--- 1/draft-ietf-dnssd-push-18.txt 2019-03-24 07:14:04.271501860 -0700 +++ 2/draft-ietf-dnssd-push-19.txt 2019-03-24 07:14:04.347503689 -0700 @@ -1,19 +1,19 @@ Internet Engineering Task Force T. Pusateri Internet-Draft Unaffiliated Intended status: Standards Track S. Cheshire -Expires: September 12, 2019 Apple Inc. - March 11, 2019 +Expires: September 25, 2019 Apple Inc. + March 24, 2019 DNS Push Notifications - draft-ietf-dnssd-push-18 + draft-ietf-dnssd-push-19 Abstract The Domain Name System (DNS) was designed to return matching records efficiently for queries for data that are relatively static. When those records change frequently, DNS is still efficient at returning the updated results when polled, as long as the polling rate is not too high. But there exists no mechanism for a client to be asynchronously notified when these changes occur. This document defines a mechanism for a client to be notified of such changes to @@ -27,21 +27,21 @@ 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 https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on September 12, 2019. + This Internet-Draft will expire on September 25, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -134,26 +134,27 @@ 10.5 Leopard in 2007. Back to My Mac was designed in an era when the data center operations staff asserted that it was impossible for a server to handle large numbers of mostly-idle TCP connections, so LLQ was defined as a UDP-based protocol, effectively replicating much of TCP's connection state management logic in user space, and creating its own poor imitations of existing TCP features like the three-way handshake, flow control, and reliability. This document builds on experience gained with the LLQ protocol, with an improved design. Instead of using UDP, this specification uses - DNS Stateful Operations (DSO) [DSO] running over TLS over TCP, and - therefore doesn't need to reinvent existing TCP functionality. Using - TCP also gives long-lived low-traffic connections better longevity - through NAT gateways without depending on the gateway to support NAT - Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control Protocol - (PCP) [RFC6887], or resorting to excessive keepalive traffic. + DNS Stateful Operations (DSO) [RFC8490] running over TLS over TCP, + and therefore doesn't need to reinvent existing TCP functionality. + Using TCP also gives long-lived low-traffic connections better + longevity through NAT gateways without depending on the gateway to + support NAT Port Mapping Protocol (NAT-PMP) [RFC6886] or Port Control + Protocol (PCP) [RFC6887], or resorting to excessive keepalive + traffic. 3. Overview A DNS Push Notification client subscribes for Push Notifications for a particular RRSet by connecting to the appropriate Push Notification server for that RRSet, and sending DSO message(s) indicating the RRSet(s) of interest. When the client loses interest in receiving further updates to these records, it unsubscribes. The DNS Push Notification server for a DNS zone is any server capable @@ -212,41 +213,41 @@ (b) A DNS Push Notification client SHOULD NOT routinely keep a DNS Push Notification subscription active 24 hours a day, 7 days a week, just to keep a list in memory up to date so that if the user does choose to bring up an on-screen display of that data, it can be displayed really fast. DNS Push Notifications are designed to be fast enough that there is no need to pre-load a "warm" list in memory just in case it might be needed later. Generally, as described in the DNS Stateful Operations specification - [DSO], a client must not keep a session to a server open indefinitely - if it has no subscriptions (or other operations) active on that - session. A client MAY close a session as soon as it becomes idle, - and then if needed in the future, open a new session when required. - Alternatively, a client MAY speculatively keep an idle session open - for some time, subject to the constraint that it MUST NOT keep a - session open that has been idle for more than the session's idle - timeout (15 seconds by default) [DSO]. + [RFC8490], a client must not keep a session to a server open + indefinitely if it has no subscriptions (or other operations) active + on that session. A client MAY close a session as soon as it becomes + idle, and then if needed in the future, open a new session when + required. Alternatively, a client MAY speculatively keep an idle + session open for some time, subject to the constraint that it MUST + NOT keep a session open that has been idle for more than the + session's idle timeout (15 seconds by default) [RFC8490]. 4. Transport Other DNS operations like DNS Update [RFC2136] MAY use either User Datagram Protocol (UDP) [RFC0768] or Transmission Control Protocol (TCP) [RFC0793] as the transport protocol, in keeping with the historical precedent that DNS queries must first be sent over UDP [RFC1123]. This requirement to use UDP has subsequently been relaxed [RFC7766]. In keeping with the more recent precedent, DNS Push Notification is defined only for TCP. DNS Push Notification clients MUST use DNS - Stateful Operations (DSO) [DSO] running over TLS over TCP [RFC7858]. + Stateful Operations [RFC8490] running over TLS over TCP [RFC7858]. 