RFC 7188 PROPOSED STANDARD ROUTING · MANET · EXTENSIBILITY
OLSRv2 and NHDP TLVs: Optimized Link State Routing Protocol Version 2 (OLSRv2) and MANET Neighborhood Discovery Protocol (NHDP) Extension TLVs
TLV rules that let NHDP and OLSRv2 tolerate unfamiliar values and support future extensions.
RFC EDITOR
Dearlove, C. and T. Clausen, "Optimized Link State Routing Protocol Version 2 (OLSRv2) and MANET Neighborhood Discovery Protocol (NHDP) Extension TLVs", RFC 7188, DOI 10.17487/RFC7188, April 2014, <https://www.rfc-editor.org/info/rfc7188>.
BIBTEX
@misc{rfc7188,
series = {Request for Comments},
number = 7188,
howpublished = {RFC 7188},
publisher = {RFC Editor},
doi = {10.17487/RFC7188},
url = {https://www.rfc-editor.org/info/rfc7188},
author = {C. Dearlove and T. Clausen},
title = {{Optimized Link State Routing Protocol Version 2 (OLSRv2) and MANET Neighborhood Discovery Protocol (NHDP) Extension TLVs}},
pagetotal = 16,
year = 2014,
month = apr,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
Internet Engineering Task Force (IETF) C. Dearlove
Request for Comments: 7188 BAE Systems ATC
Updates: 6130, 7181 T. Clausen
Category: Standards Track LIX, Ecole Polytechnique
ISSN: 2070-1721 April 2014
Optimized Link State Routing Protocol Version 2 (OLSRv2) and
MANET Neighborhood Discovery Protocol (NHDP) Extension TLVs
Abstract
This specification describes extensions to definitions of TLVs used
by the Optimized Link State Routing Protocol version 2 (OLSRv2) and
the MANET Neighborhood Discovery Protocol (NHDP) to increase their
abilities to accommodate protocol extensions. This document updates
RFC 7181 (OLSRv2) and RFC 6130 (NHDP).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in 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/rfc7188.
Copyright Notice
Copyright (c) 2014 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. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 3
4. TLV Values . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Unrecognized TLV Values . . . . . . . . . . . . . . . . . 4
4.2. TLV Value Lengths . . . . . . . . . . . . . . . . . . . . 5
4.3. Undefined TLV Values . . . . . . . . . . . . . . . . . . 5
4.3.1. NHDP TLVs: LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB . 6
4.3.2. OLSRv2 TLVs: MPR and NBR_ADDR_TYPE . . . . . . . . . 6
4.3.3. Unspecified TLV Values . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. LOCAL_IF Address Block TLVs . . . . . . . . . . . . . . . 7
5.1.1. New Registry . . . . . . . . . . . . . . . . . . . . 7
5.1.2. Modification to Existing Registry . . . . . . . . . . 8
5.2. LINK_STATUS Address Block TLVs . . . . . . . . . . . . . 8
5.2.1. New Registry . . . . . . . . . . . . . . . . . . . . 8
5.2.2. Modification to Existing Registry . . . . . . . . . . 9
5.3. OTHER_NEIGHB Address Block TLVs . . . . . . . . . . . . . 10
5.3.1. Create New Registry . . . . . . . . . . . . . . . . . 10
5.3.2. Modification to Existing Registry . . . . . . . . . . 11
5.4. MPR Address Block TLVs . . . . . . . . . . . . . . . . . 11
5.4.1. New Registry . . . . . . . . . . . . . . . . . . . . 11
5.4.2. Modification to Existing Registry . . . . . . . . . . 12
5.5. NBR_ADDR_TYPE Address Block TLVs . . . . . . . . . . . . 12
5.5.1. New Registry . . . . . . . . . . . . . . . . . . . . 12
5.5.2. Modification to Existing Registry . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 15
1. Introduction
The MANET Neighborhood Discovery Protocol (NHDP) [RFC6130] and the
Optimized Link State Routing Protocol version 2 (OLSRv2) [RFC7181]
are protocols for use in Mobile Ad Hoc Networks (MANETs) [RFC2501],
based on the Generalized MANET Packet/Message Format [RFC5444].
This document updates [RFC6130] and [RFC7181], specifically their use
of TLV (Type-Length-Value) elements, to increase the extensibility of
these protocols and to enable some improvements in their
implementation.
