DTN Research Group S. Symington
Internet-Draft The MITRE Corporation
Intended status: Experimental November 12, 2009
Expires: May 16, 2010
Delay-Tolerant Networking Previous Hop Insertion Block
draft-irtf-dtnrg-bundle-previous-hop-block-09
Abstract
This document defines an extension block that may be used with the
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
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This Internet-Draft will expire on May 16, 2010.
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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 . . . . . . . . . . . . . . . . . . . . . 8
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].
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]. The DTN Bundle Protocol defines
the bundle as its protocol data unit. This document defines an
optional bundle block called a Previous Hop Insertion Block (PHIB).
This PHIB 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
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.
In many situations, 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 may be some situations, however, in
which the EID of such an endpoint will not 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 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
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, and so in
order for the node at the receiving end of the tunnel to be able to
learn the EID of the node at the sending end of the tunnel, which is
the previous hop node of the tunneled bundle, the EID must be
provided within the tunneled bundle. The PHIB would be a vehicle for
enabling the node at the sending end of the tunnel to provide its EID
to the node at the receiving end of the tunnel. In situations in
which the EID of the forwarding endpoint cannot be inferred by the
receiving node, 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 PHIB,
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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 PHIB MAY identify this EID using its Block EID
reference count and EID references field. Otherwise, the PHIB MUST
identify this EID by providing the EID in its block-type-specific
data field.
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 the EID of an endpoint of which the
forwarding node is a member.
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:
-Generating a PHIB and inserting it into a bundle,
-Receiving bundles containing a PHIB and making the information
contained in this PHIB available for use, e.g., in forwarding
decisions.
-Deleting a PHIB from a bundle
as defined in this document.
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2. Previous Hop Insertion Block Format
The PHIB 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 PHIB 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 PHIB is determined by whether or not the EID of an
endpoint of which the node inserting the PHIB 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 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 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 PHIB,
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 PHIB 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 PHIB is a member.
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.
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
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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 a PHIB.
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 PHIBs (as defined in this specification). (PHIB
insertion is controlled via a bundle agent configuration option.)
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, 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 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 EID of an endpoint of which the inserting node is a
member, 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 an EID of an
endpoint of which it is a member 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. In this case, the choice of
which EID to insert into the PIB SHALL be made as follows:
- If the inserting node is a member of exactly one singleton
endpoint, at most one PHIB may be inserted into the bundle and the
EID of this singleton endpoint is what MUST be inserted into the
PHIB.
- If the inserting node is a member of more than one singleton
endpoint, the EID of the singleton endpoint that is expressed in
the same URI scheme as the destination of the bundle being
forwarded is what must be inserted into the PHIB. If there is
only one such singleton endpoint expressed in this URI scheme, at
most one PHIB may be inserted into the bundle and the EID of this
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singleton endpoint is what MUST be inserted into the PHIB.
- If the inserting node is a member of more than one singleton
endpoint that is expressed in the same URI scheme as the
destination of the bundle that is being forwarded, the node may
insert a PHIB into the bundle and the EID of one of these
singleton EIDs it what MUST be inserted into the PHIB. The node
MAY also insert additional PHIBs into the bundle, each of which
MUST contain a unique one of the node's additional singleton EIDs
as expressed in this URI scheme.
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 availabilt 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
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 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 PHIB
and would include that block in the calculation of their security
result. In particular, bundles including the optional PHIB would be
protected in their entirety for the extent 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 PHIB 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 PHIB 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 PHIBs should be aware 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.
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.
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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 PHIB would be one. The block type code being suggested
for the PHIB is 0x05.
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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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