One document matched: draft-boot-autoconf-brdp-00.txt
Ad-Hoc Network Autoconfiguration T. Boot
(Autoconf) Infinity Networks
Internet-Draft A. Holtzer
Expires: January 19, 2009 TNO ICT
July 18, 2008
Border Router Discovery Protocol (BRDP) based Address Autoconfiguration
draft-boot-autoconf-brdp-00.txt
Status of this Memo
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Abstract
Mobile Ad hoc Networks 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 the
best Border Router and configuring IP addresses needed for
communication between MANET nodes and nodes in the fixed
infrastructure via the selected Border Router.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol overview and functioning . . . . . . . . . . . . . . 5
3.1. Border Router Discovery Protocol (BRDP) . . . . . . . . . 5
3.2. BRDP-based Autoconf . . . . . . . . . . . . . . . . . . . 6
3.3. Path setup and session continuity . . . . . . . . . . . . 6
4. Border Router Discovery Protocol . . . . . . . . . . . . . . . 7
4.1. Border Router Information Option (BRIO) . . . . . . . . . 7
4.1.1. BRIO Base option . . . . . . . . . . . . . . . . . . . 7
4.1.2. BRIO suboptions . . . . . . . . . . . . . . . . . . . 9
4.2. BRDP processing . . . . . . . . . . . . . . . . . . . . . 11
4.2.1. Generation and transmission of BRDP messages . . . . . 11
4.2.2. BRDP message reception . . . . . . . . . . . . . . . . 12
4.2.3. BRIO cache maintainance . . . . . . . . . . . . . . . 13
4.2.4. BRDP loop prevention . . . . . . . . . . . . . . . . . 15
4.3. Unified Path Metric (UPM) . . . . . . . . . . . . . . . . 16
5. BRDP-based Autoconf . . . . . . . . . . . . . . . . . . . . . 17
5.1. Border Router selection . . . . . . . . . . . . . . . . . 17
5.1.1. Border Router Selection based on UPM . . . . . . . . . 17
5.1.2. Border Router Selection based on BRIO flags and
options . . . . . . . . . . . . . . . . . . . . . . . 17
5.2. MANET Address generation . . . . . . . . . . . . . . . . . 18
6. Path setup, routing and session continuity . . . . . . . . . . 20
7. Support for IPv4 . . . . . . . . . . . . . . . . . . . . . . . 21
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative reference . . . . . . . . . . . . . . . . . . . 23
11.2. Informative Reference . . . . . . . . . . . . . . . . . . 23
Appendix A. Change Log From Previous Version . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . . . 26
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1. Introduction
The Autoconf workgroup is chartered to standardize mechanisms to be
used by ad hoc network nodes for configuring unique local and/or
globally routable IPv6 addresses. Issues and requirements related to
prefix and/or address providing entities shall be addressed. The
reader is expected to be familiar with "Mobile Ad hoc Network
Architecture" [I-D.ietf-autoconf-manetarch] and "Address
Autoconfiguration for MANET: Terminology and Problem Statement"
[I-D.ietf-autoconf-statement].
This document describes a complete solution for Autoconf in
subordinate MANETs. The solution makes use of existing protocols to
the maximum extent feasible. One new protocol is defined for Border
Router discovery. All other mechanisms used are existing IETF
protocols.
The Autoconf solution for subordinate MANETs uses two phases:
o Discovery of one or more Border Routers
o Selection of a Border Router and autoconfiguration of globally
routable IPv6 addresses to be used in conjunction with that Border
Router
Address uniqueness is assured by IPv6 address generation mechanisms
used. After address configuration it has to be assured that traffic
sent with the configured globally routable IPv6 address actually uses
the selected Border Router. This and other issues related to routing
are outside the scope of Autoconf and will be described in another
document in more detail.
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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 [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].
Autoconf
Ad hoc Network Autoconfiguration
BRDP
Border Router Discovery Protocol
BRIO
Border Router Information Option
UPM
Uniform Path Metric
MANET Generated Address
Globally unique and topologically correct IPv6 address generated
to enable connectivity between nodes in the MANET and
Corresponding Nodes in the fixed infrastructure via a Border
Router
MANET
A routing domain containing MANET routers
[I-D.ietf-autoconf-manetarch].
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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 select a Border Router and to help to configure addresses
for communication with the fixed infrastructure.
