DNSOP Working Group R. Bellis
Internet-Draft ISC
Intended status: Standards Track S. Cheshire
Expires: May 4, 2017 Apple Inc.
J. Dickinson
S. Dickinson
Sinodun
A. Mankin
Salesforce
T. Pusateri
Unaffiliated
October 31, 2016
DNS Session Signaling
draft-ietf-dnsop-session-signal-01
Abstract
The EDNS(0) Extension Mechanism for DNS is explicitly defined to only
have "per-message" semantics. This document defines a new Session
Signaling Opcode used to carry persistent "per-session" type-length-
values (TLVs), and defines an initial set of TLVs used to manage
session timeouts and termination.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Session Lifecycle . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Client-Initiated Termination . . . . . . . . . . . . 6
3.1.2. Server-Initiated Termination . . . . . . . . . . . . 6
3.2. Connection Sharing . . . . . . . . . . . . . . . . . . . 8
3.3. Message Format . . . . . . . . . . . . . . . . . . . . . 9
3.4. Message Handling . . . . . . . . . . . . . . . . . . . . 10
3.5. TLV Format . . . . . . . . . . . . . . . . . . . . . . . 12
4. Idle Timeout TLV . . . . . . . . . . . . . . . . . . . . . . 13
5. Terminate TLV . . . . . . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6.1. DNS Session Signaling Opcode Registration . . . . . . . . 16
6.2. DNS Session Signaling RCODE Registration . . . . . . . . 16
6.3. DNS Session Signaling Type Codes Registry . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
The use of transports other than UDP for DNS is being increasingly
specified, for example, DNS over TCP [RFC1035][RFC7766] and DNS over
TLS [RFC7858]. Such transports can offer persistent, long-lived
sessions and therefore when using them for transporting DNS messages
it is of benefit to have a mechanism that can establish parameters
associated with those sessions, such as timeouts. In such situations
it is also advantageous to support server initiated messages.
The EDNS(0) Extension Mechanism for DNS [RFC6891] is explicitly
defined to only have "per-message" semantics. Whilst EDNS(0) has
been used to signal at least one session related parameter (the
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EDNS(0) TCP KeepAlive option [RFC7828]) the result is less than
optimal due to the restrictions imposed by the EDNS(0) semantics and
the lack of server initiated signalling. This document defines a new
Session Signaling Opcode used to carry persistent "per-session" type-
length-values (TLVs), and defines an initial set of TLVs used to
manage session timeouts and termination.
With EDNS(0), multiple options may be packed into a single OPT
pseudo-RR, and there is no generalized mechanism for a client to be
able to tell whether a server has processed or otherwise acted upon
each individual option within the combined OPT RR. The
specifications for each individual option need to define how each
different option is to be acknowledged, if necessary.
With Session Signaling, in contrast, there is no compelling
motivation to pack multiple operations into a single message for
efficiency reasons. Each Session Signaling operation is communicated
in its own separate DNS message, and the transport protocol can take
care of packing separate DNS messages into a single IP packet if
appropriate. For example, TCP can pack multiple small DNS messages
into a single TCP segment. The RCODE in each response message
indicates the success or failure of the operation in question.
It should be noted that the message format for Session Signaling
operations (see Section 3.3) differs from the DNS packet format used
for standard queries and responses, in that it has a shorter header
(four octets instead of usual twelve octets).
2. Terminology
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].
The term "server" means the software with a listening socket,
awaiting incoming connection requests.
The term "client" means the software which initiates a connection to
the server's listening socket.
The terms "initiator" and "responder" correspond respectively to the
initial sender and subsequent receiver of a Session Signaling TLV,
regardless of which was the "client" and "server" in the usual DNS
sense.
The term "sender" may apply to either an initiator or responder.
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The term "session" in the context of this document means the exchange
of DNS messages using an end-to-end transport protocol where:
o The connection between client and server is persistent and
relatively long-lived (i.e., minutes or hours, rather than
seconds).
o Either end of the connection may initiate messages to the other
o Messages are delivered in order
3. Protocol Details
Session Signaling messages MUST only be carried in protocols and in
environments where a session may be established according to the
definition above. Standard DNS over TCP [RFC1035][RFC7766], and DNS
over TLS [RFC7858] are suitable protocols. DNS over plain UDP is not
appropriate since it fails on the requirement for in-order message
delivery, and, in the presence of NAT gateways and firewalls with
short UDP timeouts, it fails to provide a persistent bi-directional
communication channel unless an excessive amount of keepalive traffic
is used.
