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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 6259

DTN Research Group                                          S. Symington
Internet-Draft                                     The MITRE Corporation
Expires: January 29, 2007                                  July 28, 2006


         Delay-Tolerant Networking Previous Hop Insertion Block
             draft-irtf-dtnrg-bundle-previous-hop-block-00

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines an extension block that may be used with the
   Bundle Protocol [2] within the context of a Delay-Tolerant Network
   architecture [4].  This Previous Hop Insertion Block is designed to
   be inserted by a forwarding node to provide information to its next-
   hop receiving node.  This block is always removed from the bundle by
   the receiving node so that it's duration within the bundle lasts for
   exactly one hop.  It provides a general insertion capability to
   enable any node that forwards a bundle to insert an arbitrary record
   (or records) of information into the bundle.  While this block is



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   defined to provide an arbitrary insertion capability, this
   specification also defines two specific, mandatory, information
   record formats for the information that may be carried in the
   Previous Hop Insertion block.  Using these mandatory information
   record formats, an insertion block may be used to carry the
   inserting/forwarding node's endpoint ID (EID), which may be required
   in some circumstances to support certain routing protocols (e.g.,
   flood routing).  This document defines the format and processing of
   this Previous Hop Insertion Block.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Previous Hop Insertion Block Format  . . . . . . . . . . . . .  5
   3.  Previous Hop Insertion Block Processing  . . . . . . . . . . .  6
     3.1.  Bundle Transmission  . . . . . . . . . . . . . . . . . . .  6
     3.2.  Bundle Forwarding  . . . . . . . . . . . . . . . . . . . .  6
     3.3.  Bundle Reception . . . . . . . . . . . . . . . . . . . . .  6
   4.  Mandatory Information Record Formats . . . . . . . . . . . . .  7
     4.1.  EID-only . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  EID-with-Timestamp . . . . . . . . . . . . . . . . . . . .  7
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12






















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1.  Introduction

   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 [1].

   The DTN bundle protocol [2] defines the bundle as its protocol data
   unit.  A bundle consists of a primary bundle block, which is defined
   in the Bundle Protocol, followed by at least one other type of bundle
   block.  The Bundle Protocol defines a single other type of bundle
   block, called a Bundle Payload block.  This document defines an
   additional, optional, bundle block called a Previous Hop Insertion
   Block.  This block is designed to be used by a forwarding node to
   insert information into a bundle before forwarding that bundle.  The
   intent of this Previous Hop Insertion Block is to provide a general
   insertion mechanism such that an arbitrary record of information may
   be inserted into the bundle by a forwarding node for consumption by
   the next-hop receiving node.  The lifetime of the Previous Hop
   Insertion Block is always exactly one hop in the DTN, so if a bundle
   containing a Previous Hop Insertion Block is received, the receiving
   node is assured that the information in this block was inserted by
   the previous node; likewise, the information in this block is not
   retained with the bundle when the bundle is forwarded.

   The information record(s) to be inserted into the block may have any
   content and format, providing the content and format have been
   defined and documented in order to enable the information to be
   understood.  In this specification we define two specific information
   record formats for use in the insertion block that MUST be supported.
   Each of these formats includes a field for the endpoint ID
   information of the inserting node.  Insertion of a node's EID into a
   bundle's Previous Hop Insertion Block enables the inserting/
   forwarding node to provide its EID to its next-hop receiving node.
   This previous-hop EID information may be required in some
   circumstances to support various routing protocols (e.g., flood
   routing).  Although there may be some situations in which a node that
   receives a bundle may be able to infer the EID of the node that
   forwarded the bundle to it, there are other situations in which the
   EID of the forwarding node will not be able to be inferred by the
   receiving node.  In these situations, if there is a requirement that
   the receiving node be able to determine the EID of the forwarding
   node, the forwarding node must provide this information in the
   bundle.  This specification defines the mechanism, i.e. the Previous
   Hop Insertion Block, used in conjunction with either an EID-only or
   an EID-with-timestamp information record format, whereby a node can
   insert its EID (and possibly other information) into a bundle before
   forwarding it.




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   Using the information record formats that are defined in this
   document, the information that is provided in the insertion blocks at
   each node may include not only the EID of the inserting/forwarding
   node, but also a time stamp.  This information may be further
   expanded or altered through the future definition of additional
   information record formats to provide an arbitrary information record
   insertion capability.  This document defines the format and
   processing of the Previous Hop Insertion Block.  It also defines two
   mandatory information record formats.