This specification reduces the latitude of implementations of
[RFC6130] and [RFC7181] to consider some messages, which will not be
created by implementations simply following those specifications, as
a reason to consider the message as "badly formed", and thus as a
reason to reject the message. This gives greater latitude to the
creation of extensions of these protocols, in particular extensions
that will interoperate with unextended implementations of those
protocols. As part of that, it indicates how TLVs with unexpected
value fields must be handled, and adds some additional options to
those TLVs.
Note that TLVs with unknown type or type extension are already
specified as to be ignored by [RFC6130] and [RFC7181] and also are
not a reason to reject a message.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
Additionally, this document uses the terminology of [RFC5444],
[RFC6130], and [RFC7181].
3. Applicability Statement
This document updates the specification of the protocols described in
[RFC6130] and [RFC7181].
Specifically, this specification updates [RFC6130] and [RFC7181] in
the following ways:
o Removes the latitude of rejecting a message with a TLV with a
known type, but with an unexpected TLV Value field, for the TLV
Types defined in [RFC6130] and [RFC7181].
o Specifies the handling of a TLV Value field with unexpected
length.
o Sets up IANA registries for TLV Values for the Address Block TLVs:
* LOCAL_IF, defined in [RFC6130].
* LINK_STATUS, defined in [RFC6130].
* OTHER_NEIGHB, defined in [RFC6130].
* MPR, defined in [RFC7181], now considered as a bit field.
* NBR_ADDR_TYPE, defined in [RFC7181], now considered as a bit
field.
o Defines a well-known TLV Value for "UNSPECIFIED" for the Address
Block TLV Types LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB, all
defined in [RFC6130].
4. TLV Values
NHDP [RFC6130] and OLSRv2 [RFC7181] define a number of TLVs within
the framework of [RFC5444]. These TLVs define the meaning of only
some of the contents that can be found in a TLV Value field. This
limitation may be either defining only certain TLV Values or
considering only some lengths of the TLV Value fields (or a single-
value field in a multivalue Address-Block TLV). This specification
describes how NHDP [RFC6130] and OLSRv2 [RFC7181] are to handle TLVs
with other TLV Value fields.
4.1. Unrecognized TLV Values
NHDP and OLSRv2 specify that, in addition to well-defined reasons (in
the respective protocol specifications), an implementation of these
protocols MAY recognize a message as "badly formed" and therefore
"invalid for processing" for other reasons (Section 12.1 of [RFC6130]
and Section 16.3.1 of [RFC7181]). These sections could be
interpreted as allowing rejection of a message because a TLV Value
field is unrecognized. This specification removes that latitude:
o An implementation MUST NOT reject a message because it contains an
unrecognized TLV value. Instead, any unrecognized TLV Value field
MUST be processed or ignored by an unextended implementation of
NHDP or OLSRv2, as described in the following sections.
o Hence, this specification removes the 7th, 10th, and 11th bullets
in Section 12.1 of [RFC6130].
It should be stressed that this is not a change to [RFC6130] or
[RFC7181], except with regard to not allowing this to be a reason for
rejection of a message. [RFC6130] or [RFC7181] are specified in
terms such as "if an address is associated with a value of LOST by a
LINK_STATUS TLV". Association with an unrecognized value has no
effect on any implementation strictly following such a specification.
4.2. TLV Value Lengths
The TLVs specified in [RFC6130] and [RFC7181] may be either single-
value or multivalue TLVs. In either case, the length of each item of
information encoded in the TLV Value field is the "single-length",
defined and calculated as in Section 5.4.1 of [RFC5444]. All TLVs
specified in [RFC6130] and [RFC7181] have a one- or two-octet single-
length. These are considered the expected single-lengths of such a
received TLV.
Other single-length TLV Value fields may be introduced by extensions
to [RFC6130] and [RFC7181]. This document specifies how
implementations of [RFC6130] and [RFC7181], or extensions thereof,
MUST behave on receiving TLVs of the TLV types defined in [RFC6130]
and [RFC7181], but with TLV Value fields with other single-length
values.
The following principles apply:
o If the received single-length is greater than the expected single-
length, then the excess octets MUST be ignored.
o If the received single-length is less than the expected single-
length, then the absent octets MUST be considered to have all bits
cleared (0).