BRDP is a derivative of Tree Discovery [I-D.thubert-tree-discovery],
one of the candidate protocols for Routing Over Low power and Lossy
networks (ROLL). This document describes a protocol that suits the
Autoconf requirements 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). BRIO 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, see Section 4.2.3, for advertizing.
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).
Flood reduction mechanisms MAY be used. First of all, a MANET Router
MAY filter BRIOs, based on a path metric. The path metric is the
advertized bidirectional distance to the fixed infrastructure, via
that Border Router. Secondly, a MANET flooding reduction mechanism
MAY be used, if a MANET protocol running in the MANET provides this
service.
BRDP MAY carry detailed information of the Border Router, such as a
provider name and AAA options. AAA enables providers to control
access to the Border Routers. MANET Routers MAY select a Border
Router based on preferences for a provider.
BRDP MAY also be used to select an Access Router for Mobile IPv6, as
the Border Router option provides information for paths to the fixed
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infrastructure.
3.2. BRDP-based Autoconf
BRDP provides prefix information to configure MANET Generated
Addresses. A MANET Generated Address is a globally unique and
topologically correct IPv6 address generated to enable connectivity
between nodes in the MANET and Corresponding Nodes in the fixed
infrastructure via a Border Router.
The nodes using BRDP-based Autoconf MUST implement a mechanism to
generate a unique 64-bit Interface Identifier. A 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 BRDP provided
64-bit prefix, thus forming a topologically correct address.
In this document, it is assumed the fixed infrastructure is 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 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. Path setup and session continuity
After obtaining an address and selecting a Border Router, some
additional mechanism(s) have to be used to enforce the use of the
correct Border Router and to enable session continuity. This
document does not prescribe any solutions that should be used for
this purpose. Protocols such as NEMO basic support [RFC3963] and
Mobility Support in IPv6 [RFC3775] are possible solutions that MAY be
used.
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4. Border Router Discovery Protocol
This section explains the details of BRDP discussing the Border
Router Information Option (BRIO), the generation, transmission,
forwarding and reception of BRIOs and BRIO cache maintainance.
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 |A|F|E|L|S|rsvd | Hopcount |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Border Router Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Uniform Path Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BRIO base option
Fields:
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Type:
8-bit identifier of the Router Advertisement 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. The minimum BRIO
option length is 4.
AAA(A):
Flag indicating whether the Border Router requires authentication
and authorization. When set, a Service Selection suboption
immediately follows the BRIO base option. This document does only
describe 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 fixed infrastructure. MANET Routers SHOULD stop using Border
Routers that indicate that they are 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 helps selecting BRIOs to be distributed in the MANET,
BRIO distribution SHOULD enable access to emergency response
services for all MANET nodes.
Loop-prone(L):
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.
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rsvd, reserved:
Reserved bits. Set to 0.
Hopcount:
8-bit field registering the number of hops from the advertizing
MANET Router to the Border Router. Border Routers send a BRIO
with its Hopcount set to zero. MANET Routers increment the
Hopcount by one when forwarding a BRIO. Hopcount is used to
facilitate loop-free BRIO forwarding.
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.
Uniform Path Metric (UPM):
A measure for the quality of a path. 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 selection is
based on UPM and optionally on other information. UPM is used to
facilitate loop-free BRIO forwarding.
Sequence Number:
16-bit unsigned integer set by the Border Router and incremented
with each new BRIO it sends on a link. It is propagated without
change down the tree.
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 |
+-+-+-+-+-+-+-+-+
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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].
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:
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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 BRIO MUST use a unique Border Router address.
4.2. BRDP processing
BRDP messages are initiated by Border Routers. MANET Routers forward
these messages using ICMP ND Router Advertisements. The main BRDP
processing functions of a MANET Router are generation, transmission
and reception of BRDP messages and the maintainance a BRIO cache.
4.2.1. Generation and transmission of BRDP messages
A BRDP message is a Router Advertisement that includes a set of
BRIOs. BRIOs always originate from a Border Router. A Border Router
stores the information on the interface it uses for connecting to the
infrastructure in its BRIO cache. In BRDP, a Border Router is also a
MANET Router.
