DTN Research Group S. Symington
Internet-Draft The MITRE Corporation
Intended status: Experimental June 11, 2009
Expires: December 13, 2009
Delay-Tolerant Networking Previous Hop Insertion Block
draft-irtf-dtnrg-bundle-previous-hop-block-07
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Abstract
This document defines an extension block that may be used with the
Bundle Protocol [refs.DTNBP] within the context of a Delay-Tolerant
Network architecture [refs.DTNarch]. This Previous Hop Insertion
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). The
Previous Hop Insertion block is always removed from the bundle by the
receiving node so that its duration within the bundle lasts for
exactly one hop. 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 . . . . . . . . . . . 7
3.1. Bundle Transmission . . . . . . . . . . . . . . . . . . . 7
3.2. Bundle Forwarding . . . . . . . . . . . . . . . . . . . . 7
3.3. Bundle Reception . . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 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
[refs.RFC2119].
The DTN bundle protocol [refs.DTNBP] defines the bundle as its
protocol data unit. This document defines an optional bundle block
called a Previous Hop Insertion Block. This Previous Hop Insertion
Block is designed to be inserted into a bundle by a forwarding node
to provide the endpoint ID (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. 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
an endpoint of which the node that forwarded the bundle to it is a
member, there are other situations in which the EID of such an
endpoint 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 an endpoint of which the forwarding
node is a member, the forwarding node must provide this information
in the bundle. This specification defines a mechanism, i.e. the
Previous Hop Insertion Block, whereby a node can insert such an EID
into a bundle before forwarding it. If the EID of an endpoint of
which the forwarding node is a member is already in the dictionary
field of the bundle's Primary Bundle Block, the Previous Hop
Insertion Block MAY identify this EID using its Block EID reference
count and EID references field. Otherwise, the Previous Hop Block
MUST identify this EID by providing the EID in its block-type-
specific data field.
The lifetime of the Previous Hop Insertion Block is always exactly
one hop in the DTN. If a bundle containing a Previous Hop Insertion
Block is received, the receiving node is assured that this block was
inserted by the previous node, assuming all nodes are operating
correctly; likewise, this block is not retained with the bundle when
the bundle is forwarded. If the bundle is forwarded with a Previous
Hop Insertion Block, this block must identify the EID of an endpoint
of which the forwarding node is a member.
This document defines the format and processing of the Previous Hop
Insertion Block. 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:
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-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 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 [refs.DTNBP]. 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
[refs.DTNBP]). The block type code for the Previous Hop Insertion
Block is 0x05.
-Block processing control flags (SDNV) - defined as in all bundle
protocol blocks except the primary bundle block (SDNV encoding is
described in the Bundle Protocol). The following block processing
control flag MUST be set:
-Discard block if it can't be processed.
-Block EID reference count and EID references (optional) -
composite field defined in [refs.DTNBP] 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 may be
present in the block is determined by whether or not the EID of an
endpoint of which the node inserting the block is a member is
already in the Dictionary Field of the Primary Bundle Block (e.g.,
whether this EID is the EID of the bundle's source, current
custodian, or report-to endpoint, or of some other endpoint in the
dictionary that is referenced by another block in the bundle). If
the EID of an endpoint of which the inserting node is a member is
already in the dictionary, this field MAY be present in the block.
If this field is present in the block, 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 the EID of
an endpoint of which the inserting node is a member. Presence of
this field MUST be indicated by a set "block contains an EID
reference field" flag in the block processing control flags. If
the EID of an endpoint of which the inserting node is a member is
not in the dictionary, this field MUST NOT be present in the
block, which MUST be indicated by an unset "block contains an EID
reference field" flag in the block processing control flags
-Block data length (SDNV) - defined as in all bundle protocol
blocks except the primary bundle block. SDNV encoding is
described in the Bundle Protocol. If this value is zero, there
are no block-type-specific data fields. In this case, the EID of
an endpoint of which the inserting node is a member must be in the
dictionary and it MUST be referenced in the Block EID reference
count and EID references field as described above.
