Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering
Obsoletes: RFC7242 (if approved) M. Demmer
Intended status: Standards Track UC Berkeley
Expires: May 31, 2017 J. Ott
Aalto University
S. Perreault
November 27, 2016
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-01
Abstract
This document describes a revised protocol for the TCP-based
convergence layer for Delay-Tolerant Networking (DTN). The protocol
revision is based on implementation issues in the original [RFC7242]
and updates to the Bundle Protocol contents, encodings, and
convergence layer requirements in [I-D.ietf-dtn-bpbis].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 May 31, 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
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 4
3. General Protocol Description . . . . . . . . . . . . . . . . 5
3.1. Bidirectional Use of TCPCL Sessions . . . . . . . . . . . 6
3.2. Example Message Exchange . . . . . . . . . . . . . . . . 6
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 7
4.1. Contact Header . . . . . . . . . . . . . . . . . . . . . 8
4.2. Validation and Parameter Negotiation . . . . . . . . . . 10
5. Established Session Operation . . . . . . . . . . . . . . . . 11
5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 11
5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 12
5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 12
5.2.2. Message Rejection (REJECT) . . . . . . . . . . . . . 13
5.3. Session Security . . . . . . . . . . . . . . . . . . . . 14
5.3.1. TLS Handshake Result . . . . . . . . . . . . . . . . 14
5.3.2. Example TLS Initiation . . . . . . . . . . . . . . . 15
5.4. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 15
5.4.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 16
5.4.2. Bundle Length (LENGTH) . . . . . . . . . . . . . . . 16
5.4.3. Bundle Data Transmission (DATA_SEGMENT) . . . . . . . 17
5.4.4. Bundle Acknowledgments (ACK_SEGMENT) . . . . . . . . 18
5.4.5. Bundle Refusal (REFUSE_BUNDLE) . . . . . . . . . . . 19
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 21
6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 21
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 25
8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 25
8.3. Message Types . . . . . . . . . . . . . . . . . . . . . . 26
8.4. REFUSE_BUNDLE Reason Codes . . . . . . . . . . . . . . . 26
8.5. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 27
8.6. REJECT Reason Codes . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
This document describes the TCP-based convergence-layer protocol for
Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to-
end architecture providing communications in and/or through highly
stressed environments, including those with intermittent
connectivity, long and/or variable delays, and high bit error rates.
More detailed descriptions of the rationale and capabilities of these
networks can be found in "Delay-Tolerant Network Architecture"
[RFC4838].
An important goal of the DTN architecture is to accommodate a wide
range of networking technologies and environments. The protocol used
for DTN communications is the revised Bundle Protocol (BP)
[I-D.ietf-dtn-bpbis], an application-layer protocol that is used to
construct a store-and- forward overlay network. As described in the
Bundle Protocol specification [I-D.ietf-dtn-bpbis], it requires the
services of a "convergence- layer adapter" (CLA) to send and receive
bundles using the service of some "native" link, network, or Internet
protocol. This document describes one such convergence-layer adapter
that uses the well-known Transmission Control Protocol (TCP). This
convergence layer is referred to as TCPCL.
The locations of the TCPCL and the BP in the Internet model protocol
stack are shown in Figure 1. In particular, when BP is using TCP as
its bearer with TCPCL as its convergence layer, both BP and TCPCL
reside at the application layer of the Internet model.
+-------------------------+
| DTN Application | -\
+-------------------------| |
| Bundle Protocol (BP) | -> Application Layer
+-------------------------+ |
| TCP Conv. Layer (TCPCL) | -/
+-------------------------+
| TLS (optional) | ---> Presentation Layer
+-------------------------+
| TCP | ---> Transport Layer
+-------------------------+
| IP | ---> Network Layer
+-------------------------+
| Link-Layer Protocol | ---> Link Layer
+-------------------------+
| Physical Medium | ---> Physical Layer
+-------------------------+
Figure 1: The Locations of the Bundle Protocol and the TCP
Convergence-Layer Protocol above the Internet Protocol Stack
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This document describes the format of the protocol data units passed
between entities participating in TCPCL communications. This
document does not address:
o The format of protocol data units of the Bundle Protocol, as those
are defined elsewhere in [RFC5050] and [I-D.ietf-dtn-bpbis]. This
includes the concept of bundle fragmentation or bundle
encapsulation. The TCPCL transfers bundles as opaque data blocks.
o Mechanisms for locating or identifying other bundle nodes within
an internet.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.1. Definitions Specific to the TCPCL Protocol
This section contains definitions that are interpreted to be specific
to the operation of the TCPCL protocol, as described below.
TCP Connection: A TCP connection refers to a transport connection
using TCP as the transport protocol.
TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a
TCPCL communication relationship between two bundle nodes. The
lifetime of a TCPCL session is bound to the lifetime of an
underlying TCP connection. Therefore, a TCPCL session is
initiated when a bundle node initiates a TCP connection to be
established for the purposes of bundle communication. A TCPCL
session is terminated when the TCP connection ends, due either to
one or both nodes actively terminating the TCP connection or due
to network errors causing a failure of the TCP connection. For
the remainder of this document, the term "session" without the
prefix "TCPCL" refer to a TCPCL session.
Session parameters: The session parameters are a set of values used
to affect the operation of the TCPCL for a given session. The
manner in which these parameters are conveyed to the bundle node
and thereby to the TCPCL is implementation dependent. However,
the mechanism by which two bundle nodes exchange and negotiate the
values to be used for a given session is described in Section 4.2.
Transmission: Transmission refers to the procedures and mechanisms
(described below) for conveyance of a bundle from one node to
another.
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3. General Protocol Description
The service of this protocol is the transmission of DTN bundles over
TCP. This document specifies the encapsulation of bundles,
procedures for TCP setup and teardown, and a set of messages and node
requirements. The general operation of the protocol is as follows.
