Delay-Tolerant Networking Working Group S. Burleigh
Internet Draft JPL, Calif. Inst. Of Technology
Intended status: Standards Track April 23, 2019
Expires: September 2019
Minimal TCP Convergence-Layer Protocol
draft-ietf-dtn-mtcpcl-01.txt
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Abstract
This document describes a Minimal TCP (MTCP) "convergence-layer"
protocol for the Delay-Tolerant Networking (DTN) Bundle Protocol
(BP). MTCP uses Transmission Control Protocol (TCP) to transmit BP
"bundles" from one BP node to another node to which it is
topologically adjacent in the BP network. The services provided by
the MTCP convergence-layer protocol adapter utilize a standard TCP
connection for the purposes of bundle transmission.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................3
3. MTCP Design Elements...........................................3
3.1. MTCP Sessions.............................................3
3.2. MTCP Protocol Data Units..................................4
4. MTCP Procedures................................................4
4.1. MPDU Transmission.........................................4
4.2. Reception Session Formation...............................5
4.3. MPDU Reception............................................5
5. Security Considerations........................................5
6. IANA Considerations............................................6
7. References.....................................................6
7.1. Normative References......................................6
7.2. Informative References....................................7
8. Acknowledgments................................................7
Appendix A. For More Information..................................8
1. Introduction
This document describes the Minimal TCP (MTCP) protocol, a Delay-
Tolerant Networking (DTN) Bundle Protocol (BP) [RFC5050]
"convergence layer" protocol that uses a standard TCP connection to
transmit bundles from one BP node to another node to which it is
topologically adjacent in the BP network.
Conformance to the MTCP convergence-layer protocol specification is
OPTIONAL for BP nodes.
Each BP node that conforms to the MTCP specification includes an
MTCP convergence-layer adapter (MCLA). Every MCLA engages in
communication via the Transmission Control Protocol [RFC0793].
Like any convergence-layer adapter, the MTCP CLA provides:
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. A transmission service that sends an outbound bundle (from the
bundle protocol agent) to a peer CLA via the MTCP convergence
layer protocol.
. A reception service that delivers to the bundle protocol agent
an inbound bundle that was sent by a peer CLA via the MTCP
convergence layer protocol.
Transmission of bundles via MTCP is "reliable" to the extent that
TCP itself is reliable. MTCP provides no supplementary error
detection and recovery procedures. In particular, MTCP does not
provide to the sender any interim reporting of reception progress.
2. Conventions used in this document
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 RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. MTCP Design Elements
3.1. MTCP Sessions
An MTCP "session" is formed when a TCP connection is established by
the matching of an active TCP OPEN request issued by some MCLA,
termed the session's "sender", with a passive TCP OPEN request
issued by some MCLA, termed the session's "receiver". That portion
of the state of a session that is exposed to the session's sender is
termed the "transmission element" of the session. That portion of
the state of a session that is exposed to the session's receiver is
termed the "reception element" of the session.
The values of the parameters constraining MTCP's TCP connection
establishment, including the establishment of Transport Layer
Security (TLS; [RFC8446]) sessions within the connections, SHALL be
provided by management, by means that are beyond the scope of this
specification. No TCP port number will be reserved for MTCP
connection purposes.
The use of TLS to secure MTCP sessions is optional but is strongly
recommended. When it is determined, by management, that an MTCP
session between a given sender and receiver is to be secured by TLS:
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. Following establishment of the session's TCP connection, the
sender and receiver SHALL undertake a TLS handshake in
accordance with [RFC8446] with the sender acting in the role of
"client". The parameter settings governing each such handshake
(again, determined by management) are an implementation matter,
but the handshake SHOULD conform to all recommended best
practices of [RFC7525] and its updates and successors.
. If the handshake does not result in successful establishment of
a TLS session, then the session's TCP connection SHALL be
terminated and the attempt to form an MTCP session SHALL be
abandoned.
MTCP sessions are unidirectional; that is, bundles transmitted via
an MTCP session are transmitted only from the session's sender to
its receiver. When bidirectional exchange of bundles between MCLAs
via MTCP is required, two MTCP sessions are formed, one in each
direction.
Closure of either element of a session MAY occur either upon request
of the bundle protocol agent or upon detection of any error.
