MANET Security and Routing Challenges

•Mobile Ad hoc Networks (MANETs):
•Overview
•Properties of a MANET
•spectrum of MANET applications
•routing and various routing
algorithms
•security in MANET’s.
Unit-5

MANETS
 Mobile ad hoc networks is a collection of mobile
nodes which establish a network spontaneously
and communicate over a shared wireless channel
without any pre existing infrastructure and no
minimal central administration
 It is known for its routable network properties
where each node act as a “router” to forward the
traffic to other specified node in the network

Types of MANET
There are different types of MANETs including:
 InVANETs – Intelligent vehicular ad hoc networks
make use of artificial intelligence to tackle
unexpected situations like vehicle collision and
accidents.
 Vehicular ad hoc networks (VANETs) – Enables
effective communication with another vehicle or
helps to communicate with roadside equipments.
 Internet Based Mobile Ad hoc Networks
(iMANET) – helps to link fixed as well as mobile
nodes

MANET- Characteristics
 Dynamic network topology
 Bandwidth constraints and variable link capacity
 Energy constrained nodes
 Multi-hop communications
 Limited security
 Autonomous terminal
 Distributed operation
 Light-weight terminals

 In MANET, each node act as both host and router. That is it is
autonomous in behavior.
 Multi-hop radio relaying- When a source node and destination
node for a message is out of the radio range, the MANETs are
capable of multi-hop routing.
 Distributed nature of operation for security, routing and host
configuration. A centralized firewall is absent here.
 The nodes can join or leave the network anytime, making the
network topology dynamic in nature.
 Mobile nodes are characterized with less memory, power and
light weight features.
 The reliability, efficiency, stability and capacity of wireless links
are often inferior when compared with wired links. This shows the
fluctuating link bandwidth of wireless links.
 Mobile and spontaneous behavior which demands minimum
human intervention to configure the network.
 All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric
environment.
 High user density and large level of user mobility.
 Nodal connectivity is intermittent.

Need for Ad Hoc Networks
 Setting up of fixed access points and backbone
infrastructure is not always viable
 Infrastructure may not be present in a disaster
area or war zone
 Infrastructure may not be practical for short-range
radios; Bluetooth (range ~ 10m)
 Ad hoc networks:
 Do not need backbone infrastructure support
 Are easy to deploy
 Useful when infrastructure is absent, destroyed or
impractical

Properties of MANETs
 MANET enables fast establishment of networks. When anew network is to
be established, the only requirement is to provide a new set of nodes with
limited wireless communication range. A node has limited capability, that is, it
can connect only to the nodes which are nearby. Hence it consumes limited
power.
 A MANET node has the ability to discover a neighboring node and service.
Using a service discovery protocol, a node discovers the service of a nearby
node and communicates to a remote node in the MANET.
 MANET nodes have peer-to-peer connectivity among themselves.
 MANET nodes have independent computational, switching (or routing), and
communication capabilities.
 The wireless connectivity range in MANETs includes only nearest node
connectivity.
 The failure of an intermediate node results in greater latency in
communicating with the remote server.

 Limited bandwidth available between two intermediate nodes
becomes a constraint for the MANET. The node may have
limited power and thus computations need to be energy-
efficient.
 There is no access-point requirement in MANET. Only
selected access points are provided for connection to other
networks or other MANETs.
 MANET nodes can be the iPods, Palm handheld computers,
Smartphones, PCs, smart labels, smart sensors, and
automobile-embedded systems
 MANET nodes can use different protocols, for example, IrDA,
Bluetooth, ZigBee, 802.11, GSM, and TCP/IP.MANET node
performs data caching, saving, and aggregation.
 MANET mobile device nodes interact seamlessly when they
move with the nearby wireless nodes, sensor nodes, and

MANET challenges
To design a good wireless ad hoc network, various challenges have to be
taken into account:
 Dynamic Topology: Nodes are free to move in an arbitrary fashion
resulting in the topology changing arbitrarily. This characteristic
demands dynamic configuration of the network.
 Limited security: Wireless networks are vulnerable to attack. Mobile ad
hoc networks are more vulnerable as by design any node should be
able to join or leave the network at any time. This requires flexibility and
higher openness.
 Limited Bandwidth: Wireless networks in general are bandwidth limited.
In an ad hoc network, it is all the more so because there is no backbone
to handle or multiplex higher bandwidth
 Routing: Routing in a mobile ad hoc network is complex. This depends
on many factors, including finding the routing path, selection of routers,
topology, protocol etc.

