Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering
Obsoletes: RFC7242 (if approved) M. Demmer
Intended status: Experimental UC Berkeley
Expires: February 2, 2017 J. Ott
Aalto University
S. Perreault
August 1, 2016
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-sipos-dtn-tcpclv4-02
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]. The majority
of this specification is unchanged from TCPCL version 3.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 2, 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
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 5
3. General Protocol Description . . . . . . . . . . . . . . . . 5
3.1. Bidirectional Use of TCP Connection . . . . . . . . . . . 7
3.2. Example Message Exchange . . . . . . . . . . . . . . . . 7
4. Connection Establishment . . . . . . . . . . . . . . . . . . 8
4.1. Contact Header . . . . . . . . . . . . . . . . . . . . . 9
4.1.1. Connection Option Encoding . . . . . . . . . . . . . 10
4.2. Validation and Parameter Negotiation . . . . . . . . . . 11
5. Established Connection Operation . . . . . . . . . . . . . . 14
5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 14
5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 15
5.2.1. Connection Upkeep (KEEPALIVE) . . . . . . . . . . . . 15
5.2.2. Message Rejection (REJECT) . . . . . . . . . . . . . 16
5.3. Connection Security . . . . . . . . . . . . . . . . . . . 17
5.3.1. Requester Role . . . . . . . . . . . . . . . . . . . 17
5.3.2. Responder Role . . . . . . . . . . . . . . . . . . . 18
5.3.3. TLS Handshake Result . . . . . . . . . . . . . . . . 18
5.3.4. Example TLS Initiation . . . . . . . . . . . . . . . 18
5.4. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 19
5.4.1. Bundle Data Transmission (DATA_SEGMENT) . . . . . . . 20
5.4.2. Bundle Acknowledgments (ACK_SEGMENT) . . . . . . . . 21
5.4.3. Bundle Refusal (REFUSE_BUNDLE) . . . . . . . . . . . 22
5.4.4. Bundle Length (LENGTH) . . . . . . . . . . . . . . . 24
6. Connection Termination . . . . . . . . . . . . . . . . . . . 24
6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 25
6.2. Idle Connection Shutdown . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 28
8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 29
8.3. Message Types . . . . . . . . . . . . . . . . . . . . . . 29
8.4. Connection Option Types . . . . . . . . . . . . . . . . . 30
8.5. REFUSE_BUNDLE Reason Codes . . . . . . . . . . . . . . . 31
8.6. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 32
8.7. REJECT Reason Codes . . . . . . . . . . . . . . . . . . . 32
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.1. Normative References . . . . . . . . . . . . . . . . . . 33
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10.2. Informative References . . . . . . . . . . . . . . . . . 34
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
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 revsided 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.
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+-------------------------+
| DTN Application | -\
+-------------------------| |
| Bundle Protocol (BP) | -> Application Layer
+-------------------------+ |
| TCP Conv. Layer (TCPCL) | -/
+-------------------------+
| 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
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].
o Mechanisms for locating or identifying other bundle nodes within
an internet.
Note that this document describes version 3 of the protocol.
Versions 0, 1, and 2 were never specified in an Internet-Draft, RFC,
or any other public document. These prior versions of the protocol
were, however, implemented in the DTN reference implementation
[DTNIMPL] in prior releases; hence, the current version number
reflects the existence of those prior versions.
This is an experimental protocol produced within the IRTF's Delay-
Tolerant Networking Research Group (DTNRG). It represents the
consensus of all active contributors to this group. If this protocol
is used on the Internet, IETF standard protocols for security and
congestion control should be used.
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].
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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 Connection: A TCPCL connection (as opposed to a TCP
connection) is a TCPCL communication relationship between two
bundle nodes. The lifetime of a TCPCL connection is bound to the
lifetime of an underlying TCP connection. Therefore, a TCPCL
connection is initiated when a bundle node initiates a TCP
connection to be established for the purposes of bundle
communication. A TCPCL connection 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 "connection" without the prefix "TCPCL" refer
to a TCPCL connection.
