Delay Tolerant Networking B. Sipos
Internet-Draft RKF Engineering
Obsoletes: 7242 (if approved) M. Demmer
Intended status: Standards Track UC Berkeley
Expires: November 23, 2017 J. Ott
Aalto University
S. Perreault
May 22, 2017
Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
draft-ietf-dtn-tcpclv4-02
Abstract
This document describes a revised protocol for the TCP-based
convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The
protocol revision is based on implementation issues in the original
TCPCL Version 3 and updates to the Bundle Protocol contents,
encodings, and convergence layer requirements in Bundle Protocl
Version 7. Several new IANA registries are defined for TCPCLv4 which
define some behaviors inherited from TCPCLv3 but with updated
encodings and/or semantics.
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
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 23, 2017.
Copyright Notice
Copyright (c) 2017 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
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . 7
4. Session Establishment . . . . . . . . . . . . . . . . . . . . 8
4.1. Contact Header . . . . . . . . . . . . . . . . . . . . . 10
4.1.1. Header Extension Items . . . . . . . . . . . . . . . 11
4.2. Validation and Parameter Negotiation . . . . . . . . . . 13
5. Established Session Operation . . . . . . . . . . . . . . . . 14
5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 14
5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 15
5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 15
5.2.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 16
5.3. Session Security . . . . . . . . . . . . . . . . . . . . 17
5.3.1. TLS Handshake Result . . . . . . . . . . . . . . . . 17
5.3.2. Example TLS Initiation . . . . . . . . . . . . . . . 18
5.4. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 18
5.4.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 19
5.4.2. Transfer initialization (XFER_INIT) . . . . . . . . . 19
5.4.3. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 20
5.4.4. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 22
5.4.5. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 23
6. Session Termination . . . . . . . . . . . . . . . . . . . . . 24
6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 25
6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 29
8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 29
8.3. Header Extension Types . . . . . . . . . . . . . . . . . 30
8.4. Message Types . . . . . . . . . . . . . . . . . . . . . . 31
8.5. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 31
8.6. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 32
8.7. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 33
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
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10.1. Normative References . . . . . . . . . . . . . . . . . . 33
10.2. Informative References . . . . . . . . . . . . . . . . . 34
Appendix A. Significant changes from RFC7242 . . . . . . . . . . 35
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 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.
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+-------------------------+
| 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
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.
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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 after a bundle node establishes a TCP connection to 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.
Transfer Transfer refers to the procedures and mechanisms (described
below) for conveyance of an individual bundle from one node to
another. Each transfer within TCPCLv4 is identified by a Transfer
ID number which is unique only to a single direction within a
single Session.
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 XFER_SEGMENT message header and flags, 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
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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 XFER_SEGMENT
message flags.
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 (XFER_ACK). 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 XFER_ACK message containing the cumulative length of the
bundle that has been received. The sending node MAY transmit
multiple XFER_SEGMENT messages without necessarily waiting for the
corresponding XFER_ACK responses. This enables pipelining of
messages on a channel. In addition, there is no explicit flow
control on the TCPCL layer.
Another feature is that a receiver MAY interrupt the transmission of
a bundle at any point in time by replying with a XFER_REFUSE 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 (XFER_ACK or XFER_REFUSE)
but no further data messages (XFER_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
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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 XFER_SEGMENT
messages without necessarily waiting for the corresponding XFER_ACK
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 XFER_SEGMENT messages for
different bundles without necessarily waiting for XFER_ACK 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 |
+-------------------------+ +-------------------------+
+-------------------------+
| XFER_INIT | ->
| Transfer ID [I1] |
| Total Length [L1] |
+-------------------------+
+-------------------------+
| XFER_SEGMENT (start) | ->
| Transfer ID [I1] |
| Length [L1] |
| Bundle Data 0..(L1-1) |
+-------------------------+
+-------------------------+ +-------------------------+
| XFER_SEGMENT | -> <- | XFER_ACK (start) |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L2] | | Length [L1] |
|Bundle Data L1..(L1+L2-1)| +-------------------------+
+-------------------------+
+-------------------------+ +-------------------------+
| XFER_SEGMENT (end) | -> <- | XFER_ACK |
| Transfer ID [I1] | | Transfer ID [I1] |
| Length [L3] | | Length [L1+L2] |
|Bundle Data | +-------------------------+
| (L1+L2)..(L1+L2+L3-1)|
+-------------------------+
+-------------------------+
<- | XFER_ACK (end) |
| Transfer ID [I1] |
| Length [L1+L2+L3] |
+-------------------------+
+-------------------------+ +-------------------------+
| SHUTDOWN | -> <- | SHUTDOWN |
+-------------------------+ +-------------------------+
Figure 2: A SL1e 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. Destination port number
4556 has been assigned by IANA as the well-known port number for the
TCP convergence layer. Other destination port numbers MAY be used
per local configuration. Determining a peer's destination port
number (if different from the well-known TCPCL port) is up to the
implementation. Any source port number MAY be used for TCPCL
sessions. Typically an operating system assigned number in the TCP
Ephemeral range (49152--65535) is used.