MANET challenges
 Limited wireless transmission range
 Broadcast nature of the wireless medium
 Hidden terminal problem and broadcast storms
 Packet losses due to transmission errors
 Mobility-induced route changes
 Mobility-induced packet losses
 Battery constraints
 Potentially frequent network partitions
 Ease of snooping on wireless transmissions
(security issues)

Applications of MANETS
 Military battlefield– soldiers, tanks, planes
 Sensor networks – to monitor environmental conditions over a large area
 Personal Area Network (PAN) – pervasive computing i.e. to provide flexible
connectivity between personal electronic devices or home appliances.
 Local level -To spread and share information among participants at e.g.
conference or classroom,s ports, stadiums
 Vehicular Ad hoc Networks – intelligent transportation i.e. to enable real time
vehicle monitoring and adaptive traffic control
 Civilian environments – taxi cab network, meeting rooms, sports stadiums,
boats, small aircraft
 Emergency operations – search and rescue, policing and fire fighting and to
provide connectivity between distant devices where the network infrastructure is
unavailable.
 Emergency/rescue operations for disaster relief efforts, e.g. in fire, flood, or
earthquake. Emergency rescue operations must take place where non-existing or
damaged communications infrastructure and rapid deployment of a
communication network is needed

Security in MANET’s
 Securing wireless ad-hoc networks is a highly
challenging issue.
 Understanding possible form of attacks is always
the first step towards developing good security
solutions.
 Security of communication in MANET is important
for secure transmission of information.
 Absence of any central co-ordination mechanism
and shared wireless medium makes MANET
more vulnerable to digital/cyber attacks than
wired network there are a number of attacks that
affect MANET.

 These attacks can be classified into two types:
 External Attack: External attacks are carried out by
nodes that do not belong to the network.
 It causes congestion sends false routing information
or causes unavailability of services.
 Internal Attack: Internal attacks are from
compromised nodes that are part of the network.
 In an internal attack the malicious node from the
network gains unauthorized access
and impersonates as a genuine node.
 It can analyze traffic between other nodes and may
participate in other network activities.

 Denial of Service attack: This attack aims to
attack the availability of a node or the entire
network.
 If the attack is successful the services will not be
available.
 The attacker generally uses radio signal jamming
and the battery exhaustion method.
 Impersonation: If the authentication mechanism
is not properly implemented a malicious node can
act as a genuine node and monitor the network
traffic.
 It can also send fake routing packets, and gain
access to some confidential information.
 Eavesdropping: This is a passive attack.
 The node simply observes the confidential
information.

 Routing Attacks: The malicious node makes routing
services a target because it’s an important service in
MANETs.
 There are two flavors to this routing attack.
 One is attack on routing protocol and another is attack on
packet forwarding or delivery mechanism.
 The first is aimed at blocking the propagation of routing
information to a node.
 The latter is aimed at disturbing the packet delivery against
a predefined path.
 Black hole Attack:: In this attack, an attacker advertises a
zero metric for all destinations causing all nodes around it
to route packets towards it.
 A malicious node sends fake routing information, claiming
that it has an optimum route and causes other good nodes
to route data packets through the malicious one.
 A malicious node drops all packets that it receives instead
of normally forwarding those packets. An attacker listen the
requests in a flooding based protocol.

 Wormhole Attack: In a wormhole attack, an attacker
receives packets at one point in the network,
―tunnels them to another point in the network, and
then replays them into the network from that point.
 Routing can be disrupted when routing control
message are tunnelled. This tunnel between two
colluding attacks is known as a wormhole.
 Replay Attack: An attacker that performs a replay
attack are retransmitted the valid data repeatedly to
inject the network routing traffic that has been
captured previously.
 This attack usually targets the freshness of routes, but
can also be used to undermine poorly designed
security solutions.