Exception:
o A received CONT_SEQ_NUM with a single-length < 2 SHOULD be
considered an error.
4.3. Undefined TLV Values
[RFC6130] and [RFC7181] define a number of TLVs, but for some of
these TLVs they specify meanings for only some TLV Values. This
document establishes IANA registries for these TLV Values, with
initial registrations reflecting those used by [RFC6130] and
[RFC7181], and as specified in Section 4.3.3.
There are different cases of TLV Values with different
characteristics. These cases are considered in this section.
4.3.1. NHDP TLVs: LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB
For the Address-Block TLVs LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB
TLVs, defined in [RFC6130], only a limited number of values are
specified for each. These are converted, by this specification, into
extensible registries with initial registrations for values defined
and used by [RFC6130] -- see Section 5.
An implementation of [RFC6130] that receives a LOCAL_IF, LINK_STATUS,
or OTHER_NEIGHB TLV with any TLV Value other than the values that are
defined in [RFC6130] MUST ignore that TLV Value, as well as any
corresponding attribute association to the address.
4.3.2. OLSRv2 TLVs: MPR and NBR_ADDR_TYPE
The Address-Block TLVs MPR and NBR_ADDR_TYPE, defined in [RFC7181],
are similar to those defined in [RFC6130] in having only limited
values specified (1, 2, and 3): 1 and 2 represent the presence of two
different attributes associated to an address, and 3 represents "both
1 and 2".
These TLV Value fields are, by this specification, converted to bit
fields and MUST be interpreted as such. As the existing definitions
of values 1, 2, and 3 behave in that manner, it is likely that this
will involve no change to an implementation, but any test of (for
example) Value = 1 or Value = 3 MUST be converted to a test of (for
example) Value bitand 1 = 1, where "bitand" denotes a bitwise AND
operation.
This specification creates registries for recording reservations of
the individual bits in these bit fields, with initial registrations
for values defined and used by [RFC7181] -- see Section 5.
Other TLVs defined by [RFC7181] are not affected by this
specification.
4.3.3. Unspecified TLV Values
The registries defined in Section 5 for the LOCAL_IF, LINK_STATUS,
and OTHER_NEIGHB TLVs each include an additional TLV Value
UNSPECIFIED. This TLV Value represents a defined value that, like
currently undefined TLV Values, indicates that no information is
associated with this address; the defined value will always have this
meaning. Such a TLV Value may be used to enable the creation of more
efficient multivalue Address Block TLVs or to simplify an
implementation.
The similar requirement for the MPR and NBR_ADDR_TYPES TLVs is
already satisfied by the TLV Value zero, provided that each bit in
the TLV Value is defined as set ('1') when indicating the presence of
an attribute, or clear ('0') when indicating the absence of an
attribute. Therefore, this is required for registrations from the
relevant registries; see Section 5.
For the LINK_METRIC TLV, this is already possible by clearing the
most significant bits (0 to 3) of the first octet of the TLV Value.
It is RECOMMENDED that in this case the remaining bits of the TLV
Value are either all clear ('0') or all set ('1').
5. IANA Considerations
IANA has completed the ten actions set out in the following sections.
5.1. LOCAL_IF Address Block TLVs
5.1.1. New Registry
IANA has created a new sub-registry called "LOCAL_IF TLV Values"
within the "Mobile Ad hoc NETwork (MANET) Parameters" registry.
IANA has populated this registry as specified in Table 1.
+---------+-------------+-------------------------------+-----------+
| Value | Name | Description | Reference |
+---------+-------------+-------------------------------+-----------+
| 0 | THIS_IF | The network address is | RFC 7188 |
| | | associated with this local | |
| | | interface of the sending | |
| | | router | |
| | | | |
| 1 | OTHER_IF | The network address is | RFC 7188 |
| | | associated with another local | |
| | | interface of the sending | |
| | | router | |
| | | | |
| 2-223 | | Unassigned | |
| | | | |
| 224-254 | | Reserved for Experimental Use | RFC 7188 |
| | | | |
| 255 | UNSPECIFIED | No information about this | RFC 7188 |
| | | network address is provided | |
+---------+-------------+-------------------------------+-----------+
Table 1: LOCAL_IF TLV Values
New assignments are to be made by Expert Review [RFC5226].