Session Signaling messages relate only to the specific session in
which they are being carried. Where a middle box (e.g., a DNS proxy,
forwarder, or session multiplexer) is in the path the middle box MUST
NOT blindly forward the message in either direction. This does not
preclude the use of these messages in the presence of a NAT box that
rewrites IP-layer or transport-layer headers but otherwise maintains
the effect of a single session.
A client MAY attempt to initiate Session Signaling messages at any
time on a connection; receiving a NOTIMP response in reply indicates
that the server does not implement Session Signaling, and the client
SHOULD NOT issue further Session Signaling messages on that
connection.
A server SHOULD NOT initiate Session Signaling messages until a
client-initiated Session Signaling message is received first, unless
in an environment where it is known in advance by other means that
the client supports Session Signaling. This requirement is to ensure
that the clients that do not support Session Signaling do not receive
unsolicited inbound Session Signaling messages that they would not
know how to handle.
Clients and servers SHOULD silently ignore unrecognized messages
(both requests and responses) over the connection. This allows for
backwards compatibility with future enhancements.
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3.1. Session Lifecycle
A session begins when a client makes a new connection to a server.
If a client makes a connection and then fails to send any DNS
messages, then after 30 seconds the server SHOULD abort the
connection with a TCP RST.
The client may perform as many DNS operations as it wishes on the
newly created connection. Operations SHOULD be pipelined (i.e., the
client doesn't need wait for a reply before sending the next
message). The server MUST act on messages in the order they are
received, but responses to those messages MAY be sent out of order,
if appropriate.
When a server implementing this specification receives a new
connection from a client, it MUST begin by internally assigning an
initial idle timeout of 30 seconds to that connection. At both
servers and clients, the generation or reception of any complete DNS
message, including DNS requests, responses, updates, or Session
Signaling messages, resets the idle timer for that connection
[RFC7766].
If, at any time during the life of the connection, half the idle-
timeout value (i.e., 15 seconds by default) elapses without any DNS
messages being sent or received on a connection, then the connection
is considered stale and the client MUST take action. When this
happens the client MUST either send at least one new message to reset
the idle timer - such as a Session Signaling Idle Timeout message
(see Section 4), or any other valid DNS message - or close the
connection.
If a client disconnects from the network abruptly, without cleanly
closing its connection, the server learns of this after failing to
receive further traffic from that client. If, at any time during the
life of the connection, the full idle-timeout value (i.e., 30 seconds
by default) elapses without any DNS messages being sent or received
on a connection, then the connection is considered delinquent and the
server SHOULD forcibly terminate the connection. For sessions over
TCP (or over TLS over TCP), to avoid the burden of having a
connection in TIME-WAIT state, instead of closing the connection
gracefully with a TCP FIN the server SHOULD abort the connection with
a TCP RST (or equivalent for other protocols). (In the BSD Sockets
API this is achieved by setting the SO_LINGER option to zero before
closing the socket.)
If the client wishes to keep an idle connection open for longer than
the default duration without having to send traffic every 15 seconds,
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then it uses the Session Signaling Idle Timeout message to request a
longer idle timeout, as described in Section 4.
3.1.1. Client-Initiated Termination
A client is not required to wait until half of the idle-timeout value
before closing a connection. A client SHOULD close a connection at
any time, at the client's discretion, if it determines that, at that
time, it has no current or reasonably anticipated imminent future
need for the connection.
Upon receiving an error response from the server, a client SHOULD NOT
automatically 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.
3.1.2. Server-Initiated Termination
After sending an error response to a client, the server MAY close the
connection, 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 by sending a Terminate Session request
message, as described in Section 5.
There may be rare cases where a server is overloaded and wishes to
shed load. If the server handles this by simply closing connections,
the likely behaviour of clients is to detect this as a network
failure, and reconnect.
To avoid this reconnection implosion, in this situation the server
also sends a Terminate Session request message, with an RCODE of
SERVFAIL, to inform the client of the overload situation.
After sending a Terminate Session request message, the server MUST
NOT send any further messages on that connection.