First, one node establishes a TCPCL session to the other by
initiating a TCP connection. After setup of the TCP connection is
complete, an initial contact header is exchanged in both directions
to set parameters of the TCPCL session and exchange a singleton
endpoint identifier for each node (not the singleton Endpoint
Identifier (EID) of any application running on the node) to denote
the bundle-layer identity of each DTN node. This is used to assist
in routing and forwarding messages, e.g., to prevent loops.
Once the TCPCL session is established and configured in this way,
bundles can be transferred in either direction. Each transfer is
performed in one or more logical segments of data. Each logical data
segment consists of a DATA_SEGMENT message header, a count of the
length of the segment, and finally the octet range of the bundle
data. The choice of the length to use for segments is an
implementation matter (but must be within the Segment MRU size of
Section 4.1). The first segment for a bundle MUST set the 'start'
flag, and the last one MUST set the 'end' flag in the DATA_SEGMENT
message header.
If multiple bundles are transmitted on a single TCPCL connection,
they MUST be transmitted consecutively. Interleaving data segments
from different bundles is not allowed. Bundle interleaving can be
accomplished by fragmentation at the BP layer or by establishing
multiple TCPCL sessions.
A feature of this protocol is for the receiving node to send
acknowledgments as bundle data segments arrive (ACK_SEGMENT). The
rationale behind these acknowledgments is to enable the sender node
to determine how much of the bundle has been received, so that in
case the session is interrupted, it can perform reactive
fragmentation to avoid re-sending the already transmitted part of the
bundle. For each data segment that is received, the receiving node
sends an ACK_SEGMENT code followed by an count containing the
cumulative length of the bundle that has been received. The sending
node MAY transmit multiple DATA_SEGMENT messages without necessarily
waiting for the corresponding ACK_SEGMENT responses. This enables
pipelining of messages on a channel. In addition, there is no
explicit flow control on the TCPCL layer.
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Another feature is that a receiver MAY interrupt the transmission of
a bundle at any point in time by replying with a REFUSE_BUNDLE
message, which causes the sender to stop transmission of the current
bundle, after completing transmission of a partially sent data
segment. Note: This enables a cross-layer optimization in that it
allows a receiver that detects that it already has received a certain
bundle to interrupt transmission as early as possible and thus save
transmission capacity for other bundles.
For sessions that are idle, a KEEPALIVE message is sent at a
negotiated interval. This is used to convey liveness information.
Finally, before sessions close, a SHUTDOWN message is sent to the
session peer. After sending a SHUTDOWN message, the sender of this
message MAY send further acknowledgments (ACK_SEGMENT or
REFUSE_BUNDLE) but no further data messages (DATA_SEGMENT). A
SHUTDOWN message MAY also be used to refuse a session setup by a
peer.
3.1. Bidirectional Use of TCPCL Sessions
There are specific messages for sending and receiving operations (in
addition to session setup/teardown). TCPCL is symmetric, i.e., both
sides can start sending data segments in a session, and one side's
bundle transfer does not have to complete before the other side can
start sending data segments on its own. Hence, the protocol allows
for a bi-directional mode of communication.
Note that in the case of concurrent bidirectional transmission,
acknowledgment segments MAY be interleaved with data segments.
3.2. Example Message Exchange
The following figure visually depicts the protocol exchange for a
simple session, showing the session establishment and the
transmission of a single bundle split into three data segments (of
lengths L1, L2, and L3) from Node A to Node B.
Note that the sending node MAY transmit multiple DATA_SEGMENT
messages without necessarily waiting for the corresponding
ACK_SEGMENT responses. This enables pipelining of messages on a
channel. Although this example only demonstrates a single bundle
transmission, it is also possible to pipeline multiple DATA_SEGMENT
messages for different bundles without necessarily waiting for
ACK_SEGMENT messages to be returned for each one. However,
interleaving data segments from different bundles is not allowed.
No errors or rejections are shown in this example.
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Node A Node B
====== ======
+-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+
+-------------------------+
| LENGTH | ->
| Transfer ID [I1] |
| Total Length [L1] |
+-------------------------+
+-------------------------+
| DATA_SEGMENT (start) | ->
| Transfer ID [I1] |
| Length [L1] |
| Bundle Data 0..(L1-1) |
+-------------------------+
+-------------------------+ +-------------------------+
| DATA_SEGMENT | -> <- | ACK_SEGMENT (start) |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L2] | | Length [L1] |
|Bundle Data L1..(L1+L2-1)| +-------------------------+
+-------------------------+
+-------------------------+ +-------------------------+
| DATA_SEGMENT (end) | -> <- | ACK_SEGMENT |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L3] | | Length [L1+L2] |
|Bundle Data | +-------------------------+
| (L1+L2)..(L1+L2+L3-1)|
+-------------------------+
+-------------------------+
<- | ACK_SEGMENT (end) |
| Transfer ID [I1] |
| Length [L1+L2+L3] |
+-------------------------+
+-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN |
+-------------------------+ +-------------------------+
Figure 2: A Simple Visual Example of the Flow of Protocol Messages on
a Single TCP Session between Two Nodes (A and B)
4. Session Establishment
For bundle transmissions to occur using the TCPCL, a TCPCL session
MUST first be established between communicating nodes. It is up to
the implementation to decide how and when session setup is triggered.
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For example, some sessions MAY be opened proactively and maintained
for as long as is possible given the network conditions, while other
sessions MAY be opened only when there is a bundle that is queued for
transmission and the routing algorithm selects a certain next-hop
node.
To establish a TCPCL session, a node MUST first establish a TCP
connection with the intended peer node, typically by using the
services provided by the operating system. Port number 4556 has been
assigned by IANA as the well-known port number for the TCP
convergence layer. Other port numbers MAY be used per local
configuration. Determining a peer's port number (if different from
the well-known TCPCL port) is up to the implementation.
