested + clients that the printer in question is now gone. + +6.6. Client-Initiated Termination + + An individual subscription is terminated by sending an UNSUBSCRIBE + TLV for that specific subscription, or all subscriptions can be + cancelled at once by the client closing the connection. When a + client terminates an individual subscription (via UNSUBSCRIBE) or all + subscriptions on that connection (by closing the connection) it is + signaling to the server that it is longer interested in receiving + those particular updates. It is informing the server that the server + may release any state information it has been keeping with regards to + these particular subscriptions. + + After terminating its last subscription on a connection via + UNSUBSCRIBE, a client MAY close the connection immediately, or it may + keep it open if it anticipates performing further operations on that + connection in the future. If a client wishes to keep an idle + connection open, it MUST continue to meet its keepalive obligations + [I-D.ietf-dnsop-session-signal] or the server is entitled to close + the connection (see below). + + If a client plans to terminate one or more subscriptions on a + connection and doesn't intend to keep that connection open, then as + an efficiency optimization it MAY instead choose to simply close the + connection, which implicitly terminates all subscriptions on that + connection. This may occur because the client computer is being shut + down, is going to sleep, the application requiring the subscriptions + has terminated, or simply because the last active subscription on + that connection has been cancelled. + + When closing a connection, a client will generally do an abortive + disconnect, sending a TCP RST. This immediately discards all + remaining inbound and outbound data, which is appropriate if the + client no longer has any interest in this data. In the BSD Sockets + API, sending a TCP RST is achieved by setting the SO_LINGER option + with a time of 0 seconds and then closing the socket. + + If a client has performed operations on this connection that it would + not want lost (like DNS updates) then the client SHOULD do an orderly + disconnect, sending 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 TLS support is REQUIRED in DNS Push Notifications. There is no provision for opportunistic encryption using a mechanism like "STARTTLS". DNSSEC is RECOMMENDED for DNS Push Notifications. TLS alone does not provide complete security. TLS certificate verification can provide reasonable assurance that the client is really talking to the server @@ -1204,21 +1077,21 @@ 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. 7.3. TLS Compression - In order to reduce the chances of compression related attacks, TLS- + 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 the draft version of TLS 1.3 [I-D.ietf-tls-tls13], TLS- level compression has been removed completely. 7.4. TLS Session Resumption TLS Session Resumption is permissible on DNS Push Notification servers. The server may keep TLS state with Session IDs [RFC5246] or operate in stateless mode by sending a Session Ticket [RFC5077] to the client for it to store. However, once the connection is closed, @@ -1228,170 +1101,179 @@ Use of TLS Session Resumption allows a new TLS connection to be set up more quickly, but the client will still have to recreate any desired subscriptions. 8. IANA Considerations This document defines the service name: "_dns-push-tls._tcp". It is only applicable for the TCP protocol. This name is to be published in the IANA Service Name Registry. - This document defines three DNS OpCodes: SUBSCRIBE with (tentative) - value 6, UNSUBSCRIBE with (tentative) value 7, and RECONFIRM with - (tentative) value 8. + This document defines three DNS Session Signaling TLV types: + SUBSCRIBE with (tentative) value 64, PUSH with (tentative) value 65, + UNSUBSCRIBE with (tentative) value 66, and RECONFIRM with (tentative) + value 67. 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 Shankar Rao, Markus Stenberg, Dave Thaler, and Soraia Zlatkovic. 10. References 10.1. Normative References - [I-D.bellis-dnsop-session-signal] - Bellis, R., Cheshire, S., Marcon, J., Mankin, A., and T. - Pusateri, "DNS Session Signaling", draft-bellis-dnsop- - session-signal-00 (work in progress), July 2016. + [I-D.ietf-dnsop-session-signal] + Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., + Mankin, A., and T. Pusateri, "DNS Session Signaling", + draft-ietf-dnsop-session-signal-00 (work in progress), + August 2016. [I-D.ietf-tls-tls13] Rescorla, E., "The Transport Layer Security (TLS) Protocol - Version 1.3", draft-ietf-tls-tls13-13 (work in progress), - May 2016. + Version 1.3", draft-ietf-tls-tls13-18 (work in progress), + October 2016. - [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI - 10.17487/RFC0768, August 1980, + [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, + DOI 10.17487/RFC0768, August 1980, . - [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC - 793, DOI 10.17487/RFC0793, September 1981, + [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, + RFC 793, DOI 10.17487/RFC0793, September 1981, . [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, . [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - - Application and Support", STD 3, RFC 1123, DOI 10.17487/ - RFC1123, October 1989, + Application and Support", STD 3, RFC 1123, + DOI 10.17487/RFC1123, October 1989, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ - RFC2119, March 1997, + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, . [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, + (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, + Extensions: Extension Definitions", RFC 6066, + DOI 10.17487/RFC6066, January 2011, . - [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms - for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/ - RFC6891, April 2013, - . - [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, April 2013, . [RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS- Based Authentication of Named Entities (DANE) TLSA Records with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October 2015, . [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and D. Wessels, "DNS Transport over TCP - Implementation Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, . - [RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The - edns-tcp-keepalive EDNS0 Option", RFC 7828, DOI 10.17487/ - RFC7828, April 2016, - . - 10.2. Informative References + [I-D.dukkipati-tcpm-tcp-loss-probe] + Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis, + "Tail Loss Probe (TLP): An Algorithm for Fast Recovery of + Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work + in progress), February 2013. + [I-D.ietf-dnssd-hybrid] Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service Discovery", draft-ietf-dnssd-hybrid-03 (work in progress), - November 2015. - - [I-D.ietf-dprive-dns-over-tls] - Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., - and P. Hoffman, "Specification for DNS over TLS", draft- - ietf-dprive-dns-over-tls-09 (work in progress), March - 2016. + February 2016. [I-D.sekar-dns-llq] Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns- llq-01 (work in progress), August 2006. [IPJ.9-4-TCPSYN] Eddy, W., "Defenses Against TCP SYN Flooding Attacks", The - Internet Protocol Journal, Cisco Systems, Volume 9, Number - 4, December 2006. + Internet Protocol Journal, Cisco Systems, Volume 9, + Number 4, December 2006. + + [obs] "Observer Pattern", . [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996, August 1996, . [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication Format", RFC 4287, DOI 10.17487/RFC4287, December 2005, . - [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", RFC - 4953, DOI 10.17487/RFC4953, July 2007, + [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", + RFC 4953, DOI 10.17487/RFC4953, July 2007, . [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, "Transport Layer Security (TLS) Session Resumption without Server-Side State", RFC 5077, DOI 10.17487/RFC5077, January 2008, . [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, February 2013, . [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, + . + + [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, . + [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., + and P. Hoffman, "Specification for DNS over Transport + Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May + 2016, . + [XEP0060] Millard, P., Saint-Andre, P., and R. Meijer, "Publish- Subscribe", XSF XEP 0060, July 2010. Authors' Addresses Tom Pusateri Seeking affiliation Hilton Head Island, SC USA