Connection parameters: The connection parameters are a set of values
used to affect the operation of the TCPCL for a given connection.
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.
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 connection 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 connection 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.
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Once the TCPCL connection is established and configured in this way,
bundles can be transmitted in either direction. Each bundle is
transmitted in one or more logical segments of formatted bundle data.
Each logical data segment consists of a DATA_SEGMENT message header,
a Self-Delimiting Numeric Value (SDNV) as defined in [RFC6256]
containing the length of the segment, and finally the byte range of
the bundle data. The choice of the length to use for segments is an
implementation matter. 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.
An optional feature of the 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 connection is interrupted, it can perform reactive
fragmentation to avoid re-sending the already transmitted part of the
bundle.
When acknowledgments are enabled, then for each data segment that is
received, the receiving node sends an ACK_SEGMENT code followed by an
SDNV 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.
Another optional 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 connections that are idle, a KEEPALIVE message may optionally be
sent at a negotiated interval. This is used to convey liveness
information.
Finally, before connections close, a SHUTDOWN message is sent on the
channel. After sending a SHUTDOWN message, the sender of this
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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 connection setup by a
peer.
3.1. Bidirectional Use of TCP Connection
There are specific messages for sending and receiving operations (in
addition to connection setup/teardown). TCPCL is symmetric, i.e.,
both sides can start sending data segments in a connection, 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 connection 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 |
+-------------------------+ +-------------------------+
+-------------------------+
| DATA_SEGMENT (start) | ->
| SDNV length [L1] | ->
| Bundle Data 0..(L1-1) | ->
+-------------------------+
+-------------------------+ +-------------------------+
| DATA_SEGMENT | -> <- | ACK_SEGMENT |
| SDNV length [L2] | -> <- | SDNV length [L1] |
|Bundle Data L1..(L1+L2-1)| -> +-------------------------+
+-------------------------+
+-------------------------+ +-------------------------+
| DATA_SEGMENT (end) | -> <- | ACK_SEGMENT |
| SDNV length [L3] | -> <- | SDNV length [L1+L2] |
|Bundle Data | -> +-------------------------+
| (L1+L2)..(L1+L2+L3-1)|
+-------------------------+
+-------------------------+
<- | ACK_SEGMENT |
<- | SDNV 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. Connection Establishment
For bundle transmissions to occur using the TCPCL, a TCPCL connection
must first be established between communicating nodes. It is up to
the implementation to decide how and when connection setup is
triggered. For example, some connections may be opened proactively
and maintained for as long as is possible given the network
conditions, while other connections 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 connection, a node must first establish a TCP
connection with the intended peer node, typically by using the
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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 connection by sending a SHUTDOWN message. If
connection 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.
The format for the Contact Header is as follows:
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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 | Option count (SDNV) |
+---------------+---------------+---------------+---------------+
| Options list (sequence of TLV) |
+---------------+---------------+---------------+---------------+
Figure 3: Contact Header Format
The fields of the contact header are:
magic: A four-byte field that always contains the byte sequence 0x64
0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII (and UTF-
8).
version: A one-byte field value containing the value 4 (current
version of the protocol).
Option count: A SDNV-encoded count of connection options to follow.
Option list: A sequence of type-length-value (TLV) encoded
connection options as shown in Figure 4 and described in
Section 4.1.1
Each option within a contact header represents the configuration of
the peer which has sent the contact header. The manner in which
options are configured and chosen for the various parameters in the
contact header is implementation dependent.
4.1.1. Connection Option Encoding
Each of the contact header Options SHALL be encoded as a sequence of
TLV data as shown in Figure 4.
Option Type: An SDNV-encoded field which SHALL determine the
encoding and interpretation of the option value.
Value Length: An SDNV-encoded field which SHALL define the length
(in octets) of the Value Data to follow. The Value Length does
not include the length of the Option Type or Value Length fields
themselves.
Value Data: The encoded type-dependent data of the option.
