Ad-Hoc Network Autoconfiguration T. Boot
(Autoconf) Infinity Networks
Internet-Draft A. Holtzer
Intended status: Standards Track TNO ICT
Expires: January 14, 2010 July 13, 2009
Border Router Discovery Protocol (BRDP) based Address Autoconfiguration
draft-boot-autoconf-brdp-02.txt
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Abstract
Mobile Ad hoc Networks (MANET) may be attached to a fixed
infrastructure network, like the Internet. This document specifies a
mechanism for Border Router discovery and utilization in such a
subordinate, possibly multi-homed, MANET. It provides facilities for
choosing preferred Border Router(s) and configuring IP address(es)
needed for communication between MANET nodes and nodes on the
Internet via the selected Border Router. Autonomous MANETs do not
have Border Routers; a self-sufficient Address Autoconfiguration
mechanism for Autonomous MANETs is defined as well.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Protocol overview and functioning . . . . . . . . . . . . . . 7
3.1. Border Router Discovery Protocol (BRDP) . . . . . . . . . 7
3.2. BRDP-based Address Autoconfiguration . . . . . . . . . . . 7
3.3. Issues with Address Autoconfiguration in a MANET . . . . . 8
4. Border Router Discovery Protocol . . . . . . . . . . . . . . . 9
4.1. Border Router Information Option (BRIO) . . . . . . . . . 9
4.1.1. BRIO Base option . . . . . . . . . . . . . . . . . . . 9
4.1.2. BRIO suboptions . . . . . . . . . . . . . . . . . . . 12
4.2. BRDP processing . . . . . . . . . . . . . . . . . . . . . 13
4.2.1. BRDP message generation and transmission . . . . . . . 13
4.2.2. BRDP message reception . . . . . . . . . . . . . . . . 15
4.2.3. BRIO-Cache maintenance . . . . . . . . . . . . . . . . 16
4.2.4. BRDP loop prevention . . . . . . . . . . . . . . . . . 17
4.3. Unified Path Metric (UPM) . . . . . . . . . . . . . . . . 18
5. BRDP-based Address Autoconfiguration . . . . . . . . . . . . . 20
5.1. Border Router selection . . . . . . . . . . . . . . . . . 20
5.1.1. Border Router Selection based on UPM . . . . . . . . . 20
5.1.2. Border Router Selection based on BRIO flags and
options . . . . . . . . . . . . . . . . . . . . . . . 21
5.2. MANET address generation and configuration . . . . . . . . 21
5.3. Support for Autonomous MANETs . . . . . . . . . . . . . . 22
6. Support for IPv4 . . . . . . . . . . . . . . . . . . . . . . . 23
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 23
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.1. Normative reference . . . . . . . . . . . . . . . . . . . 24
10.2. Informative Reference . . . . . . . . . . . . . . . . . . 24
Appendix A. Change Log From Previous Versions . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
This document describes a complete solution for configuring globally
routable and/or unique local IPv6 addresses for ad hoc network nodes.
The new Border Router Discovery Protocol (BRDP) is defined for Border
Router discovery. Existing IETF mechanisms can be used for address
generation, but may use BRDP provided information as an enhancement.
BRDP provided information may also be used for other purposes, such
as source address selection [RFC3484].
The Address Autoconfiguration solution for subordinate MANETs uses
two phases:
o Discovery of one or more Border Routers
o Selection of a Border Router and Address Autoconfiguration of
globally routable IPv6 addresses to be used in conjunction with
that Border Router
In case of an Autonomous MANET no Border Routers have to be
discovered. In that case Unique Local Addresses [RFC4193] are
generated by individual MANET routers.
BRDP is a simple distance vector protocol that distributes Border
Router information, where each MANET Router selects one or more
Border Routers and forwards the Border Router information in the
MANET. It extends the IPv6 Neighbor Discovery Protocol (NDP)
[RFC4861] to make it carry information, such as prefix information
and metrics which help a MANET Router to select a Border Router and
to help to configure globally unique addresses for communication with
nodes on the Internet.
Address uniqueness is assured by the IPv6 address generation
mechanisms used. Additional mechanisms may be used, such as
Duplicate Address Detection. However, in a MANET the overhead of
performing Duplicate Address Detection can easily outweigh the
benefits. For such a case, [RFC4862] specifies that Duplicate
Address Detection can be disabled.