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. Flooding attacks are possible with any protocol, and a benefit of TCP is that there are already established industry best practices to guard against SYN flooding and similar attacks [SYN] [RFC4953]. Use of TCP also allows DNS Push Notifications to take advantage of @@ -273,24 +274,24 @@ employ various techniques to limit subscriptions to a manageable level. Correspondingly, the client is free to establish simultaneous sessions to alternate DNS servers that support DNS Push Notifications for the zone and distribute subscriptions at the client's discretion. In this way, both clients and servers can react to resource constraints. 6. Protocol Operation The DNS Push Notification protocol is a session-oriented protocol, - and makes use of DNS Stateful Operations (DSO) [DSO]. + and makes use of DNS Stateful Operations (DSO) [RFC8490]. - For details of the DSO message format refer to the DNS Stateful - Operations specification [DSO]. Those details are not repeated here. + For details of the DSO message format refer to the DNS Stateful Oper- + ations specification [RFC8490]. Those details are not repeated here. DNS Push Notification clients and servers MUST support DSO. A single server can support DNS Queries, DNS Updates, and DNS Push Notifications (using DSO) on the same TCP port. A DNS Push Notification exchange begins with the client discovering the appropriate server, using the procedure described in Section 6.1, and then making a TLS/TCP connection to it. A typical DNS Push Notification client will immediately issue a DSO @@ -336,21 +337,21 @@ In many contexts, the recursive resolver will be able to handle Push Notifications for all names that the client may need to follow. Use of VPN tunnels and split-view DNS can create some additional complexity in the client software here; the techniques to handle VPN tunnels and split-view DNS for DNS Push Notifications are the same as those already used to handle this for normal DNS queries. If the recursive resolver does not support DNS over TLS, or does support DNS over TLS but is not listening on TCP port 853, or does support DNS over TLS on TCP port 853 but does not support DSO on that - port, then the DSO Session session establishment will fail [DSO]. + port, then the DSO Session session establishment will fail [RFC8490]. If the recursive resolver does support DSO but not Push Notification subscriptions, then it will return the DSO error code, DSOTYPENI (11). In some cases, the recursive resolver may support DSO and Push Notification subscriptions, but may not be able to subscribe for Push Notifications for a particular name. In this case, the recursive resolver should return an informative error code to the client so that the client can make an informed decision how to handle the @@ -468,50 +469,50 @@ 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 cached data. 6.2. DNS Push Notification SUBSCRIBE After connecting, and requesting a longer idle timeout and/or - keepalive interval if necessary, a DNS Push Notification client then - indicates its desire to receive DNS Push Notifications for a given - domain name by sending a SUBSCRIBE request to the server. A - SUBSCRIBE request is encoded in a DSO message [DSO]. This - specification defines a primary DSO TLV for DNS Push Notification - SUBSCRIBE Requests (tentatively DSO Type Code 0x40). + keepalive interval if necessary, a DNS Push Notification client + then indicates its desire to receive DNS Push Notifications for + a given domain name by sending a SUBSCRIBE request to the server. + A SUBSCRIBE request is encoded in a DSO message [RFC8490]. + This specification defines a primary DSO TLV for DNS Push + Notification SUBSCRIBE Requests (tentatively DSO Type Code 0x40). The entity that initiates a SUBSCRIBE request is by definition the client. A server MUST NOT send a SUBSCRIBE request over an existing session from a client. If a server does send a SUBSCRIBE request over a DSO session initiated by a client, this is a fatal error and the client should immediately abort the connection with a TCP RST (or equivalent for other protocols). 6.2.1. SUBSCRIBE Request A SUBSCRIBE request begins with the standard DSO 12-byte header - [DSO], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE request - message is illustrated in Figure 1. + [RFC8490], followed by the SUBSCRIBE primary TLV. A SUBSCRIBE + request message is illustrated in Figure 1. The MESSAGE ID field MUST be set to a unique value, that the client is not using for any other active operation on this DSO session. For the purposes here, a MESSAGE ID is in use on this session if the client has used it in a request for which it has not yet received a response, or if the client has used it for a subscription which it has not yet cancelled using UNSUBSCRIBE. In the SUBSCRIBE response the server MUST echo back the MESSAGE ID value unchanged. - The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS OPCODE field contains the OPCODE value + The other header fields MUST be set as described in the DSO spec- + ification [RFC8490]. The DNS OPCODE field contains the OPCODE value for DNS Stateful Operations (6). The four count fields MUST be zero, and the corresponding four sections MUST be empty (i.e., absent). The DSO-TYPE is SUBSCRIBE (tentatively 0x40). The DSO-LENGTH is the length of the DSO-DATA that follows, which specifies the name, type, and class of the record(s) being sought. