Analysis of NAT-Based Internet Connectivity for Multi-Homed On-Demand Ad Hoc Networks

1. CNDS 2004 (WMC 2004) San Diego, 22.01.2004 Analysis of NAT-Based Internet Connectivity for Multi-Homed On-Demand Ad Hoc Networks Engelstad, P.E. and Egeland, G.University of Oslo (UniK) / Telenor R&D, 1331 Fornebu, NorwayPresented by: Geir Egeland http://www.unik.no/~paalee/research.htm

2. Motivation • Already seeing users communicating with mobile terminals in an ad hoc manner using Bluetooth (Bluejacking) • Mobile ad-hoc networks (MANET) may need to connect to nodes in the fixed Internet • Some nodes connected to external IP-networks may operate as gateways for other MANET nodes • Previously proposed solutions (proxy RREP): • MIP-FA based gateways making modifications to Mobile IPv4 and using Ad-hoc On demand Distance Vector (AODV) • Internet draft by Belding-Royer et al. • MSc. Thesis on ”MIPMANET” by Alriksson F. And Jönsson U., August 1999 • NAT based gateways implementing an Network Address Translator at the gateway • Uppsala University’s implementaton of AODV

3. External Host Internet Gateway Gateway Background (1): Ad-hoc on demand Distance Vector (AODV) • Reactive ad-hoc routing protocol • Generates routes only when needed • Uses Route Request (RREQ) and Route Reply (RREP) to form forward and return route • Maintains routing tables at the nodes, so that data packets not have to contain routes • A node in a MANET may want to connect to a host on the Internet MANET

4. Background (2): MIP-FA Home Agent External Host • Overview • A gateway with FA-support (MIP-FA) which understands AODV • A MANET node with MIPv4 support • The MANET registers the MIP-FA Gateway with its Home Agent • Drawbacks • High complexity • MIP and AODV makes unsynchronized modifications to routing table • MIP requires global IPv4 addresses • Advantages • MANET nodes can use its Home Address and be globally routable Internet Gateway Foreign Agent Source Node MANET

5. 1 2 3 4 Background (3): NAT External Host • Overview • A gateway uses NAT to hide non-routable addresses in MANET • Drawbacks • The well-known drawbacks with the use of NATs • Mobility (i.e. Sessions through the gateway break when the node moves to a new MANET) • Advantages • Less complex, easy to implement and deploy • Does not rely on MIPv4 deployment and fixed IPv4 address Internet Gateway Network Address Translator Source Node MANET

6. F F F F Route Discovery with Proxy RREP External Host • How gateways discover that the XH is present on the Internet • MIP-FA Gateway (Belding-Royer et.al.): Source Node sets F-bit in RREQ • AODV-UU NAT-solution: Require different IP address spaces • Source Node (SN) broadcasts a RREQ to establish route to External Host (XH) • Gateway impersonates XH, by sending a RREPon behalf of XH. This is a “Proxy RREP” • SN forwards packets to XH using the route established by the Proxy RREP. • The gateway forwards the packet to XH Internet Gateway Gateway (NAT) Source Node MANET RREQ: Route RequestRREP: Route ReplyXH: External HostNAT: Network Address Translation

7. F F F F Proxy RREPs and Multi Homing External Host • The Source Node (SN) broadcasts a RREQ to establish route to the external Host (XH) • Both gateways send a Proxy RREP on behalf of the XH • The Source Node forwards packets to XH using the route established by one of the Proxy RREPs. • The “winning” gateway forwards the packet to the XH Internet NAT NAT Source Node MANET RREQ: Route RequestRREP: Route ReplyXH: External HostNAT: Network Address Translation

8. ? F F F F F F Race Conditions – a route needs to be re-discovered External Host • The Source Node (SN) broadcasts a RREQ to establish route to the external Host (XH) • Both gateways send a Proxy RREP on behalf of the XH, GW1 wins • SN sends packets for XH via GW1. • After link break or route timeout, SN broadcasts a new RREQ to re-establish the route to XH • Both gateways send a Proxy RREP on behalf of XH, but this time GW2 “wins” • SN sends subsequent packets for XH via GW2, connection fails Internet GW1(NAT) GW2(NAT) Source Node MANET RREQ: Route RequestRREP: Route ReplyXH: External HostGW: Gateway