Additional mechanisms may be used for solving problems with ingress
filtering, which occur when traffic is sent to the Internet via a
border router that doesn't correspond with the source address of the
packets. In a multi-homed MANET, the probability of such a problem
to occur is highly increased due to mobility. This problem can be
solved by using BRDP based routing [I-D.boot-brdp-based-routing] in
which the routing mechanism assures traffic to the Internet is
forwarded to the Border Router that corresponds with the source
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address of the packets.
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2. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Readers are expected to be familiar with all the terms defined
"Mobility Related Terminology" [RFC3753], "Mobile Ad hoc Network
Architecture" [I-D.ietf-autoconf-manetarch] and "Address
Autoconfiguration for MANET: Terminology and Problem Statement"
[I-D.ietf-autoconf-statement].
Border Router
MANET Router that connects the MANET to the Internet
BRDP
Border Router Discovery Protocol
BRIO
Border Router Information Option
BRIO-Cache
Table, populated with information on discovered Border Routers,
learned through received or initiated Border Router Information
Options
MANET
A routing domain containing MANET routers
[I-D.ietf-autoconf-manetarch]
Subordinate MANET
a MANET, connected to the Internet
Autonomous MANET
a MANET, not connected to the Internet
MANET Generated Address
Globally unique and topologically correct IPv6 address generated
to enable connectivity between nodes in the MANET and
Corresponding Nodes on the Internet via a Border Router
UPM
Uniform Path Metric
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3. Protocol overview and functioning
In this section, the subcomponents of BRDP-based Address
Autoconfiguration are briefly introduced.
3.1. Border Router Discovery Protocol (BRDP)
BRDP is a simple distance vector protocol that distributes Border
Router information, where each MANET Router selects one or more
Border Routers and forwards the Border Router information in the
MANET. It extends the IPv6 Neighbor Discovery Protocol (NDP)
[RFC4861] to make it carry information and metrics which help a MANET
Router to generate and configure globally unique addresses for
communication with nodes on the Internet.
BRDP is a derivative of Tree Discovery [I-D.thubert-tree-discovery].
It suits the Autoconf Working Group Charter and is particularly
designed for Address Autoconfiguration in subordinate, possibly
multi-homed, Mobile Ad hoc Networks.
BRDP uses ICMP Router Advertisement (RA) messages in NDP to
distribute Border Router information by extending it with the Border
Router Information Option (BRIO). BRDP allows MANET Routers to
advertise Border Router reachability, including information for
selecting a preferred Border Router. A MANET Router selects at least
one BRIO from its cache, for dissemination in the MANET.
BRIOs are distributed hop by hop from a Border Router downwards in
the MANET using a tree structure. The presence of multiple Border
Routers results in multiple, potentially overlapping logical trees,
i.e. a Directed Acyclic Graph (DAG).
The amount of flooding of BRDP messages MAY be reduced. A MANET
Router MAY filter BRIOs, based on the Unified Path Metric (UPM). The
UPM is the advertized bidirectional distance to the Internet Default
Free Zone (DFZ), via that Border Router.
BRDP MAY carry more detailed information of the Border Router, such
as a provider name and AAA options. AAA enables access network
providers to control access to their network. MANET Routers MAY
select a Border Router based on preferences for a provider.
3.2. BRDP-based Address Autoconfiguration
BRDP provides prefix information to configure MANET Generated
Addresses. The prefix information is sent in the BRIO in the form of
the Border Router address and the prefix length. A MANET Generated
Address is a globally unique and topologically correct IPv6 address
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generated to enable connectivity between nodes in the MANET and
Corresponding Nodes on the Internet via a Border Router.
The nodes using BRDP-based Address Autoconfiguration MUST implement a
mechanism to generate a unique 64-bit Interface Identifier. An
extremely high probability of uniqueness can be achieved by using
Modified EUI-64 format-based Interface Identifiers [RFC4291] or by
generating these identifiers randomly [RFC4941] or by means of a
well-distributed hash function [RFC3972].
The generated Interface Identifier is combined with a 64-bit prefix,
which is provided by BRDP, thus forming a topologically correct
address.