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.
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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:
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... |
+---------------+---------------+---------------+---------------+
| EID Data contd. |
+---------------+---------------+---------------+---------------+
| TCPCLv4 Header Extension Items... |
+---------------+---------------+---------------+---------------+
Figure 3: Contact Header Format
See Section 4.2 for details on the use of each of these contact
header fields. 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.
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Segment MRU: A 64-bit unsigned integer indicating the largest
allowable single-segment data payload size to be received in this
session. Any XFER_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.
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 SHALL be used to indicate the lack of EID rather than a
truly empty EID. This case allows an endpoint to avoid exposing
EID information on an untrusted network. A non-zero-length EID
Data SHALL contain 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>. This EID encoding
is consistent with [I-D.ietf-dtn-bpbis].
Header Extension Values: The remaining items of the contact header
represent protocol extension data not defined by this
specification. The encoding of each Header Extension Item is
identical form as described in Section 4.1.1.
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CAN_TLS | 0x01 | If bit is set, indicates that the sending |
| | | peer is capable of TLS security. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 1: Contact Header Flags
4.1.1. Header Extension Items
Each of the Header Extension items SHALL be encoded in an identical
Type-Length-Value (TLV) container form as indicated in Figure 4. The
fields of the header extension item are:
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Flags: A one-octet field containing generic bit flags about the
item, which are listed in Table 2. If a TCPCL endpoint receives
an extension item with an unknown Item Type and the CRITICAL flag
set, the endpoint SHALL close the TCPCL session with SHUTDOWN
reason code of "Contact Failure". If the CRITICAL flag is not
set, an endpoint SHALL skip over and ignore any item with an
unkonwn Item Type.
Item Type: A 16-bit unsigned integer field containing the type of
the extension item. Each type This specification does not define
any extension types directly, but does allocate an IANA registry
for such codes (see Section 8.3).
Item Length: A 32-bit unsigned integer field containing the number
of Item Value octets to follow.
Item Value: A variable-length data field which is interpreted
according to the associated Item Type. This specification places
no restrictions on an extensions use of available Item Value data.
Extension specification SHOULD avoid the use of large data
exchanges within the TCPCLv4 contact header as no bundle transfers
can begin until the a full contact exchange and negotiation has
been completed.
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
+---------------+---------------+---------------+---------------+
| Item Flags | Item Type | Item Length...|
+---------------+---------------+---------------+---------------+
| length contd. | Item Value... |
+---------------+---------------+---------------+---------------+
| value contd. |
+---------------+---------------+---------------+---------------+
Figure 4: Header Extention Item Format
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
| | | peer must handle the extension item. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 2: Header Extension Item Flags
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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
its operation to conform to the older version of the protocol. This
decision is an implementation matter. When establishing the TCPCL
session, a node SHOULD send the contact header for the latest version
of TCPCL that it can use.
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. There is no logical minimum value for the keepalive
interval, but when used for many sessions on an open, shared
network a short interval could lead to excessive traffic. For
shared network use, endpoints SHOULD choose a keepalive interval
no shorter than 30 seconds. There is no logical maximum value for
the keepalive interval, but an idle TCP connection is liable for
closure by the host operating system if the keepalive time is
longer than tens-of-minutes. Endpoints SHOULD choose a keepalive
interval no longer than 10 minutes (600 seconds).
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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
+---------------+
| Message Type |
+---------------+
Figure 5: Format of the Message Header
The message header fields are as follows:
Message Type: Indicates the type of the message as per Table 3
below.
The message types defined in this specificaiton are listed in
Table 3. Encoded values are listed in Section 8.4.
