DTN Research Group S. Symington
Internet-Draft The MITRE Corporation
Intended status: Experimental March 24, 2009
Expires: September 25, 2009
Delay-Tolerant Networking Previous Hop Insertion Block
draft-irtf-dtnrg-bundle-previous-hop-block-06
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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 its
endpoint ID (EID) to the next-hop receiving node. Knowledge of the
EID of a previous-hop node 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 it's 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 . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Normative References . . . . . . . . . . . . . . . . . . . 10
6.2. Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
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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 by a forwarding node to provide its
endpoint ID (EID) 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 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 a
mechanism, i.e. the Previous Hop Insertion Block, whereby a node can
insert its EID into a bundle before forwarding it. If the EID of the
inserting node is already in the dictionary field of the bundle's
Primary Bundle Block, the Previous Hop 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
it 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 the new
forwarding node.
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:
-Generating a Previous Hop Insertion Block and inserting it into a
bundle,
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-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 the Bundle
Protocol). 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
the node inserting the block 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 the inserting node 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
inserting node's EID. Presence of this field is indicated by a
set "block contains an EID reference field" flag in the block
processing control flags. If the EID of the inserting node is not
already 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
inserting node's EID must have already been 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 the node
inserting this Previous Hop Insertion Block.
-Inserting Node's EID SSP - A null-terminated array of bytes
that comprises the scheme-specific part (SSP) of the EID of the
node inserting this Previous Hop Insertion Block.
If the Block EID reference count and EID references field is not
present in the block, the above two EID scheme name and SSP data
fields MUST BE present. Otherwise, these fields MAY 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 inserting node's EID, the Previous Hop Insertion
Block MAY reference these strings and, if it does, it need not
include any block-type-specific data fields. Otherwise, the
inserting node MUST include its EID's scheme name and SSP as the
block's 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.
3.3. Bundle Reception
If the bundle includes a Previous Hop Insertion Block, the EID
identified in these blocks 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 receiving node may use either mechanism to
determine the EID being identified.
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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 (but not from source to
destination), using the 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 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 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 CH-RSA-AES-PAYLOAD-PSH 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 their EIDs. 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-09.txt, work-in-progress,
March 2008.
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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