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A Terminate Session request message MUST NOT be initiated by a
client. If a server receives a Terminate Session request message
this is an error and the server MUST immediately terminate the
connection with a TCP RST (or equivalent for other protocols).
Upon receipt of a Terminate Session request from the server, the
client MUST make note of the reconnect delay for this server, and
then immediately close the connection. This is to place the burden
of TCP's TIME-WAIT state on the client.
After sending the Terminate Session request the server SHOULD allow
the client five seconds to close the connection, and if the client
has not closed the connection after five seconds then the server
SHOULD abort the connection with a TCP RST (or equivalent for other
protocols). (In the BSD Sockets API this is achieved by setting the
SO_LINGER option to zero before closing the socket.)
In the case where the server is canceling some, but not all, of the
existing operations on a connection, with a REFUSED (5) RCODE
(perhaps because it has been reconfigured and is no longer
authoritative for those names), the RECONNECT DELAY MAY be zero,
indicating that the client SHOULD immediately attempt to re-establish
its operations. It is likely that some of the new attempts will be
successful and some will not.
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 RECONNECT delay 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).
Apart from the cases described above, a server MUST NOT close a
connection with a 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 server only closes a
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 server SHOULD send a Terminate Session
message informing the client of the reason for the connection being
closed, and allow the client five seconds to receive it before the
server resorts to forcibly aborting the connection.
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After a connection is closed by the server, the client SHOULD try to
reconnect, to that server, or to another suitable server, if more
than one is available. If reconnecting to the same server, the
client MUST respect the indicated delay before attempting to
reconnect.
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 sending a Terminate Session message, as described above.
Upon reception of the Termination TLV the client is expected to close
the connection, and if it does not then the server will abort the
connection five seconds later.
3.2. Connection Sharing
A client that supports Session Signaling SHOULD NOT make multiple
connections to the same DNS server.
A single server may support multiple services, including DNS Updates
[RFC2136], DNS Push Notifications [I-D.ietf-dnssd-push], and other
services, for one or more DNS zones. When a client discovers that
the target server for several different operations is the same target
hostname and port, the client SHOULD use a single shared connection
for all those operations. A client SHOULD NOT open multiple
connections to the same target host and port just because the names
being operated on are different or happen to fall within different
zones. This is to reduce unnecessary connection load on the DNS
server.
For the purposes here, the determination of "same server" is made by
comparing the target hostname and port of the desired DNS server, not
the IP address(es) that the target hostname resolves to. The
hostname and port of the desired DNS server in question may be
obtained via manual configuration, may be learned automatically from
"_dns-update-tls._tcp.<zone>" or "_dns-push-tls._tcp.<zone>" SRV
records, or may be learned by other means used by other protocols.
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 Updates and DNS
Push Notifications), and wishes to have clients use a single shared
connection for operations on that server, then the administrator MUST
specify the same target server hostname for all the desired zones
and/or roles, either in the appropriate manual configuration data
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(for clients that are configured manully) or in the appropriate SRV
records (for clients that learn configuration from the network).
However, server implementers and operators should be aware that even
when the same target hostname is correctly used, 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
coordinate with each other, so a DNS server MUST be prepared to
accept multiple connections from different source ports on the same
client IP address. This is undesirable from an efficiency
standpoint, but it may be unavoidable in some situations, so a DNS
server MUST be prepared to accept multiple connections from the same
client IP address.
Independent client devices behind the same NAT gateway will also
typically appear to the DNS server to be different source ports on
the same client IP address.
3.3. Message Format
A Session Signaling message begins with the first 4 octets of the
standard DNS message header [RFC1035], with the Opcode field set to
the Session Signaling Opcode. A Session Signaling message does not
contain the QDCOUNT, ANCOUNT, NSCOUNT and ARCOUNT fields fields used
in standard DNS queries and responses. This 4-octet header is
followed by a single Session Signaling operation TLV. The operation
TLV may be followed by one or more modifier TLVs, such as the
Terminate TLV (0), which, in error responses, indicates the time
interval during which the client SHOULD NOT re-attempt a failed
operation. Future specifications may define additional modifier TLVs
that may be used in addition to the operation TLV. A Session
Signaling message MUST contain exactly one operation TLV.