The Designated Experts are required to use the guidelines specified
in [RFC6130] and [RFC7181].
5.1.2. Modification to Existing Registry
IANA maintains a sub-registry called "LOCAL_IF Address Block TLV Type
Extensions" within the "Mobile Ad hoc NETwork (MANET) Parameters"
registry. This sub-registry already had an entry for value 0. IANA
has replaced the entry in the Description column for this value with
the text "This value is to be interpreted according to the registry
LOCAL_IF TLV Values". The resulting table is as specified in
Table 2.
+-----------+-----------------------------------------+-------------+
| Type | Description | Reference |
| Extension | | |
+-----------+-----------------------------------------+-------------+
| 0 | This value is to be interpreted | RFC 6130, |
| | according to the registry LOCAL_IF TLV | RFC 7188 |
| | Values | |
| | | |
| 1-255 | Unassigned | |
+-----------+-----------------------------------------+-------------+
Table 2: LOCAL_IF Address Block TLV Type Extensions Modifications
5.2. LINK_STATUS Address Block TLVs
5.2.1. New Registry
IANA has created a new sub-registry called "LINK_STATUS TLV Values"
within the "Mobile Ad hoc NETwork (MANET) Parameters" registry.
IANA has populated this registry as specified in Table 3.
+---------+-------------+-------------------------------+-----------+
| Value | Name | Description | Reference |
+---------+-------------+-------------------------------+-----------+
| 0 | LOST | The link on this interface | RFC 7188 |
| | | from the router with that | |
| | | network address has been lost | |
| | | | |
| 1 | SYMMETRIC | The link on this interface | RFC 7188 |
| | | from the router with that | |
| | | network address has the | |
| | | status of symmetric | |
| | | | |
| 2 | HEARD | The link on this interface | RFC 7188 |
| | | from the router with that | |
| | | network address has the | |
| | | status of heard | |
| | | | |
| 3-223 | | Unassigned | |
| | | | |
| 224-254 | | Reserved for Experimental Use | RFC 7188 |
| | | | |
| 255 | UNSPECIFIED | No information about this | RFC 7188 |
| | | network address is provided | |
+---------+-------------+-------------------------------+-----------+
Table 3: LINK_STATUS TLV Values
New assignments are to be made by Expert Review [RFC5226].
The Designated Experts are required to use the guidelines specified
in [RFC6130] and [RFC7181].
5.2.2. Modification to Existing Registry
IANA maintains a sub-registry called "LINK_STATUS Address Block TLV
Type Extensions" within the "Mobile Ad hoc NETwork (MANET)
Parameters" registry. This sub-registry already had an entry for
value 0. IANA has replaced the entry in the Description column for
this value with the text "This value is to be interpreted according
to the registry LINK_STATUS TLV Values". The resulting table is as
specified in Table 4.
+-----------+------------------------------------------+------------+
| Type | Description | Reference |
| Extension | | |
+-----------+------------------------------------------+------------+
| 0 | This value is to be interpreted | RFC 6130, |
| | according to the registry LINK_STATUS | RFC 7188 |
| | TLV Values | |
| | | |
| 1-255 | Unassigned | |
+-----------+------------------------------------------+------------+
Table 4: LINK_STATUS Address Block TLV Type Extensions Modifications
5.3. OTHER_NEIGHB Address Block TLVs
5.3.1. Create New Registry
IANA has created a new sub-registry called "OTHER_NEIGHB TLV Values"
within the "Mobile Ad hoc NETwork (MANET) Parameters" registry.
IANA has populated this registry as specified in Table 5.
+---------+-------------+-------------------------------+-----------+
| Value | Name | Description | Reference |
+---------+-------------+-------------------------------+-----------+
| 0 | LOST | The neighbor relationship | RFC 7188 |
| | | with the router with that | |
| | | network address has been lost | |
| | | | |
| 1 | SYMMETRIC | The neighbor relationship | RFC 7188 |
| | | with the router with that | |
| | | network address is symmetric | |
| | | | |
| 2-223 | | Unassigned | |
| | | | |
| 224-254 | | Reserved for Experimental Use | RFC 7188 |
| | | | |
| 255 | UNSPECIFIED | No information about this | RFC 7188 |
| | | network address is provided | |
+---------+-------------+-------------------------------+-----------+
Table 5: OTHER_NEIGHB Address Block TLV Values
New assignments are to be made by Expert Review [RFC5226].