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 @@ -593,21 +594,21 @@ where one or both of TYPE or CLASS are 255, the server MUST send Push Notification Updates for ALL record changes that match the subscription, not just some of them. 6.2.2. SUBSCRIBE Response Each SUBSCRIBE request generates exactly one SUBSCRIBE response from the server. A SUBSCRIBE response begins with the standard DSO 12-byte header - [DSO], possibly followed by one or more optional TLVs, such as a + [RFC8490], possibly followed by one or more optional TLVs, such as a Retry Delay TLV. The MESSAGE ID field MUST echo the value given in the ID field of the SUBSCRIBE request. This is how the client knows which request is being responded to. A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. If a client receives a SUBSCRIBE response message containing a SUBSCRIBE TLV then the response message is processed but the SUBSCRIBE TLV MUST be silently ignored. @@ -652,41 +653,41 @@ server right away. If multiple SRV records were returned as described in Section 6.1, Paragraph 7, a subsequent server can be tried immediately. If the client has other successful subscriptions to this server, these subscriptions remain even though additional subscriptions may be refused. Neither the client nor the server are required to close the connection, although, either end may choose to do so. If the server sends a nonzero RCODE then it SHOULD append a Retry - Delay TLV [DSO] to the response specifying a delay before the client - attempts this operation again. Recommended values for the delay for - different RCODE values are given below. These recommended values - apply both to the default values a server should place in the Retry - Delay TLV, and the default values a client should assume if the + Delay TLV [RFC8490] to the response specifying a delay before the + client attempts this operation again. Recommended values for the + delay for different RCODE values are given below. These recommended + values apply both to the default values a server should place in the + Retry Delay TLV, and the default values a client should assume if the server provides no Retry Delay TLV. For RCODE = 1 (FORMERR) the delay may be any value selected by the implementer. A value of five minutes is RECOMMENDED, to reduce the risk of high load from defective clients. For RCODE = 2 (SERVFAIL) the delay should be chosen according to the level of server overload and the anticipated duration of that overload. By default, a value of one minute is RECOMMENDED. If a more serious server failure occurs, the delay may be longer in accordance with the specific problem encountered. For RCODE = 4 (NOTIMP), which occurs on a server that doesn't - implement DNS Stateful Operations [DSO], it is unlikely that the - server will begin supporting DSO in the next few minutes, so the - retry delay SHOULD be one hour. Note that in such a case, a + implement DNS Stateful Operations [RFC8490], it is unlikely that + the server will begin supporting DSO in the next few minutes, so + the retry delay SHOULD be one hour. Note that in such a case, a server that doesn't implement DSO is unlikely to place a Retry Delay TLV in its response, so this recommended value in particular applies to what a client should assume by default. For RCODE = 5 (REFUSED), which occurs on a server that implements DNS Push Notifications, but is currently configured to disallow DNS Push Notifications, the retry delay may be any value selected by the implementer and/or configured by the operator. If the server being queried is listed in a @@ -724,156 +725,159 @@ 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 allow the session to remain open, or MAY send a DNS Push Notification Retry Delay Operation TLV instructing the client to close the session, as - described in the DSO specification [DSO]. Clients MUST correctly + described in the DSO specification [RFC8490]. Clients MUST correctly handle both cases. 6.3. DNS Push Notification Updates Once a subscription has been successfully established, the server generates PUSH messages to send to the client as appropriate. In the case that the answer set was already non-empty at the moment the subscription was established, an initial PUSH message will be sent immediately following the SUBSCRIBE Response. Subsequent changes to the answer set are then communicated to the client in subsequent PUSH messages. 