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Special Subjects in Computer Engineering

This article explores different methods for address assignment in wireless ad-hoc networks, including auto-configuration, DHCP, and duplicate address detection (DAD). It discusses the challenges and potential solutions for assigning unique addresses in these networks, as well as the implementation of weak DAD with link state and dynamic source routing. The article also addresses potential problems caused by duplicate MAC and IP addresses and the adverse interaction with higher layers.

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Special Subjects in Computer Engineering

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  1. Special Subjects in Computer Engineering By: Mohammad Nassiri Bu-Ali Sina University, Hamedan

  2. Address Assignment in Wireless Ad-Hoc Networks

  3. Routing • To route packets to a destination, need a mechanism to name the destinations • IPv4 – IP address • 802.11 – MAC address • Routable network layer (IP) address must be unique network-wide • Link layer address need only be unique on the link Address Assignment

  4. IP Address Auto-configuration • Unique Key needed for each host. Address Assignment

  5. IP Address Auto-configuration • Key may be too large to fit in the IP address: • IPv4 address 32 bits • 802.11 address 48 bits Address Assignment

  6. IP Address Auto-configuration • Random Address Selection Address Assignment

  7. Dynamic Host Configuration Protocol (DHCP) Address Assignment

  8. DHCP in Multi-Hop Wireless Networks • DHCP may be used so long as each host is reachable from a DHCP server Address Assignment

  9. DHCP in Multi-Hop Wireless Networks • If a host cannot reach a DHCP server, it cannot get an IP address Address Assignment

  10. Auto-Configuration in Ad Hoc Networks • How to assign unique addresses ? • DHCP server may not be available, or may become partitioned from other hosts • If loss of connectivity to DHCP server acceptable, DHCP can be extended for use in ad hoc networks • Turn each host that has an IP address into a DHCP relay Address Assignment

  11. Auto-Configuration in Ad Hoc Networks • Can we assign unique addresses when no DHCP server present ? • Random address selection • Potential for duplication Address Assignment

  12. Duplicate Address Detection (DAD) in Ad Hoc Networks DAD in conjunction with reactive routing: • Host picks an address randomly • Host performs route discovery for the chosen address • If a route reply is received, address duplication is detected • If no route reply received within a timeout interval, assign the address Address Assignment

  13. Duplicate Address Detection (DAD) in Ad Hoc Networks How to pick the timeout interval ? Address Assignment

  14. DAD in Ad Hoc Networks • When upper bound on message delays not known, difficult to pick a timeout interval • Too small • Address duplication may occur • Too large • Time wasted • If partitions can occur for unbounded intervals of time, timeout mechanism ineffective Address Assignment

  15. Example: Initially Partitioned Network Address Assignment

  16. Merged Network • Duplicate address detection (DAD) important To avoid misrouting Address Assignment

  17. Potential Solution: Detect Merger of Partitions • Assign largest key in a partition as partition identifies Address Assignment

  18. Potential Solution: Detect Merger of Partitions • Different keys for two end of a new link detects a merge Address Assignment

  19. Potential Solution: Detect Merger of Partitions • Search for duplicate addresses in the newly merged partition • Overhead Address Assignment

  20. Potential Solution: Detect Merger of Partitions • Need to manage partition identifiers • Detection when a partition divides into two partitions • Need to update partition identifiers • Involves delays • Window of vulnerability to address duplication Address Assignment

  21. Alternative Approach • If you cannot solve a problem Change the problem ! • Weak duplicate address detection Address Assignment

  22. Weak DAD Requirement Packets from a given host to a given address should be routed to the same destination, despite duplication of the address Address Assignment

  23. Example: Initially Partitioned Network Address Assignment

  24. Merged Network: Acceptable Behavior with Weak DAD Address Assignment

  25. Merged Network: Unacceptable Behavior Address Assignment

  26. Weak DAD: Implementation Integrate duplicate address detection with route maintenance Address Assignment

  27. Weak DAD with Link State Routing • Each host has a unique key • In all routing-related packets (link state updates) IP addresses tagged by keys • (IP, key) pair Address Assignment

  28. Weak DAD with Link State Routing Address Assignment

  29. A potential Problem Problem caused by duplicate MAC and duplicate IP addresses Address Assignment

  30. A potential Problem • Nodes P and Q both have MAC address m. • Nodes M and R both have IP address a. • Now, two partitions merge … Address Assignment

  31. A potential Problem Address Assignment

  32. A potential Problem • Now, node A wants to send a packet to M. • Nex-hop is b • Send the frame to Mac address of b (which is m) • Node P and Q (in vicinity of A) both accept the frame and forward to their corresponding network layer • The packet will be, then, forwarded towards M and R. • Unacceptable in Weak DAD. Address Assignment

  33. Weak DAD with Dynamic Source Routing • Address duplication not always detected • Duplication detected before misrouting can occur • Weak • Reliable, but potentially delayed, DAD Address Assignment

  34. Weak DAD with Dynamic Source Routing Address Assignment

  35. Adverse Higher Layer Interaction • Higher layers interaction may result in undesirable behavior with weak DAD • IP addresses, which are network layer addresses, are often also used at higher layers Address Assignment

  36. Higher Layer Interaction Address Assignment

  37. Example: Networks merge Address Assignment

  38. Example: Networks merge Address Assignment

  39. Reading Asignment • Read the following paper: N. H. Vaidya, Weak Duplicate Address Detection in Mobile Ad Hoc Networks, In Proc. Of ACM MOBIHOC, Lausanne, Switzerland, 2002. Address Assignment

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