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The order of items within the Option list SHALL not be significant.
Each option type SHALL be present no more than one time in a Contact
Header. Each option type SHALL be considered to have a default value
if not present in a contact header. The option type defines how the
particular Value Data is encoded and interpreted. If a TCPCL peer
receives an Option Type which is unknown to it, the peer may send a
SHUTDOWN and terminate the connection. Otherwise, the peer SHALL
ignore the option and continue contact header processing.
+-----------------------+
| Option Type (SDNV) |
+-----------------------+
| Value Length (SDNV) |
+-----------------------+
| Value Data (variable) |
+-----------------------+
Figure 4: Connection Option Format
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 connection and to
negotiate values for the connection 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 terminate the connection. 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 connection due to the version mismatch or may adapt 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 connection 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).
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The negotatiated parameters defined by this specification are listed
in Table 1 and described in the following paragraphs.
+--------------+------+---------------------------------------------+
| Type | Code | Description |
+--------------+------+---------------------------------------------+
| Handle | 0x1 | Determine how peer handles LENGTH messages. |
| LENGTH | | |
| | | |
| Acknowledge | 0x2 | Determine how peer handles acknowledgment |
| Intermediate | | of non-final bundle segments. |
| | | |
| Acknowledge | 0x3 | Determine how peer handles acknowledgement |
| Bundle | | of final bundle segments and bundle |
| | | refusal. |
| | | |
| Keepalive | 0x4 | The maximum keepalive interval of the peer. |
| | | |
| Peer EID | 0x5 | The Endpoint ID of the peer. |
| | | |
| BP Versions | 0x6 | The set of BP versions supported by the |
| | | peer. |
| | | |
| Segment MRU | 0x7 | The largest segment length supported by the |
| | | peer. |
| | | |
| Handle TLS | 0x8 | Determine how peer handles STARTTLS |
| | | messages. |
+--------------+------+---------------------------------------------+
Table 1: Connection Option Types
Handle LENGTH: This parameter is a value enumerated by Table 2 and
encoded as a single octet. The value determines whether LENGTH
messages (as described in Section 5.4.4) are handled by this peer.
If the value is IGNORE then the LENGTH message SHOULD NOT be sent
to this peer. If the value is ALLOW then the LENGTH message
SHOULD be sent to this peer. If the value is REQUIRE then the
LENGTH message SHALL be sent to this peer. The default Handle
LENGTH value is ALLOW.
Acknowledge Intermediate: This parameter is a value enumerated by
Table 2 and encoded as a single octet. The value determines how
any non-final ACK_SEGMENT (i.e. one with its E flag not set as
described in Section 5.4.2) is handled by this peer.
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If the value is IGNORE then any non-final ACK_SEGMENT message
SHOULD NOT be sent to this peer. If the value is ALLOW then any
non-final ACK_SEGMENT message SHOULD be sent to this peer. If the
value is REQUIRE then any non-final ACK_SEGMENT message SHALL be
sent to this peer. The default Acknowledge Intermediate value is
ALLOW.
Acknowledge Bundle: This parameter is a value enumerated by Table 2
and encoded as a single octet. The value determines how any final
ACK_SEGMENT (i.e. one with its E flag set as described in
Section 5.4.2) is handled by this peer. This value also
determines how any REFUSE_BUNDLE message is handled by this peer.
If the value is IGNORE then any final ACK_SEGMENT or REFUSE_BUNDLE
message SHOULD NOT be sent to this peer. If the value is ALLOW
then any final ACK_SEGMENT or REFUSE_BUNDLE message SHOULD be sent
to this peer. If the value is REQUIRE then any final ACK_SEGMENT
or REFUSE_BUNDLE message SHALL be sent to this peer. The default
Acknowledge Bundle value is ALLOW.
Keepalive: This parameter is encoded as a two-octet unsigned integer
in network byte order (U16). The value is the maximum keepalive
time interval (in seconds) for this peer. The negotiated
keepalive interval is set to the minimum value from both contact
headers. If one or both contact headers contains the value zero,
then the keepalive feature (described in Section 5.2.1) is
disabled. The default Keepalive value is zero.