6.3.1. PUSH Message A PUSH unidirectional message begins with the standard DSO 12-byte - header [DSO], followed by the PUSH primary TLV. A PUSH message is - illustrated in Figure 2. + header [RFC8490], followed by the PUSH primary TLV. A PUSH message + is illustrated in Figure 2. In accordance with the definition of DSO unidirectional messages, the MESSAGE ID field MUST be zero. There is no client response to a PUSH message. - The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS OPCODE field contains the OPCODE value + The other header fields MUST be set as described in the DSO spec- + ification [RFC8490]. The DNS OPCODE field contains the OPCODE value for DNS Stateful Operations (6). The four count fields MUST be zero, and the corresponding four sections MUST be empty (i.e., absent). The DSO-TYPE is PUSH (tentatively 0x41). The DSO-LENGTH is the length of the DSO-DATA that follows, which specifies the changes being communicated. The DSO-DATA contains one or more change notifications. A PUSH Message MUST contain at least one change notification. If a PUSH Message is received that contains no change notifications, this is a fatal error, and the receiver MUST immediately terminate the - connection with a TCP RST (or equivalent for other protocols). The - change notifications are formatted similarly to how DNS Resource - Records are conventionally expressed in DNS messages, and are - interpreted as described below. + connection with a TCP RST (or equivalent for other protocols). - If the signed 32-bit TTL is in the range 0 to 604,800 seconds (one - week), then a new DNS Resource Record with the given name, type, - class and RDATA is added. The maximum record lifetime supported in a - PUSH Message is one week. In the event that the DNS record in - question has an actual TTL greater than one week, the TTL is reported - in the PUSH Message as being one week. A TTL of 0 means that this - record should be retained for as long as the subscription is active, - and should be discarded immediately the moment the subscription is - cancelled. + The change notification records are formatted similarly to how DNS + Resource Records are conventionally expressed in DNS messages, as + illustrated in Figure 2, and are interpreted as described below. - If the signed 32-bit TTL has the value -1, then the DNS Resource - Record with the given name, type, class and RDATA is removed. + The TTL field holds an unsigned 32-bit integer [RFC2181]. If the TTL + is in the range 0 to 2,147,483,647 seconds (2^31 - 1, or 0x7FFFFFFF), + then a new DNS Resource Record with the given name, type, class and + RDATA is added. A TTL of 0 means that this record should be retained + for as long as the subscription is active, and should be discarded + immediately the moment the subscription is cancelled. - If the signed 32-bit TTL has the value -2, then this is a - 'collective' remove notification. For collective remove - notifications RDLEN MUST be zero and consequently the RDATA MUST be - empty. If a change notification is received where TTL = -2 and RDLEN - is not zero, this is a fatal error, and the receiver MUST immediately + If the TTL has the value 0xFFFFFFFF, then the DNS Resource Record + with the given name, type, class and RDATA is removed. + + If the TTL has the value 0xFFFFFFFE, then this is a 'collective' + remove notification. For collective remove notifications RDLEN MUST + be zero and consequently the RDATA MUST be empty. If a change + notification is received where TTL = 0xFFFFFFFE and RDLEN is not + zero, this is a fatal error, and the receiver MUST immediately terminate the connection with a TCP RST (or equivalent for other protocols). There are three types of collective remove notification: - For collective remove notifications, if CLASS is ANY, then for the - given name this deletes all records of all types in all classes. In - this case TYPE MUST be set to ANY on tranmission, and MUST be + For collective remove notifications, if CLASS is 255 (ANY), then for + the given name this deletes all records of all types in all classes. + In this case TYPE MUST be set to zero on transmission, and MUST be silently ignored on reception. - For collective remove notifications, if CLASS is not ANY and TYPE is - is ANY then for the given name this deletes all records of all types - in the specified class. + For collective remove notifications, if CLASS is not 255 (ANY) and + TYPE is 255 (ANY) then for the given name this deletes all records of + all types in the specified class. - For collective remove notifications, if CLASS is not ANY and TYPE is - is not ANY then for the given name this deletes all records of the - specified type in the specified class. + For collective remove notifications, if CLASS is not 255 (ANY) and + TYPE is not 255 (ANY) then for the given name this deletes all + records of the specified type in the specified class. Summary of change notification types: Delete all RRsets from a name, in all classes - TTL=-2, RDLENGTH=0, TYPE=ANY, CLASS=ANY + TTL=0xFFFFFFFE, RDLENGTH=0, CLASS=255 (ANY) Delete all RRsets from a name, in given class: - TTL=-2, RDLENGTH=0, TYPE=ANY - CLASS