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Internet Research Task Force (IRTF)                         S. SymingtonRequest for Comments: 6259                         The MITRE CorporationCategory: Experimental                                          May 2011ISSN: 2070-1721Delay-Tolerant Networking Previous-Hop Insertion BlockAbstract   This document defines an extension block for use with the Delay-   Tolerant Networking (DTN) Bundle Protocol.  This Previous-Hop   Insertion Block (PHIB) extension block is designed to be inserted by   a forwarding node to provide the endpoint identifier (EID) of an   endpoint of which the forwarding node is a member so that this EID   may be conveyed to the next-hop receiving node.  Knowledge of an EID   of an endpoint of which a previous-hop node is a member may be   required in some circumstances to support certain routing protocols   (e.g., flood routing).  If this EID cannot be provided by the   convergence layer or other means, the PHIB defines the mechanism   whereby the EID can be provided with the bundle.  Each PHIB is always   removed from the bundle by the receiving node so that its presence   within the bundle is limited to exactly one hop.  This document   defines the format and processing of this PHIB.  This document is a   product of the Delay-Tolerant Networking Research Group and has been   reviewed by that group.  No objections to its publication as an RFC   were raised.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for examination, experimental implementation, and   evaluation.   This document defines an Experimental Protocol for the Internet   community.  This document is a product of the Internet Research Task   Force (IRTF).  The IRTF publishes the results of Internet-related   research and development activities.  These results might not be   suitable for deployment.  This RFC represents the consensus of the   Delay-Tolerant Networking Research Group of the Internet Research   Task Force (IRTF).  Documents approved for publication by the IRSG   are not a candidate for any level of Internet Standard; seeSection 2   of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6259.Symington                     Experimental                      [Page 1]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.Table of Contents1. Introduction ....................................................21.1. Requirements Language ......................................42. Previous-Hop Insertion Block Format .............................43. Previous-Hop Insertion Block Processing .........................63.1. Bundle Transmission ........................................63.2. Bundle Forwarding ..........................................63.3. Bundle Reception ...........................................74. Security Considerations .........................................85. IANA Considerations .............................................96. References ......................................................96.1. Normative References .......................................96.2. Informative References .....................................91.  Introduction   This document defines an extension block for use with the Bundle   Protocol [RFC5050] within the context of a Delay-Tolerant Networking   architecture [RFC4838].  The DTN Bundle Protocol defines the bundle   as its protocol data unit and defines "bundle blocks" to carry data   of different types.  This document defines an optional bundle block   called a Previous-Hop Insertion Block (PHIB).   The PHIB is inserted into a bundle by a forwarding node to provide   the endpoint identifier (EID) of an endpoint of which the forwarding   node is a member so that this EID may be conveyed to the next-hop   receiving node.  (Hereafter, an EID of an endpoint of which a node is   a member will be referred to as an "M-EID" of that node.  A node may   have one or more M-EIDs, depending on the number of endpoints to   which it belongs.  An EID of a singleton endpoint of which a node is   a member will be referred to as a "singleton M-EID" of that node.)   In situations where there is a requirement that the receiving node be   able to determine an M-EID of a forwarding node, but the M-EID of the   forwarding node cannot be inferred by the receiving node through   existing mechanisms, the forwarding node must explicitly provide thisSymington                     Experimental                      [Page 2]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   M-EID in the bundle.  This specification defines the mechanism   whereby a node can insert such an M-EID into a bundle before   forwarding it to the bundle's next hop.   This previous-hop M-EID information may be used in some circumstances   to support various routing protocols.  For example, the PHIB could be   helpful when implementing flood routing because each receiving node   could use the PHIB to determine which EID to exclude from the list of   adjacent nodes to which it forwards received bundles as it does its   part in flooding the bundle.  A node will flood the bundle to all   neighboring nodes except for the node from which it received the   bundle, as identified in the PHIB.   The PHIB could also be used in conjunction with the Bundle   Authentication Block (BAB) of the DTN Bundle Security Protocol   [DTNBSP] to provide the security-source EID for the BAB.  