In this document, it is assumed the MANET is connected to the
Internet and globally unique addresses are used. Border Routers MUST
have a globally unique and reachable 64-bit prefix. The mechanisms
described in this document are compatible with private networks and
usage of Unique Local Addresses [RFC4193]. An implementation MAY
provide configuration options for Border Router selection based on
offered global prefixes or unique local prefixes, in cases where both
types are used in the same MANET.
3.3. Issues with Address Autoconfiguration in a MANET
After Address Autoconfiguration, additional mechanism(s) would be
needed to enable usage of the correct Border Router and to enable
session continuity. This document does not prescribe any solutions
for this purpose. Usage of the correct Border Router is provided by
BRDP Based Routing [I-D.boot-brdp-based-routing] and session
continuity can be arranged with Mobility Support in IPv6 [RFC3775],
NEMO basic support [RFC3963] or Shim6 [RFC5533].
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4. Border Router Discovery Protocol
This section explains the details of the BRDP protocol. Topics are
the Border Router Information Option (BRIO), the generation,
transmission, forwarding and reception of BRIOs and BRIO cache
maintenance.
4.1. Border Router Information Option (BRIO)
The Border Router Information Option carries information that allows
a MANET Router to select and utilize a Border Router.
4.1.1. BRIO Base option
The BRIO is a container option, which MAY contain a number of
suboptions. The BRIO base option groups the minimum information set
that is mandatory in all cases.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Prefix Length |A|F|E|L|S|D| r |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | Hopcount | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Uniform Path Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Border Router Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BRIO base option
Fields:
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Type:
8-bit identifier of the Border Router Information Option type.
The value of this option identifier is to be determined.
Length:
8-bit unsigned integer. The length of the option (including the
type and length fields) in units of 8 octets. A BRIO without
suboptions has a length value of 4.
Prefix Length:
8-bit unsigned integer. The number of leading bits in the Border
Router Address, that indicates the assigned prefix for that Border
Router. The Prefix Length is used for BRDP Based Routing
[I-D.boot-brdp-based-routing].
AAA(A):
Flag indicating whether the Border Router requires authentication,
authorization and accounting. When set, a Service Selection
suboption immediately follows the BRIO base option. This document
only describes BRIO forwarding rules considering the A-flag and
Service Selection suboption. Details on performing AAA are out-
of-scope for this document.
Floating(F):
When the F-flag is set, the Border Router has lost contact with
the Internet. MANET Routers SHOULD stop using MANET generated
source addresses based on the prefix of a Border Router that
indicates that it is floating.
Emergency Response Services(E):
When the E-flag is set, the Border Router provides support for
emergency response services. Details on applications for
emergency response services are out-of-scope for this document.
The E-flag contributes to the distribution of BRIOs in the MANET
in the BRIO selection mechanism. Access to emergency response
services SHOULD be enabled for all MANET nodes.
Loop-prone(L):
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When the L-flag is set, an upstream MANET Router cannot guarantee
a loop-free path to the Border Router advertized in this BRIO.
Solicitation Response(S):
When the S-flag is set, the Border Router requests forwarding of
the BRIO downstream the BRIO forwarding tree as a response to a
special Router Solicitation. This provides a mechanism to speed
up convergence, requested by a downstream MANET Router.
DHCP (D):
When the D-flag is set, the Border Router is acting as a DHCP
server or DHCP relay agent [RFC3315].
r, reserved:
Reserved bits. Currently unused, set to 0.
Sequence Number:
16-bit unsigned integer. It is set by the Border Router and
incremented with each new BRIO it sends on a link. The sequence
number is propagated without change down the tree.
Hopcount:
8-bit field registering the number of hops from the advertizing
MANET Router to the Border Router. Border Routers send an
original BRIO with its Hopcount set to zero. MANET Routers
increment the Hopcount by one when forwarding a BRIO.
Uniform Path Metric (UPM):
A measure for the quality of the bi-directional path between the
MANET Router and the Default Free Zone of the Internet. Uniform
Path Metric is set to some initial value by the Border Router and
is incremented by each MANET Router forwarding the BRIO.
Border Router Address:
128-bit address of the Border Router. The Border Router is
expected to add its own address as a /128 prefix in the MANET
routing system.
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4.1.2. BRIO suboptions
In addition to the BRIO Base option, a number of suboptions are
defined. Suboptions MAY have alignment requirements.
