Internet Research Task Force (IRTF) S. Symington
Request for Comments: 6259 The MITRE Corporation
Category: Experimental May 2011
ISSN: 2070-1721
Delay-Tolerant Networking Previous-Hop Insertion Block
Abstract
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; see Section 2
of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6259.
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction ....................................................2
1.1. Requirements Language ......................................4
2. Previous-Hop Insertion Block Format .............................4
3. Previous-Hop Insertion Block Processing .........................6
3.1. Bundle Transmission ........................................6
3.2. Bundle Forwarding ..........................................6
3.3. Bundle Reception ...........................................7
4. Security Considerations .........................................8
5. IANA Considerations .............................................9
6. References ......................................................9
6.1. Normative References .......................................9
6.2. Informative References .....................................9
1. 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 this
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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 in Section 3.
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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 in RFC 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 processed
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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.
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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 1
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 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:
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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, the
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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.
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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] (see Section 2):
Additional Entry for the Bundle Block Type Codes Registry:
+-------+----------------------------------------+----------------+
| Value | Description + Reference |
+-------+----------------------------------------+----------------+
| 5 | Previous-Hop Insertion Block + This document |
+-------+----------------------------------------+----------------+
6. References
6.1. 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.
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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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