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Duplicate address detection and
autoconfiguration in OLSR
Saadi Boudjit; Cedric Adjih; Anis Laouiti; Paul Muhlethaler
Hipercom Project
National Institute in Computer science and Control
INRIA - France
Outline

OLSR Overview

Autoconfiguration

AutoConfiguration in IPv6

AutoConfiguration in Ad Hoc networks

DAD-MPR flooding algorithm and Autoconfiguration in OLSR

Conclusion
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OLSR Overview


OLSR: Proactive
MPR flooding
Among the 1-hop neighbors of node m, only a
subset of nodes are selected as MPRs and
hence retransmit the messages of m.
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OLSR Overview


Recently: RFC 3626 (IETF/MANET)
Link State protocol
-
Periodic messages
Neighbor sensing:
“HELLO” messages: list of neighbors
-
Topology discovery (Topology Control):
List of neighbors sent to the whole net (in “TC” messages)
- Routes:


Computed to all nodes
Routes computed independently of traffic
- OLSR Gateways:
Host and Network Association “HNA” messages
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AutoConfiguration

What is the autoconfiguration ?



Automatic assignment of parameters which are necessary to a node to join a network (IP address for
example);
But also automatic reassignment of network parameters in case of conflict.
Why ad hoc networks need autoconfiguration ?

Manual configuration is impractical in large scale Manets;

User-friendliness is necessary for new emerging applications like wireless internet.
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AutoConfiguration in IPv6

Automatic configuration
Two methods :


Stateless Address Autoconfiguration
Periodic broadcast of the network related information by the Router;
Stateful Address Autoconfiguration
Hosts rely on a DHCP server to acquire the network related information, necessary
to its configuration;
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Stateless AutoConfiguration
IPv6 Router
IPv6 Address 2001:0660:1000::ID4
IPv6 Address 2001:0660:1000::ID2
“Neighbor Advertisement” Message
IPV6 LAN
MAC address MAC5
Link-local Address fe80::ID5
“Neighbor Sollicitation” Message
IPv6 Address 2001:0660:1000::ID3
“Neighbor Sollicitation “ Message
MAC address MAC1
Link-local Address fe80::ID1
Unique Address …
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Stateless AutoConfiguration
IPv6 Router
IPv6 Address 2001:0660:1000::ID4
IPv6 Address 2001:0660:1000::ID2
“Router Advertisement” Message
Bit M
Prefix 2001:0660:1000
IPV6 LAN
“Router Sollicitation” Message ff02::2
IPv6 Address 2001:0660:1000::ID3
MAC address MAC1
Link-local Address fe80::ID1
IPv6 global unicast address 2001:0660:1000::ID1
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Stateful AutoConfiguration
IPv6 Router
IPv6 Address 2001:0660:1000::ID4
IPv6 Address 2001:0660:1000::ID2
DHCP Server
IPv6 Address 2001:0660:1000::ID
IPV6 LAN
“DHCP Advertisement” Message containing its IPv6 address
IPv6 Address 2001:0660:1000::ID3
“DHCP Sollicitation” Message ff02::1:2
DHCP Client
MAC address MAC1
Link-local Address fe80::ID1
unique address…
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Stateful AutoConfiguration
IPv6 Router
IPv6 Address 2001:0660:1000::ID4
IPv6 address 2001:0660:1000::ID2
DHCP Server
IPv6 Address 2001:0660:1000::ID
IPV6 LAN
“DHCP response” Message, extension=2001:0660:1000::
“DHCP request” Message, address extension
IPv6 address 2001:0660:1000::ID3
DHCP client
MAC address MAC1
Link-local address fe80::ID1
Unique address…
IPv6 global unicast address 2001:0660:1000::ID1
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AutoConfiguration in Ad Hoc networks
More difficult in MANET environment than that in hardwired networks due to:

Instability of mobile nodes;

Openness of Ad Hoc networks;