If the node is unable to establish a TCP connection for any reason,
then it is an implementation matter to determine how to handle the
connection failure. A node MAY decide to re-attempt to establish the
connection. If it does so, it MUST NOT overwhelm its target with
repeated connection attempts. Therefore, the node MUST retry the
connection setup only after some delay (a 1-second minimum is
RECOMMENDED), and it SHOULD use a (binary) exponential backoff
mechanism to increase this delay in case of repeated failures. In
case a SHUTDOWN message specifying a reconnection delay is received,
that delay is used as the initial delay. The default initial delay
SHOULD be at least 1 second but SHOULD be configurable since it will
be application and network type dependent.
The node MAY declare failure after one or more connection attempts
and MAY attempt to find an alternate route for bundle data. Such
decisions are up to the higher layer (i.e., the BP).
Once a TCP connection is established, each node MUST immediately
transmit a contact header over the TCP connection. The format of the
contact header is described in Section 4.1.
Upon receipt of the contact header, both nodes perform the validation
and negotiation procedures defined in Section 4.2
After receiving the contact header from the other node, either node
MAY also refuse the session by sending a SHUTDOWN message. If
session setup is refused, a reason MUST be included in the SHUTDOWN
message.
4.1. Contact Header
Once a TCP connection is established, both parties exchange a contact
header. This section describes the format of the contact header and
the meaning of its fields.
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The format for the Contact Header 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
+---------------+---------------+---------------+---------------+
| magic='dtn!' |
+---------------+---------------+---------------+---------------+
| Version | Flags | Keepalive Interval |
+---------------+---------------+---------------+---------------+
| Segment MRU... |
+---------------+---------------+---------------+---------------+
| contd. |
+---------------+---------------+---------------+---------------+
| Transfer MRU... |
+---------------+---------------+---------------+---------------+
| contd. |
+---------------+---------------+---------------+---------------+
| EID Length | EID Data... |
+---------------+---------------+---------------+---------------+
| contd. |
+---------------+---------------+---------------+---------------+
Figure 3: Contact Header Format
The fields of the contact header are:
magic: A four-octet field that always contains the octet sequence
0x64 0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII (and
UTF-8).
Version: A one-octet field value containing the value 4 (current
version of the protocol).
Flags: A one-octet field of single-bit flags, interpreted according
to the descriptions in Table 1.
Keepalive Interval: A 16-bit unsigned integer indicating the longest
allowable interval in seconds between KEEPALIVE messages received
in this session.
Segment MRU: A 64-bit unsigned integer indicating the largest
allowable single-segment data payload size to be received in this
session. Any DATA_SEGMENT sent to this peer SHALL have a data
payload no longer than the peer's Segment MRU. The two endpoints
of a single session MAY have different Segment MRUs, and no
relation between the two is required.
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Transfer MRU: A 64-bit unsigned integer indicating the largest
allowable total-bundle data size to be received in this session.
Any bundle transfer sent to this peer SHALL have a Total bundle
data payload no longer than the peer's Transfer MRU. This value
can be used to perform proactive bundle fragmentation. The two
endpoints of a single session MAY have different Transfer MRUs,
and no relation between the two is required.
EID Length and EID Data: Together these fields represent a variable-
length text string. The EID Length is a 16-bit unsigned integer
indicating the number of octets of EID Data to follow. A zero EID
Length is a special case which indicates the lack of EID rather
than a truly empty EID. A non-zero-length EID Data contains the
UTF-8 encoded EID of some singleton endpoint in which the sending
node is a member, in the canonical format of <scheme
name>:<scheme-specific part>.
+---------+------+--------------------------------------------------+
| Type | Code | Description |
+---------+------+--------------------------------------------------+
| CAN_TLS | 0x01 | If bit is set, indicates that the sending peer |
| | | is capable of TLS security. |
+---------+------+--------------------------------------------------+
Table 1: Contact Header Flags
4.2. Validation and Parameter Negotiation
Upon reception of the contact header, each node follows the following
procedures to ensure the validity of the TCPCL session and to
negotiate values for the session parameters.
If the magic string is not present or is not valid, the connection
MUST be terminated. The intent of the magic string is to provide
some protection against an inadvertent TCP connection by a different
protocol than the one described in this document. To prevent a flood
of repeated connections from a misconfigured application, a node MAY
elect to hold an invalid connection open and idle for some time
before closing it.
If a node receives a contact header containing a version that is
greater than the current version of the protocol that the node
implements, then the node SHALL shutdown the session with a reason
code of "Version mismatch". If a node receives a contact header with
a version that is lower than the version of the protocol that the
node implements, the node MAY either terminate the session (with a
reason code of "Version mismatch"). Otherwise, the node MAY adapt
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its operation to conform to the older version of the protocol. This
decision is an implementation matter.
A node calculates the parameters for a TCPCL session by negotiating
the values from its own preferences (conveyed by the contact header
it sent to the peer) with the preferences of the peer node (expressed
in the contact header that it received from the peer). The
negotatiated parameters defined by this specification are described
in the following paragraphs.
Session Keepalive: Negotiation of the Session Keepalive parameter is
performed by taking the minimum of this two contact headers'
Keepalive Interval. If the negotiated Session Keepalive is zero
(i.e. one or both contact headers contains a zero Keepalive
Interval), then the keepalive feature (described in Section 5.2.1)
is disabled.
Enable TLS: Negotiation of the Enable TLS parameter is performed by
taking the logical AND of the two contact headers' CAN_TLS flags.
If the negotiated Enable TLS value is true then TLS negotiation
feature (described in Section 5.3) begins immediately following
the contact header exchange.
Once this process of parameter negotiation is completed, the protocol
defines no additional mechanism to change the parameters of an
established session; to effect such a change, the session MUST be
terminated and a new session established.
5. Established Session Operation
This section describes the protocol operation for the duration of an
established session, including the mechanism for transmitting bundles
over the session.
