Internet DRAFT - draft-ietf-manet-nhdp-optimization
draft-ietf-manet-nhdp-optimization
Mobile Ad hoc Networking (MANET) C. Dearlove
Internet-Draft BAE Systems ATC
Updates: 6130, 7181 T. Clausen
(if approved) LIX, Ecole Polytechnique
Intended status: Standards Track January 23, 2015
Expires: July 27, 2015
An Optimization for the MANET Neighborhood Discovery Protocol (NHDP)
draft-ietf-manet-nhdp-optimization-04
Abstract
The link quality mechanism of the 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 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 RFC6130 "Mobile Ad Hoc Network (MANET)
Neighborhood Discovery Protocol (NHDP)", and RFC7181 "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".
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Dearlove & Clausen Expires July 27, 2015 [Page 1]
Internet-Draft NHDP Optimization January 2015
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 27, 2015.
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.
Dearlove & Clausen Expires July 27, 2015 [Page 2]
Internet-Draft NHDP Optimization January 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Applicability Statement . . . . . . . . . . . . . . . . . . . . 5
4. Changes to NHDP . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Interface Information Bases . . . . . . . . . . . . . . . . 6
4.2. HELLO Message Processing . . . . . . . . . . . . . . . . . 6
4.3. Information Base Changes . . . . . . . . . . . . . . . . . 6
4.4. Constraints . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Changes to OLSRv2 . . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Dearlove & Clausen Expires July 27, 2015 [Page 3]
Internet-Draft NHDP Optimization January 2015
1. Introduction
The MANET Neighborhood Discovery Protocol (NHDP) [RFC6130], Section
14, 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 just 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 reestablished, 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, in particular 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 Expires July 27, 2015 [Page 4]
Internet-Draft NHDP Optimization January 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 [RFC6779bis].
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 which 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 yield 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 by this specification describing how the updates to [RFC6130]
may be handled so as to be 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
Dearlove & Clausen Expires July 27, 2015 [Page 5]
Internet-Draft NHDP Optimization January 2015
any of these changes are made then all of these changes MUST be made.
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 When creating a 2-Hop Tuple, set N2_lost := L_lost.
4.3. Information Base Changes
In Section 13, replace the second bullet point by:
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.
and replace the paragraph after the bullet points by:
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.
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:
Dearlove & Clausen Expires July 27, 2015 [Page 6]
Internet-Draft NHDP Optimization January 2015
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 2, renumbering point
2 as point 1.
4.4. Constraints
In Appendix B, 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].
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
MPR Set and Routing Set calculation, but not includes that
information in control traffic, this means that an implementation
must be (i) behaving as if a 2-Hop Tuple only exists if
Dearlove & Clausen Expires July 27, 2015 [Page 7]
Internet-Draft NHDP Optimization January 2015
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".
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".
Dearlove & Clausen Expires July 27, 2015 [Page 8]
Internet-Draft NHDP Optimization January 2015
6. IANA Considerations
This document has no actions for IANA.
[This section may be removed by the RFC Editor.]
7. 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].
8. Acknowledgments
The authors would like to thank Liz Cullen (BAE Systems) for first
illustrating the issue addressed in this specification.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
9.2. Informative References
[RFC6779bis]
Herberg, U., Cole, R., Chakeres, I., and T. Clausen,
"Definition of Managed Objects for the Neighborhood
Discovery Protocol", draft-ietf-manet-rfc6779bis (work in
progress), August 2014.
Dearlove & Clausen Expires July 27, 2015 [Page 9]
Internet-Draft NHDP Optimization January 2015
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 Expires July 27, 2015 [Page 10]