Peer EID: This parameter is a byte string containing 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>. The default Peer EID value is the empty string.
BP Versions: This parameter is a sequence of bytes, each containing
an individual Bundle Protocol version number supported by this
peer. The set of supported BP versions of the connection is the
intersection of the BP versions indicated by both of the contact
headers.
If interoperating with a TCPCL Version 3 node, a TCPCL Version 4
node MAY assume that the TCPCL Version 3 node supports exactly one
BP Version: 0x06 of [RFC5050]. If there is no common supported BP
version then the connection SHOULD be shutdown with reason
"Contact Failure", as no possible bundle exchange can occur.
Otherwise, the default BP Versions value is the single version 4
(this specification).
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Segment MRU: This parameter is an SDNV-encoded integer. The value
indicates the maximum Data Length within of DATA_SEGMENT which
this peer will accept, or zero if there is no maximum length. Any
DATA_SEGMENT send to this peer SHALL have a data payload no longer
than this peer's maximum length. The default Segment MRU value is
zero.
+---------+------+--------------------------------------------------+
| Name | Code | Description |
+---------+------+--------------------------------------------------+
| IGNORE | 0x01 | The peer sending this option will ignore any |
| | | such messages. |
| | | |
| ALLOW | 0x02 | The peer sending this option will process any |
| | | such messages and act upon the data. |
| | | |
| REQUIRE | 0x03 | The peer sending this option will refuse to |
| | | operate without such messages. |
+---------+------+--------------------------------------------------+
Table 2: Receiver Handle Enumeration
Once this process of parameter negotiation is completed, the protocol
defines no additional mechanism to change the parameters of an
established connection; to effect such a change, the connection MUST
be terminated and a new connection established.
5. Established Connection Operation
This section describes the protocol operation for the duration of an
established connection, including the mechanisms for transmitting
bundles over the connection.
5.1. Message Type Codes
After the initial exchange of a contact header, all messages
transmitted over the connection are identified by a one-byte header
with the following structure:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| type | flags |
+-+-+-+-+-+-+-+-+
Figure 5: Format of the One-Byte Message Header
type: Indicates the type of the message as per Table 3 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 |
| | | 5.4.1. |
| | | |
| ACK_SEGMENT | 0x2 | Acknowledges reception of a data segment, |
| | | as described in Section 5.4.2. |
| | | |
| REFUSE_BUNDLE | 0x3 | Indicates that the transmission of the |
| | | current bundle SHALL be stopped, as |
| | | described in Section 5.4.3. |
| | | |
| KEEPALIVE | 0x4 | KEEPALIVE message for the connection, as |
| | | described in Section 5.2.1. |
| | | |
| SHUTDOWN | 0x5 | Indicates that one of the nodes |
| | | participating in the connection wishes to |
| | | cleanly terminate the connection, as |
| | | described in Section 6. |
| | | |
| LENGTH | 0x6 | Contains the length (in bytes) of the next |
| | | bundle, as described in Section 5.4.4. |
+---------------+------+--------------------------------------------+
Table 3: TCPCL Message Types
5.2. Upkeep and Status Messages
5.2.1. Connection Upkeep (KEEPALIVE)
The protocol includes a provision for transmission of KEEPALIVE
messages over the TCP connection to help determine if the 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.
The format of a KEEPALIVE message is a one-byte message type code of
KEEPALIVE (as described in Table 2) with no additional data. Both
sides SHOULD send a KEEPALIVE message whenever the negotiated
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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-byte SHUTDOWN message (as described in
Table 2) and by closing the TCP connection.