 Jamming: In jamming, attacker initially keep
monitoring wireless medium in order to determine
frequency at which destination node is receiving signal
from sender. It then transmit signal on that frequency
so that error free receptor is hindered.
 Man- in- the- middle attack: An attacker sites
between the sender and receiver and sniffs any
information being sent between two nodes. In some
cases, attacker may impersonate the sender to
communicate with receiver or impersonate the
receiver to reply to the sender.
 Gray-hole attack: This attack is also known as routing
misbehavior attack which leads to dropping of
messages. Gray-hole attack has two phases. In the
first phase the node advertise itself as having a valid
route to destination while in second phase, nodes

Routing MANETs
 These networks do not have fixed infrastructure
and routing requires distributed and cooperative
actions from all nodes in the network
 The major difference between routing in MANET
and regular internet is the route discovery
mechanism
 MANET-specific routing protocols have been
proposed, that handle topology changes well, but
they have large control overhead and are not
scalable for large networks. Another major
difference in the routing is the network address

Traditional Routing
 A routing protocol sets up a routing table in
routers
 A node makes a local choice depending on global

Distance-vector & Link-state Routing
 Both assume router knows
 address of each neighbor
 cost of reaching each neighbor
 Both allow a router to determine global routing
information by talking to its neighbors
 Distance vector - router knows cost to each
destination
 Link state - router knows entire network topology
and computes shortest path

Distance Vector Routing:
Example


2


Routing and Mobility
 Finding a path from a source to a destination
 Issues
 Frequent route changes
 amount of data transferred between route changes may be
much smaller than traditional networks
 Route changes may be related to host movement
 Low bandwidth links
 Goal of routing protocols
 decrease routing-related overhead
 find short routes
 find “stable” routes (despite mobility)

Routing Protocols
 Proactive protocols
 Traditional distributed shortest-path protocols
 Maintain routes to destinations even if they are not
needed
 Always maintain routes:- Little or no delay for route
determination
 Consume bandwidth to keep routes up-to-date
 Maintain routes which may never be used
 Examples: Destination Sequenced Distance Vector
(DSDV), Wireless Routing Algorithm (WRP), Global
State Routing (GSR), Source-tree Adaptive Routing
(STAR), Cluster-Head Gateway Switch Routing (CGSR),
Topology Broadcast Reverse Path Forwarding (TBRPF),
Optimized Link State Routing (OLSR)
 Advantages: low route latency, State information, QoS
guarantee related to connection set-up or other real-time
requirements
 Disadvantages: high overhead (periodic updates) and

 Reactive protocols
 Determine route if and when needed
 Source initiates route discovery
 only obtain route information when needed
 Advantages: no overhead from periodic update,
scalability as long as there is only light traffic and
low mobility.
 Disadvantages: high route latency, route caching
can reduce latency
 Ex: Dynamic Source Routing (DSR), Ad hoc-On
demand distance Vector (AODV), Temporally
ordered Routing Algorithm (TORA), Associativity-
Based Routing (ABR)

 Hybrid protocols
 Adaptive; Combination of proactive and reactive
 maintain routes to nearby nodes even if they are not
needed and maintain routes to far away nodes only
when needed
 Example : ZRP (zone routing protocol)

Dynamic Source Routing
 The Dynamic Source Routing protocol (DSR) is a
simple and efficient routing protocol designed
specifically for use in multi-hop wireless ad hoc
networks of mobile nodes.
 DSR allows the network to be completely self-
organizing and self-configuring, without the need
for any existing network infrastructure or
administration.
 The protocol is composed of the two main
mechanisms of "Route Discovery" and "Route
Maintenance", which work together to allow
nodes to discover and maintain routes to arbitrary
destinations in the ad hoc network

Route discovery
 If the source does not have a route to the destination
in its route cache, it broadcasts a route request
(RREQ) message specifying the destination node for
which the route is requested.
 The RREQ message includes a route record which
specifies the sequence of nodes traversed by the
message.
 When an intermediate node receives a RREQ, it
checks to see if it is already in the route record, if it is,
it drops the message. This is done to prevent routing
loops. If the intermediate node had received the
RREQ before, then it also drops the message.
 The intermediate node forwards the RREQ to the next
hop according to the route specified in the header.
 When the destination receives the RREQ, it sends
back a route reply message

 If the destination has a route to the source in its route
cache, then it can send a route response (RREP)
message along this route.
 Otherwise, the RREP message can be sent along the
reverse route back to the source.
 Intermediate nodes may also use their route cache to
reply to RREQs.
 If an intermediate node has a route to the destination
in its cache, then it can append the route to the route
record in the RREQ, and send an RREP back to the
source containing this route.
 This can help limit flooding of the RREQ.
 If the cached route is out-of-date, it can result in the
source receiving stale routes.