9. Test bed experiment (1) External Host • AODV-implementation by Uppsala University • IEEE 802.11b • Linux (2.2.20 kernel) • MAC-layer filtering • Gateways with equal configuration • Best performance: 14% of sessions break due to race condition • Introduced a random delay from a uniform distribution [0,Tmax] ms in the GWs • Share of sessions that breaks approx. 50% Internet GW1(NAT) GW2(NAT) Intermediate Node MANET Source Node

10. Test bed experiment (2) Share of RREPs received 14 Tmax [ms]

11. Simulation setup • Glomosim, with AODV module • IEEE 802.11, Two-Ray channel model • Traffic pattern: Constant Bit Rate (CBR), 1024 byte packets • 50 nodes • Radio Range 50m, 200mx200m square • Radio Range 10m, 40mx40m square

12. Simulation #1 • Testing Race Conditions due to Route Timeout: • Static scenario, and varying Packet Transmission Interval (PTI): • Race Conditons have a dramatic impact on performance when PTI exceeds Active Route Timeout of AODV (of 3 sec.).

13. Simulation #2 • Network configurations/ topologies that leads to bad performance? • When gateways are an equal number of hops away from SN • (i.e. on right hand side of figure...) Distribution of different network with bad performance Percentage of networks

14. Simulation #3 • Testing effects of terrain size (i.e. of node density or of ”strength” of connectivity): • Fully connected network: Probability that session breaks = 0.5 • Problem decreases as terrain size increases, because probability that gateways are an equal number of hops away, decreases.

15. Simulation #4 • Testing Race Conditions due to link breaks, by adding mobility: • Random Way Point (with zero rest-time and variable max velocity) • PTI = 1 sec, i.e. safely below the Active Route Timeout of AODV

16. Summary of results • Test bed experiment showed that race conditions occurs due to Proxy RREPs • Simulations showed that race conditions reduce performance in small on-demand ad hoc networks. • Race Conditions due to route timeout represents a non-negligible problem, especially for interactive applications where the packet transmission interval easily exceeds the Active Route Timeout of AODV • Race Conditions due to link breaks (e.g. caused by mobility, radio fading, etc.) is a serious problem for all sessions, independent of packet transmission intervals.

17. Proposed working solution External Host F • SN discovers that XH is not present locally after unsuccessful route establishment on MANET • SN sets a “Gateway bit” in RREQ for XH • Gateways responds with a RREP establishing route to the GW (i.e. no race conditions will occur) • RREP contains extensions with • XH’s destination IP-address • The functionality/capabilities of the gateway • SN tunnels traffic to selected GW • GW decapsulates and forwards to XH • GW tunnels return traffic from XH to SN Internet src=SNdst=XH IP-payload F Inner IP-header F GW2(NAT) GW1(NAT) F src=SNdst=GW1 src=SNdst=XH IP-payload Intermediate Node Outer IP-header Inner IP-header MANET F Source Node F RREQ: Route RequestRREP: Route ReplyXH: External HostSN: Source Node

19. E Route discovery in AODV S F C J M G B L K A D H I N Represents a node that has received RREQ for D from S

20. Route discovery in AODV Broadcast transmission S E F C J M G B L K A D H I N Represents transmission of RREQ

21. Route discovery in AODV S E F C J M G B L K A D H I N Represents links on Reverse Path

22. Route discovery in AODV S E F C J M G B L K A D H I N Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

23. Route discovery in AODV S E F C J M G B L K A D H I N

24. Route discovery in AODV S E F C J M G B L K A D H I N

25. Route discovery in AODV S E F C J M G B L K A D H I N Routing table entries used to forward data packetRoute is not included in packet