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 uknown to it
(possibly due to an unhandled protocol mismatch) or is inappropriate
for the current connection state (e.g. a KEEPALIVE or LENGTH message
received after feature negotation has disabled those features), 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 |
+-----------------------------+
| Rejected Message Header |
+-----------------------------+
| Reason Code (byte) |
+-----------------------------+
Figure 6: 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
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 connection |
| Unexpected | | is in a state in which the message is not |
| | | expected. |
+-------------+------+----------------------------------------------+
Table 4: REJECT Reason Codes
5.3. Connection Security
This version of the TCPCL supports establishing a connection-level
Transport Layer Security (TLS) session within an existing TCPCL
connection.
When TLS is used within the TCPCL it affects the entire connection,
and it can technically be initiated by either endpoint of the
connection. By convention, this protocol uses the endpoint which
initiated the underlying TCP connection as the initiator of the TLS
session request. Once a TLS session is established within TCPCL,
there is no mechanism provided to end the TLS session and downgrade
the connection. If a non-TLS connection is desired after a TLS
session is started then the entire TCPCL connection MUST be shutdown
first.
5.3.1. Requester Role
A STARTTLS message SHOULD be sent by the TCP client immediately after
reception of the TCPCL Contact Header from the server. Upon sending
a STARTTLS message, the requester SHALL enter a waiting state.
While in the waiting state, upon reception of a confirmation STARTTLS
message the requestor SHALL begin a TLS handshake in accordance with
[RFC5246]. While in the waiting state, the recepiton of any message
other than a STARTTLS reply MAY cause a connection shutdown depending
upon security policy of the endpoint.
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5.3.2. Responder Role
Upon reception of a STARTTLS message while not already within a TLS
session and while not acting as a TLS requester and if the endpoint
supports TLS connections, a STARTTLS message SHALL be sent in
response. If an endpoint receives a STARTTLS message but cannot
support a TLS connection (for any reason) then a REJECT message SHALL
be sent in response containing a Reason Code of "Message Unsupported.
Upon reception of a STARTTLS message while already within a TLS
session, a REJECT message SHOULD be sent in response containing a
Reason Code of "Message Unexpected". Upon sending a response
STARTTLS message the responder SHALL begin a TLS handshake in
accordance with [RFC5246].
5.3.3. TLS Handshake Result
If a TLS handshake cannot negotiate a TLS session, either endpoint of
the TCPCL connection SHOULD cause a TCPCL shutdown with reason "TLS
negotiation failed". After a TLS handshake failure, if the
connection is not shutdown then either endpoint MAY request a new TLS
handshake. Unless the TLS parameters change between two sequential
handshakes, the subsequent handshake is likely to fail just as the
earlier one.
After a TLS session is successfuly established, both TCPCL endpoints
SHALL re-exchange TCPCL Contact Header messages. Any information
cached from the prior Contact Header exchange SHALL be discarded.
This re-exchange avoids man-in-the-middle attack in identical fashon
to [RFC2595].
5.3.4. Example TLS Initiation
A summary of a typical STARTTLS usage is shown in the sequence below
where the client/requester role is represented by the prefix "C" and
the server/responder role is represented by the prefix "S".
Unordered or "simultaneous" actions are shown as "C/S".
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Node A Node B
====== ======
+-------------------------+
| Open TCP Connnection | ->
+-------------------------+ +-------------------------+
<- | Accept Connection |
+-------------------------+
+-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+
... plaintext TCPCL messaging ...
+-------------------------+
| STARTTLS | ->
+-------------------------+ +-------------------------+
<- | STARTTLS |
+-------------------------+
+-------------------------+ +-------------------------+
| TLS Negotiation | -> <- | TLS Negotiation |
+-------------------------+ +-------------------------+
+-------------------------+ +-------------------------+
| Contact Header | -> <- | Contact Header |
+-------------------------+ +-------------------------+
... secured TCPCL messaging ...
+-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN |
+-------------------------+ +-------------------------+
Figure 7: 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. Each of the messages
contains a Bundle ID number which is used to correlate messages
originating from sender and receiver of a bundle. The Bundle ID
provides a similar behaivior to a datagram sequence number, but there
are no requirements on Bundle ID ordering or reuse.