The Designated Experts are required to use the guidelines specified
in [RFC6130] and [RFC7181].
5.3.2. Modification to Existing Registry
IANA maintains a sub-registry called "OTHER_NEIGHB Address Block TLV
Type Extensions" within the "Mobile Ad hoc NETwork (MANET)
Parameters" registry. This sub-registry already had an entry for
value 0. IANA has replaced the entry in the Description column for
this value with the text "This value is to be interpreted according
to the registry OTHER_NEIGHB TLV Values". The resulting table is as
specified in Table 6.
+-----------+------------------------------------------+------------+
| Type | Description | Reference |
| Extension | | |
+-----------+------------------------------------------+------------+
| 0 | This value is to be interpreted | RFC 6130, |
| | according to the registry OTHER_NEIGHB | RFC 7188 |
| | TLV Values | |
| | | |
| 1-255 | Unassigned | |
+-----------+------------------------------------------+------------+
Table 6: OTHER_NEIGHB Address Block TLV Type Extensions Modifications
5.4. MPR Address Block TLVs
5.4.1. New Registry
IANA has created a new sub-registry called "MPR TLV Bit Values"
within the "Mobile Ad hoc NETwork (MANET) Parameters" registry.
IANA has populated this registry as specified in Table 7.
+-----+-------+----------+------------------------------+-----------+
| Bit | Value | Name | Description | Reference |
+-----+-------+----------+------------------------------+-----------+
| 7 | 0x01 | Flooding | The neighbor with that | RFC 7188 |
| | | | network address has been | |
| | | | selected as flooding MPR | |
| | | | | |
| 6 | 0x02 | Routing | The neighbor with that | RFC 7188 |
| | | | network address has been | |
| | | | selected as routing MPR | |
| | | | | |
| 0-5 | | | Unassigned | |
+-----+-------+----------+------------------------------+-----------+
Table 7: MPR Address Block TLV Bit Values
New assignments are to be made by Expert Review [RFC5226].
The Designated Experts are required to use the guidelines specified
in [RFC6130] and [RFC7181]. Additionally, the Designated Experts are
required to ensure that the following sense is preserved:
o For each bit in the field, a set bit (1) means that the address
has the designated property, while an unset bit (0) means that no
information about the designated property is provided. In
particular, an unset bit must not be used to convey any specific
information about the designated property.
5.4.2. Modification to Existing Registry
IANA maintains a sub-registry called "MPR Address Block TLV Type
Extensions" within the "Mobile Ad hoc NETwork (MANET) Parameters"
registry. This sub-registry already had an entry for value 0. IANA
has replaced the entry in the Description column for this value with
the text "This value is to be interpreted according to the registry
MPR TLV Bit Values". The resulting table is as specified in Table 8.
+-----------+-----------------------------------------+-------------+
| Type | Description | Reference |
| Extension | | |
+-----------+-----------------------------------------+-------------+
| 0 | This value is to be interpreted | RFC 7181, |
| | according to the registry MPR TLV Bit | RFC 7188 |
| | Values | |
| | | |
| 1-255 | Unassigned | |
+-----------+-----------------------------------------+-------------+
Table 8: MPR Address Block TLV Type Extensions Modifications
5.5. NBR_ADDR_TYPE Address Block TLVs
5.5.1. New Registry
IANA has created a new sub-registry called "NBR_ADDR_TYPE Address
Block TLV Bit Values" within the "Mobile Ad hoc NETwork (MANET)
Parameters" registry.
IANA has populated this registry as specified in Table 9.
+-----+-------+------------+----------------------------+-----------+
| Bit | Value | Name | Description | Reference |
+-----+-------+------------+----------------------------+-----------+
| 7 | 0x01 | ORIGINATOR | The network address is an | RFC 7188 |
| | | | originator address | |
| | | | reachable via the | |
| | | | originating router | |
| | | | | |
| 6 | 0x02 | ROUTABLE | The network address is a | RFC 7188 |
| | | | routable address reachable | |
| | | | via the originating router | |
| | | | | |
| 0-5 | | | Unassigned | |
+-----+-------+------------+----------------------------+-----------+
Table 9: NBR_ADDR_TYPE Address Block TLV Bit Values
New assignments are to be made by Expert Review [RFC5226].