Absence of a central administration.
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AutoConfiguration in Ad Hoc networks
Scenario 1 : A mobile node joins and then leaves a MANET once.
A
B
MANET
- An unused IP address is allocated to a node on it’s arrival and becomes free on it’s
departure.
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AutoConfiguration in Ad Hoc networks
Scenario 2 : Network partitions and merges
B
Partition 2
Partition 2
A
A
Partition 1
Partition 1
(a)
(b)
- If one or more configured nodes go out of others’ transmission range  The network
becomes partitioned;
- When these nodes approach each other, the partitions merge later  Possibility of
address conflict.
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AutoConfiguration in Ad Hoc networks
Scenario 3 : Merger of two independent MANETS
A
B
MANET 1
MANET 2
- There may be some duplicate addresses in both of them  Some(or all) nodes in
one MANET may need to change their addresses.
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AutoConfiguration in Ad Hoc networks
Solutions :
Several solutions have been proposed, which can be divided into the following three categories:
(1) Conflict-detection allocation algorithms;
(2) Conflict-free allocation algorithms;
(3) Best-effort allocation algorithms.
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1- Conflict-detection allocation
Principle :
1- A new node chooses an IP address tentatively, and requests for approval from all the
configured nodes in the network;
2- If the conflict is found by veto from a node with the same IP address, the procedure is
repeated until there is no duplicate address.
Illustration: OLSR for IPv6 Networks
Saadi Boudjit, Pascale Minet, Cedric Adjih, Anis Laouiti
HIPERCOM Project, INRIA, France
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2- Conflict-free allocation
Principle :
1- A node taking part in allocation assigns an unused IP address to a new node;
2- This is achieved by the assumption that the nodes taking part in allocation have disjoint
address pools. Thus they could be sure that the allocated addresses are different.
3- Every time when a mobile node joins, an address pool is divided into halves between it and a
configured node.
Illustration: DCDP(Dynamic Configuration and Distribution Protocol)
Sajal K.Das - University of Texas (USA)
Archan Misra, Subir Das, Anthony Mc Auley – Telcordia Technologies(USA)
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3- Best-effort allocation
Principle :
1- The nodes responsible for allocation try to assign an unused IP address to a new node as far
as they know  The same free IP address in the global address pool could be assigned
to two or more new nodes arriving at almost the same time ;
2- The new node uses conflict detection to guarantee that it is a free IP address;
Illustration: DDHCP(Distributed Dynamic Host Configuration Protocol)
Sanket Nesargi, Ravi Prakash
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4- Summary of DAD algorithms
Conflict-free allocation
algorithms
Conflict-detection
allocation algorithms
Best-effort allocation
algorithms
Active DAD algorithms
Passive DAD algorithms
Distribute additional control
information in the network to
prevent address duplication
Continuously monitor routing
protocol control traffic to
detect address duplicates
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AutoConfiguration in OLSR
Our autoconfiguration mechanism is divided into two
parts:
1- Initial address assignment (2 ways)


The arriving node can perform a random selection in a well known
pool of addresses;
One of the neighbors selects the address on behalf of the arriving
node.
2- Duplicate Address Detection “Proactive DAD”:

Periodic broadcast of MAD messages;

MAD messages must reach all the nodes in the network.
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AutoConfiguration in OLSR
1- Initial address assignment
HELLO
HELLO
HELLO
HELLO
HELLO
Temporary address
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AutoConfiguration in OLSR
1- Initial address assignment
DR
MAD
MAD
MAD
UNIQUE ADDRESS CONFIRMATION
Unique address
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AutoConfiguration in OLSR
2- Proactive DAD
After a node being configured, it must periodically broadcast MAD(Multiple Address
Declaration) messages containing:

An identifier of the node (Node ID);

The list of interface addresses of the node on which OLSR is running;
In order to perform DAD when a merge of two previously disconnected MANETs occur.
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AutoConfiguration in OLSR
2- Proactive DAD
MAD
MAD
MAD
MAD
MAD
MAD
A configured node
MAD messages will reach all the nodes in the network
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AutoConfiguration in OLSR
A node detects and address conflict if:

It receives a MAD message having the same address as its
own, but with a different identifier.
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AutoConfiguration in OLSR
Possibilities for MAD diffusion:

Pure flooding

Drawbacks:



Not using the optimizations of the underlying routing protocol;
High bandwidth consumption
MPR flooding