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Bundle IDs SHOULD be unique within a limited scope dependant upon
implementation needs. Sequential bundle transfers SHALL NOT use the
same Bundle ID. Bundle ID numbers MAY be reused after a window of
either count or time. Bundle ID reuse SHOULD take into account
unacknowledged bundle segments if acknowledgement is used within a
connection. For example, Bundle IDs in the range 1--50 inclusive can
be used for sequential bundle transmissions in ascending order before
recycling back to 1. This allows discrimination between 50 adjacent
bundle transfers.
A TCPCL endpoint SHALL support Bundle IDs at least between 0 and 2^14
(two-bytes encoded). A TCPCL endpoint MAY support larger Bundle IDs
depending upon implementation needs. For bidirectional bundle
transfers, a TCPCL endpoint SHOULD NOT rely on any relation between
Bundle IDs originating from each side of the TCPCL connection. Upon
reception of a Bundle ID not able to be handled by an endpoint, a
REFUSE_BUNDLE message SHOULD be sent in response.
5.4.1. 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 |
+-----------------------------+
| Bundle ID (SDNV) |
+-----------------------------+
| Data length (SDNV) |
+-----------------------------+
| Data contents (byte string) |
+-----------------------------+
Figure 8: Format of DATA_SEGMENT Messages
4 5 6 7
+-+-+-+-+
|0|0|S|E|
+-+-+-+-+
Figure 9: Format of DATA_SEGMENT Header flags
The type portion of the message header contains the value 0x1.
The flags portion of the message header byte contains two optional
values in the two low-order bits, denoted 'S' and 'E' above. The 'S'
bit MUST be set to one if it precedes the transmission of the first
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segment of a new bundle. The 'E' bit MUST be set to one when
transmitting the last segment of a bundle.
Following the message header, the length field is an SDNV containing
the number of bytes of bundle data that are transmitted in this
segment. Following this length is the actual data contents.
Determining the size of the segment is an implementation matter. In
particular, a node may, based on local policy or configuration, only
ever transmit bundle data in a single segment, in which case both the
'S' and 'E' bits MUST be set to one.
In the Bundle Protocol specification [RFC5050], a single bundle
comprises a primary bundle block, a payload block, and zero or more
additional bundle blocks. The relationship between the protocol
blocks and the convergence-layer segments is an implementation-
specific decision. In particular, a segment MAY contain more than
one protocol block; alternatively, a single protocol block (such as
the payload) MAY be split into multiple segments.
However, a single segment MUST NOT contain data of more than a single
bundle.
Once a transmission 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.
5.4.2. 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 offers an optional feature whereby a
receiving node transmits acknowledgments of reception of data
segments. This feature is enabled if, and only if, during the
exchange of contact headers, both parties set the flag to indicate
that intermediate or final acknowledgments are enabled (see
Section 4.1).
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 |
+-----------------------------+
| Bundle ID (SDNV) |
+-----------------------------+
| Acknowledged length (SDNV) |
+-----------------------------+
Figure 10: Format of ACK_SEGMENT Messages
To transmit an acknowledgment, a node first transmits a message
header with the ACK_SEGMENT type code and all flags set to zero, then
transmits an SDNV containing the cumulative length in bytes of the
received segment(s) of the current bundle. The length MUST fall on a
segment boundary. That is, only full segments can be acknowledged.
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.
5.4.3. Bundle Refusal (REFUSE_BUNDLE)
As bundles may be large, the TCPCL supports an optional mechanisms 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 Bundle ID of the refusal.
The format of the message is as follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Bundle ID (SDNV) |
+-----------------------------+
Figure 11: Format of REFUSE_BUNDLE Messages
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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 5: REFUSE_BUNDLE Reason Codes
The receiver MUST, for each bundle preceding the one to be refused,
have either acknowledged all DATA_SEGMENTs or refused the bundle.
This allows the sender to identify the bundles accepted and refused
by means of a simple FIFO list of segments and acknowledgments.