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-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 the EID of an endpoint
of which the node inserting this Previous Hop Insertion Block
is a member.
-Inserting Node's EID SSP - A null-terminated array of bytes
that comprises the scheme-specific part (SSP) of the EID of an
endpoint of which the node inserting this Previous Hop
Insertion Block is a member.
If the Block EID reference count and EID references field is not
present in the block, 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 block,
the above two EID scheme name and SSP block-type-specific data
fields MUST NOT be present.
The Structure of a Previous Hop Insertion Block is as follows:
Previous Hop Insertion Block 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
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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 a Previous Hop Insertion Block (as defined in this
specification).
3.2. Bundle Forwarding
Before forwarding a bundle, the node SHALL delete the Previous Hop
Insertion Block that was in the bundle when it was received (if any).
As described in the Bundle Protocol, the node MAY 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 a Previous Hop Insertion Block 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 EID of an endpoint of which the inserting node is a
member, the Previous Hop Insertion Block 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 Previous
Hop Insertion Block. If the Previous Hop Insertion Block is
constructed such that it does not reference any strings from the
dictionary, the inserting node MUST include the scheme name and SSP
of an EID of an endpoint of which it is a member as the block's
block-type-specific data fields.
3.3. Bundle Reception
If the bundle includes a Previous Hop Insertion Block, the EID
identified in this block SHALL be made available for use at this node
(e.g., in forwarding decisions). If the EID is identified both by a
reference in the block's Block EID reference count and EID references
field and by a scheme name and SSP in the block-type-specific fields,
the block is not considered to be well-formed. In the case of
reception of such an ill-formed block, if the identified EIDs are the
same, the receiving node MAY process the block as if it were well-
formed. However, if the identified EIDs differ, the receiving node
MUST NOT process the block and must take action on the block as
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specified by the block's Block Processing Control Flags.
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4. Security Considerations
The DTN Bundle Security Protocol [refs.DTNBPsec] defines 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 ciphersuites that may be used to
calculate security results carried in these security blocks. All
ciphersuites that use the strict canonicalisation algorithm
[refs.DTNBPsec] 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, using the BAB-HMAC
ciphersuite defined in the Bundle Security Protocol. Ciphersuites
that use the mutable canonicalisation algorithm to calculate and
verify security results (e.g., the PIB-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 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 canonicalisation. Lastly, the Previous
Hop Insertion Block will not be encrypted by the PCB-RSA-AES128-
PAYLOAD-PIB-PCB end-to-end confidentiality ciphersuite, which only
allows for payload and PSH encryption. If encryption of this block
is desired, the Extension Security Block (ESB) could be used for this
purpose.
Nodes receiving bundles with Previous Hop Insertion Blocks should be
aware that forwarding nodes that insert Previous Hop Insertion Blocks
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
Previous Hop Insertion Block.
Note that if some Bundle Protocol implementation does not support the
Previous Hop Insertion Block but does not properly implement the
"Discard block if it can't be processed" flag, then a Previous Hop
Insertion Block may unexpectedly persist for longer than a single
hop.
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5. IANA Considerations
If the bundle protocol becomes a standards track protocol, then we
may want to consider having IANA establish a register of block types,
of which the Previous Hop Insertion Block would be one.
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6. References
6.1. Normative References
[refs.RFC2119]
Bradner, S. and J. Reynolds, "Key words for use in RFCs to
Indicate Requirement Levels", RFC 2119, October 1997.
[refs.DTNBP]
Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, November 2007.
[refs.DTNBPsec]
Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification",
draft-irtf-dtnrg-bundle-security-08.txt, work-in-progress,
March 2009.
6.2. Informative References
[refs.DTNarch]
Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Network Architecture", RFC 4838, April 2007.
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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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