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, Norway Presented by: Geir Egeland CNDS 2004 (WMC 2004) San Diego,

2 Motivation l Already seeing users communicating with mobile terminals in an ad hoc manner using Bluetooth (Bluejacking) l 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 l 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 Internet External Host Background (1): Ad-hoc on demand Distance Vector (AODV) l Reactive ad-hoc routing protocol –Generates routes only when needed l Uses Route Request (RREQ) and Route Reply (RREP) to form forward and return route l Maintains routing tables at the nodes, so that data packets not have to contain routes l A node in a MANET may want to connect to a host on the Internet MANET Gateway

4 Background (2): MIP-FA l 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 l Drawbacks –High complexity –MIP and AODV makes unsynchronized modifications to routing table –MIP requires global IPv4 addresses l Advantages –MANET nodes can use its Home Address and be globally routable Internet Home Agent External Host Foreign AgentGateway MANET Source Node

5 Background (3): NAT l Overview –A gateway uses NAT to hide non-routable addresses in MANET l 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) l Advantages –Less complex, easy to implement and deploy –Does not rely on MIPv4 deployment and fixed IPv4 address Internet External Host Network Address Translator Gateway MANET Source Node

6 Route Discovery with Proxy RREP l 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 l Source Node (SN) broadcasts a RREQ to establish route to External Host (XH) l Gateway impersonates XH, by sending a RREP on behalf of XH. This is a “Proxy RREP” l SN forwards packets to XH using the route established by the Proxy RREP. l The gateway forwards the packet to XH Internet External Host Gateway (NAT) Gateway MANET Source Node F F F F RREQ: Route Request RREP: Route Reply XH: External Host NAT: Network Address Translation

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

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

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

10 Test bed experiment (2) Share of RREPs received 14 T max [ms]

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

12 Simulation #1 l 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 l 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 l 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 l 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 l Test bed experiment showed that race conditions occurs due to Proxy RREPs l Simulations showed that race conditions reduce performance in small on-demand ad hoc networks. l 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 l 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 l SN discovers that XH is not present locally after unsuccessful route establishment on MANET l SN sets a “Gateway bit” in RREQ for XH l Gateways responds with a RREP establishing route to the GW (i.e. no race conditions will occur) l RREP contains extensions with –XH’s destination IP-address –The functionality/capabilities of the gateway l SN tunnels traffic to selected GW –GW decapsulates and forwards to XH l GW tunnels return traffic from XH to SN Internet External Host GW2 (NAT) MANET Source Node GW1 (NAT) Intermediate Node src=SN dst=XH Inner IP- header Outer IP- header IP-payloadsrc=SN dst=GW1 src=SN dst=XH Inner IP- header IP-payload RREQ: Route Request RREP: Route Reply XH: External Host SN: Source Node F F F F F F

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

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

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

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

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

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