The bundle refusal MAY be sent before the entire data segment is
received. If a sender receives a REFUSE_BUNDLE message, the sender
MUST complete the transmission of any partially sent DATA_SEGMENT
message (so that the receiver stays in sync). 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.
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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 bundle.
5.4.4. Bundle Length (LENGTH)
The LENGTH message contains the total length, in bytes, of the next
bundle, formatted as an SDNV. Its purpose is to allow nodes to
preemptively refuse bundles that would exceed their resources. It is
an optimization.
The format of the LENGTH message is as follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Bundle ID (SDNV) |
+-----------------------------+
| Total bundle length (SDNV) |
+-----------------------------+
Figure 13: Format of LENGTH Messages
LENGTH messages MUST NOT be sent unless the corresponding flag bit is
set in the contact header. If the flag bit is set, LENGTH messages
MAY be sent at the sender's discretion. 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 bundle).
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 right bundle.
Upon reception of a LENGTH message when either LENGTH has not been
negotiated or not immediately before the start of a starting
DATA_SEGMENT the reciever MAY send a REJECT message with a Reason
Code of "Message Unexpected".
6. Connection Termination
This section describes the procedures for ending a TCPCL connection.
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6.1. Shutdown Message (SHUTDOWN)
To cleanly shut down a connection, a SHUTDOWN message MUST be
transmitted by either node at any point following complete
transmission of any other message. In case acknowledgments have been
negotiated, a node SHOULD acknowledge all received data segments
first and then shut down the connection.
The format of the SHUTDOWN message is as follows:
+-----------------------------------+
| Message Header |
+-----------------------------------+
| Reason Code (optional byte) |
+-----------------------------------+
| Reconnection Delay (optional U16) |
+-----------------------------------+
Figure 14: Format of SHUTDOWN Messages
4 5 6 7
+-+-+-+-+
|0|0|R|D|
+-+-+-+-+
Figure 15: Format of SHUTDOWN Header flags
It is possible for a node to convey additional information regarding
the reason for connection termination. To do so, the node MUST set
the 'R' bit in the message header flags and transmit a one-byte
reason code immediately following the message header. The specified
values of the reason code are:
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+------------+------+-----------------------------------------------+
| Name | Code | Description |
+------------+------+-----------------------------------------------+
| Idle | 0x00 | The connection is being closed due to |
| timeout | | 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 |
| | | connection. |
| | | |
| Contact | 0x03 | The node cannot interpret or negotiate |
| Failure | | contact header option. |
| | | |
| TLS | 0x04 | The node failed to negotiate TLS session and |
| failure | | cannot continue the connection. |
+------------+------+-----------------------------------------------+
Table 6: SHUTDOWN Reason Codes
It is also possible to convey a requested reconnection delay to
indicate how long the other node must wait before attempting
connection re-establishment. To do so, the node sets the 'D' bit in
the message header flags and then transmits an SDNV 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 connection. 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). Note that in the figure above, the
reconnection delay SDNV is represented as a two-byte field for
convenience.
A connection 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.
If either node terminates a connection 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 a node
does not want its peer to reopen the connection immediately, it
SHOULD set the 'D' bit in the flags and include a reconnection delay
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to indicate when the peer is allowed to attempt another connection
setup.
If a connection is to be terminated before another protocol message
has completed, then the node MUST NOT transmit the SHUTDOWN message
but still SHOULD close the TCP connection. In particular, if the
connection is to be closed (for whatever reason) while a node is in
the process of transmitting a bundle data segment, the receiving node
is still expecting segment data and might erroneously interpret the
SHUTDOWN message to be part of the data segment.
6.2. Idle Connection Shutdown
The protocol includes a provision for clean shutdown of idle TCP
connections. Determining the length of time to wait before closing
idle connections, 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 connection by
transmitting a SHUTDOWN message indicating the reason code of 'Idle
timeout' (as described in Table 4). 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 connection
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 connection, then the node that has falsified its
identity may be able to obtain bundles that it should not have.
Therefore, a node SHALL NOT use the endpoint identifier conveyed in
the TCPCL connection message to derive a peer node's identity unless
it can corroborate it via other means.