When a MANET Router sends a Router Advertisement, it SHOULD include a
set of BRIOs by appending them to the message as described in
Section 4.1. The maximum number of BRIOs in a single BRDP message is
a MANET Router configuration parameter. BRIOs are selected from the
BRIO cache. BRIO selection is done based on the information stored
in the BRIO cache. Note that BRIO selection MAY be depending on the
requirements of the implementation. As a minimum, the following
rules apply to a MANET Router selecting BRIOs for sending or
forwarding:
o BRIOs with the L-flag set SHOULD NOT be selected. The BRIO
selection algorithm MUST implement a loop avoidance mechanism,
described in Section 4.2.4.
o At a minimum, one BRIO with the E-flag set MUST be selected, when
such an entry exists in the BRIO Cache.
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o BRIO selection SHOULD select a number of BRIOs with distinct
Service Selection Identifiers, where the selection mechanism MAY
use a preference scheme selecting and filtering Service Selection
Identifiers.
o The UPM and Hopcount fields of the BRIO to be sent are updated.
The calculated UPM increment is added to the UPM and the Hopcount
is incremented by 1. Incremention of UPM MAY be governed by a
hysteresis and dampening mechanism. Also forecasting information
MAY be used.
Router Advertisements are sent in response to Router Solicitation
messages or unsolicited with a uniformly-distributed random interval
that falls between 30 milliseconds, specified in RFC3775 [RFC3775]
and 1800 seconds, specified in RFC4861 [RFC4861]. BRDP assumes
unsolicited multicast Router Advertisements have a somewhat stable
interval. The RA Advertisement Interval Option MAY provide the
maximum interval being used [RFC3775] or alternatively the interval
can be measured during BRIO reception. In addition, the MANET Router
MAY send a Router Advertisement when an important change in a to be
sent BRIO would occur. The Border Router MAY request that the sent
BRIO SHOULD be forwarded instantly downstream in the MANET, by
setting the S-flag. These additional Router Advertisements are
processed similar to responses on Router Solicitations.
A BRDP flooding reduction mechanism MAY be used, in order to reduce
redundant BRIO distribution. Some MANET protocols can provide
information for the flooding reduction mechanism. No additional
protocol is required.
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 or by selecting a BRIO that failed the loop prevention
check, as indicated by the L-flag. The MANET Router SHOULD include
an alternative BRIO for the same Service Selection Identifier in the
to be sent BRDP message, if such a BRIO is available in the cache.
4.2.2. BRDP message reception
When a MANET Router receives a BRDP message, it stores the Border
Router information included in the message in a BRIO cache table.
This information includes the BRIO itself and context information,
such as the BRIO sender, a timestamp indicating when the most recent
message was received and a measured or signaled RA interval.
When a BRDP message is received, the Sequence Number fields of the
contained BRIOs are checked; the Sequence Number of a received BRIO
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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. 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.
4.2.3. BRIO cache maintainance
Each MANET Router maintains a BRIO cache that stores all information
on Border Routers. This information is obtained by receiving BRIOs
or, in case of a Border Router, by getting information from the
interface that connects to the fixed infrastructure. The cache also
maintains context information for the BRIO such as the BRIO 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 own usage as
explained in Section 5.1.
Unique cache entries are maintained on (Border Router Address,
address of the neighbor router that forwarded the BRIO) tuples.
Status information is also maintained at Border Router Address and
Service Selection Identifier aggregation level. Also information on
neighbor MANET Routers is maintained.
BRIO entries in the cache stay valid for a certain period of time.
During this period, they can be used for Border Router selection by
the MNR. The lifetime of a BRIO is determined by using the timing
information sent along with the RA (RFC3775, section 7.3).
Some values in the BRIO cache can be updated independent of incoming
BRDP messages. A MANET Router MAY update the UPM based on link
quality measurements performed in an environment with changing
network topology. A MANET Router SHOULD indicate in its BRIO cache
which BRIO entries are currently selected for forwarding and which
BRIO entry contains the information about the Border Router that is
currently selected for infrastructure connectivity. Border Router
Selection MAY take place after the UPM of a BRIO entry has been
updated.
For each Border Router listed in the 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
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higher Sequence Number than the previously sent BRIO for that Border
Router, the threshold variables are set to equal 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 updated if either the UPM or Hopcount of the outgoing
BRIO is lower than the threshold.
In case the link to the MANET Router from which a BRIO has been
received is broken, the UPM of the BRIO entry in the cache is set to
the maximum value, i.e. 4294967295.