4.1.2.1. Pad suboption
The Pad suboption format is as follows:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Type = 0 |
+-+-+-+-+-+-+-+-+
Figure 2: Pad suboption
Fields:
Type = 0
8-bit identifier of the Pad suboption type. The option identifier
is determined as 0.
The format of the Pad suboption has neither an suboption length nor
suboption data fields. The Pad suboption is used to insert one octet
of padding in the BRIO to enable alignment, either between suboptions
or for the whole suboption container.
4.1.2.2. Service Selection suboption
Each BRIO MAY have a single Service Selection suboption, identifying
the Service Provider and/or the provided service offered by the
Border Router. The Service Selection suboption MUST be the first
BRIO suboption.
The Service Selection suboption is equivalent to the Service
Selection Mobility Option defined in "Service Selection for Mobile
IPv6" [RFC5149].
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Length | Identifier... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Service Selection suboption
Fields:
Type = 1
8-bit identifier of the Service Selection suboption type. The
suboption identifier is determined as 1.
Length:
8-bit unsigned integer. The length represents the length of the
Service Selection Identifier in octets, excluding the suboption
type and length fields. Usage of the Length field is equivalent
to [RFC5149].
Identifier:
A variable length UTF-8 encoded Service Selection Identifier
string used to identify the Border Router service provider and
optionally the type of service. Valid examples are 'ims', 'voip'
and 'voip.companyxyz.example.com'.
A Border Router MAY offer multiple services using multiple BRIOs.
However, each of those BRIOs MUST use a unique Border Router address.
4.2. BRDP processing
The main BRDP processing functions of a MANET Router are BRDP message
generation, transmission and reception and the maintenance of a BRIO-
Cache. MANET Routers forward BRDP messages using ICMP ND Router
Advertisements.
4.2.1. BRDP message generation and transmission
A BRDP message is part of a Router Advertisement and includes a set
of BRIOs. It provides the current state of paths to the Border
Routers listed in the set of BRIOs. BRIOs originate from a Border
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Router, and contain initially metric information on connectivity to
the Internet. BRIOs are forwarded downwards in the MANET.
When a MANET Router sends a ICMP ND Router Advertisement, it SHOULD
include a set of BRIOs by appending them to the message. The maximum
number of BRIOs in a single BRDP message is a MANET Router
configuration parameter. BRIO selection for advertisement is done
based on the information stored in the BRIO-Cache. As a minimum, the
following rules apply to a MANET Router selecting BRIOs for
advertisement:
o BRIOs with the L-flag set SHOULD NOT be selected.
o BRIOs that do not pass the loop prevention check described in
Section 4.2.4 SHOULD NOT be selected.
o At minimum, one BRIO with the E-flag set MUST be selected, when
such an entry exists in the BRIO-Cache.
o BRIO selection SHOULD select a number of BRIOs with distinct
Service Selection Identifiers. The BRIO selection mechanism MAY
use a preference scheme selecting and filtering Service Selection
Identifiers.
The UPM and Hopcount fields of the advertised BRIOs are updated. An
UPM-increment, based on uniformized bi-directional link metrics, is
added to the UPM and the Hopcount is incremented by 1. UPM-increment
MAY be governed by a hysteresis and dampening mechanism. Also
forecasted information MAY be used.
Each BRIO originating from a Border Router has an increased Sequence
Number. This BRIO is forwarded in the MANET and refreshes entries in
BRIO-Caches of downstream MANET Routers.
Router Advertisements are sent in response to Router Solicitation
messages or unsolicited with a uniformly-distributed random interval
between MinRtrAdvInterval and MaxRtrAdvInterval [RFC4861]. The
MaxRtrAdvInterval falls between a minimum of 30 milliseconds,
specified in [RFC3775] and a maximum of 1800 seconds, specified in
[RFC4861]. In addition, the MANET Router MAY send a Router
Advertisement when an important change in a to be sent BRIO would
occur.
When a MANET Router sends Router Advertisements more frequently than
an upstream MANET Router, this MANET Router MAY repeatedly send BRIOs
with a constant Sequence Number but with an updated UPM or Hopcount.
The ICMP ND Router Advertisement SHOULD include the Advertisement
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Interval Option [RFC3775]. This option contains the interval at
which the sending router sends unsolicited multicast Router
Advertisements.