   The capabilities described in this document are OPTIONAL for
   deployment with the Bundle Protocol.  Bundle Protocol implementations
   claiming to support Previous Hop Insertion Blocks MUST be capable of:

      -Generating a Previous Hop Insertion Block and inserting it into a
      bundle,

      -Receiving bundles containing a Previous Hop Insertion Block and
      making the information contained in this Previous Hop Insertion
      Block's information record field available for use, e.g., in
      forwarding decisions.

      -Deleting a Previous Hop Insertion Block from a bundle

   as defined in this document.


























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2.  Previous Hop Insertion Block Format

   The Previous Hop Insertion Block uses the Canonical Bundle Block
   Format as defined in the bundle protocol [2].  That is, it is
   comprised of the following elements:

      -Block-type code (one byte) - defined as in all bundle protocol
      blocks except the primary bundle block (as described in the Bundle
      Protocol).  The block type code for the Previous Hop Insertion
      Block is 0x05

      -Block processing control flags (one byte) - defined as in all
      bundle protocol blocks except the primary bundle block (as
      described in the Bundle Protocol).  The following block processing
      control flag MUST be set:

         -Discard block if it can't be processed.

      -Block data length (SDNV) - defined as in all bundle protocol
      blocks except the primary bundle block.  SDNV encoding is
      described in the bundle protocol.

      -Block-type-specific data fields as follows:

         -Information Record Format ID - A one-byte-long field.  Its
         value identifies the format of the information record that
         comes later in the block.  Some mandatory information record
         formats are specified in Section 4.  Additional information
         record formats MAY be defined in separate specifications.

         -Information Record - Contains the data being inserted by the
         forwarding node, formatted as identified by the value of the
         Information Record Format ID field.

   The Structure of a Previous Hop Insertion Block is as follows:

   Previous Hop Insertion Block Format:
   +-----+------+-------+-------------+-------------+
   |Type |Flags |Length |Info. Record |Info. Record |
   |     |      |       | Format ID   |             |
   +-----+------+-------+-------------+-------------+

   Figure 1








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3.  Previous Hop Insertion Block Processing

   The following are the processing steps that a bundle node must take
   relative to generation, reception, and processing of Previous Hop
   Insertion Blocks.

3.1.  Bundle Transmission

   When an outbound bundle is created per the parameters of the bundle
   transmission request, this bundle MAY (as influenced by local policy)
   include one or more Previous Hop Insertion Blocks (as defined in this
   specification).

3.2.  Bundle Forwarding

   Before forwarding a bundle, the node SHALL delete all of the Previous
   Hop Insertion Blocks that were in the bundle when it was received.
   The node SHALL delete all strings (scheme names and scheme-specific
   parts--SSPs) in the bundle's dictionary to which no endpoint ID
   references in the bundle currently refer (if any).

   The node MAY insert one or more Previous Hop Insertion Blocks into
   the bundle before forwarding it, as dictated by local policy.

3.3.  Bundle Reception

   If the bundle includes one or more Previous Hop Insertion Blocks, the
   information records in these blocks SHALL be made available for use
   at this node (e.g., in forwarding decisions).






















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4.  Mandatory Information Record Formats

   This section defines the mandatory information record formats for
   this specification.  Additional formats may be defined elsewhere.

4.1.  EID-only

   The EID-only record format has record-format ID 0x00000001.

   The EID-only record format consists of two fields:

      The EID Scheme Offset - a 16-bit unsigned integer; its value is
      the offset within the dictionary byte array of the first character
      of the scheme name of the EID of the inserting/forwarding node.

      The EID SSP Offset - a 16-bit unsigned integer; its value is the
      offset within the dictionary byte array of the first character of
      the scheme-specific part of the EID of the inserting/forwarding
      node.

4.2.  EID-with-Timestamp

   The EID-with-Timestamp record format has record-format ID 0x00000002.

   The EID-with-Timestamp record format consists of three fields, the
   first two of which are the same as the fields in the EID-only record
   format:

      The EID Scheme Offset - a 16-bit unsigned integer; its value is
      the offset within the dictionary byte array of the first character
      of the scheme name of the EID of the inserting/forwarding node.