5.1. Message Type Codes
After the initial exchange of a contact header, all messages
transmitted over the session are identified by a one-octet header
with the following structure:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| type | flags |
+-+-+-+-+-+-+-+-+
Figure 4: Format of the One-Octet Message Header
type: Indicates the type of the message as per Table 2 below.
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flags: Optional flags defined based on message type.
The types and values for the message type code are as follows.
+---------------+------+--------------------------------------------+
| Type | Code | Description |
+---------------+------+--------------------------------------------+
| DATA_SEGMENT | 0x1 | Indicates the transmission of a segment of |
| | | bundle data, as described in Section |
| | | 5.4.3. |
| | | |
| ACK_SEGMENT | 0x2 | Acknowledges reception of a data segment, |
| | | as described in Section 5.4.4. |
| | | |
| REFUSE_BUNDLE | 0x3 | Indicates that the transmission of the |
| | | current bundle SHALL be stopped, as |
| | | described in Section 5.4.5. |
| | | |
| KEEPALIVE | 0x4 | KEEPALIVE message for the session, as |
| | | described in Section 5.2.1. |
| | | |
| SHUTDOWN | 0x5 | Indicates that one of the nodes |
| | | participating in the session wishes to |
| | | cleanly terminate the session, as |
| | | described in Section 6. |
| | | |
| LENGTH | 0x6 | Contains the length (in octets) of the |
| | | next bundle, as described in Section |
| | | 5.4.2. |
| | | |
| REJECT | TBD | Contains a TCPCL message rejection, as |
| | | described in Section 5.2.2. |
+---------------+------+--------------------------------------------+
Table 2: TCPCL Message Types
5.2. Upkeep and Status Messages
5.2.1. Session Upkeep (KEEPALIVE)
The protocol includes a provision for transmission of KEEPALIVE
messages over the TCPCL session to help determine if the underlying
TCP connection has been disrupted.
As described in Section 4.1, one of the parameters in the contact
header is the Keepalive Interval. Both sides populate this field
with their requested intervals (in seconds) between KEEPALIVE
messages.
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The format of a KEEPALIVE message is a one-octet message type code of
KEEPALIVE (as described in Table 2) with no additional data. Both
sides SHOULD send a KEEPALIVE message whenever the negotiated
interval has elapsed with no transmission of any message (KEEPALIVE
or other).
If no message (KEEPALIVE or other) has been received for at least
twice the Keepalive Interval, then either party MAY terminate the
session by transmitting a one-octet SHUTDOWN message (as described in
Table 2, with reason code "Idle Timeout") and by closing the session.
Note: The Keepalive Interval SHOULD not be chosen too short as TCP
retransmissions MAY occur in case of packet loss. Those will have to
be triggered by a timeout (TCP retransmission timeout (RTO)), which
is dependent on the measured RTT for the TCP connection so that
KEEPALIVE messages MAY experience noticeable latency.
5.2.2. Message Rejection (REJECT)
If a TCPCL endpoint receives a message which is unknown to it
(possibly due to an unhandled protocol mismatch) or is inappropriate
for the current session state (e.g. a KEEPALIVE message received
after contact header negotation has disabled that feature), there is
a protocol-level message to signal this condition in the form of a
REJECT reply.
The format of a REJECT message follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Reason Code (U8) |
+-----------------------------+
| Rejected Message Header |
+-----------------------------+
Figure 5: Format of REJECT Messages
The Rejected Message Header is a copy of the Message Header to which
the REJECT message is sent as a response. The REJECT Reason Code is
an 8-bit unsigned integer and indicates why the REJECT itself was
sent. The specified values of the reason code are:
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+-------------+------+----------------------------------------------+
| Name | Code | Description |
+-------------+------+----------------------------------------------+
| Message | 0x01 | A message was received with a Message Type |
| Type | | code unknown to the TCPCL endpoint. |
| Unknown | | |
| | | |
| Message | 0x02 | A message was received but the TCPCL |
| Unsupported | | endpoint cannot comply with the message |
| | | contents. |
| | | |
| Message | 0x03 | A message was received while the session is |
| Unexpected | | in a state in which the message is not |
| | | expected. |
+-------------+------+----------------------------------------------+
Table 3: REJECT Reason Codes
5.3. Session Security
This version of the TCPCL supports establishing a session-level
Transport Layer Security (TLS) session within an existing TCPCL
session. Negotation of whether or not to initiate TLS within TCPCL
session is part of the contact header as described in Section 4.2.
When TLS is used within the TCPCL it affects the entire session. By
convention, this protocol uses the endpoint which initiated the
underlying TCP connection as the "client" role of the TLS handshake
request. Once a TLS session is established within TCPCL, there is no
mechanism provided to end the TLS session and downgrade the session.
If a non-TLS session is desired after a TLS session is started then
the entire TCPCL session MUST be shutdown first.
After negotiating an Enable TLS parameter of true, and before any
other TCPCL messages are sent within the session, the session
endpoints SHALL begin a TLS handshake in accordance with [RFC5246].
The parameters within each TLS negotation are implementation
dependent but any TCPCL endpoint SHOULD follow all recommended best
practices of [RFC7525].
5.3.1. TLS Handshake Result
If a TLS handshake cannot negotiate a TLS session, both endpoints of
the TCPCL session SHALL cause a TCPCL shutdown with reason "TLS
negotiation failed".
After a TLS session is successfuly established, both TCPCL endpoints
SHALL re-exchange TCPCL Contact Header messages. Any information
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cached from the prior Contact Header exchange SHALL be discarded.
This re-exchange avoids man-in-the-middle attack in identical fashion
to [RFC2595].
5.3.2. Example TLS Initiation
A summary of a typical CAN_TLS usage is shown in the sequence in
Figure 6 below.