The Border Router MAY request that the sent BRIO SHOULD be forwarded
instantly downstream in the MANET, by setting the S-flag.
A MANET Router SHOULD inform downstream MANET Routers in case the
path to a previous advertized Border Router is lost, by at least 3
times retransmitting the previously sent BRIO with a UPM value of
4294967295. When an alternative BRIO for the same Service Selection
Identifier is available, this BRIO SHOULD be advertised, for
continued connectivity to this Service.
In case a Border Router loses its connection to the infrastructure it
will lose its Border Router functionality and become a normal MANET
Router. In that case it performs the same procedure as a MANET
Router that has lost the path to a previous advertised Border Router.
In addition, it sets the F-flag.
For each Border Router listed in the BRIO-Cache, the UPM-loop-
prevention-threshold and the Hopcount-loop-prevention-threshold
variables are maintained. These variables are used by the loop
prevention mechanism described in Section 4.2.4. The thresholds are
set or updated when sending BRDP messages. When sending a BRIO with
a higher Sequence Number than the previously sent BRIO for that
Border Router, the threshold variables are set to the UPM and
Hopcount values in BRIO to be sent. When sending a BRIO with the
same Sequence Number as the previously sent BRIO, the loop-
prevention-thresholds are independently updated if either the UPM or
Hopcount of the outgoing BRIO is lower than their thresholds.
A MANET Router that detects an attractive candidate BRIO but is
prohibited from using it because of the loop prevention check, MAY
send a special Router Solicitation message to the Border Router. The
Border Router responds to such a Router Solicitation message with a
BRIO with the S-flag set. Sending Router Solicitations MUST be rate
limited. A next version of this document would include a
specification for the special Router Solicitation message.
4.2.2. BRDP message reception
When a BRDP message is received, the Sequence Number fields of the
contained BRIOs are checked; the Sequence Number of a received BRIO
MUST be equal to or higher than the Sequence Number in the cache for
an existing entry in the cache, with wrap-around checking.
Otherwise, the BRIO will be discarded.
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BRIO messages do not need to be forwarded at fixed time intervals,
because the RA intervals on different MANET Routers are not
synchronized. Therefore, large gaps in Sequence Numbers may occur.
Increment values between 0 and 65000 are accepted. Increment values
between 65001 and 65535 are rejected.
Information in received BRIOs is stored in a BRIO-Cache table. Other
information is stored as well, such as the BRIO sender, a timestamp
indicating when the most recent message was received and the measured
or signaled RA interval.
4.2.3. BRIO-Cache maintenance
Each MANET Router maintains a BRIO-Cache that stores all information
on Border Routers. Unique cache entries are maintained on (Border
Router Address, address of the neighbor router that forwarded the
BRIO) tuples. This information is obtained by receiving BRIOs or, in
case of a Border Router, by getting information from the interface
that connects to the Internet. The BRIO-Cache also maintains context
information for the BRIO such as the BRIO sender, link metrics and
UPM-increment for this sender, history, statistics and status
information. History information includes a timestamp indicating
when the most recent message was received and a measured or signaled
RA interval. Status information includes the BRIO selection outcome
for BRIO forwarding as explained in Section 4.2.1 and the Border
Router selected for address generation as explained in Section 5.1.
BRIO entries in the BRIO-Cache stay valid for a certain period of
time. During this period, they can be used for Border Router
selection by the MANET Router, for forwarding BRIOs and for address
generation. BRIO-Cache information could also be useful for source
address selection [RFC3484]. The lifetime of a BRIO is determined by
using the timing information sent along with the RA ([RFC3775],
section 7.3) or statistics of received BRIOs.
Some values in the BRIO-Cache can be updated independent of incoming
BRDP messages. A MANET Router MAY update the UPM-increment based on
link quality measurements performed in an environment with changing
link metrics. A MANET Router SHOULD indicate in its BRIO-Cache which
BRIO entries are currently selected for forwarding and for address
generation. Border Router Selection MAY take place after the UPM of
a BRIO entry has been updated.
In case the link to the MANET Router from which a BRIO has been
received is broken, the UPM and the Hopcount of the BRIO entry in the
cache are set to the maximum value, i.e. 4294967295 and 255.
