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rfc:rfc7466

Internet Engineering Task Force (IETF) C. Dearlove Request for Comments: 7466 BAE Systems ATC Updates: 6130, 7181 T. Clausen Category: Standards Track LIX, Ecole Polytechnique ISSN: 2070-1721 March 2015

       An Optimization for the Mobile Ad Hoc Network (MANET)
               Neighborhood Discovery Protocol (NHDP)

Abstract

 The link quality mechanism of the Mobile Ad Hoc Network (MANET)
 Neighborhood Discovery Protocol (NHDP) enables "ignoring" some 1-hop
 neighbors if the measured link quality from that 1-hop neighbor is
 below an acceptable threshold while still retaining the corresponding
 link information as acquired from the HELLO message exchange.  This
 allows immediate reinstatement of the 1-hop neighbor if the link
 quality later improves sufficiently.
 NHDP also collects information about symmetric 2-hop neighbors.
 However, it specifies that if a link from a symmetric 1-hop neighbor
 ceases being symmetric, including while "ignored" (as described
 above), then corresponding symmetric 2-hop neighbors are removed.
 This may lead to symmetric 2-hop neighborhood information being
 permanently removed (until further HELLO messages are received) if
 the link quality of a symmetric 1-hop neighbor drops below the
 acceptable threshold, even if only for a moment.
 This specification updates RFC 6130 "Mobile Ad Hoc Network (MANET)
 Neighborhood Discovery Protocol (NHDP)" and RFC 7181 "The Optimized
 Link State Routing Protocol Version 2 (OLSRv2)" to permit, as an
 option, retaining, but ignoring, symmetric 2-hop information when the
 link quality from the corresponding 1-hop neighbor drops below the
 acceptable threshold.  This allows immediate reinstatement of the
 symmetric 2-hop neighbor if the link quality later improves
 sufficiently, thus making the symmetric 2-hop neighborhood more
 "robust".

Dearlove & Clausen Standards Track [Page 1] RFC 7466 NHDP Optimization March 2015

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/rfc7466.

Copyright Notice

 Copyright (c) 2015 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 .....................................................4
 3. Applicability Statement .........................................4
 4. Changes to NHDP .................................................4
    4.1. Interface Information Bases ................................5
    4.2. HELLO Message Processing ...................................5
    4.3. Information Base Changes ...................................5
    4.4. Constraints ................................................6
 5. Changes to OLSRv2 ...............................................6
 6. Security Considerations .........................................8
 7. References ......................................................8
    7.1. Normative References .......................................8
    7.2. Informative References .....................................8
 Acknowledgements ...................................................9
 Authors' Addresses .................................................9

Dearlove & Clausen Standards Track [Page 2] RFC 7466 NHDP Optimization March 2015

1. Introduction

 Section 14 of the MANET Neighborhood Discovery Protocol (NHDP)
 [RFC6130] contains a link admission mechanism known as "link quality"
 that allows a router using that protocol to "take considerations
 other than message exchange into account for determining when a link
 is and is not a candidate for being considered as HEARD or
 SYMMETRIC."  Specifically, [RFC6130] permits a router to disallow
 consideration of some of its 1-hop neighbors for as long as the
 quality of the link from that 1-hop neighbor is below an acceptable
 link quality threshold.
 A feature of this mechanism is that while the link quality remains
 too low, the link information, established by the exchange of HELLO
 messages, is retained.  Thus, if the link quality later goes above
 the required threshold (note that a hysteresis mechanism means that
 two thresholds are used), then the link is immediately established
 and will be immediately available for use.
 [RFC6130] collects not only 1-hop neighbor information, but also
 information about symmetric 2-hop neighbors.  However, [RFC6130]
 specifies that if a 1-hop neighbor was, but no longer is, considered
 symmetric, then the corresponding 2-Hop Tuples that may have been
 recorded for that 2-hop neighbor are to be removed without a
 retention mechanism for a (possibly temporary) loss due to link
 quality.
 This means that if there is a short period in which link quality is
 too low, then when the link quality is re-established all 1-hop
 neighbor information is immediately available for use again.
 However, the corresponding symmetric 2-hop neighbor information has
 been removed and is not available for use until restored by receipt
 of the next corresponding HELLO message.
 This specification describes how [RFC6130] can be modified to avoid
 this situation by retaining (but not using) 2-hop information,
 similar to what is done with 1-hop information.  This modification is
 strictly optional, and routers that do and do not implement it can
 interwork entirely successfully (as they also can with different link
 quality specifications).  In addition, by a suitable interpretation
 (that ignored 2-Hop Tuples are not externally advertised), this
 change can be invisible to any other protocols using [RFC6130], in
 particular [RFC7181].  However, the impact on [RFC7181] when 2-Hop
 Tuples are not so handled is also described (owing to the existence
 of implementations of that protocol that are not modularly separated
 from [RFC6130]).
 This specification therefore updates [RFC6130] and [RFC7181].