specifies class (usually class "IN") + TTL=0xFFFFFFFE, RDLENGTH=0, CLASS specifies class, TYPE=255 (ANY) Delete specified RRset from a name, in given class: - TTL=-2, RDLENGTH=0 + TTL=0xFFFFFFFE, RDLENGTH=0 CLASS and TYPE specify the RRset being deleted Delete an individual RR from a name: - TTL=-1 + TTL=0xFFFFFFFF CLASS, TYPE, RDLENGTH and RDATA specify the RR being deleted. Add individual RR to a name TTL>=0 CLASS, TYPE, RDLENGTH, RDATA and TTL specify the RR being added. Note that it is valid for the RDATA of an added or removed DNS Resource Record to be empty (zero length). For example, an Address Prefix List Resource Record [RFC3123] may have empty RDATA. - Therefore, a change notification with RDLEN=0 does not automatically - indicate a remove notification. If RDLEN=0 and TTL >= 0, this change - notification signals the addition of a record with the given name, - type, class, and empty RDATA. If RDLEN=0 and TTL = -1, this change - notification signals the removal specifically of that single record - with the given name, type, class, and empty RDATA. + indicate a remove notification. If RDLEN=0 and TTL is the in the + range 0 - 0x7FFFFFFF, this change notification signals the addition + of a record with the given name, type, class, and empty RDATA. If + RDLEN=0 and TTL = 0xFFFFFFFF, this change notification signals the + removal specifically of that single record with the given name, type, + class, and empty RDATA. + + If the TTL is any value other than 0xFFFFFFFF, 0xFFFFFFFE, or a value + in the range 0 - 0x7FFFFFFF, then the receiver SHOULD silently ignore + this particular change notification record. The connection is not + terminated and other valid change notification records within this + PUSH message are processed as usual. For efficiency, when generating a PUSH message, a server SHOULD include as many change notifications as it has immediately available to send, rather than sending each change notification as a separate DSO message. Once it has exhausted the list of change notifications immediately available to send, a server SHOULD then send the PUSH message immediately, rather than waiting to see if additional change notifications become available. For efficiency, when generating a PUSH message, a server SHOULD use standard DNS name compression, with offsets relative to the beginning of the DNS message [RFC1035]. When multiple change notifications in a single PUSH message have the same owner name, this name compression can yield significant savings. Name compression should be performed as specified in Section 18.14 of the Multicast DNS specification [RFC6762], namely, owner names should always be compressed, and names - appearing within only the RDATA of the following DNS types should be - compressed: + appearing within RDATA should be compressed for only the RR types + listed below: NS, CNAME, PTR, DNAME, SOA, MX, AFSDB, RT, KX, RP, PX, SRV, NSEC - Servers MAY generate PUSH messages up to a DNS message length of - 16,382 bytes, counting from the start of the DSO 12-byte header. + Servers may generate PUSH messages up to a maximum DNS message length + of 16,382 bytes, counting from the start of the DSO 12-byte header. Including the two-byte length prefix that is used to frame DNS over a byte stream like TLS, this makes a total of 16,384 bytes. Servers - SHOULD NOT generate PUSH messages larger than this. Where the + MUST NOT generate PUSH messages larger than this. Where the immediately available change notifications are sufficient to exceed a - DNS message length of 16,382 bytes, the change notifications SHOULD - be communicated in separate PUSH messages of up to 16,382 bytes each. + DNS message length of 16,382 bytes, the change notifications MUST be + communicated in separate PUSH messages of up to 16,382 bytes each. DNS name compression becomes less effective for messages larger than 16,384 bytes, so little efficiency benefit is gained by sending messages larger than this. If a client receives a PUSH message with a DNS message length larger than 16,382 bytes, the this is a fatal error, and the receiver MUST immediately terminate the connection with a TCP RST (or equivalent for other protocols). 1 1 1 1 1 1 @@ -895,21 +899,21 @@ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | DSO-LENGTH (number of octets in DSO-DATA) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ \ NAME \ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | TYPE | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | CLASS | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | TTL | | - | (32-bit signed big-endian integer) | > DSO-DATA + | (32-bit unsigned big-endian integer) | > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | | RDLEN | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | \ RDATA (sized as necessary) \ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | : NAME, TYPE, CLASS, TTL, RDLEN, RDATA : | : Repeated As Necessary : / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / Figure 2: PUSH Message @@ -928,23 +932,23 @@ record addition/deletion is silently