A cache cleanup routine SHOULD run at regular intervals to get rid of
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stale entries. Stale entries are removed when the entry is not
updated for 5400 seconds or all of the following conditions are met:
o The stale entry is not used by the MANET Router itself for address
generation.
o The stale entry was not selected for forwarding in the last three
Router Advertisement.
o The stale entry was not recently updated by a received BRIO. In
this context, recently is defined as the maximum of a) three times
its own unsolicited multicast Router Advertisements interval and
b) three times the senders unsolicited multicast Router
Advertisements interval.
Cache entries MAY also be removed, under the condition that the BRIO-
Cache has reached a configured maximum number of entries and a new,
to be stored BRIO is received. A removal candidate is selected based
on:
o The candidate entry is not used by the MANET Router itself.
o The candidate entry was not selected for forwarding in the last
Router Advertisement.
o The candidate entry is redundant; other information for the same
Border Router is stored in the cache with a better UPM and / or
was received more recently.
o The candidate entry is redundant; other information for the same
Service Selection Identifier is stored in the cache with a better
UPM and / or was received more recently.
o The candidate entry is less attractive; other Border Routers are
stored in the cache with better UPM and / or were received more
recently.
4.2.4. BRDP loop prevention
A BRDP loop check mechanism prevents that a MANET Router forwards an
earlier advertized BRIO.
BRDP loop-free operation is guaranteed as long as at least one of the
following conditions is true:
o The to be sent BRIO has a higher Sequence Number than a BRIO for
this Border Router that was sent before. The loop check mechanism
uses wrap-around logic. Increments up to 32768 are acceptable
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(wrap-around logic needs checking).
o The to be sent BRIO is generated from the same BRIO-Cache entry as
the BRIO that was sent most recently.
o The to be sent BRIO has the same Sequence Number as the BRIO for
this Border Router that was sent before but the BRIO-Cache entry
UPM is equal to or lower than the UPM-loop-prevention-threshold
for this Border Router.
o The to be sent BRIO has the same Sequence Number as the BRIO for
this Border Router that was sent before but the BRIO-Cache entry
Hopcount is equal to or lower than the Hopcount-loop-prevention-
threshold for this Border Router.
In some circumstances, a MANET Router MAY select a BRIO for
forwarding that fails the loop prevention check or with the L-flag
set. For example, the link to the upstream neighbor is lost and an
alternative path is available, with a higher UPM and a higher
Hopcount or with a lower Sequence Number. The MANET Router cannot
assure this candidate BRIO is not reflecting its own advertized
message, but it could be better sending this BRIO than sending
nothing or repeatedly sending a BRIO with a maximum UPM and Hopcount
value. When a MANET Router forwards a BRIO that failed the loop
prevention check, the L-flag MUST be set. A looped BRIO results in a
Hopcount counting to infinity.
4.3. Unified Path Metric (UPM)
Unified Path Metric (UPM) is a measure for the quality of the path
between the MANET Router and the Internet Default Free Zone. It is a
united metric for both inbound and outbound paths. On each hop, the
UPM is incremented with an UPM-increment, which is derived from the
routing protocol and / or is obtained from lower layers.
It is on forehand not known what is more important; Border Router
selection based on path metric to the Border Router or the path
metric for the reverse path. In BRDP, UPM is used for optimizing
Border Router selection for both the inbound and the outbound
traffic. Note that actual traffic will use the path provided by the
routing protocols, not by BRDP.
Since the UPM uses 32 bits, its maximum value is 4294967295. On each
hop, an UPM-increment is calculated for each MANET Router from which
a BRIO has been received. UPM-increments have a value between 1 and
16777215.
Further discussion on metrics and how the UPM-increment value is
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determined is outside the scope of this document.
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5. BRDP-based Address Autoconfiguration
5.1. Border Router selection
When a MANET Router needs to communicate to nodes on the Internet, it
MUST select a set of Border Routers for address generation. A MANET
Router MAY generate multiple addresses for smooth handover
implementing make-before-break or distributing traffic over multiple
Border Routers. A description how Border Routers can be used
concurrently is out-of-scope for this document.
Information concerning available Border Routers is kept in the BRIO-
Cache.
The Border Router selection mechanism MAY be triggered by received
BRDP messages, changes in metrics on links to neighbors advertising
BRDP messages, changes in MANET metrics to Border Routers used or on
a time-driven basis.