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+--------------+----------------------------------------------------+
| Type | Description |
+--------------+----------------------------------------------------+
| XFER_INIT | Contains the length (in octets) of the next |
| | transfer, as described in Section 5.4.2. |
| | |
| XFER_SEGMENT | Indicates the transmission of a segment of bundle |
| | data, as described in Section 5.4.3. |
| | |
| XFER_ACK | Acknowledges reception of a data segment, as |
| | described in Section 5.4.4. |
| | |
| XFER_REFUSE | Indicates that the transmission of the current |
| | bundle SHALL be stopped, as described in Section |
| | 5.4.5. |
| | |
| KEEPALIVE | Used to keep TCPCL session active, as described in |
| | Section 5.2.1. |
| | |
| SHUTDOWN | Indicates that one of the nodes participating in |
| | the session wishes to cleanly terminate the |
| | session, as described in Section 6. |
| | |
| MSG_REJECT | Contains a TCPCL message rejection, as described |
| | in Section 5.2.2. |
+--------------+----------------------------------------------------+
Table 3: 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.
The format of a KEEPALIVE message is a one-octet message type code of
KEEPALIVE (as described in Table 3) 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).
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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
Section 6.1, 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 (MSG_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
MSG_REJECT reply.
The format of a MSG_REJECT message follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Reason Code (U8) |
+-----------------------------+
| Rejected Message Header |
+-----------------------------+
Figure 6: Format of MSG_REJECT Messages
The fields of the MSG_REJECT message are:
Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 4.
Rejected Message Header: The Rejected Message Header is a copy of
the Message Header to which the MSG_REJECT message is sent as a
response.
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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 4: MSG_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 7 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 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.
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 XFER_INIT message and some
number of XFER_SEGMENT and XFER_ACK 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. Transfer initialization (XFER_INIT)
The XFER_INIT 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 XFER_INIT 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 XFER_INIT
content is acceptable.
The Total Bundle Length field within a XFER_INIT message SHALL be
treated as authoritative by the receiver. If, for whatever reason,
the actual total length of bundle data received differs from the
value indicated by the XFER_INIT message, the receiver SHOULD treat
the transmitted data as invalid.
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The format of the XFER_INIT message is as follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
| Total bundle length (U64) |
+-----------------------------+
Figure 8: Format of XFER_INIT Messages
The fields of the XFER_INIT message are:
Transfer ID: A 64-bit unsigned integer identifying the transfer
about to begin.
Total bundle length: A 64-bit unsigned integer indicating the size
of the data-to-be-transferred.
XFER_INIT messages SHALL be sent immediately before transmission of
any XFER_SEGMENT messages. XFER_INIT messages MUST NOT be sent
unless the next XFER_SEGMENT message has the 'START' 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
XFER_INIT message without waiting for the next XFER_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 XFER_INIT message not immediately before the
start of a starting XFER_SEGMENT the reciever SHALL send a MSG_REJECT
message with a Reason Code of "Message Unexpected".
5.4.3. Data Transmission (XFER_SEGMENT)
Each bundle is transmitted in one or more data segments. The format
of a XFER_SEGMENT message follows in Figure 9.
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+------------------------------+
| Message Header |
+------------------------------+
| Message Flags (U8) |
+------------------------------+
| Transfer ID (U64) |
+------------------------------+
| Data length (U64) |
+------------------------------+
| Data contents (octet string) |
+------------------------------+
Figure 9: Format of XFER_SEGMENT Messages
The fields of the XFER_SEGMENT message are:
Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 5.
Transfer ID: A 64-bit unsigned integer identifying the transfer
being made.
Data length: A 64-bit unsigned integer indicating the number of
octets in the Data contents to follow.
Data contents: The variable-length data payload of the message.
+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| END | 0x01 | If bit is set, indicates that this is the |
| | | last segment of the transfer. |
| | | |
| START | 0x02 | If bit is set, indicates that this is the |
| | | first segment of the transfer. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 5: XFER_SEGMENT Flags
The flags portion of the message contains two optional values in the
two low-order bits, denoted 'START' and 'END' in Table 5. The
'START' bit MUST be set to one if it precedes the transmission of the
first segment of a transfer. The 'END' 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 'START'
and 'END' bits MUST be set to one.
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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 'END' bit set. No interleaving of multiple
transfers from the same endpoint is possible within a single TCPCL
session. Simultaneous transfers between two endpoints MAY be
achieved using multiple TCPCL sessions.
5.4.4. Data Acknowledgments (XFER_ACK)
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 XFER_ACK message follows in Figure 10.
+-----------------------------+
| Message Header |
+-----------------------------+
| Message Flags (U8) |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
| Acknowledged length (U64) |
+-----------------------------+
Figure 10: Format of XFER_ACK Messages
The fields of the XFER_ACK message are:
Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 5.