Node A Node B
====== ======
+-------------------------+
| Open TCP Connnection | ->
+-------------------------+ +-------------------------+
<- | Accept Connection |
+-------------------------+
+-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| TLS Negotiation | -> <- | TLS Negotiation |
| (as client) | | (as server) |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+
... secured TCPCL messaging ...
+-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN |
+-------------------------+ +-------------------------+
Figure 6: A simple visual example of TCPCL TLS Establishment between
two nodes
5.4. Bundle Transfer
All of the message in this section are directly associated with
tranfering a bundle between TCPCL endpoints.
A single TCPCL transfer results in a bundle (handled by the
convergence layer as opaque data) being exchanged from one endpoint
to the other. In TCPCL a transfer is accomplished by dividing a
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single bundle up into "segments" based on the receving-side Segment
MRU (see Section 4.1).
A single transfer (and by extension a single segment) SHALL NOT
contain data of more than a single bundle. This requirement is
imposed on the agent using the TCPCL rather than TCPCL itself.
5.4.1. Bundle Transfer ID
Each of the bundle transfer messages contains a Transfer ID number
which is used to correlate messages originating from sender and
receiver of a bundle. A Transfer ID does not attempt to address
uniqueness of the bundle data itself and has no relation to concepts
such as bundle fragmentation. Each invocation of TCPCL by the bundle
protocol agent, requesting transmission of a bundle (fragmentary or
otherwise), results in the initiation of a single TCPCL transfer.
Each transfer entails the sending of a LENGTH message and some number
of DATA_SEGMENT and ACK_SEGMENT messages; all are correlated by the
same Transfer ID.
Transfer IDs from each endpoint SHALL be unique within a single TCPCL
session. The initial Transfer ID from each endpoint SHALL have value
zero. Subsequent Transfer ID values SHALL be incremented from the
prior Transfer ID value by one. Upon exhaustion of the entire 64-bit
Transfer ID space, the sending endpoint SHALL terminate the session
with SHUTDOWN reason code "Resource Exhaustion".
For bidirectional bundle transfers, a TCPCL endpoint SHOULD NOT rely
on any relation between Transfer IDs originating from each side of
the TCPCL session.
5.4.2. Bundle Length (LENGTH)
The LENGTH message contains the total length, in octets, of the
bundle data in the associated transfer. The total length is
formatted as a 64-bit unsigned integer.
The purpose of the LENGTH message is to allow nodes to preemptively
refuse bundles that would exceed their resources or to prepare
storage on the receiving node for the upcoming bundle data. See
Section 5.4.5 for details on when refusal based on LENGTH content is
acceptable.
The Total Bundle Length field within a LENGTH message SHALL be used
as informative data by the receiver. If, for whatever reason, the
actual total length of bundle data received differs from the value
indicated by the LENGTH message, the receiver SHOULD accept the full
set of bundle data as valid.
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The format of the LENGTH message is as follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
| Total bundle length (U64) |
+-----------------------------+
Figure 7: Format of LENGTH Messages
LENGTH messages SHALL be sent immediately before transmission of any
DATA_SEGMENT messages. LENGTH messages MUST NOT be sent unless the
next DATA_SEGMENT message has the 'S' bit set to "1" (i.e., just
before the start of a new transfer).
A receiver MAY send a BUNDLE_REFUSE message as soon as it receives a
LENGTH message without waiting for the next DATA_SEGMENT message.
The sender MUST be prepared for this and MUST associate the refusal
with the correct bundle via the Transfer ID fields.
Upon reception of a LENGTH message not immediately before the start
of a starting DATA_SEGMENT the reciever SHALL send a REJECT message
with a Reason Code of "Message Unexpected".
5.4.3. Bundle Data Transmission (DATA_SEGMENT)
Each bundle is transmitted in one or more data segments. The format
of a DATA_SEGMENT message follows in Figure 8 and its use of header
flags is shown in Figure 9.
+------------------------------+
| Message Header |
+------------------------------+
| Transfer ID (U64) |
+------------------------------+
| Data length (U64) |
+------------------------------+
| Data contents (octet string) |
+------------------------------+
Figure 8: Format of DATA_SEGMENT Messages
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4 5 6 7
+-+-+-+-+
|0|0|S|E|
+-+-+-+-+
Figure 9: Format of DATA_SEGMENT Header flags
The flags portion of the message header octet contains two optional
values in the two low-order bits, denoted 'S' and 'E' in Figure 9.
The 'S' bit MUST be set to one if it precedes the transmission of the
first segment of a transfer. The 'E' bit MUST be set to one when
transmitting the last segment of a transfer. In the case where an
entire transfer is accomplished in a single segment, both the 'S' and
'E' bits MUST be set to one.
Following the message header, the length field is a 64-bit unsigned
integer containing the number of octets of bundle data that are
transmitted in this segment. Following the length are the actual
data contents.
Once a transfer of a bundle has commenced, the node MUST only send
segments containing sequential portions of that bundle until it sends
a segment with the 'E' bit set. No interleaving of multiple
transfers from the same endpoint is possible (within a single TCPCL
session).
5.4.4. Bundle Acknowledgments (ACK_SEGMENT)
Although the TCP transport provides reliable transfer of data between
transport peers, the typical BSD sockets interface provides no means
to inform a sending application of when the receiving application has
processed some amount of transmitted data. Thus, after transmitting
some data, a Bundle Protocol agent needs an additional mechanism to
determine whether the receiving agent has successfully received the
segment. To this end, the TCPCL protocol provides feedback messaging
whereby a receiving node transmits acknowledgments of reception of
data segments.
The format of an ACK_SEGMENT message follows in Figure 10 and its use
of header flags is the same as for DATA_SEGMENT (shown in Figure 9).
The flags of an ACK_SEGMENT message SHALL be identical to the flags
of the DATA_SEGMENT message for which it is a reply.