ignored. Processing of other additions and deletions in this message is not affected. The DSO session is not closed. This is to allow for the unavoidable race condition where a client sends an outbound UNSUBSCRIBE while inbound 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 PUSH message is sent. For example, a PUSH message adding a given record may match both a SUBSCRIBE request with - the same TYPE and a different SUBSCRIBE request with TYPE=ANY. It is - not the case that two PUSH messages are sent because the new record - matches two active subscriptions. + the same TYPE and a different SUBSCRIBE request with TYPE=ANY (255). + 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" 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. @@ -963,41 +967,41 @@ record is still there. Once a subscription is cancelled (individually, or as a result of the DSO session being closed) record aging for records covered by the subscription resumes and records are removed from the local cache when their TTL reaches zero. 6.4. DNS Push Notification UNSUBSCRIBE To cancel an individual subscription without closing the entire DSO session, the client sends an UNSUBSCRIBE message over the established DSO session to the server. The UNSUBSCRIBE message is encoded as a - DSO unidirectional message [DSO]. This specification defines a + DSO unidirectional message [RFC8490]. This specification defines a primary unidirectional DSO TLV for DNS Push Notification UNSUBSCRIBE Messages (tentatively DSO Type Code 0x42). A server MUST NOT initiate an UNSUBSCRIBE message. If a server does send an UNSUBSCRIBE message over a DSO session initiated by a client, this is a fatal error and the client should immediately abort the connection with a TCP RST (or equivalent for other protocols). 6.4.1. UNSUBSCRIBE Message An UNSUBSCRIBE unidirectional message begins with the standard DSO - 12-byte header [DSO], followed by the UNSUBSCRIBE primary TLV. An - UNSUBSCRIBE message is illustrated in Figure 3. + 12-byte header [RFC8490], followed by the UNSUBSCRIBE primary TLV. + An UNSUBSCRIBE message is illustrated in Figure 3. In accordance with the definition of DSO unidirectional messages, the MESSAGE ID field MUST be zero. There is no server response to an UNSUBSCRIBE message. - The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS OPCODE field contains the OPCODE value + The other header fields MUST be set as described in the DSO spec- + ification [RFC8490]. The DNS OPCODE field contains the OPCODE value for DNS Stateful Operations (6). The four count fields MUST be zero, and the corresponding four sections MUST be empty (i.e., absent). The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42). The DSO-LENGTH field contains the value 2, the length of the 2-octet MESSAGE ID contained in the DSO-DATA. The DSO-DATA contains the value given in the MESSAGE ID field of an active SUBSCRIBE request. This is how the server knows which @@ -1073,29 +1077,29 @@ that the disputed records are in fact no longer valid, then subsequent DNS PUSH Messages will be generated to inform interested clients. Thus, one client discovering that a previously-advertised device (like a network printer) is no longer present has the side effect of informing all other interested clients that the device in question is now gone. 6.5.1. RECONFIRM Message A RECONFIRM unidirectional message begins with the standard DSO - 12-byte header [DSO], followed by the RECONFIRM primary TLV. A - RECONFIRM message is illustrated in Figure 4. + 12-byte header [RFC8490], followed by the RECONFIRM primary TLV. + A RECONFIRM message is illustrated in Figure 4. In accordance with the definition of DSO unidirectional messages, the MESSAGE ID field MUST be zero. There is no server response to a RECONFIRM message. - The other header fields MUST be set as described in the DSO - specification [DSO]. The DNS OPCODE field contains the OPCODE value + The other header fields MUST be set as described in the DSO spec- + ification [RFC8490]. The DNS OPCODE field contains the OPCODE value for DNS Stateful Operations (6). The four count fields MUST be zero, and the corresponding four sections MUST be empty (i.e., absent). The DSO-TYPE is RECONFIRM (tentatively 0x43). The DSO-LENGTH is the length of the data that follows, which specifies the name, type, class, and content of the record being disputed. 