Transfer ID: A 64-bit unsigned integer identifying the transfer
being acknowledged.
Acknowledged length: A 64-bit unsigned integer indicating the total
number of octets in the transfer which are being acknowledged.
A receving TCPCL endpoing SHALL send an XFER_ACK message in response
to each received XFER_SEGMENT message. The flags portion of the
XFER_ACK header SHALL be set to match the corresponding DATA_SEGEMNT
message being acknowledged. The acknowledged length of each XFER_ACK
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contains the sum of the data length fields of all XFER_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. Transfer Refusal (XFER_REFUSE)
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 XFER_INIT or XFER_SEGMENT message, the
node MAY transmit a XFER_REFUSE 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 XFER_REFUSE message. A
XFER_REFUSE can be used in cases where the agent's bundle storage is
temporarily depleted or somehow constrained. A XFER_REFUSE 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 XFER_REFUSE message is as follows:
+-----------------------------+
| Message Header |
+-----------------------------+
| Reason Code (U8) |
+-----------------------------+
| Transfer ID (U64) |
+-----------------------------+
Figure 11: Format of XFER_REFUSE Messages
The fields of the XFER_REFUSE message are:
Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 6.
Transfer ID: A 64-bit unsigned integer identifying the transfer
being refused.
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+------------+------------------------------------------------------+
| Name | Semantics |
+------------+------------------------------------------------------+
| Unknown | Reason for refusal is unknown or not specified. |
| | |
| Completed | The receiver now has the complete bundle. The sender |
| | MAY now consider the bundle as completely received. |
| | |
| No | The receiver's resources are exhausted. The sender |
| Resources | SHOULD apply reactive bundle fragmentation before |
| | retrying. |
| | |
| Retransmit | The receiver has encountered a problem that requires |
| | the bundle to be retransmitted in its entirety. |
+------------+------------------------------------------------------+
Table 6: XFER_REFUSE Reason Codes
The receiver MUST, for each transfer preceding the one to be refused,
have either acknowledged all XFER_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 XFER_REFUSE message, the sender
MUST complete the transmission of any partially sent XFER_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 XFER_SEGMENT for the same bundle
after transmitting a XFER_REFUSE message since messages MAY cross on
the wire; if this happens, subsequent segments of the bundle SHOULD
also be refused with a XFER_REFUSE message.
Note: If a bundle transmission is aborted in this way, the receiver
MAY not receive a segment with the 'END' flag set to '1' for the
aborted bundle. The beginning of the next bundle is identified by
the 'START' 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.
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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.
After transmitting a SHUTDOWN message, an endpoint MAY immediately
close the associated TCP connection. Once the SHUTDOWN message is
sent, any further received data on the TCP connection SHOULD be
ignored. Any delay between request to terminate the TCP connection
and actual closing of the connection (a "half-closed" state) MAY be
ignored by the TCPCL endpoint.
The format of the SHUTDOWN message is as follows:
+-----------------------------------+
| Message Header |
+-----------------------------------+
| Message Flags (U8) |
+-----------------------------------+
| Reason Code (optional U8) |
+-----------------------------------+
| Reconnection Delay (optional U16) |
+-----------------------------------+
Figure 12: Format of SHUTDOWN Messages
The fields of the SHUTDOWN message are:
Message Flags: A one-octet field of single-bit flags, interpreted
according to the descriptions in Table 7.
Reason Code: A one-octet refusal reason code interpreted according
to the descriptions in Table 8. The Reason Code is present or
absent as indicated by one of the flags.
Reconnection Delay: A 16-bit unsigned integer indicating the desired
delay until further TCPCL sessions to the sending endpoint. The
Reconnection Delay is present or absent as indicated by one of the
flags.
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+----------+--------+-----------------------------------------------+
| Name | Code | Description |
+----------+--------+-----------------------------------------------+
| D | 0x01 | If bit is set, indicates that a Reconnection |
| | | Delay field is present. |
| | | |
| R | 0x02 | If bit is set, indicates that a Reason Code |
| | | field is present. |
| | | |
| Reserved | others |
+----------+--------+-----------------------------------------------+
Table 7: SHUTDOWN Flags
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 flags and transmit a one-octet reason code
immediately following the message header. The specified values of
the reason code are:
+---------------+---------------------------------------------------+
| Name | Description |
+---------------+---------------------------------------------------+
| Idle timeout | The session is being closed due to idleness. |
| | |
| Version | The node cannot conform to the specified TCPCL |
| mismatch | protocol version. |
| | |
| Busy | The node is too busy to handle the current |
| | session. |
| | |
| Contact | The node cannot interpret or negotiate contact |
| Failure | header option. |
| | |
| TLS failure | The node failed to negotiate TLS session and |
| | cannot continue the session. |
| | |
| Resource | The node has run into some resoure limit and |
| Exhaustion | cannot continue the session. |
+---------------+---------------------------------------------------+
Table 8: 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
flags and then transmits an 16-bit unsigned integer specifying the
requested delay, in seconds, following the message header (and
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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.