The PHIB   can be used to carry the BAB's security-source EID instead of   conveying this EID using a reference in the BAB's EID-reference field   or including the EID as part of the BAB's key-information parameters.   In many situations, a node that receives a bundle may be able to   infer an M-EID of the node that forwarded the bundle.  In some   situations, however, no M-EID will be able to be inferred by the   receiving node.  For example, if tunneling DTN bundles across some   portion of the DTN network, it is not possible for the node at the   receiving end of the tunnel to determine from the convergence layer   the M-EID of the node at the sending end of the tunnel.  The node at   the receiving end of the tunnel will receive an encapsulating bundle   from one of its adjacent nodes, and it may be able to tell the M-EID   of this adjacent node using the convergence-layer protocol.  However,   the node at the sending end of the tunnel is most likely not adjacent   to the node at the receiving end of the tunnel, so in order for the   node at the receiving end of the tunnel to be able to learn the M-EID   of the node at the sending end of the tunnel, which is the previous-   hop node of the tunneled bundle, the M-EID must be provided within   the tunneled bundle.  In this case, the PHIB is the vehicle for   enabling the node at the sending end of the tunnel to provide its   M-EID to the node at the receiving end of the tunnel.   EIDs may be presented in two ways within the PHIB.  If the M-EID of   the forwarding node is already in the Dictionary field of the   bundle's primary bundle block, the PHIB MAY identify this EID using   its Block EID-reference count and EID-reference field.  Otherwise,   the PHIB MUST identify this EID by providing the EID in its block-   type-specific data field.  These two alternative ways of presenting   EIDs in the PHIB are further discussed inSection 3.Symington                     Experimental                      [Page 3]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   The lifetime of the PHIB is always exactly one hop in the DTN.  If a   bundle containing a PHIB is received, the receiving node is assured   that this PHIB was inserted by the previous node, assuming all nodes   are operating correctly; likewise, this PHIB is not retained with the   bundle when the bundle is forwarded.  If the bundle is forwarded with   a PHIB, this PHIB MUST identify an M-EID of the forwarding node.   This document defines the format and processing of the PHIB.  The   capabilities described in this document are OPTIONAL for deployment   with the Bundle Protocol.  Bundle Protocol implementations claiming   to support the PHIB MUST be capable of:   o  generating a PHIB and inserting it into a bundle,   o  receiving bundles containing a PHIB and making the information      contained in this PHIB available for use, e.g., in forwarding      decisions, and   o  deleting a PHIB from a bundle   as defined in this document.1.1.  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 inRFC 2119 [RFC2119].2.  Previous-Hop Insertion Block Format   The PHIB uses the Canonical Bundle Block Format as defined in the   Bundle Protocol Specification [RFC5050].  That is, the PHIB is   comprised of the following elements, which are defined as in all   bundle protocol blocks except the primary bundle block.  Note that   Self-Delimiting Numeric Value (SDNV) encoding is also described in   the Bundle Protocol Specification:   o  Block-type code (one byte) - The block-type code for the PHIB is      0x05.   o  Block processing control flags (SDNV) - The following block      processing control flag MUST be set:         Discard block if it can't be processedSymington                     Experimental                      [Page 4]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   o  Block EID-reference count and EID-references (optional) -      composite field defined in [RFC5050] containing a count of EID-      references (expressed as an SDNV) followed by an EID-reference      (expressed as a pair of SDNVs).      Whether or not this field is allowed in the PHIB is determined by      whether or not an M-EID of the node inserting the PHIB is already      in the Dictionary field of the primary bundle block (e.g., whether      an M-EID of the inserting node is also an M-EID of the bundle's      source, current custodian, or report-to endpoint, or is the same      as some other endpoint in the dictionary that is referenced by      another block in the bundle).      If an M-EID of the inserting node is already in the dictionary,      this field MAY be present in the PHIB.  If this field is present      in the PHIB, the value of the EID-reference count MUST be one,      meaning that the field contains exactly one EID-reference, which      MUST be a reference to an M-EID of the inserting node.  Presence      of this field MUST be indicated by a set "block contains an EID-      reference field" flag in the block processing control flags.      If no M-EID of the inserting node is in the dictionary, this field      MUST NOT be present in the PHIB, which MUST be indicated by an      unset "block contains an EID-reference field" flag in the block      processing control flags.   