Since Session Signaling messages contain no ARCOUNT field, there is,
by design, no way to add an EDNS(0) option to a Session Signaling
message. If functionality provided by current or future EDNS(0)
options is desired for Session Signaling messages, a Session
Signaling operation TLV or modifier TLV needs to be defined to carry
the necessary information.
Similarly there is, by design, no way to add a TSIG record to a
Session Signaling message. If this capability becomes necessary in
the future a Session Signaling modifier TLV needs to be defined to
perform this function.
Note however that, while Session Signaling _messages_ cannot include
EDNS(0) or TSIG records, a Session Signaling _session_ is typically
used to carry a whole series of DNS messages of different kinds,
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including Session Signaling messages, and other DNS message types
like Query [RFC1034][RFC1035] and Update [RFC2136], and those
messages can carry EDNS(0) and TSIG records. This specification
explicitly prohibits use of the EDNS(0) TCP Keepalive Option
[RFC7828] in messages sent on a Session Signaling session (because it
duplicates the functionality provided by the Session Signaling Idle
Timeout TLV), but messages may contain other EDNS(0) options where
appropriate.
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 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ TLV-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
The MESSAGE ID, QR, Opcode and RCODE fields have their usual meanings
[RFC1035].
In a request message (QR=0) the RCODE is generally set to zero on
transmission, and silently ignored on reception, except where
specified otherwise (for example, the Terminate Session operation,
where the RCODE indicates the reason for termination).
The Z bits are currently unused, and in both requests and responses
the Z bits SHOULD be set to zero (0) on transmission and silently
ignored on reception, unless a future document specifies otherwise.
3.4. Message Handling
On a connection between a client and server that support Session
Signaling, once the client has sent at least one Session Signaling
message (or it is known in advance by other means that the client
supports Session Signaling) either end may unilaterally send Session
Signaling messages at any time, and therefore either client or server
may be the initiator of a message. The initiator MUST set the value
of the QR bit in the DNS header to zero (0), and the responder MUST
set it to one (1).
Every Session Signaling request message (QR=0) MUST elicit a response
(QR=1), which MUST have the same MESSAGE ID in the DNS message header
as in the corresponding request.
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An initiator MUST NOT reuse a MESSAGE ID that is already in use for
an outstanding request, unless specified otherwise by the relevant
specification for the Session Signaling TLV in question. At the very
least, this means that a MESSAGE ID MUST NOT be reused for a
particular SSOP-TYPE while the initiator is waiting for a response to
a previous request with the same SSOP-TYPE, unless specified
otherwise by the relevant specification for the Session Signaling TLV
in question. (For a long-lived operation, such as a DNS Push
Notification subscription [I-D.ietf-dnssd-push] the MESSAGE ID for
the operation MUST NOT be reused for a new subscription as long as
the existing subscription is active.)
The namespaces of 16-bit MESSAGE IDs are disjoint in each direction.
For example, it is _not_ an error for both client and server to send
a request message with the same ID. In effect, the 16-bit MESSAGE ID
combined with the identity of the initiator (client or server) serves
as a 17-bit unique identifier for a particular operation on a
session.
If a client or server receives a response (QR=1) where the MESSAGE ID
does not match any of its outstanding operations, this is a fatal
error and it MUST immediately terminate the connection with a TCP RST
(or equivalent for other protocols).
The RCODE value in a response may be one of the following values:
+------+------------+-----------------------------------------------+
| Code | Mnemonic | Description |
+------+------------+-----------------------------------------------+
| 0 | NOERROR | TLV processed successfully |
| | | |
| 1 | FORMERR | TLV format error |
| | | |
| 4 | NOTIMP | Session Signaling not supported |
| | | |
| 5 | REFUSED | TLV declined for policy reasons |
| | | |
| 11 | SSOPNOTIMP | Session Signaling operation Type Code not |
| | | supported |
+------+------------+-----------------------------------------------+
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3.5. TLV Format
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| SSOP-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| SSOP-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ SSOP-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
SSOP-TYPE: A 16 bit field in network order giving the type of the
current Session Signaling TLV per the IANA DNS Session Signaling
Type Codes Registry.
SSOP-LENGTH: A 16 bit field in network order giving the size in
octets of SSOP-DATA.
SSOP-DATA: Type-code specific.
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4. Idle Timeout TLV
The Idle Timeout TLV (1) is be used by a client to reset a
connection's idle timer, and at the same time to request what the
idle timeout should be from this point forward in the connection.