A cache cleanup routine SHOULD run at regular intervals to get rid of
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.
o The stale entry was not selected for forwarding in the last Router
Advertisement.
o The stale entry was not recently updated by a received BRIO. In
this context, recently is defined as a) within its own unsolicited
multicast Router Advertisements interval and b) shorter than 3
times the measured 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.
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4.2.4. BRDP loop prevention
A MANET Router MUST check specific attributes of candidate BRIOs in
order to ensure loop-free operation. Each BRIO sent out by and
originating from a Border Router has an increased Sequence Number.
This BRIO is forwarded in the MANET and each receiving MANET Router
uses it to update the old outdated BRIO Sequence Number stored in the
BRIO cache. Between these BRIO Sequence updates, MANET Routers MAY
repeatedly send BRIOs with a constant Sequence Number and an updated
UPM or Hopcount.
UPM, Hopcount and their loop-prevention-threshold values are used in
BRDP loop prevention. Loop-free operation is guaranteed as long as
at least one of the following conditions is true:
o The BRIO has a higher Sequence Number than a BRIO for this Border
Router sent before. Using wrap-around logic, increments up to
32768 are acceptable. (wrap-around logic needs checking)
o The BRIO has the same Sequence Number as a BRIO for this Border
Router sent before and the UPM value is equal to or lower than the
UPM-loop-prevention-threshold for this Border Router.
o The BRIO has the same Sequence Number as a BRIO for this Border
Router sent before and the Hopcount is equal to or lower than the
Hopcount-loop-prevention-threshold for this Border Router.
When no candidate BRIO for a Border Router is available, the MANET
Router SHOULD select the previously sent BRIO. In such a case, the
downstream branch for that BRIO is getting 'frozen', meaning it has
to wait for up-to-date information if it wants to be sure to have a
loop-free path. Downstream MANET Routers MAY jump to other branches
of the BRIO forwarding tree, as long as their path to the Border
Router is shortened by lower UPM or by lower Hopcount. A new BRIO
sent by the Border Router, thus with a newer Sequence Number, 'thaws'
a "loop-prone BRIO forwarding tree".
In some circumstances, a MANET Router MAY select a BRIO for
forwarding that fails the loop prevention check. 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 selecting this
candidate BRIO provides a loop-free topology, but it could be better
than sending nothing or repeatedly sending a BRIO with a maximum UPM
value. When a MANET Router forwards a BRIO that failed the loop
prevention check, the L-flag MUST be set.
When a MANET Router selected a BRIO that failed the loop prevention
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check, a duplicate packet detection mechanism MUST be implemented.
MANET Routers that select a BRIO with the L-flag set SHOULD have a
duplicate packet detection mechanism implemented. Details on
duplicate packet detection are out-of-scope for this document.
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 to at most twice the reception rate of the attractive
candidate BRIO. A next version of this document will include a
specification for the special Router Solicitation message.
4.3. Unified Path Metric (UPM)
Unified Path Metric (UPM) is a measure for the quality of the path
between nodes. It is a common metric for both the inbound and the
outbound path. Every entry in the BRIO cache has an associated UPM
value. UPM MAY be depending on information obtained from lower
layers.
In BRDP, bidirectional UPM is used for optimizing Border Router
selection for both inbound and outbound traffic. In some cases it is
far more important to select the best path from the Border Router to
the MANET Router than the reverse path. Before composing a set of
BRIOs, the UPM increment is calculated for each MANET Router from
which a BRIO has been received. UPM increments have a minimum value
of 1 and SHOULD incorporate bidirectional MANET link metrics for that
neighbor.
Since the UPM uses 32 bits, the maximum value is 4294967295. Using a
32-bit UPM and a maximum hop count of 255 the UPM increment value per
hop MUST be between 1 and 16777215. The UPM increment therefore is a
24-bit value.
Further discussion on metrics and how the UPM value is determined is
outside the scope of this document.
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5. BRDP-based Autoconf
5.1. Border Router selection
When a MANET Router needs to communicate to the fixed infrastructure,
it MUST select a set of Border Routers. Information concerning
available Border Routers is kept in the BRIO cache.
The Border Router selection mechanism MAY also 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 indicates the best
Border Router. 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 Border Router.
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.
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
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service. Details on authentication and authorization to the
Border Router are out-of-scope of this document.
o A Border Router could indicate that it is not connected to the
fixed infrastructure, signaled with the F-flag. Usage of this
Border Router SHOULD be avoided, since it is not a Border Router
anymore.