The Border Router selection algorithm SHOULD be based on Service
Selection Identifiers (if available) and UPM. UPM is used for
selecting the Border Router with the best connectivity to the
Internet. However, such a Border Router MAY require authorization.
The A-flag and the Service Selection Identifier provide the prime
information for selecting a preferred provider or preferred service.
The Border Router selection algorithm MAY be extended with any other
information. Future defined BRIO suboptions could provide additional
information. Border Router selection MAY be based on the type of the
Border Router Address, e.g. a globally unique address or a unique
local address.
Border Router selection does not select a routing path to the Border
Router.
5.1.1. Border Router Selection based on UPM
Assuming authentication requirements (if any) are satisfied, the
MANET Router uses the UPM for Border Router selection preferring the
best bi-directional path between the MANET Router and the Internet.
Note that the BRIO UPM includes the initial metric set by the Border
Router and is not solely a metric between the MANET Router and the
Border Router. The initial metric set by Border Routers can be used
for Border Router preference and for load balancing.
In order to use an up-to-date UPM in the selection procedure the UPM-
increment is calculated by the MANET Router before selecting a Border
Router. UPM is discussed in Section 4.3.
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5.1.2. Border Router Selection based on BRIO flags and options
Some BRIO flags MUST and some flags MAY assist in Border Router
selection.
o The A-flag and the Service Selection Identifier provide the prime
information for selecting a preferred provider or preferred
service. Details on authentication and authorization to the
Border Router are out-of-scope of this document.
o A (previous) Border Router could indicate that it is not connected
to the Internet anymore, signaled with the F-flag. Usage of this
Border Router SHOULD be avoided.
o For emergency response applications, a Border Router providing
such services, indicated by the E-flag, SHOULD be selected.
o The guarantee for a loop-free path to a Border Router can
temporary be withdrawn, indicated by the L-flag set. Usage of
this Border Router SHOULD be avoided.
The Border Router selection algorithm could be extended with using
future defined BRIO suboptions or other information.
5.2. MANET address generation and configuration
The MANET Router MUST use a topologically correct address when
communicating with corresponding nodes on the Internet.
Topologically correct addresses SHOULD be generated for each Border
Router used.
A MANET Generated Address has a /128 prefix. It is constructed from
a 64-bit Interface Identifier and a 64-bit prefix from the Border
Router Address. A 64-bit prefix length from the Border Router is
used since for a 64-bit Interface Identifier the use of a 64-bit
prefix for Stateless Address Autoconfiguration (SLAAC) is prescribed
in [RFC2464]. The generated 128-bit address SHOULD be advertised in
the MANET routing system. The MANET Generated Address MAY also be
used for other traffic, either inside the MANET or towards the
Internet.
For the Interface Identifier used, the BRDP-based MANET Address
Generation MUST implement a mechanism for generating a unique
Interface Identifier. Known mechanisms are:
o Modified EUI-64 format-based Interface Identifier, [RFC4291],
based on IEEE 802 48-bit MAC address or IEEE EUI-64 identifier.
However, this method does not guarantee identifiers are unique as
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duplicate MAC addresses can occur.
o Generation of randomized Interface Identifiers, [RFC4941].
o Well-distributed hash function, [RFC3972].
After MANET Address Generation, RFC4429 Optimistic Duplicate Address
Detection [RFC4429] MAY be used, if one thinks the benefit outweigh
the overhead. A passive Duplicate Address Detection could be used as
an alternative. Still, uniqueness is not fully guaranteed. Main
reasons for non-uniqueness are merging of MANET segments, node
movement, node misbehavior or address spoofing attacks. Details on
handling a duplicate address condition are out-of-scope for this
document.
Address generation for globally unique addresses and unique local
addresses [RFC4193] is similar. Nodes SHOULD NOT use unique local
addresses to communicate with a Border Router with a globally unique
address. Nodes SHOULD NOT use globally unique addresses to
communicate with a Border Router with a unique local address.
A MANET Generated Addresses clean-up routine SHOULD run at regular
intervals to get rid of stale addresses.
When a node has selected a Border Router for which the D-flag is set,
it MAY use DHCP [RFC3315] for configuration parameters or prefix
delegation [RFC3633]. DHCP processing makes use of co-located DHCP
Client and DHCP Relay functions and is unicast only. DHCP is not
used for address configuration, since it could introduce a lot of
overhead in a MANET.