Drawbacks:


MPR calculation is based on the assumption that there is no address
duplication in the neighborhood of a node.
Therefore, OLSR relaying optimization rules may not be sufficient to
ensure diffusion in some conflictual cases.
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AutoConfiguration in OLSR
Illustration:
• Two conflicting nodes X1 and X2 in the
2-hop neighbors of node I;
• Node I could not calculate its MPR set
correctly;
• MAD messages of X1 and X2 can not be
propagated throughout the entire network;
• Consequently, nodes X1 and X2 will not
detect the address conflict.
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AutoConfiguration in OLSR



New rules are added to the classical MPR flooding algorithm for MAD
message diffusion;
The set is called DAD-MPR flooding, for Duplicate Address Detecting
MPR flooding;
In the absence of packet loss, the DAD-MPR flooding algorithm will
allow a MAD message to reach all the nodes in the network.
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DAD-MPR flooding algorithm
Rules added to the classical MPR flooding algorithm:
Rule1:

The MAD duplicate message detection will be based on the node
originator address, the message sequence number, plus the node
identifier;
Rule2:

If a given node N receives a MAD message from a neighbor M, it will
repeat this message if one of its 1-hop neighbors has the same address
as the one contained in the MAD message.

In this case the MAD TTL value must be set to 1 to avoid the
transmission of the MAD message beyond the conflicting nodes;
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Proof of correctness
• We assume that there are only two nodes
in conflict ,A1 and A2, in the network and
they are d hops away from each other;
• We denote by Ni the set of nodes which are
exactly at distance i of A1 and d-i of A2 for
i є {1, …, d-1};
• Those sets contain nodes that are precisely
on a shortest path from A1 to A2;
• Hence several cases can occur, depending on
on the distance d,
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Proof of correctness
• distance d = 1 , 2
• Nodes A1 and A2 are in the radio
range of each other, the conflict will
be detected by both nodes;
• Node B detects the conflict
and by applying the Rule2,
the nodes A1 and A2 will
receive the MAD messages
of each other;
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Proof of correctness
• distance d = 3
• Nodes A1 and A2 calculate their MPR set
correctly. A1 chooses B as an MPR to reach
node C, and A2 chooses C as MPR to reach B;
• Nodes B and C don’t choose each other as MPR,
consequently, A1 MAD messages will never reach
A2, and A2 MAD messages will never reach A1;
• Node B detects that one of its 1-hop
neighbors, A1, has the same address as the one
contained in the MAD message originating from
node A2  using Rule2, node B relay the MAD
message of A2 to reach A1;
• By the same manner, MAD messages of A1 will
reach A2 and the conflict will be detected;
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Proof of correctness
• distance d = 4
• Nodes A1 and A2 don’t have duplications
in their 1-hop and 2-hop neighbors,
 they calculate their MPR set properly;
• Nodes B and D don’t have duplications
in their 1-hop and 2-hop neighbors,
 they calculate their MPR set properly;
• The MAD messages of A1 and A2 will reach
all the intermediary nodes B, C, and D;
• Node C looks to the nodes A1 and A2 as a
single node, say A  C chooses only one
node between B and D as an MPR to cover A;
• Therefore, we are sure that one of the two
nodes (A1 and A2) receives the MAD
messages generated by the other node and
then detects the conflict.
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Proof of correctness
• distance d ≥ 5
• Nodes A1 and A2 and all the intermediary
nodes don’t have duplications in their 1-hop
and 2-hop neighbors;
• Hence all the intermediary nodes calculate
their MPR set correctly;
• Using the classical MPR flooding algorithm,
the MAD messages of A1 and A2 will be
correctly propagated to the nodes A2 and A1
respectively;
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Conclusion
- Proposed:
- changes to the classical MPR flooding algorithm
- Duplicate address detection algorithm
- relies on two procedures
- very well integrated with OLSR
- originality: proactive DAD
- low complexity
- Future work includes the adoption of:
- Refinements for address conflict resolution
- Handling the case of multiple conflicts
- Taking into account the case of nodes with multiple interfaces
- Considering implementation issues in more details
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Questions ...............................??????
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