The Designated Experts are required to use the guidelines specified
in [RFC6130] and [RFC7181]. Additionally, the Designated Experts are
required to ensure that the following sense is preserved:
o For each bit in the field, a set bit (1) means that the address
has the designated property, while an unset bit (0) means that no
information about the designated property is provided. In
particular, an unset bit must not be used to convey any specific
information about the designated property.
5.5.2. Modification to Existing Registry
IANA maintains a sub-registry called "NBR_ADDR_TYPE Address Block TLV
Type Extensions" within the "Mobile Ad hoc NETwork (MANET)
Parameters" registry. This sub-registry already had an entry for
value 0. IANA has replaced the entry in the Description column for
this value with the text "This value is to be interpreted according
to the registry NBR_ADDR_TYPE TLV Bit Values". The resulting table
is as specified in Table 10.
+-----------+-------------------------------------------+-----------+
| Type | Description | Reference |
| Extension | | |
+-----------+-------------------------------------------+-----------+
| 0 | This value is to be interpreted according | RFC 7181, |
| | to the registry NBR_ADDR_TYPE Address | RFC 7188 |
| | Block TLV Bit Values | |
| | | |
| 1-255 | Unassigned | |
+-----------+-------------------------------------------+-----------+
Table 10: NBR_ADDR_TYPE Address Block TLV Type Extensions
Modifications
6. Security Considerations
The updates made to [RFC6130] and [RFC7181] have the following
implications on the security considerations:
o Created IANA registries for retaining TLV values for TLVs, already
defined in the already published specifications of the two
protocols, and with initial registrations for the TLV values
defined by these specifications. This does not give rise to any
additional security considerations.
o Enabled protocol extensions for registering TLV values in the
created IANA registries. Such extensions MUST specify appropriate
security considerations.
o Created, in some registries, a registration for "UNSPECIFIED"
values for more efficient use of multivalue Address Block TLVs.
The interpretation of an address being associated with a TLV of a
given type and with the value "UNSPECIFIED" is identical to that
address not being associated with a TLV of that type. Thus, this
update does not give rise to any additional security
considerations.
o Reduced the latitude of implementations of the two protocols to
reject a message as "badly formed" due to the value field of a TLV
being unexpected. These protocols are specified in terms such as
"if an address is associated with a value of LOST by a LINK_STATUS
TLV". Association with an unknown value (or a value newly defined
to mean no link status information) has no effect on such a
specification. Thus, this update does not give rise to any
additional security considerations.
o Did not introduce any opportunities for attacks on the protocols
through signal modification that are not already present in the
two protocols.
7. Acknowledgments
The authors would like to gratefully acknowledge the following people
for intense technical discussions, early reviews, and comments on the
specification (listed alphabetically): Ulrich Herberg (Fujitsu
Laboratories of America) and Henning Rogge (Frauenhofer FKIE).
The authors would also like to express their gratitude to Adrian
Farrel for his assistance and contributions to the successful and
timely completion of this specification.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized MANET Packet/Message Format", RFC 5444,
February 2009.
[RFC6130] Clausen, T., Dean, J., and C. Dearlove, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, April 2011.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2", RFC
7181, April 2014.
8.2. Informative References
[RFC2501] Macker, J. and S. Corson, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Authors' Addresses
Christopher Dearlove
BAE Systems Advanced Technology Centre
West Hanningfield Road
Great Baddow, Chelmsford
United Kingdom
Phone: +44 1245 242194
EMail: chris.dearlove@baesystems.com
URI: http://www.baesystems.com/
Thomas Heide Clausen
LIX, Ecole Polytechnique
Phone: +33 6 6058 9349
EMail: T.Clausen@computer.org
URI: http://www.ThomasClausen.org/
ISO Plain Language
On this page
PROBLEMThe NHDP and OLSRv2 specifications left room for implementations to reject a message containing an unfamiliar value in a known TLV.
MECHANISMRFC 7188 forbids rejection for an unrecognized TLV value, defines how to handle unexpected value lengths, converts two TLV types into bit fields and registers TLV values with IANA.