Once the client has sent at least one Session Signaling message (or
it is known in advance by other means that the client supports
Session Signaling) the Idle Timeout TLV also MAY be initiated by a
server, to unilaterally inform the client of a new idle timeout this
point forward in this connection.
It is not required that the Idle Timeout TLV be used in every
session. While many Session Signaling operations (such as DNS Push
Notifications [I-D.ietf-dnssd-push]) will be used in conjunction with
a long-lived connection, not all Session Signaling operations require
a long-lived connection, and in some cases the default 30-second
timeout may be perfectly appropriate.
The SSOP-DATA for the the Idle Timeout TLV is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IDLE TIMEOUT (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IDLE TIMEOUT: the idle timeout for the current session, specified as
a 32 bit word in network order in units of milliseconds. This is
the timeout at which the server will forcibly terminate the
connection with a TCP RST (or equivalent for other protocols);
after half this interval the client MUST take action to either
preserve the connection, or close it if it is no longer needed.
In a client-initiated Session Signaling Idle Timeout message, the
IDLE TIMEOUT contains the client's requested value for the idle
timeout. In a server response to a client-initiated message, the
IDLE TIMEOUT contains the server's chosen value for the idle timeout,
which the client MUST respect. This is modeled after the DHCP
protocol, where the client requests a certain lease lifetime using
DHCP option 51 [RFC2132], but the server is the ultimate authority
for deciding what lease lifetime is actually granted.
In a server-initiated Session Signaling Idle Timeout message, the
IDLE TIMEOUT unilaterally informs the client of the new idle timeout
this point forward in this connection. In a client response to a
server-initiated message, there is no SSOP-DATA. SSOP-LENGTH is
zero. The RCODE MUST be zero.
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<< SC: Do we even need a client response to this server-initiated
message? The response conveys no information. On the other hand, it
may simplify the specification if we say that _all_ request messages
elicit exactly one response message. Please weigh in with opinions.
We need to decide this. Currently draft-ietf-dnssd-push says that
push notification messages from server to client do not elicit any
response message from the client. We need to decide if this is
allowed. >>
Note that the lower the IDLE TIMEOUT value, the higher the load on
client and server. For example, an IDLE TIMEOUT value of 200ms would
result in a continuous stream of at least ten messages per second, in
both directions, to keep the connection alive. And, in this example,
a single packet loss and retransmission could introduce a momentary
pause in the stream of messages, long enough to cause the server to
overzealously abort the connection.
Because of this concern, the server MUST NOT send a Idle Timeout
message (either a response to a client-initiated request, or a
server-initiated message) with an IDLE TIMEOUT value less than ten
seconds. If a client receives an Idle Timeout message specifying an
IDLE TIMEOUT value less than ten seconds this is an error and the
client MUST immediately terminate the connection with a TCP RST (or
equivalent for other protocols).
The Idle Timeout TLV (1) has similar intent to the EDNS(0) TCP
Keepalive Option [RFC7828]. A client/server pair that supports
Session Signaling MUST NOT use the EDNS(0) TCP KeepAlive option
within any message on a connection once bi-directional Session
Signaling support has been confirmed. Once bi-directional Session
Signaling support has been confirmed, if either client or server
receives a DNS message over the session that contains an EDNS(0) TCP
KeepAlive option, this is an error and the receiver of the EDNS(0)
TCP KeepAlive option MUST immediately terminate the connection with a
TCP RST (or equivalent for other protocols).
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5. Terminate TLV
The Terminate TLV (0) is be used by a server to request that a client
close the connection, and not to reconnect for the indicated time
interval. It is also used as a modifier on error responses, to
indicate how long the client should wait before retrying that
particular operation.
<< SC: Perhaps we should change the name of TLV (0) to be "retry
delay" instead of "Terminate"? >>
The SSOP-DATA for the the Terminate TLV is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RECONNECT DELAY (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RECONNECT DELAY: a time value, specified as a 32 bit word in network
order in units of milliseconds, within which the client MUST NOT
establish a new session to the current server.
The RECOMMENDED value is 10 seconds.
In the case of a client request that returns a nonzero RCODE value,
the server MAY append a Terminate TLV (0) to the response, indicating
the time interval during which the client SHOULD NOT attempt this
operation again.