Closure of either element of an MTCP session SHALL cause the
corresponding TCP connection to be terminated (unless termination of
that connection was in fact the cause of the closure of that session
element). Since termination of the associated TCP connection will
result in errors at the other element of the session, termination of
either element of the session will effectively terminate the
session.
3.2. MTCP Protocol Data Units
An MTCP protocol data unit (MPDU) is simply a serialized bundle in a
CBOR representation that indicates the length of that serialized
bundle. An MPDU is constructed as follows.
Each MPDU SHALL be a single serialized BP bundle, termed the
"encapsulated bundle", represented as a CBOR byte string of definite
length (NOT an indefinite-length byte string).
4. MTCP Procedures
4.1. MPDU Transmission
When an MCLA is requested by the bundle protocol agent to send a
bundle to a peer MCLA identified by some IP address and port number:
. If no MTCP session enabling transmission to that MCLA has been
formed, the MCLA SHALL attempt to form that session. If this
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attempt is unsuccessful, the MCLA SHALL inform the bundle
protocol agent that its data sending procedures with regard to
this bundle have concluded and transmission of the bundle was
unsuccessful; no further steps of this procedure will be
attempted.
. The MCLA SHALL form an MPDU from the subject bundle.
. The MCLA SHALL attempt to send this MPDU to the peer MCLA by
TCP via the transmission element of the session formed for this
purpose.
o If that transmission is completed without error, the MCLA
SHALL inform the bundle protocol agent that its data
sending procedures with regard to this bundle have
concluded and transmission of the bundle was successful.
o Otherwise:
. The transmission element SHALL be closed.
. The MCLA SHALL inform the bundle protocol agent that
its data sending procedures with regard to this
bundle have concluded and transmission of the bundle
was unsuccessful.
4.2. Reception Session Formation
An MCLA that is required to receive (rather than only transmit)
bundles SHALL issue a passive TCP OPEN. Whenever TCP matches that
passive OPEN with an active TCP OPEN issued by some MCLA, an MTCP
session is formed as noted earlier; MPDUs may be received via the
reception element of such session.
4.3. MPDU Reception
From the moment at which an MTCP session reception element is first
exposed to the moment at which it is closed, in a continuous cycle,
the corresponding session's receiver SHALL:
. Attempt to receive, by TCP via the corresponding session, a
serialized BP bundle represented as a CBOR byte string of
definite length. If this attempt fails for any reason, the
reception element SHALL be closed and no further steps of this
procedure will be attempted.
. Deliver the received serialized bundle to the bundle protocol
agent.
5. Security Considerations
Because MTCP constitutes a nearly negligible extension of TCP, it
introduces virtually no security considerations beyond the well-
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known TCP security considerations. To address these considerations,
the use of TLS to secure MTCP sessions is strongly recommended.
Even when TLS is used to secure an MTCP session, the ciphersuite
specified for the TLS session may be insecure. For example, TLS can
be configured to support authentication without confidentiality.
MCLA management MUST ensure that the ciphersuites employed to secure
MTCP sessions meet transport security requirements. This constraint
echoes constraints on STARTTLS in [RFC2595].
An adversary could mount a denial-of-service attack by repeatedly
establishing and terminating MTCP sessions; well-understood DOS
attack mitigations would apply.
Maliciously formed bundle lengths could disrupt the operation of
MTCP session receivers, but MTCP implementations need to be robust
against incorrect bundle lengths in any case.
Maliciously crafted serialized bundles could be received and
delivered to the bundle protocol agent, but that is not an MTCP-
specific security consideration: all bundles delivered to the BPA by
all convergence-layer adapters need to be processed in awareness of
this possibility.
6. IANA Considerations
No new IANA considerations apply.
7. References
7.1. Normative References
[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,
May 2015.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, DOI 10.17487/RFC0793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, August 2018.
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7.2. Informative References
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
2595, August 2018.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, November 2007.
8. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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Appendix A. For More Information
Please refer comments to dtn@ietf.org. The Delay Tolerant Networking
Research Group (DTNRG) Web site is located at http://www.dtnrg.org.
Copyright (c) 2019 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info).
Authors' Address
Scott Burleigh
Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
US
Phone: +1 818 393 3353
Email: Scott.Burleigh@jpl.nasa.gov
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