Dearlove & Clausen Standards Track [Page 3] RFC 7466 NHDP Optimization March 2015

 This update to [RFC6130] does not change the definition of a
 symmetric 2-hop neighbor but adds new state information to each 2-Hop
 Tuple of [RFC6130].  This is to retain some 2-hop neighbor
 information while recording it as currently not to be used.  The new
 state information and retained 2-Hop Tuples are reflected in the
 corresponding tables of the updated NHDP-MIB module [NHDP-MIB].

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 [RFC6130] and
 [RFC7181].

3. Applicability Statement

 This specification updates [RFC6130].  The optimization presented in
 this specification is simply permissive, as it allows retaining
 information that otherwise would have been removed but does not use
 that information except when it could have been used by [RFC6130].
 This can, in some cases, ensure that the symmetric 2-hop neighborhood
 is more robust against temporary link quality changes and
 consequently yields a more stable network.  The only other
 consequence of this optimization is that state for some otherwise
 expired 2-Hop Tuples may be maintained for longer.
 This specification also updates [RFC7181].  This could have been
 avoided had instead [RFC6130] been updated so as to make the changes
 to it invisible to any other protocol using it.  However, as it is
 known that some implementations of [RFC7181] are not independent of
 the implementation of [RFC6130] that they use, it is useful to
 indicate the direct impact on [RFC7181].
 A router that implements the optimization described in this
 specification will interoperate successfully with routers that
 implement [RFC6130] but do not implement this optimization.

4. Changes to NHDP

 The following changes are made to [RFC6130] if using this
 specification.  Note that while this specification is OPTIONAL, if
 any of these changes are made, then all of these changes MUST be
 made.

Dearlove & Clausen Standards Track [Page 4] RFC 7466 NHDP Optimization March 2015

4.1. Interface Information Bases

 The 2-Hop Set is modified by adding this additional element to each
 2-Hop Tuple:
    N2_lost is a boolean flag, which indicates the state of the
    corresponding Link Tuple.  If L_status = SYMMETRIC (and thus
    L_lost = false), then N2_lost = false.  If L_SYM_time has not
    expired, and L_lost = true (and hence L_status = LOST), then
    N2_lost = true.
 In all other cases, including other cases with L_status = LOST, there
 will be no such 2-Hop Tuples.

4.2. HELLO Message Processing

 In Section 12.6 of [RFC6130], make the following changes:
 o  In point 2, change "L_status = SYMMETRIC" to "L_SYM_time not
    expired".
 o  In point 2, point 1, point 1, under "then create a 2-Hop Tuple
    with:", add a second bullet point "N2_lost: = L_lost".  (Note that
    "2-Hop Neighbor Tuple" has been corrected here to "2-Hop Tuple"
    per [Err4276].)

4.3. Information Base Changes

 In Section 13, replace the second bullet point with:
 o  A Link Tuple's L_status changes from SYMMETRIC, L_SYM_time
    expires, or the Link Tuple is removed.  In this case, the actions
    specified in Section 13.2 are performed.
 Replace the paragraph after the bullet points with:
 If a Link Tuple is removed, or if L_HEARD_time expires and either
 L_status changes from SYMMETRIC or L_SYM_time expires, then the
 actions specified in Section 13.2 MUST be performed before the
 actions specified in Section 13.3 are performed for that Link Tuple.

Dearlove & Clausen Standards Track [Page 5] RFC 7466 NHDP Optimization March 2015

 In Section 13.2 of [RFC6130], add the following before all other
 text:
 For each Link Tuple that has L_SYM_time not expired:
 1.  If L_SYM_time then expires, or if the Link Tuple is removed:
     1.  Remove each 2-Hop Tuple for the same MANET interface with:
         +  N2_neighbor_iface_addr_list contains one or more network
            addresses in L_neighbor_iface_addr_list.
 2.  If L_status then changes from SYMMETRIC to LOST because L_lost is
     set to true:
     1.  For each 2-Hop Tuple for the same MANET interface with:
         +  N2_neighbor_iface_addr_list contains one or more network
            addresses in L_neighbor_iface_addr_list;
         set N2_lost := true.
 Also, in Section 13.2 of [RFC6130], remove point 1 and renumber point
 2 as point 1.