These concerns may be mitigated through the use of the Bundle
Security Protocol [RFC6257]. In particular, the Bundle
Authentication Block defines mechanism for secure exchange of bundles
between DTN nodes. Thus, an implementation could delay trusting the
presented endpoint identifier until the node can securely validate
that its peer is in fact the only member of the given singleton
endpoint.
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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 connection, 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 TCP
connection, 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 connection. This burden could cause denial of
service on other, well-behaving connections. There is also nothing
to prevent a malicious node from continually establishing connections
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]
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.
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+------------------------+-------------------------------------+
| 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 |
+-------+-------------+---------------------+
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.
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+----------+---------------+
| Code | Message Type |
+----------+---------------+
| 0x0 | Reserved |
| | |
| 0x1 | DATA_SEGMENT |
| | |
| 0x2 | ACK_SEGMENT |
| | |
| 0x3 | REFUSE_BUNDLE |
| | |
| 0x4 | KEEPALIVE |
| | |
| 0x5 | SHUTDOWN |
| | |
| 0x6 | LENGTH |
| | |
| 0x7 | REJECT |
| | |
| 0x8 | STARTTLS |
| | |
| 0x9--0xf | Unassigned |
+----------+---------------+
Message Type Codes
8.4. Connection Option Types
IANA will createe, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Option Types"
and initialize it with the contents below. The registration
procedure is RFC Required for values less than 2^14 (16384). Values
greater than or equal to 2^14 (16384) are to be used for experimental
option types.
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+-------------+--------------------------+
| Code | Option Type |
+-------------+--------------------------+
| 0x0 | Reserved |
| | |
| 0x1 | Handle LENGTH |
| | |
| 0x2 | Acknowledge Intermediate |
| | |
| 0x3 | Acknowledge Bundle |
| | |
| 0x4 | Keepalive |
| | |
| 0x5 | Peer EID |
| | |
| 0x6 | BP Versions |
| | |
| 0x7 | Segment MRU |
| | |
| 0x8 | Handle TLS |
| | |
| 0x9--0x3ffe | Unassigned |
| | |
| 0x3fff-- | Experimental |
+-------------+--------------------------+
Message Type Codes
8.5. 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
8.6. 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 |
| | |
| 0x03 | Contact Failure |
| | |
| 0x04 | TLS failure |
| | |
| 0x05--0xFF | Unassigned |
+------------+------------------+
SHUTDOWN Reason Codes
8.7. 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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[RFC6256] Eddy, W. and E. Davies, "Using Self-Delimiting Numeric
Values in Protocols", RFC 6256, DOI 10.17487/RFC6256, May
2011, <http://www.rfc-editor.org/info/rfc6256>.
[I-D.ietf-dtn-bpbis]
Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol",
draft-ietf-dtn-bpbis-04 (work in progress), July 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-02 (work in
progress), July 2016.
Appendix A. Significant changes from RFC7242
The areas in which changes from [RFC7242] have been made to existing
messages are:
o Added a bundle identification number to all bundle-related
messages (LENGTH, DATA_SEGMENT, ACK_SEGMENT, REFUSE_BUNDLE).
o Added bundle protocol version negotation to contact header.
o Use flags in ACK_SEGMENT to mirror flags from DATA_SEGMENT.
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The areas in which extensions from [RFC7242] have been made as new
messages and codes are:
o Changed contact header negotation from single-octet bit flags to
extensible TLV-encoded options.
o Added contact option to negotiate maximum segment size (per each
direction).
o Added contact option to negotiate acceptable Bundle Protoocl
versions.
o Added REJECT message to indicate an unknown or unhandled message
was received.
o Added STARTTLS message and connection 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
Joerg Ott
Aalto University
Department of Communications and Networking
PO Box 13000
Aalto 02015
Finland
Email: jo@netlab.tkk.fi
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Simon Perreault
Quebec, QC
Canada
Email: simon@per.reau.lt
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