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+-----------------------------+
| Message Header |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
| Acknowledged length (U64) |
+-----------------------------+
Figure 10: Format of ACK_SEGMENT Messages
A receving TCPCL endpoing SHALL send an ACK_SEGMENT message in
response to each received DATA_SEGMENT message. The flags portion of
the ACK_SEGMENT header SHALL be set to match the corresponding
DATA_SEGEMNT message being acknowledged. The acknowledged length of
each ACK_SEGMENT contains the sum of the data length fields of all
DATA_SEGMENT messages received so far in the course of the indicated
transfer.
For example, suppose the sending node transmits four segments of
bundle data with lengths 100, 200, 500, and 1000, respectively.
After receiving the first segment, the node sends an acknowledgment
of length 100. After the second segment is received, the node sends
an acknowledgment of length 300. The third and fourth
acknowledgments are of length 800 and 1800, respectively.
5.4.5. Bundle Refusal (REFUSE_BUNDLE)
As bundles can be large, the TCPCL supports an optional mechanism by
which a receiving node MAY indicate to the sender that it does not
want to receive the corresponding bundle.
To do so, upon receiving a LENGTH or DATA_SEGMENT message, the node
MAY transmit a REFUSE_BUNDLE message. As data segments and
acknowledgments MAY cross on the wire, the bundle that is being
refused SHALL be identified by the Transfer ID of the refusal.
There is no required relation between the Transfer MRU of a TCPCL
endpoint (which is supposed to represent a firm limitation of what
the endpoint will accept) and sending of a REFUSE_BUNDLE message. A
REFUSE_BUNDLE can be used in cases where the agent's bundle storage
is temporarily depleted or somehow constrained. A REFUSE_BUNDLE can
also be used after the bundle header or any bundle data is inspected
by an agent and determined to be unacceptable.
The format of the REFUSE_BUNDLE message is as follows:
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+-----------------------------+
| Message Header |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
Figure 11: Format of REFUSE_BUNDLE Messages
4 5 6 7
+-+-+-+-+
| RCode |
+-+-+-+-+
Figure 12: Format of REFUSE_BUNDLE Header flags
The RCode field, which stands for "reason code", contains a value
indicating why the bundle was refused. The following table contains
semantics for some values. Other values MAY be registered with IANA,
as defined in Section 8.
+------------+-------+----------------------------------------------+
| Name | RCode | Semantics |
+------------+-------+----------------------------------------------+
| Unknown | 0x0 | Reason for refusal is unknown or not |
| | | specified. |
| | | |
| Completed | 0x1 | The receiver now has the complete bundle. |
| | | The sender MAY now consider the bundle as |
| | | completely received. |
| | | |
| No | 0x2 | The receiver's resources are exhausted. The |
| Resources | | sender SHOULD apply reactive bundle |
| | | fragmentation before retrying. |
| | | |
| Retransmit | 0x3 | The receiver has encountered a problem that |
| | | requires the bundle to be retransmitted in |
| | | its entirety. |
+------------+-------+----------------------------------------------+
Table 4: REFUSE_BUNDLE Reason Codes
The receiver MUST, for each transfer preceding the one to be refused,
have either acknowledged all DATA_SEGMENTs or refused the bundle
transfer.
The bundle transfer refusal MAY be sent before an entire data segment
is received. If a sender receives a REFUSE_BUNDLE message, the
sender MUST complete the transmission of any partially sent
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DATA_SEGMENT message. There is no way to interrupt an individual
TCPCL message partway through sending it. The sender MUST NOT
commence transmission of any further segments of the refused bundle
subsequently. Note, however, that this requirement does not ensure
that a node will not receive another DATA_SEGMENT for the same bundle
after transmitting a REFUSE_BUNDLE message since messages MAY cross
on the wire; if this happens, subsequent segments of the bundle
SHOULD also be refused with a REFUSE_BUNDLE message.
Note: If a bundle transmission is aborted in this way, the receiver
MAY not receive a segment with the 'E' flag set to '1' for the
aborted bundle. The beginning of the next bundle is identified by
the 'S' bit set to '1', indicating the start of a new transfer, and
with a distinct Transfer ID value.
6. Session Termination
This section describes the procedures for ending a TCPCL session.
6.1. Shutdown Message (SHUTDOWN)
To cleanly shut down a session, a SHUTDOWN message MUST be
transmitted by either node at any point following complete
transmission of any other message. A receiving node SHOULD
acknowledge all received data segments before sending a SHUTDOWN
message to end the session. A transmitting node SHALL treat a
SHUTDOWN message received mid-transfer (i.e. before the final
acknowledgement) as a failure of the transfer.
The format of the SHUTDOWN message is as follows:
+-----------------------------------+
| Message Header |
+-----------------------------------+
| Reason Code (optional U8) |
+-----------------------------------+
| Reconnection Delay (optional U16) |
+-----------------------------------+
Figure 13: Format of SHUTDOWN Messages
4 5 6 7
+-+-+-+-+
|0|0|R|D|
+-+-+-+-+
Figure 14: Format of SHUTDOWN Header flags
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It is possible for a node to convey additional information regarding
the reason for session termination. To do so, the node MUST set the
'R' bit in the message header flags and transmit a one-octet reason
code immediately following the message header. The specified values
of the reason code are:
+--------------+------+---------------------------------------------+
| Name | Code | Description |
+--------------+------+---------------------------------------------+
| Idle timeout | 0x00 | The session is being closed due to |
| | | idleness. |
| | | |
| Version | 0x01 | The node cannot conform to the specified |
| mismatch | | TCPCL protocol version. |
| | | |
| Busy | 0x02 | The node is too busy to handle the current |
| | | session. |
| | | |
| Contact | 0x03 | The node cannot interpret or negotiate |
| Failure | | contact header option. |
| | | |
| TLS failure | 0x04 | The node failed to negotiate TLS session |
| | | and cannot continue the session. |
| | | |
| Resource | 0x05 | The node has run into some resoure limit |
| Exhaustion | | and cannot continue the session. |
+--------------+------+---------------------------------------------+
Table 5: SHUTDOWN Reason Codes
It is also possible to convey a requested reconnection delay to
indicate how long the other node MUST wait before attempting session
re-establishment. To do so, the node sets the 'D' bit in the message
header flags and then transmits an 16-bit unsigned integer specifying
the requested delay, in seconds, following the message header (and
optionally, the SHUTDOWN reason code). The value 0 SHALL be
interpreted as an infinite delay, i.e., that the connecting node MUST
NOT re-establish the session. In contrast, if the node does not wish
to request a delay, it SHOULD omit the reconnection delay field (and
set the 'D' bit to zero).