1 1 1 1 1 1 @@ -1140,21 +1144,21 @@ DNS wildcarding is not supported. That is, a wildcard ("*") in a RECONFIRM message matches only a literal wildcard character ("*") in the zone, and nothing else. Aliasing is not supported. That is, a CNAME in a RECONFIRM message matches only a literal CNAME record in the zone, and nothing else. 6.6. DNS Stateful Operations TLV Context Summary This document defines four new DSO TLVs. As suggested in Section 8.2 - of the DNS Stateful Operations specification [DSO], the valid + of the DNS Stateful Operations specification [RFC8490], the valid contexts of these new TLV types are summarized below. The client TLV contexts are: C-P: Client request message, primary TLV C-U: Client unidirectional message, primary TLV C-A: Client request or unidirectional message, additional TLV CRP: Response back to client, primary TLV CRA: Response back to client, additional TLV @@ -1197,21 +1201,21 @@ subscriptions on that DSO session (by ending the session) 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 session via UNSUBSCRIBE, a client MAY close the session immediately, or it may keep it open if it anticipates performing further operations on that session in the future. If a client wishes to keep an idle session open, it MUST - respect the maximum idle time required by the server [DSO]. + respect the maximum idle time required by the server [RFC8490]. If a client plans to terminate one or more subscriptions on a session and doesn't intend to keep that session open, then as an efficiency optimization it MAY instead choose to simply close the session, which implicitly terminates all subscriptions on that session. 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 session has been cancelled. @@ -1272,28 +1276,28 @@ recommendations will continue to change. Updated versions or errata may exist for these recommendations. 7.2. TLS Name Authentication As described in Section 6.1, the client discovers the DNS Push Notification server using an SRV lookup for the record name "_dns-push-tls._tcp.". The server connection endpoint SHOULD then be authenticated using DANE TLSA records for the associated SRV record. This associates the target's name and port number with a - trusted TLS certificate [RFC7673]. This procedure uses the TLS Sever - Name Indication (SNI) extension [RFC6066] to inform the server of the - name the client has authenticated through the use of TLSA records. - Therefore, if the SRV record passes DNSSEC validation and a TLSA - record matching the target name is useable, an SNI extension must be - used for the target name to ensure the client is connecting to the - server it has authenticated. If the target name does not have a - usable TLSA record, then the use of the SNI extension is optional. + trusted TLS certificate [RFC7673]. This procedure uses the TLS + Server Name Indication (SNI) extension [RFC6066] to inform the server + of the name the client has authenticated through the use of TLSA + records. Therefore, if the SRV record passes DNSSEC validation and a + TLSA record matching the target name is useable, an SNI extension + must be used for the target name to ensure the client is connecting + to the server it has authenticated. If the target name does not have + a usable TLSA record, then the use of the SNI extension is optional. See Usage Profiles for DNS over TLS and DNS over DTLS [RFC8310] for more information on authenticating domain names. 7.3. TLS Session Resumption TLS Session Resumption is permissible on DNS Push Notification servers. The server may keep TLS state with Session IDs [RFC8446] or operate in stateless mode by sending a Session Ticket [RFC5077] to the client for it to store. However, closing the TLS connection terminates the DSO session. When the TLS session is resumed, the DNS @@ -1339,25 +1343,20 @@ 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, Soraia Zlatkovic, Sara Dickinson, and Andrew Sullivan. Ted Lemon provided clarifying text that was greatly appreciated. 10. References 10.1. Normative References - [DSO] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., - Lemon, T., and T. Pusateri, "DNS Stateful Operations", - draft-ietf-dnsop-session-signal-18 (work in progress), - October 2018. - [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, . [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, @@ -1375,20 +1374,24 @@ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 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, . + [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS + Specification", RFC 2181, DOI 10.17487/RFC2181, July 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, . [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, . @@ -1414,38 +1417,43 @@ . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . + [RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S., + Lemon, T., and T. Pusateri, "DNS Stateful Operations", + RFC 8490, DOI 10.17487/RFC8490, March 2019, + . + [ST] "Service Name and Transport Protocol Port Number Registry", . 10.2. Informative References [DisProx] Cheshire, S., "Discovery Proxy for Multicast DNS-Based - Service Discovery", draft-ietf-dnssd-hybrid-08 (work in - progress), March 2018. + Service Discovery", draft-ietf-dnssd-hybrid-10 (work in + progress), March 2019. [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. - [LLQ] Sekar, K., "DNS Long-Lived Queries", draft-sekar-dns- - llq-01 (work in progress), August 2006. + [LLQ] Cheshire, S. and M. Krochmal, "DNS Long-Lived Queries", + draft-sekar-dns-llq-03 (work in progress), March 2019. [obs] "Observer Pattern", . [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, . [RFC3123] Koch, P., "A DNS RR Type for Lists of Address Prefixes (APL RR)", RFC 3123, DOI 10.17487/RFC3123, June 2001,