      The EID SSP Offset - a 16-bit unsigned integer; its value is the
      offset within the dictionary byte array of the first character of
      the scheme-specific part of the EID of the inserting/forwarding
      node.

      The Elapsed Time field - The Elapsed Time field is a 4-byte field
      that indicates the time at which the bundle is being processed by
      the forwarding node, encoded as a number of seconds past the
      bundle's creation time.










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5.  Security Considerations

   There are two documents that pertain to providing security within
   DTN: the DTN Security Overview [5] and the Bundle Security Protocol
   [3].  These documents define three security-related blocks to provide
   hop-by-hop authentication, end-to-end authentication, and end-to-end
   confidentiality of bundles or parts of bundles, as well as a set of
   mandatory ciphersuites that may be used to calculate security results
   carried in these security blocks.  All ciphersuites that use the
   strict canonicalisation algorithm [3] to calculate and verify
   security results (e.g., many hop-by-hop authentication ciphersuites)
   apply to all blocks in the bundle, and so would apply to bundles that
   include an optional Previous Hop Insertion Block and would include
   that block in the calculation of their security result.  In
   particular, bundles including the optional Previous Hop Insertion
   Block would be protected in their entirety for the duration of a
   single hop, from a forwarding node to an adjacent receiving node (but
   not from source to destination), using the mandatory BAH-HMAC
   ciphersuite defined in the Bundle Security Protocol.  Ciphersuites
   that use the mutable canonicalisation algorithm to calculate and
   verify security results (e.g., the mandatory PSH-RSA-SHA256
   ciphersuite and most end-to-end authentication ciphersuites) will
   (correctly) omit the Previous Hop Insertion Block from their
   calculation.  The fact that several different instantiations of this
   block may be present in the bundle as the bundle transits the network
   will not interfere with end-to-end security protection when using
   ciphersuites that use mutable canonicalisation.  Lastly, the Previous
   Hop Insertion Block will not be encrypted by the mandatory CH-RSA-
   AES-PAYLOAD-PSH end-to-end confidentiality ciphersuite, which only
   allows for payload and PSH encryption.

   The Bundle Authentication Block (BAB) currently includes a mandatory
   security source field over which an authenticator is calculated.
   This security source field contains the EID of the node forwarding
   the bundle.  If a bundle's dictionary already contains both strings
   (the scheme and the SSP) that comprise the EID of the forwarding
   node, however, e.g., as a result of the inclusion of an EID-only or
   an EID-with-Timestamp-formatted information record in a Previous Hop
   Insertion Block that is in the bundle, then it would be redundant to
   include the forwarding node's EID in the BAB as well.  In this case,
   it would make sense to omit the security source field from the BAB.
   However, as currently defined, the security source field is mandatory
   in the BAB.  The BAB should be redefined to make the security source
   field optional to enable the elimination of such potential
   redundancy.






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6.  IANA Considerations

   None at this time.  If the bundle protocol becomes a standards track
   protocol, then we may want to consider having IANA establish a
   register of header types, and in particular for this specification a
   separate register of information record formats.













































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7.  References

7.1.  Normative References

   [1]  Bradner, S. and J. Reynolds, "Key words for use in RFCs to
        Indicate Requirement Levels", RFC 2119, October 1997.

   [2]  Scott, K. and S. Burleigh, "Bundle Protocol Specification",
        draft-irtf-dtnrg-bundle-spec-05.txt, work-in-progress,
        April 2006.

   [3]  Symington, S., Farrell, S., and H. Weiss, "Bundle Security
        Protocol Specification",
        draft-irtf-dtnrg-bundle-security-01.txt, work-in-progress,
        March 2006.

7.2.  Informative References

   [4]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R.,
        Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant Network
        Architecture", draft-irtf-dtnrg-arch-05.txt, work-in-progress,
        March 2006.

   [5]  Farrell, S., Symington, S., and H. Weiss, "Delay-Tolerant
        Network Security Overview",
        draft-irtf-dtnrg-sec-overview-01.txt, work-in-progress,
        March 2006.
























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Author's Address

   Susan Flynn Symington
   The MITRE Corporation
   7515 Colshire Drive
   McLean, VA  22102
   US

   Phone: +1 (703) 983-7209
   Email: susan@mitre.org
   URI:   http://mitre.org/








































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