A session shutdown MAY occur immediately after TCP connection
establishment or reception of a contact header (and prior to any
further data exchange). This MAY, for example, be used to notify
that the node is currently not able or willing to communicate.
However, a node MUST always send the contact header to its peer
before sending a SHUTDOWN message.
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If either node terminates a session prematurely in this manner, it
SHOULD send a SHUTDOWN message and MUST indicate a reason code unless
the incoming connection did not include the magic string. If the
magic string was not present, a node SHOULD close the TCP connection
without sending a SHUTDOWN message. If a node does not want its peer
to reopen a connection immediately, it SHOULD set the 'D' bit in the
flags and include a reconnection delay to indicate when the peer is
allowed to attempt another session setup.
If a session is to be terminated before another protocol message has
completed being sent, then the node MUST NOT transmit the SHUTDOWN
message but still SHOULD close the TCP connection. This means that a
SHUTDOWN cannot be used to preempt any other TCPCL messaging in-
progress (particularly important when large segment sizes are being
transmitted).
6.2. Idle Session Shutdown
The protocol includes a provision for clean shutdown of idle
sessions. Determining the length of time to wait before closing idle
sessions, if they are to be closed at all, is an implementation and
configuration matter.
If there is a configured time to close idle links and if no bundle
data (other than KEEPALIVE messages) has been received for at least
that amount of time, then either node MAY terminate the session by
transmitting a SHUTDOWN message indicating the reason code of 'Idle
timeout' (as described in Table 5). After receiving a SHUTDOWN
message in response, both sides MAY close the TCP connection.
7. Security Considerations
One security consideration for this protocol relates to the fact that
nodes present their endpoint identifier as part of the contact header
exchange. It would be possible for a node to fake this value and
present the identity of a singleton endpoint in which the node is not
a member, essentially masquerading as another DTN node. If this
identifier is used outside of a TLS-secured session or without
further verification as a means to determine which bundles are
transmitted over the session, then the node that has falsified its
identity would be able to obtain bundles that it otherwise would not
have. Therefore, a node SHALL NOT use the EID value of an unsecured
contact header to derive a peer node's identity unless it can
corroborate it via other means. When TCPCL session security is
mandatory, an endpoint SHALL transmit initial unsecured contact
header values indicated in Table 6 in order. These values avoid
unnecessarily leaking endpoing parameters and will be ignored when
secure contact header re-exchange occurs.
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+--------------------+---------------------------------------------+
| Parameter | Value |
+--------------------+---------------------------------------------+
| Flags | The USE_TLS flag is set. |
| | |
| Keepalive Interval | Zero, indicating no keepalive. |
| | |
| Segment MRU | Zero, indicating all segments are refused. |
| | |
| Transfer MRU | Zero, indicating all transfers are refused. |
| | |
| EID | Empty, indating lack of EID. |
+--------------------+---------------------------------------------+
Table 6: Recommended Unsecured Contact Header
TCPCL can be used to provide point-to-point transport security, but
does not provide security of data-at-rest and does not guarantee end-
to-end bundle security. The mechanisms defined in [RFC6257] and
[I-D.ietf-dtn-bpsec] are to be used instead.
Even when using TLS to secure the TCPCL session, the actual
ciphersuite negotiated between the TLS peers MAY be insecure. TLS
can be used to perform authentication without data confidentiality,
for example. It is up to security policies within each TCPCL node to
ensure that the negotiated TLS ciphersuite meets transport security
requirements. This is identical behavior to STARTTLS use in
[RFC2595].
Another consideration for this protocol relates to denial-of-service
attacks. A node MAY send a large amount of data over a TCPCL
session, requiring the receiving node to handle the data, attempt to
stop the flood of data by sending a REFUSE_BUNDLE message, or
forcibly terminate the session. This burden could cause denial of
service on other, well-behaving sessions. There is also nothing to
prevent a malicious node from continually establishing sessions and
repeatedly trying to send copious amounts of bundle data. A
listening node MAY take countermeasures such as ignoring TCP SYN
messages, closing TCP connections as soon as they are established,
waiting before sending the contact header, sending a SHUTDOWN message
quickly or with a delay, etc.
8. IANA Considerations
In this section, registration procedures are as defined in [RFC5226]
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8.1. Port Number
Port number 4556 has been previously assigned as the default port for
the TCP convergence layer in [RFC7242]. This assignment is unchanged
by protocol version 4.
+------------------------+-------------------------------------+
| Parameter | Value |
+------------------------+-------------------------------------+
| Service Name: | dtn-bundle |
| | |
| Transport Protocol(s): | TCP |
| | |
| Assignee: | Simon Perreault <simon@per.reau.lt> |
| | |
| Contact: | Simon Perreault <simon@per.reau.lt> |
| | |
| Description: | DTN Bundle TCP CL Protocol |
| | |
| Reference: | [RFC7242] |
| | |
| Port Number: | 4556 |
+------------------------+-------------------------------------+
8.2. Protocol Versions
IANA has created, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version
Numbers" and initialized it with the following table. The
registration procedure is RFC Required.
