ITIS 60108010 Wireless Network Security

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ITIS 6010/8010 Wireless Network Security

• Dr. Weichao Wang

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• AODV (Ad hoc On-demand Distance Vector)
• On-demand protocol routes are established when
  needed, nodes not on active paths do not have to
  maintain any information, routes will expire if
  not used
• Using hello message to discover local topology
  (why DSDV does not need this)
• Routes have lifetime
• Using sequence numbers to prevent loop
• Still a table driven protocol

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• Three kinds of packets
• Route request (RREQ)
• Route reply (RREP)
• Route error (RERR)
• Path discovery
• Every node has two value sequence number and
  broadcast id
• Broadcast RREQ lts, d, seq_s, seq_d, broad_s, hopgt

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• The pair lts, broad_sgt uniquely identifies the
  RREQ. Broad_s will be incremented every time a
  RREQ is sent.
• Processing of RREQ
• Remembers reverse path to s s, seq_s, hop count,
  previous node, route lifetime
• If it has an active route, will reply with RREP
• Otherwise, rebroadcast RREQ and increase hop by 1
• Expanding ring search for destination

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• Sending a RREP
• The RREP must have a fresher sequence number of
  destination
• The RREP is unicast back to the source lts, d,
  seq_d, hop count, lifetimegt
• How can the intermediate nodes figure out hops to
  destination?
• The nodes along the path can setup forward routes
  to the destination
• The fresher route is preferred over short route

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• Routing entry contains
• Destination, next hop, hop count, seq_d, lifetime
  of the path, neighbors have used this route
• Link failure response
• RERR is sent back with incremented sequence
  number and infinity hop count
• All active routes using this next hop will get a
  copy of this RERR and the information will be
  propagated
• New RREQ or local repair can be adopted
• Does AODV support multiple paths b/w a source and
  a destination?

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• DSR (Dynamic Source Routing)
• An on-demand routing protocol
• Nodes gather topology information by overhearing
  network traffic
• Achieves much less control traffic compared to
  DSDV (attention here)
• Source routing is used in every data packet
• Achieve loop-free
• Support unidirectional routes

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• Route discovery
• A node may discover and cache multiple routes to
  a destination
• Route request packet lts, d, broad_sgt
• The neighbor will
• If knows a route to d send back a reply with the
  full route
• Otherwise, add its own node id and broadcast
  again
• The node IDs show the accumulated path from the
  source and can be used to send route reply

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• Route cache by overhearing
• May get multiple routes to the same destination
• Accelerate route discovery
• Cut unnecessary intermediate nodes
• Ensuring packet delivery
• Active acknowledgement
• Passive acknowledgement
• Preventing route reply storms
• Route error discovery and propagation
• Attach the broken link in new RREQ to prevent it
  from being reused

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• Advantages and disadvantages
• Simple routing protocol with low overhead
• High latency in finding routes
• Not scalable

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• Zone Routing Protocol (ZRP)
• Reactive and proactive protocol each has
  advantages and disadvantages
• Can we combine them?
• For nearby nodes, use proactive approach for
  faraway nodes, use reactive approach
• ZRP has a flat view of the network. It is not a
  hierarchical protocol

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• Concept of zone
• Every node has its own zone with a radius of r
  hops
• Zones of different nodes will overlap
• Peripheral nodes and interior nodes
• Routing
• Within the zone, use proactive (intrazone)
• Outside of the zone, use reactive (interzone)
• Each can be a family of routing protocols

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• Discovery of local topology
• Hello beacons to detect active neighbors
• Zone notification messages to determine nodes in
  zone
• Intrazone routing

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• Interzone routing
• Instead of broadcast, the RREQ is sent to
  peripheral nodes through bordercast
• Can be achieved through multicast or multiple
  unicast
• If the peripheral node knows the route, sends
  back a reply (source routing or previous hop of
  the peripheral nodes)
• Otherwise, bordercast again
• Sharply reduce overhead compared to broadcast

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• The size of a zone
• If r 1, it goes back to pure reactive
• If r 8, it goes back to proactive
• Route maintenance
• When a link breaks, the node can find an
  alternative route based on its zone knowledge
• Overhead control
• Since zones overlap, a node may receive the same
  RREQ multiple times
• How to guarantee the RREQ only propagate to outer
  areas?

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• Overhead control
• Query detection
• If a node has forwarded or overheard a RREQ, it
  does not transfer in the reverse direction
• Early termination
• If a node knows that the target of bordercast
  already gets the RREQ, it discards the packet
• Random delay of bordercast