WHY IT MATTERSThe rules give protocol extensions more room to interoperate with implementations that have not added them. RFC 7188 updates RFC 6130 and RFC 7181 and was updated by RFC 7722.
§1Why the TLV Rules Changed
The MANET Neighborhood Discovery Protocol (NHDP) and Optimized Link State Routing Protocol version 2 (OLSRv2) carry information in Type-Length-Value (TLV) elements. The base specifications already said to ignore TLVs with unknown types or type extensions, but could be read to allow rejection of a message with an unrecognized value in a known TLV.
RFC 7188 removes that latitude and defines how implementations handle unexpected values and lengths. This lets extensions introduce new TLV values without requiring every router to understand them before messages can be accepted.
A router should not discard a whole message only because one TLV value is unfamiliar. The updated rule makes it easier to add protocol extensions.
§4.1Do Not Reject an Unknown Value
An implementation must not reject a message because it contains an unrecognized TLV value. It must process or ignore that value according to the rules for the relevant TLV. The RFC removes specified reasons for treating messages as badly formed in NHDP.
This does not otherwise change what the base protocols mean. If an address is associated with an unknown value, an implementation following the base specification has no defined property to apply from that value.
If a router sees an unknown value, it continues processing the message or ignores that value. It must not reject the message for that reason alone.
§4.2Handling Unexpected Value Lengths
A TLV value may contain one item or several items. For the TLVs defined by NHDP and OLSRv2, each item's expected length is one or two octets. Extensions may define other lengths.
If an item's received length is greater than expected, an implementation ignores the extra octets. If it is shorter, the missing octets are treated as zero bits. One exception is a CONT_SEQ_NUM value shorter than 2, which should be treated as an error.
For a value that is too long, ignore the extra bytes. For a value that is too short, treat the missing bytes as zero, except for the stated CONT_SEQ_NUM case.
§4.3Registered Values and Bit Fields
RFC 7188 creates registries for values used by NHDP TLVs LOCAL_IF, LINK_STATUS and OTHER_NEIGHB. An implementation must ignore an undefined value for those TLVs, along with the attribute association that value would make for an address.
For OLSRv2, MPR and NBR_ADDR_TYPE values become bit fields. Values 1 and 2 identify separate attributes, while 3 means both. Implementations must test the relevant bit rather than compare the whole value. The NHDP registries also define UNSPECIFIED to mean that no information is associated with an address.
Some TLV values now identify separate properties with individual bits. A router can recognize known properties while leaving unknown bits or values without an assigned meaning.
§5IANA Registries for TLV Values
IANA created five subregistries in the MANET Parameters registry: three for NHDP TLV values and two for OLSRv2 bit values. The NHDP value registries reserve 224 through 254 for experimental use and assign 255 to UNSPECIFIED. The bit registries identify the defined properties and leave other bits unassigned.
New value assignments use Expert Review. Designated experts must follow the guidelines in the NHDP and OLSRv2 specifications.
Official registries record the meanings assigned to TLV values and bits. Experts review requests to add new meanings.
- 0LOST — The link from the router at the address has been lost.
- 1SYMMETRIC — The link has symmetric status.
- 2HEARD — The link has heard status.
- 224-254Experimental — Reserved for experimental use.
- 255UNSPECIFIED — No information about the address is provided.
§6Security Considerations
The RFC states that its changes add no new security considerations. The registries, UNSPECIFIED values and reduced ability to reject unfamiliar values do not change the base protocols' security behavior.
Any future extension that registers TLV values must specify its own appropriate security considerations. The update does not add new opportunities for attacks through signal modification beyond those already present in NHDP and OLSRv2.
The changed rules do not add a new attack described by the RFC. A future extension must explain the security issues of its own TLV values.
§7References
[RFC5444]RFC 5444Clausen, T., Dearlove, C., Dean, J., and C. Adjih, "Generalized MANET Packet/Message Format", RFC 5444, February 2009.February 2009[RFC6130]RFC 6130Clausen, T., Dean, J., and C. Dearlove, "Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)", RFC 6130, April 2011.April 2011[RFC7181]RFC 7181Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg, "The Optimized Link State Routing Protocol Version 2", RFC 7181, April 2014.April 2014[RFC5226]RFC 5226Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.May 2008