o  Block data length (SDNV) - If this value is zero, there are no      block-type-specific data fields.  In this case, the M-EID of the      inserting node must be in the dictionary and it MUST be referenced      in the Block EID-reference count and EID-references field as      described above.   o  Block-type-specific data fields (optional) as follows:      *  Inserting Node's EID Scheme Name - A null-terminated array of         bytes that comprises the scheme name of an M-EID of the node         inserting this PHIB.      *  Inserting Node's EID SSP - A null-terminated array of bytes         that comprises the scheme-specific part (SSP) of an M-EID of         the node inserting this PHIB.      If the Block EID-reference count and EID-references field is not      present in the PHIB, the above two EID scheme name and SSP block-      type-specific data fields MUST be present.  If the Block EID-      reference count and EID-references field is present in the PHIB,      the above two EID scheme name and SSP block-type-specific data      fields MUST NOT be present.Symington                     Experimental                      [Page 5]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   The structure of a PHIB is as follows:   PHIB Format:   +----+------------+--------------------------------- -+-------------+   |type|flags (SDNV)|EID-ref count and list (comp) (opt)|length (SDNV)|   +----+------------+-----------------------------------+-------------+   | Inserting Node EID Scheme Name (opt)| Inserting Node EID SSP (opt)|   +-------------------------------------------------------------------+                                 Figure 13.  Previous-Hop Insertion Block Processing   The following are the processing steps that a bundle node must take   relative to generation, reception, and processing of a PHIB.3.1.  Bundle Transmission   When an outbound bundle is created per the parameters of the bundle   transmission request, this bundle MAY include one or more PHIBs.   Whether or not PHIBs are included is a local bundle agent   configuration option and may be influenced by other factors, such as   the routing protocol in use.3.2.  Bundle Forwarding   Before forwarding a bundle, the node SHALL delete all PHIBs that were   in the bundle when it was received (if any).  As described in the   Bundle Protocol Specification, the node MAY delete all strings   (scheme names and 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 PHIBs into the bundle before   forwarding it, as dictated by local policy.  If there are already   strings (scheme names and SSPs) in the bundle's dictionary that   denote the M-EID of the inserting node, the PHIB MAY reference these   strings and, if it does, it MUST NOT include any block-type-specific   data fields.  The inserting node MUST NOT insert strings into the   bundle's dictionary in order that they may be referenced by only the   PHIB.  If the PHIB is constructed such that it does not reference any   strings from the dictionary, the inserting node MUST include the   scheme name and SSP of one of its M-EIDs as the PHIB's block-type-   specific data fields.   The node that is inserting a PHIB into the bundle may have more than   one endpoint in which it is a member.  The choice of which M-EID to   insert into the PIB SHALL be made as follows:Symington                     Experimental                      [Page 6]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   o  If the inserting node is a member of exactly one singleton      endpoint, the node may insert at most one PHIB into the bundle and      the EID of this singleton endpoint is what MUST be inserted into      the PHIB.   o  If the inserting node is a member of more than one singleton      endpoint, then:         If the inserting node has a priori knowledge of the URI schemes         supported by the next-hop node and if the inserting node has         one or more singleton M-EIDs that are expressible in one or         more of those URI schemes, then the inserting node MAY insert         one or more PHIBs into the bundle being forwarded.  The EIDs in         the inserted PHIBs MUST be unique, they MUST be singleton         M-EIDs of the inserting node, and they MUST be expressed in URI         schemes supported by the next-hop node.  Mechanisms for         determining what URI schemes are supported by particular next-         hop neighbors are not defined here.         If the inserting node has one or more singleton M-EIDs that are         expressible in the same URI scheme as the destination of the         bundle that is being forwarded, then the inserting node MAY         insert one or more PHIBs into the bundle being forwarded.  The         EIDs in the inserted PHIBs MUST be unique, they MUST be         singleton M-EIDs of the inserting node, and they MUST be         expressed in the destination URI scheme of the bundle.         Else, if the inserting node has neither a singleton M-EID that         is expressible in a URI scheme known to be supported by the         next-hop node nor a singleton M-EID that is expressible in the         same URI scheme as the destination of the bundle that is being         forwarded, then the inserting node MAY insert one or more PHIBs         into the bundle being forwarded.  