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 8). 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
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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 9 in order. These values avoid
unnecessarily leaking endpoing parameters and will be ignored when
secure contact header re-exchange occurs.
+--------------------+---------------------------------------------+
| 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 9: 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 XFER_REFUSE message, or forcibly
terminate the session. This burden could cause denial of service on
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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].
Some of the registries below are created new for TCPCLv4 but share
code values with TCPCLv3. This was done to disambiguate the use of
these values between TCPCLv3 and TCPCLv4 while preserving the
semantics of some values.
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. Each TCPCL endpoint identifies its TCPCL
protocol version in its initial contact (see Section 8.2), so there
is no ambiguity about what protocol is being used.
+------------------------+-------------------------------------+
| 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
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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. Header Extension Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Header Extension Types" and initialized it with the contents of
Table 10. The registration procedure is RFC Required within the
lower range 0x0001--0x3fff. Values in the range 0x8000--0xffff are
resrved for use on private networks for functions not published to
the IANA.
+----------------+--------------------------+
| Code | Message Type |
+----------------+--------------------------+
| 0x0000 | Reserved |
| | |
| 0x0001--0x3fff | Unassigned |
| | |
| 0x8000--0xffff | Private/Experimental Use |
+----------------+--------------------------+
Table 10: Header Extension Type Codes
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8.4. Message Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
Message Types" and initialized it with the contents of Table 11. The
registration procedure is RFC Required.
+-----------+--------------+
| Code | Message Type |
+-----------+--------------+
| 0x00 | Reserved |
| | |
| 0x01 | XFER_SEGMENT |
| | |
| 0x02 | XFER_ACK |
| | |
| 0x03 | XFER_REFUSE |
| | |
| 0x04 | KEEPALIVE |
| | |
| 0x05 | SHUTDOWN |
| | |
| 0x06 | XFER_INIT |
| | |
| 0x07 | MSG_REJECT |
| | |
| 0x08--0xf | Unassigned |
+-----------+--------------+
Table 11: Message Type Codes
8.5. XFER_REFUSE Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
XFER_REFUSE Reason Codes" and initialized it with the contents of
Table 12. 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 |
+----------+---------------------------+
Table 12: XFER_REFUSE Reason Codes
8.6. SHUTDOWN Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
SHUTDOWN Reason Codes" and initialized it with the contents of
Table 13. 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 |
+------------+------------------+
Table 13: SHUTDOWN Reason Codes
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8.7. MSG_REJECT Reason Codes
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry, a sub-
registry titled "Bundle Protocol TCP Convergence-Layer Version 4
MSG_REJECT Reason Codes" and initialized it with the contents of
Table 14. The registration procedure is RFC Required.
+-----------+----------------------+
| Code | Rejection Reason |
+-----------+----------------------+
| 0x00 | reserved |
| | |
| 0x01 | Message Type Unknown |
| | |
| 0x02 | Message Unsupported |
| | |
| 0x03 | Message Unexpected |
| | |
| 0x04-0xFF | Unassigned |
+-----------+----------------------+
Table 14: 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>.
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[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>.
[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-04 (work in
progress), March 2017.
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Appendix A. Significant changes from RFC7242
The areas in which changes from [RFC7242] have been made to existing
headers and messages are:
o Changed contact header content to limit number of negotiated
options.
o Added contact option to negotiate maximum segment size (per each
direction).
o Added contact header extension capability.
o Defined new IANA registries for message / type / reason codes to
allow renaming some codes for clarity.
o Expanded Message Header to octet-aligned fields instead of bit-
packing.
o Added a bundle transfer identification number to all bundle-
related messages (XFER_INIT, XFER_SEGMENT, XFER_ACK, XFER_REFUSE).
o Use flags in XFER_ACK to mirror flags from XFER_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 MSG_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
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Brian Sipos
RKF Engineering Solutions, LLC
7500 Old Georgetown Road
Suite 1275
Bethesda, MD 20814-6198
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
Simon Perreault
Quebec, QC
Canada
Email: simon@per.reau.lt
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