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 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.
The Border Router selection algorithm MAY incorporate a hysteresis
and dampening mechanism to prevent 'flip-flopping' between Border
Routers. It MAY also take into account other information, such as
history / statistics and status information tracked in the BRIO
cache.
A MANET Router MAY select multiple Border Routers for smooth handover
implementing make-before-break. It MAY also use multiple Border
Routers concurrently. A description how Border Routers can be used
concurrently or how traffic is distributed over the Border Routers is
out-of-scope for this document.
5.2. MANET Address generation
The MANET Router MUST use a topologically correct address when
communicating with corresponding nodes via the fixed infrastructure.
Topologically correct addresses SHOULD be generated for each Border
Router used. Only when it is known that for all Border Routers with
a shared Service Selection Identifier or set of Service Selection
Identifiers a commonly used address is accepted, a previously
generated acceptable address can be re-used.
A MANET Generated Address is used as a /128 prefix. It is
constructed from a 64-bits Interface Identifier and a 64-bits prefix
from the Border Router Address. This generated /128 address SHOULD
be advertised in the MANET routing system. The MANET Generated
Address MAY also be used for other traffic, either inside the MANET
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or towards the fixed infrastructure. For communication towards the
fixed infrastructure, this address SHOULD only be used if the MANET
Router is sure that the traffic is sent via the Border Router that
was used for address generation.
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
[RFC4291], based on IEEE 802 48-bit MAC address or IEEE EUI-64
identifier. However, this method does not guarantee identifiers
are unique as duplicate MAC addresses can occur.
o Generation of randomized Interface Identifiers, [RFC4941].
o Well-distributed hash function, RFC3972 [RFC3972].
After MANET Address Generation, RFC4429 Optimistic Duplicate Address
Detection [RFC4429] SHOULD be used. 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 this condition are out-of-scope for
this document.
Address generation for globally unique addresses and RFC4193 unique
local addresses [RFC4193] is similar. Nodes MUST NOT use unique
local addresses to communicate with a Border Router with a globally
unique address. Nodes MUST NOT use globally unique addresses to
communicate with a Border Router with a unique local address.
In case a MANET Generated Addresses is needed, but no BRIO
information is available, a MANET Router MAY generate an address
using a unique local addresses [RFC4193] /64 prefix.
A MANET Generated Addresses clean-up routine SHOULD run at regular
intervals to get rid of stale addresses.
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6. Path setup, routing and session continuity
Border Router selection and BRDP-based Autoconf is a MANET Router
local mechanism. Without an additional mechanism, other MANET
Routers are not notified of Border Router selections. As a
consequence, it is not enforced that the Border Router chosen will
actually be used for packets sent to a corresponding node via the
fixed infrastructure. To ensure the use of the correct Border
Routers other solutions are necessary. These solutions MAY be found
in the direction of NEMO or a Routing Header. In addition to path
setup, routing and session continuity are necessary for providing and
maintaining connectivity between nodes in a MANET and nodes in the
fixed infrastructure. Since this document focuses on
autoconfiguration, mechanisms for path setup, routing and session
continuity are outside its scope. These issues are to be discussed
in future documents.
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7. Support for IPv4
BRDP-based Address Autoconfiguration is designed for IP version 6.
The used mechanism for address generation extends the functionality
specified in "IPv6 Stateless Address Autoconfiguration" (RFC4862,
[RFC4862]). Therefore it does not support IPv4.
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8. 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.
9. 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 anonimity 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 autoconfiguration security
considerations is to be included in a next version of this document.
10. 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 Benny Tops
and Ronald in 't Velt for reviewing.
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11. References
11.1. Normative reference
[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.
[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.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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",
RFC 3963, January 2005.
11.2. Informative Reference
[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.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
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RFC 3753, June 2004.
[RFC5149] Korhonen, J., Nilsson, U., and V. Devarapalli, "Service
Selection for Mobile IPv6", RFC 5149, February 2008.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[I-D.thubert-tree-discovery]
Thubert, P., "Nested Nemo Tree Discovery",
draft-thubert-tree-discovery-06 (work in progress),
July 2007.
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Appendix A. Change Log From Previous Version
o 00: Initial Document.
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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Boot & Holtzer Expires January 19, 2009 [Page 26]
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