The EIDs in the inserted         PHIBs MUST be unique, and they MUST be singleton M-EIDs of the         inserting node.3.3.  Bundle Reception   If the bundle includes a PHIB, the EID identified in the PHIB SHALL   be made available for use at the receiving node (e.g., in forwarding   decisions or, if the receiving node is the bundle-destination, the   EID may be made available to the receiving application; whether or   not it is made available to the receiving application is an   implementation matter).  If the EID is identified both by a reference   in the PHIB's block EID-reference count and EID-references field and   by a scheme name and SSP in the block-type-specific fields, the PHIB   is not considered to be well-formed.  In the case of reception of   such an ill-formed PHIB, if the identified EIDs are the same, theSymington                     Experimental                      [Page 7]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   receiving node MAY process the PHIB as if it were well-formed.   However, if the identified EIDs differ, the receiving node MUST NOT   process the PHIB and must take action on the PHIB as specified by the   PHIB's block processing flags.4.  Security Considerations   The DTN Bundle Security Protocol [DTNBSP] defines security-related   blocks to provide hop-by-hop bundle authentication and integrity,   end-to-end integrity, and end-to-end confidentiality of bundles or   parts of bundles, as well as a set of ciphersuites that may be used   to calculate security-results carried in these security blocks.  The   PHIB will not be encrypted when using the PCB-RSA-AES128-PAYLOAD-PIB-   PCB ciphersuite with the Payload Confidentiality Block (PCB) to   provide end-to-end confidentiality.  This ciphersuite only allows for   payload and Payload Integrity Block (PIB) encryption.  If encryption   of the PHIB block is desired, the Extension Security Block (ESB)   could be used for this purpose.   All ciphersuites that use the strict canonicalization algorithm   [DTNBSP] 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 PHIB and would   include that block in the calculation of their security-result.  In   particular, bundles including the optional PHIB would have their   integrity protected in their entirety for the extent of a single hop,   from a forwarding node to an adjacent receiving node, using the   Bundle Authentication Block (BAB) with the BAB-HMAC (Hashed Message   Authentication Code) ciphersuite defined in the Bundle Security   Protocol Specification.   Ciphersuites that use the mutable canonicalization algorithm to   calculate and verify security-results (e.g., the PIB-RSA-SHA256   ciphersuite and most end-to-end authentication ciphersuites used with   the PIB) will (correctly) omit the PHIB from their calculation.  The   fact that several different instantiations of this PHIB block may be   added to and deleted from the bundle as the bundle transits the   network will not interfere with end-to-end security protection when   using ciphersuites that use mutable canonicalization.   As stated above, the BAB can be used to ensure the integrity of the   PHIB.  Nodes receiving bundles with PHIBs should be aware, however,   that forwarding nodes that insert PHIBs might lie about the EIDs of   endpoints of which they are members.  Lying in this way could provide   a mechanism for subverting routing strategies that base routing   decisions on EID information in the PHIB.Symington                     Experimental                      [Page 8]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011   Note that if some Bundle Protocol implementation does not support the   PHIB but does not properly implement the "Discard block if it can't   be processed" flag, then a PHIB may unexpectedly persist for longer   than a single hop.5.  IANA Considerations   This specification allocates a codepoint from the "Bundle Block   Types" registry defined in [RFC6255] (seeSection 2):   Additional Entry for the Bundle Block Type Codes Registry:     +-------+----------------------------------------+----------------+     | Value | Description                            + Reference      |     +-------+----------------------------------------+----------------+     |   5   | Previous-Hop Insertion Block           + This document  |     +-------+----------------------------------------+----------------+6.  References6.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5050]  Scott, K. and S. Burleigh, "Bundle Protocol              Specification",RFC 5050, November 2007.   [RFC6255]  Blanchet, M., "Delay-Tolerant Networking (DTN) Bundle              Protocol IANA Registries",RFC 6255, May 2011.6.2.  Informative References   [RFC4838]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,              R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant              Networking Architecture",RFC 4838, April 2007.   [DTNBSP]   Symington, S., Farrell, S., Weiss, H., and P. Lovell,              "Bundle Security Protocol Specification",RFC 6257,              May 2011.Symington                     Experimental                      [Page 9]

RFC 6259            DTN Previous-Hop Insertion Block            May 2011Author'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/Symington                     Experimental                     [Page 10]