Route maintenance
 When a node detects a broken link while trying to
forward a packet to the next hop, it sends a route
error (RERR) message back to the source
containing the link in error.
 Then an RERR message is received, all routes
containing the link in error are deleted at that
node

Route Discovery: at source
Source need to send
packet to Destination
Lookup Cache for route Source
to Destination
Route
found
?
Start Route
Discovery
Protocol
Continue
normal
processin
g
Route
Discovery
finished
Packet
in
buffer?
Send
packet to
next-hop
don
e
Buffer
packet
no
Write route in
packet header
yes
yes
no
wait

Route Discovery: At an intermediate node
Accept route
request
packet
<src,id> in
recently
seen
requests
list?
Discard
route
request
yes
no
Host’s
address
already in
patrial
route
Discard
route
request
yes
Store <src,id> in
list
Broadcast packet
Send route
reply packet
done
myAdd
r=targe
t
noAppend
myAddr to
partial route
no
yes

A
B
C
E
D
G
H
F
A
A
A-B
A-C
A-C-E
A-C-E
A-C-E
A-B-D
A-B-D-G
A-B-D-G
A-B-D-G
Route Discovery
A-B-C
A-B-C
Route Request (RREQ)
Route Reply (RREP)
Route Discovery is issued with exponential back-off intervals.
Initiator ID
Initiator seq#
Target ID
Partial route
RREQ FORMAT

A
B
C
E
D
G
H
F
G
RERR
RERR
Route Cache (A)
G: A, B, D, G G:
A, C, E, H, G
F: B, C, F
Route Maintenance

Dynamic Source Routing (DSR) Ex:2
 When node S wants to send a packet to node D,
but does not know a route to D, node S initiates a
route discovery
 Source node S floods Route Request (RREQ)
 Each node appends own identifier when
forwarding RREQ

Route Discovery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
Represents a node that has received RREQ for D from S
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L
[S]
[X,Y] Represents list of identifiers appended to RREQ

B
A
S E
F
H
J
D
C
G
I
K
• Node H receives packet RREQ from two neighbors:
potential for collision
Z
Y
M
N
L
[S,E]
[S,C]

B
A
S E
F
H
J
D
C
G
I
K
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
Z
Y
M
N
L
[S,C,G]
[S,E,F]

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
• Nodes J and K both broadcast RREQ to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
N
L
[S,C,G,K]
[S,E,F,J]

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
• Node D does not forward RREQ, because node D
is the intended target of the route discovery
M
N
L
[S,E,F,J,M]

 Destination D on receiving the first RREQ, sends
a Route Reply (RREP)
 RREP is sent on a route obtained by reversing
the route appended to received RREQ
 RREP includes the route from S to D on which
RREQ was received by node D

Route Reply in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
RREP [S,E,F,J,D]
Represents RREP control message

Dynamic Source Routing (DSR)
 Node S on receiving RREP, caches the route
included in the RREP
 When node S sends a data packet to D, the
entire route is included in the packet header
 hence the name source routing
 Intermediate nodes use the source route included
in a packet to determine to whom a packet should
be forwarded

DSR Optimization: Route
Caching
 Each node caches a new route it learns by any
means
 When node S finds route [S,E,F,J,D] to node D,
node S also learns route [S,E,F] to node F
 When node K receives Route Request [S,C,G]
destined for node, node K learns route [K,G,C,S]
to node S
 When node F forwards Route Reply RREP
[S,E,F,J,D], node F learns route [F,J,D] to node D
 When node E forwards Data [S,E,F,J,D] it learns
route [E,F,J,D] to node D
 A node may also learn a route when it overhears
Data