+-------+-------------+---------------------+
| Value | Description | Reference |
+-------+-------------+---------------------+
| 0 | Reserved | [RFC7242] |
| | | |
| 1 | Reserved | [RFC7242] |
| | | |
| 2 | Reserved | [RFC7242] |
| | | |
| 3 | TCPCL | [RFC7242] |
| | | |
| 4 | TCPCLbis | This specification. |
| | | |
| 5-255 | Unassigned |
+-------+-------------+---------------------+
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8.3. Message Types
IANA has created, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Message Types"
and initialized it with the contents below. The registration
procedure is RFC Required.
+----------+---------------+
| Code | Message Type |
+----------+---------------+
| 0x0 | Reserved |
| | |
| 0x1 | DATA_SEGMENT |
| | |
| 0x2 | ACK_SEGMENT |
| | |
| 0x3 | REFUSE_BUNDLE |
| | |
| 0x4 | KEEPALIVE |
| | |
| 0x5 | SHUTDOWN |
| | |
| 0x6 | LENGTH |
| | |
| TBD | REJECT |
| | |
| TBD--0xf | Unassigned |
+----------+---------------+
Message Type Codes
8.4. REFUSE_BUNDLE Reason Codes
IANA has created, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer REFUSE_BUNDLE
Reason Codes" and initialized it with the contents of Table 3. The
registration procedure is RFC Required.
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+----------+---------------------------+
| Code | Refusal Reason |
+----------+---------------------------+
| 0x0 | Unknown |
| | |
| 0x1 | Completed |
| | |
| 0x2 | No Resources |
| | |
| 0x3 | Retransmit |
| | |
| 0x4--0x7 | Unassigned |
| | |
| 0x8--0xf | Reserved for future usage |
+----------+---------------------------+
REFUSE_BUNDLE Reason Codes
8.5. SHUTDOWN Reason Codes
IANA has created, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer SHUTDOWN
Reason Codes" and initialized it with the contents of Table 4. The
registration procedure is RFC Required.
+-----------+------------------+
| Code | Shutdown Reason |
+-----------+------------------+
| 0x00 | Idle timeout |
| | |
| 0x01 | Version mismatch |
| | |
| 0x02 | Busy |
| | |
| TBD | Contact Failure |
| | |
| TBD | TLS failure |
| | |
| TBD--0xFF | Unassigned |
+-----------+------------------+
SHUTDOWN Reason Codes
8.6. REJECT Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
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IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer REJECT Reason
Codes" and initialized it with the contents of Table 4. The
registration procedure is RFC Required.
+-----------+----------------------+
| Code | Rejection Reason |
+-----------+----------------------+
| 0x00 | reserved |
| | |
| 0x01 | Message Type Unknown |
| | |
| 0x02 | Message Unsupported |
| | |
| 0x03 | Message Unexpected |
| | |
| 0x04-0xFF | Unassigned |
+-----------+----------------------+
REJECT Reason Codes
9. Acknowledgments
This memo is based on comments on implementation of [RFC7242]
provided from Scott Burleigh.
10. References
10.1. Normative References
[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>.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, DOI 10.17487/RFC5050, November
2007, <http://www.rfc-editor.org/info/rfc5050>.
[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>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
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[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, <http://www.rfc-editor.org/info/rfc7525>.
[I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol",
draft-ietf-dtn-bpbis-06 (work in progress), October 2016.
[refs.IANA-BP]
IANA, "Bundle Protocol registry", May 2016.
10.2. Informative References
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999,
<http://www.rfc-editor.org/info/rfc2595>.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
April 2007, <http://www.rfc-editor.org/info/rfc4838>.
[RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification", RFC 6257,
DOI 10.17487/RFC6257, May 2011,
<http://www.rfc-editor.org/info/rfc6257>.
[RFC7242] Demmer, M., Ott, J., and S. Perreault, "Delay-Tolerant
Networking TCP Convergence-Layer Protocol", RFC 7242,
DOI 10.17487/RFC7242, June 2014,
<http://www.rfc-editor.org/info/rfc7242>.
[I-D.ietf-dtn-bpsec]
Birrane, E. and K. McKeever, "Bundle Protocol Security
Specification", draft-ietf-dtn-bpsec-03 (work in
progress), October 2016.
Appendix A. Significant changes from RFC7242
The areas in which changes from [RFC7242] have been made to existing
messages are:
o Changed contact header content to limit number of negotiated
options.
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o Added contact option to negotiate maximum segment size (per each
direction).
o Added a bundle transfer identification number to all bundle-
related messages (LENGTH, DATA_SEGMENT, ACK_SEGMENT,
REFUSE_BUNDLE).
o Use flags in ACK_SEGMENT to mirror flags from DATA_SEGMENT.
o Removed all uses of SDNV fields and replaced with fixed-bit-length
fields.
The areas in which extensions from [RFC7242] have been made as new
messages and codes are:
o Added contact negotation failure SHUTDOWN reason code.
o Added REJECT message to indicate an unknown or unhandled message
was received.
o Added TLS session security mechanism.
o Added TLS failure SHUTDOWN reason code.
Authors' Addresses
Brian Sipos
RKF Engineering Solutions, LLC
1229 19th Street NW
Wasington, DC 20036
US
Email: BSipos@rkf-eng.com
Michael Demmer
University of California, Berkeley
Computer Science Division
445 Soda Hall
Berkeley, CA 94720-1776
US
Email: demmer@cs.berkeley.edu
Sipos, et al. Expires May 31, 2017 [Page 30]
Internet-Draft DTN TCPCLv4 November 2016
Joerg Ott
Aalto University
Department of Communications and Networking
PO Box 13000
Aalto 02015
Finland
Email: jo@netlab.tkk.fi
Simon Perreault
Quebec, QC
Canada
Email: simon@per.reau.lt
Sipos, et al. Expires May 31, 2017 [Page 31]