5.3. Support for Autonomous MANETs
Autonomous MANETs do not have Border Routers, and MANET Routers will
have empty BRIO-Caches. No 64-bit prefixes from the Border Router
Addresses are available, and globally unique IPv6 addresses cannot be
generated. For communication within the MANET, a MANET Router MAY
generate an address using a self-generated unique local addresses
[RFC4193] /64 prefix. Alternatively some mechanism could provide
already in-use /64 unique local prefix(es) in the MANET, these
prefixes MAY be used as well.
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6. Support for IPv4
BRDP-based Address Autoconfiguration is currently designed for IP
version 6. The used mechanism for address generation extends the
functionality specified in "IPv6 Stateless Address Autoconfiguration"
[RFC4862]. Because of certain scenarios where IPv4 and IPv6 coexist
in a network, BRDP support for IPv4 is currently under consideration.
7. IANA considerations
The IANA is requested to define a new IPv6 Neighbor Discovery option
for the Border Router Information Option, defined in this document.
+------+----------------------------------+-----------+
| Type | Description | Reference |
+------+----------------------------------+-----------+
| TBA | Border Router Information Option | [RFCXXXX] |
+------+----------------------------------+-----------+
Figure 4: IANA BRIO assignment
The registry for these options can be found at:
http://www.iana.org/assignments/icmpv6-parameters
The IANA is requested to create a new registration for BRIO
suboptions.
8. Security Considerations
BRDP-based Address Autoconfiguration inherits security considerations
from MANET technology. Since it is a new mechanism based on ND it
inherits security considerations from ND.
Traffic anonymity and traffic flow confidentiality are important
issues in MANET communications. Considerations related to traffic
flows should be discussed in context with the mechanisms that are
chosen to perform path setup, routing and session continuity and are
therefore not covered by this document.
A more detailed description on Address Autoconfiguration security
considerations is to be included in a next version of this document.
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9. Acknowledgments
The authors want to thank anyone involved in IETF on MANET and NEMO
technology for their efforts on mobile network infrastructures.
Special thanks to Pascal Thubert, Thomas Clausen and Ryuji Wakikawa
for their efforts in defining MANEMO technology, which inspired the
authors to compose this document. Also special thanks to Ronald in
't Velt for reviewing.
10. References
10.1. Normative reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
10.2. Informative Reference
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
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RFC 3963, January 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC5149] Korhonen, J., Nilsson, U., and V. Devarapalli, "Service
Selection for Mobile IPv6", RFC 5149, February 2008.
[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", RFC 5533, June 2009.
[I-D.ietf-autoconf-statement]
Baccelli, E., Mase, K., Ruffino, S., and S. Singh,
"Address Autoconfiguration for MANET: Terminology and
Problem Statement", draft-ietf-autoconf-statement-04 (work
in progress), February 2008.
[I-D.ietf-autoconf-manetarch]
Chakeres, I., Macker, J., and T. Clausen, "Mobile Ad hoc
Network Architecture", draft-ietf-autoconf-manetarch-07
(work in progress), November 2007.
[I-D.boot-brdp-based-routing]
Boot, T., "Border Router Discovery Protocol (BRDP) Based
Routing", draft-boot-brdp-based-routing-00 (work in
progress), November 2008.
[I-D.thubert-tree-discovery]
Thubert, P., "Nested Nemo Tree Discovery",
draft-thubert-tree-discovery-08 (work in progress),
June 2009.
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Appendix A. Change Log From Previous Versions
00:
Initial Document.
Changes from -00 to -01:
Added fields in BRIO: D-flag, Prefix Length
Added section on DHCP for obtaining configuration parameters
Added section on autonomous MANETs
Removed section about path setup, routing and session continuity
Changes from -01 to -02:
Made several changes to the text throughout the document, mainly
for clarification.
Authors' Addresses
Teco Boot
Infinity Networks B.V.
Elperstraat 4
Schoonloo 9443TL
The Netherlands
Email: teco@inf-net.nl
Arjen Holtzer
TNO Information and Communication Technology
Brassersplein 2
Delft 2612CT
The Netherlands
Email: arjen.holtzer@tno.nl
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