Dynamic Source Routing:
Advantages
 Routes maintained only between nodes who
need to communicate
 reduces overhead of route maintenance
 Route caching can further reduce route discovery
overhead
 A single route discovery may yield many routes to
the destination, due to intermediate nodes
replying from local caches

Dynamic Source Routing: Disadvantages
 Packet header size grows with route length due
to source routing
 Flood of route requests may potentially reach all
nodes in the network
 Potential collisions between route requests
propagated by neighboring nodes
 insertion of random delays before forwarding RREQ
 Increased contention if too many route replies
come back due to nodes replying using their local
cache
 Route Reply Storm problem
 Stale caches will lead to increased overhead

Ad Hoc On-Demand Distance Vector Routing
(AODV)
 AODV is another reactive protocol as it reacts to
changes and maintains only the active routes in the
caches or tables for a pre-specified expiration time.
 It uses the same route discovery mechanism used by
DSR.
 DSR includes source routes in packet headers and
resulting large headers can sometimes degrade
performance, particularly when data contents of a
packet are small.
 AODV attempts to improve on DSR by maintaining
routing tables at the nodes, so that data packets do not
have to contain routes.
 AODV retains the desirable feature of DSR that routes
are maintained only between nodes which need to
communicate.
 However, as opposed to DSR, which uses source
routing, AODV uses hop-by-hop routing by maintaining

Route Discovery
 The route discovery process is initiated when a
source needs a route to a destination and it does
not have a route in its routing table.
 To initiate route discovery, the source floods the
network with a RREQ packet specifying the
destination for which the route is requested.
 When a node receives an RREQ packet, it
checks to see whether it is the destination or
whether it has a route to the destination.
 If either case is true, the node generates an
RREP packet, which is sent back to the source
along the reverse path.

 At intermediate nodes duplicate RREQ packets are
discarded.
 Then the source node receives the first RREP, it can
begin sending data to the destination.
 To determine the relative degree out-of-datedness of
routes, each entry in the node routing table and all
RREQ and RREP packets are tagged with a
destination sequence number.
 A larger destination sequence number indicates a
more current (or more recent) route.
 Upon receiving an RREQ or RREP packet, a node
updates its routing information to set up the reverse
or forward path, respectively, only if the route
contained in the RREQ or RREP packet is more
current than its own route.

Route Maintenance.
 When a node detects a broken link while
attempting to forward a packet to the next hop, it
generates a RERR packet that is sent to all
sources using the broken link.
 The RERR packet erases all routes using the link
along the way.
 If a source receives a RERR packet and a route
to the destination is still required, it initiates a new
route discovery process.
 Routes are also deleted from the routing table if
they are unused for a certain amount of time.

 Local HELLO messages are used to determine
local
connectivity
 Can reduce response time to routing requests
 Can trigger updates when necessary
 Sequence numbers are assigned to routes and
routing table entries
 Used to supersede stale cached routing entries
 Every node maintains two counters
 Node sequence number
 Broadcast ID

 AODV utilizes routing tables to store routing
information.
 The routing table stores:
AODV (cont.)
destination
addr
next-hop
addr
destination
sequence
hop count life time

1. If a node wants to send a packet to some destination. At
first, it checks its routing table to determine whether it has
a current route to the destination or not.
=>If yes, it forwards the packet to next hop node of the
route.
=>If no, it initiates a route discovery process.
The AODV routing procedure

 The Route discovery process:
 It begins with the creation of a RouteRequest (RREQ) packet.
Broadcasting is done via flooding.
 Broadcast ID gets incremented each time a source node uses
RREQ.
 Broadcast ID and source IP address form a unique identifier for
the RREQ.
RREQ packet format
TheAODV routing procedure (cont.)
Type Reserved Hop Count
Broadcast ID
Destination IPAddress
Destination Sequence Number
Source IPAddress
Source Sequence Number
Time Stamp

2.Sender S broadcasts a RREQ to all its neighbors, each node
receiving RREQ forwards RREQ to its neighbors.
*Sequence numbers help to avoid the possibility of forwarding the same
packet more than once.
3.An intermediate node (not the destination) may also send a
RouteReply (RREP) packet provided that it knows a more
recent path than the one previously known to sender S.
RREPpacket format
TheAODV routing procedure (cont.)
Type Reserved Hop Count
Destination IPAddress
Destination Sequence Number
Source IPAddress
Life Time

 4. As an intermediate node receives the RREP
packet, it sets up a forward path entry to the
destination in its routing table.
 5. The source node can begin data transmission
upon receiving the first RREP.
The AODV routing procedure (cont.)