When appended to a DNS response message for some client request, the
Terminate TLV (0) is considered a modifier TLV. The indicated time
interval during which the client SHOULD NOT retry applies only to the
failed operation, not to the session as a whole.
When sent in a DNS request message, from server to client, the
Terminate Session TLV (0) is considered an operation TLV. It applies
to the session as a whole, and the client MUST close the connection,
as described previously. The RCODE MUST indicate the reason for the
termination. RCODE NOERROR indicates a routine shutdown. RCODE
SERVFAIL indicates that the server is overloaded due to resource
exhaustion. RCODE REFUSED indicates that the server has been
reconfigured and is no longer able to perform one of the functions
currently being performed on this connection (for example, a DNS Push
Notification server could be reconfigured such that is is no longer
accepting DNS Push Notification requests for one or more of the
currently subscribed names).
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This document specifies only these three RCODE values for Terminate
Session request. Servers sending Terminate Session requests SHOULD
use one of these three values. However, future circumstances may
create situations where other RCODE values are appropriate in
Terminate Session requests, so clients MUST be prepared to accept
Terminate Session requests with any RCODE value.
6. IANA Considerations
6.1. DNS Session Signaling Opcode Registration
IANA are directed to assign a value (tentatively 6) in the DNS
Opcodes Registry for the Session Signaling Opcode.
6.2. DNS Session Signaling RCODE Registration
IANA are directed to assign a value (tentatively 11) in the DNS RCODE
Registry for the SSOPNOTIMP error code.
6.3. DNS Session Signaling Type Codes Registry
IANA are directed to create the DNS Session Signaling Type Codes
Registry, with initial values as follows:
+-----------+--------------------------------+----------+-----------+
| Type | Name | Status | Reference |
+-----------+--------------------------------+----------+-----------+
| 0 | SSOP-Terminate | Standard | RFC-TBD |
| | | | |
| 1 | SSOP-IdleTimeout | Standard | RFC-TBD |
| | | | |
| 3 - 63 | Unassigned, reserved for | | |
| | session management TLVs | | |
| | | | |
| 64 - | Unassigned | | |
| 63487 | | | |
| | | | |
| 63488 - | Reserved for local / | | |
| 64511 | experimental use | | |
| | | | |
| 64512 - | Reserved for future expansion | | |
| 65535 | | | |
+-----------+--------------------------------+----------+-----------+
Registration of additional Session Signaling Type Codes requires
publication of an appropriate IETF "Standards Action" or "IESG
Approval" document [RFC5226].
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7. Security Considerations
If this mechanism is to be used with DNS over TLS, then these
messages are subject to the same constraints as any other DNS over
TLS messages and MUST NOT be sent in the clear before the TLS session
is established.
8. Acknowledgements
TBW
9. References
9.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
<http://www.rfc-editor.org/info/rfc2132>.
[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,
<http://www.rfc-editor.org/info/rfc2136>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>.
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[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,
<http://www.rfc-editor.org/info/rfc7766>.
[RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
edns-tcp-keepalive EDNS0 Option", RFC 7828,
DOI 10.17487/RFC7828, April 2016,
<http://www.rfc-editor.org/info/rfc7828>.
9.2. Informative References
[I-D.ietf-dnssd-push]
Pusateri, T. and S. Cheshire, "DNS Push Notifications",
draft-ietf-dnssd-push-08 (work in progress), July 2016.
[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, <http://www.rfc-editor.org/info/rfc7858>.
Authors' Addresses
Ray Bellis
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City CA 94063
USA
Phone: +1 650 423 1200
Email: ray@isc.org
Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino CA 95014
USA
Phone: +1 408 974 3207
Email: cheshire@apple.com
Bellis, et al. Expires May 4, 2017 [Page 18]
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John Dickinson
Sinodun Internet Technologies
Magadalen Centre
Oxford Science Park
Oxford OX4 4GA
United Kingdom
Email: jad@sinodun.com
Sara Dickinson
Sinodun Internet Technologies
Magadalen Centre
Oxford Science Park
Oxford OX4 4GA
United Kingdom
Email: sara@sinodun.com
Allison Mankin
Salesforce
Email: allison.mankin@gmail.com
Tom Pusateri
Unaffiliated
Phone: +1 843 473 7394
Email: pusateri@bangj.com
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