4.4. Constraints

 In Appendix B of [RFC6130], under "In each 2-Hop Tuple:", change the
 first bullet point to:
 o  There MUST be a Link Tuple associated with the same MANET
    interface with:
  • L_neighbor_iface_addr_list = N2_neighbor_iface_addr_list; AND
  • L_SYM_time not expired; AND
  • L_lost = N2_lost.

5. Changes to OLSRv2

 If the implementation of [RFC6130] conceals from any protocol using
 it the existence of all 2-Hop Tuples with N2_lost = true, then no
 changes are required to any protocol using [RFC6130]; in particular,
 no changes are required to [RFC7181].

Dearlove & Clausen Standards Track [Page 6] RFC 7466 NHDP Optimization March 2015

 However, if instead the implementation of [RFC6130] makes all 2-Hop
 Tuples visible, including those with N2_lost = true, then protocols
 using [RFC6130] MUST ignore such 2-Hop Tuples.
 For [RFC7181], given that this protocol uses 2-hop information for
 Multipoint Relay (MPR) Set and Routing Set calculation but does not
 include that information in control traffic, this means that an
 implementation must be behaving (i) as if a 2-Hop Tuple only exists
 if N2_lost=false and (ii) as if a change of N2_lost (from false to
 true, or true to false) corresponds to a 2-Hop Tuple appearing or
 being removed.  Specifically, this means behaving as if all of the
 following changes were to be made to [RFC7181]:
 o  In Section 17.6 of [RFC7181], point 1, replace the final two
    bullet points with:
  • A 2-Hop Tuple with N2_out_metric != UNKNOWN_METRIC and N2_lost

= false is added or removed; OR

  • A 2-Hop Tuple with N2_out_metric != UNKNOWN_METRIC has N2_lost

changed; OR

  • The N2_out_metric of any 2-Hop Tuple with N2_lost = false

changes, and either the flooding MPR selection process uses

       metric values (see Section 18.4), or the change is to or from
       UNKNOWN_METRIC.
 o  In Section 17.6 of [RFC7181], point 3, replace the final two
    bullet points with:
  • A 2-Hop Tuple with N2_in_metric != UNKNOWN_METRIC and N2_lost =

false is added or removed; OR

  • A 2-Hop Tuple with N2_in_metric != UNKNOWN_METRIC has N2_lost

changed; OR

  • The N2_in_metric of any 2-Hop Tuple with N2_lost = false

changes.

 o  In Section 17.7 of [RFC7181], in the fifth bullet point, add "and
    N2_lost = false" after "N2_out_metric != UNKNOWN_METRIC".
 o  In Section 18.4 of [RFC7181], in the third bullet point, add ",
    N2_lost = false" after "N2_out_metric != UNKNOWN_METRIC".
 o  In Section 18.5 of [RFC7181], in the third bullet point, add ",
    N2_lost = false" after "N2_in_metric != UNKNOWN_METRIC".

Dearlove & Clausen Standards Track [Page 7] RFC 7466 NHDP Optimization March 2015

 o  In Section 19.1 of [RFC7181], in the final main bullet point
    (marked as "(OPTIONAL)"), add "and N2_lost = false" after
    "N2_out_metric != UNKNOWN_METRIC".
 o  In Appendix C.7 of [RFC7181], in point 1, add "and N2_lost =
    false" after "N2_out_metric != UNKNOWN_METRIC".

6. Security Considerations

 The update to [RFC6130] enables the retention and reuse of some
 information collected by that protocol, for only the duration that it
 could have been used in any case.  As such, this protocol introduces
 no new security considerations to an implementation of [RFC6130]  or
 of any other protocol that uses it, such as [RFC7181].

7. References

7.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC6130]  Clausen, T., Dean, J., and C. Dearlove, "Mobile Ad Hoc
            Network (MANET) Neighborhood Discovery Protocol (NHDP)",
            RFC 6130, April 2011,
            <http://www.rfc-editor.org/info/rfc6130>.
 [RFC7181]  Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
            "The Optimized Link State Routing Protocol Version 2", RFC
            7181, April 2014,
            <http://www.rfc-editor.org/info/rfc7181>.

7.2. Informative References

 [Err4276]  RFC Errata, Errata ID 4276, RFC 6130.
 [NHDP-MIB]
            Herberg, U., Cole, R., Chakeres, I., and T. Clausen,
            "Definition of Managed Objects for the Neighborhood
            Discovery Protocol", Work in Progress, draft-ietf-manet-
            rfc6779bis, August 2014.

Dearlove & Clausen Standards Track [Page 8] RFC 7466 NHDP Optimization March 2015

Acknowledgements

 The authors would like to thank Liz Cullen (BAE Systems) for first
 illustrating the issue addressed in this specification.

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/

Dearlove & Clausen Standards Track [Page 9]

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