Illustration of route establishment in AODV
 1. Node S needs a routing path to node D.
 2. Node S creates a RREQ packet
RREQ [D’s IP addr, seq#, S’s IP addr, seq#, hopcount]
 Node S broadcasts RREQ to its neighbors.
B
RREQ{D, D’seq, S, S’seq, 0}
S A
D
C

 2. NodeArebroadcasts RREQ to all its neighbors.
S A
B
C
D
Illustration of route establishment inAODV (cont.)

 3. Since, node C known a route to D.
 Node C creates a RREP packet and unicasts RREP to A.
 Set forward path in node C’s routing table.
B
S A
D
C
RREP{D, D’seq, S, S’seq, 1}
C’s Routing table
dest nexthop hopcount
D D 1

 3. Node A creates a RREP packet and unicasts RREP to S.
 4. Set forward path in node A’s routing table.
B
S A
C
D
RREP{D, D’seq, S, S’seq, 2}
C’s Routing table
D D 1
A’s Routing table
D C 2

 4. Set forward path in node S’s routing table.
S A
B
D
C
C’s Routing table
D D 1
A’s Routing table
D C 2
S’s Routing table
D A 3

Route maintenance in AODV (Path broken due to host mobility)
1.If intermediate nodes or the destination move.
The next hop links break.
Routing tables are updated for the link failures.
All active neighbors are informed by RouteError
(RERR) packet.
2.When a source node receives an RRER, it can reinitiate
the route discovery process.
3.It can be also dealt with by a local fix scheme.

A
C
D
RERR
Illustration of route maintenance in AODV
 Assume link between C and D breaks.
 Node C invalidates route to D in route table.
 Node C creates RERR packet and sends to its upstream
neighbors.
 Node A sends RERR to S.
 Node S rediscovers route if still needed.
B
RERR
S

 Advantage:
 The routes are established on demand and the destination
sequence number can find the latest route to the
destination.
 Disadvantage:
 The intermediate nodes can lead to inconsistent routes if
the source sequence number is very old.
 The periodic beaconing leads to unnecessary bandwidth
consumption.
AODV (cont.)

Ex:3-Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
Represents a node that has received RREQ for D from S
M
N
L

Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L

Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Represents links on Reverse Path
Z
Y
M
N
L

Reverse Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
Z
Y
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
• Node D does not forward RREQ, because node D
is the intended target of the RREQ
M
N
L

Forward Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
Forward links are setup when RREP travels along
the reverse path
Represents a link on the forward path

Link Failure
 A neighbor of node X is considered active for a routing table
entry if the neighbor sent a packet within active_route_timeout
interval which was forwarded using that entry
 Neighboring nodes periodically exchange hello message
 When the next hop link in a routing table entry breaks, all active
neighbors are informed
 Link failures are propagated by means of Route Error (RERR)
messages, which also update destination sequence numbers

Route Error
 When node X is unable to forward packet P (from node S to
node D) on link (X,Y), it generates a RERR message
 Node X increments the destination sequence number for D
cached at node X
 The incremented sequence number N is included in the RERR
 When node S receives the RERR, it initiates a new route
discovery for D using destination sequence number at least as
large as N
 When node D receives the route request with destination
sequence number N, node D will set its sequence number to N,
unless it is already larger than N

AODV: Summary
 Routes need not be included in packet headers
 Nodes maintain routing tables containing entries
only for routes that are in active use
 At most one next-hop per destination maintained
at each node
 DSR may maintain several routes for a single
destination
 Sequence numbers are used to avoid old/broken
routes
 Sequence numbers prevent formation of routing
loops
 Unused routes expire even if topology does not

DSDV(Destination Sequence Distance
Vector)
 An example of proactive algorithm
 An enhancement to distance vector routing for ad-hoc
networks
 Distance vector routing is used as routing information
protocol (RIP) in wired networks.
 It performs extremely poorly with certain network
changes due to the count-to-infinity problem.
 Each node exchanges its neighbor table periodically with
its neighbors.
 Changes at one node in the network propagate slowly
through the network.
 The strategies to avoid this problem which are used in
fixed networks do not help in the case of wireless ad-hoc
networks, due to the rapidly changing topology. This
might create loops or unreachable regions within the

Distance Vector(count to infinity
problem)

 DSDV adds the concept of sequence numbers to the
distance vector algorithm.
 Each routing advertisement comes with a sequence
number. Within ad-hoc networks, advertisements may
propagate along many paths.
 Sequence numbers help to apply the advertisements
in correct order.
 This avoids the loops that are likely with the
unchanged distance vector algorithm.
 Each node maintains a routing table which stores
next hop, cost metric towards each destination and a
sequence number
 Each node periodically forwards routing table to
neighbors.
 Each node increments and appends its sequence

 Each node increments and appends its sequence
number when sending its local routing table.
 Each route is tagged with a sequence number;
routes with greater sequence numbers are preferred.
 Each node advertises a monotonically increasing
even sequence number for itself.
 When a node decides that a route is broken, it
increments the sequence number of the route and
advertises it with infinite metric.
 Destination advertises new sequence number.

Example of DSDV
Destination Next Hop Distance Sequence Number
A A 0 S205_A
B B 1 S334_B
C C 1 S198_C
D D 1 S567_D
E D 2 S767_E
F D 2 S45_F
Destination Next Hop Distance Sequence Number
A A 0 S304_A
B D 3 S424_B
C C 1 S297_C
D D 1 S687_D
E D 2 S868_E
F D 2 S164_F
A’s Routing Table Before Change
A’s Routing Table After Change

15
14
13
12
11
10 9
8
7
6
5
4
3
2
1
Routing table for Node 1
DSDV (cont.)
Example:
Dest NextNode Dist seqNo
2 2 1 22
3 2 2 26
4 5 2 32
5 5 1 134
6 6 1 144
7 2 3 162
8 5 3 170
9 2 4 186
10 6 2 142
11 6 3 176
12 5 3 190
13 5 4 198
14 6 3 214
15 5 4 256

DSDV (cont.)
 Each node, upon receiving an update, quickly
disseminates it to its neighbors in order to propagate
the broken-link information to the whole network.
 Thus a single link break leads to the propagation of
table update information to the whole network.

15
14
13
12
11
10
98
7
6
5
4
3
2
1
Routing table for Node 1
DSDV (cont.)
Dest NextNode Dist seqNo
2 2 1 22
3 2 2 26
4 5 2 32
5 5 1 134
6 6 1 144
7 2 3 162
8 5 3 170
9 2 4 186
10 6 2 142
11 5 4 180
12 5 3 190
13 5 4 198
14 6 3 214
15 5 4 256

 When X receives information from Y about a route to
Z
 Let destination sequence number for Z at X be S(X),
S(Y) is sent from Y
 If S(X) > S(Y), then X ignores the routing information
received from Y
 If S(X) = S(Y), and cost of going through Y is smaller
than the route known to X, then X sets Y as the next
hop to Z
 If S(X) < S(Y), then X sets Y as the next hop to Z, and
S(X) is updated to equal S(Y)
X Y Z

 Advantages
 Simple (almost like Distance Vector)
 Loop free through destination seq. numbers
 No latency caused by route discovery
 Disadvantages
 No sleeping nodes
 Overhead: most routing information never used

Cluster-head Gateway Switch Routing
(CGSR)
 Similar to DSDV
 It is a hierarchical routing and proactive protocol.
 When a source routes the packets to destination,
the routing tables are already available at the
nodes.
 A cluster higher in hierarchy sends the packets to
the cluster lower in hierarchy.
 Each cluster can have several daughters and
forms a tree-like structure in CGSR. CGSR forms
a cluster structure.
 The nodes aggregate into clusters using an
appropriate algorithm.

 The algorithm defines a cluster-head, the node used
for connection to other clusters.
 It also defines a gateway node which provides
switching (communication) between two or more
cluster-heads.
 There will thus be three types of nodes—
 (i) internal nodes in a cluster which transmit and
receive the messages and packets through a cluster-
head
 (ii) cluster-head in each cluster such that there is a
cluster-head which dynamically schedules the route
paths.
 It controls a group of ad-hoc hosts, monitors
broadcasting within the cluster, and forwards the
messages to another cluster-head,
 (iii) gateway node to carry out transmission and

 The cluster structure leads to a higher performance of
the routing protocol as compared to other protocols
because it provides gateway switch-type traffic
redirections and clusters provide an effective
membership of nodes for connectivity

CGSR works as follow:
 periodically, every node sends a hello message
containing its ID and a monotonically increasing
sequence number
 Using these messages, every cluster-head maintains
a table containing the IDs of nodes belonging to it and
their most recent sequence numbers.
 Cluster-heads exchange these tables with each other
through gateways; eventually, each node will have an
entry in the affiliation table of each cluster-head. This
entry shows the node’s ID & cluster-head of that
node.
 Each cluster-head and each gateway maintains a
routing table with an entry for every cluster-head that
shows the next gateway on the shortest path to that
cluster head.

Disadvantages:
 The same disadvantage common to all hierarchal
algorithms related to cluster formation and
maintenance.

 Combines both reactive and proactive schemes.
 Finds loop free routes to the destination.
 Flat structure (as opposed to hierarchical) – why
? Hierarchical schemes can lead to congestion
localization
 ZRP limits the scope of the proactive procedure
to the node’s local neighborhood ? dramatic
reduction in cost.
 The on-demand search for nodes outside the
zone, albeit global, is done by querying only a
subset of the nodes in the network.
 Notice that changes in network topology has local
Zone Routing Protocol (ZRP)

 Each node, individually creates its own
neighborhood which it calls a routing zone.
 The zone is defined as a collection of nodes
whose minimum distance (in hops) from the node
in question is no greater than a value that is
called the “zone radius”.
 Peripheral nodes are those nodes whose
minimum distance from the node in question is
equal to the zone radius.
 Note that routing zones of nodes might overlap
heavily

 All nodes within hop distance at most d from a
node X are said to be in the routing zone of node
X
 All nodes at hop distance exactly d are said to be
peripheral nodes of node X’s routing zone
 Intra-zone routing: Proactively maintain routes to
all nodes within the source node’s own
zone.(Intra-Zone Routing Protocol (IARP))
 Inter-zone routing: Use an on-demand protocol
(similar to DSR or AODV) to determine routes to
outside zone. Inter-Zone Routing Protocol (IERP)

Radius of routing zone = 2

ADVANTAGES:
 Provides some notion of scalability.
 The absence of hierarchies eliminates definitive
points of congestion.
DISADVANTAGES
 What should the zone size be ?
 Can we have variable size zones ? How can we
dynamically form these zones ?

Optimized Link State Routing(OLSR)
 Link state detection using HELLO messages to
avoid asymmetric links Proactive control message
diffusion using MPR nodes to reduce control
messages

multipoint relays: MPR nodes
 MPR set definition The MPR set mi of a node i is
an arbitrary subset of its symmetric 1-hop
neighborhood ni which satisfies the following
condition: every node in the 2-hop neighborhood
n 2 i of i must have at least a symmetric link
towards a node in mi

Optimized Link State Routing
(OLSR)
 Nodes C and E are multipoint relays of node A
 Multipoint relays of A are its neighbors such that
each two-hop neighbor of A is a one-hop neighbor
of one multipoint relay of A
 Nodes exchange neighbor lists to know their 2-hop
neighbors and choose the multipoint relays
A
B F
C
D
E H
G
K
J
Node that has broadcast state information from A

Optimized Link State Routing
(OLSR)
 Nodes C and E forward information received from
A
 Nodes E and K are multipoint relays for node H
 Node K forwards information received from H
A
B F
C
D
E H
G
K
J
Node that has broadcast state information from A

MANET Security and Routing Challenges

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