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

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

http://www.unik.no/~paalee/research.htm

CNDS 2004 (WMC 2004)

San Diego, 22.01.2004







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

Internet

External Host

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

GatewayGateway

4

Background (2): MIP-FA

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

Home AgentExternal Host

Foreign AgentGateway

MANETSource Node

5

Background (3): NAT

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

External Host

Network Address Translator

Gateway

MANETSource Node

1

2 3

4

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Route Discovery with Proxy RREP

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 RREP on 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

External Host

Gateway (NAT)Gateway

MANETSource Node

RREQ: Route RequestRREP: Route ReplyXH: External HostNAT: Network Address Translation


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Proxy RREPs and Multi Homing

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

External Host

NAT

MANETSource Node



NAT

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Race Conditions – a route needs to be re-discovered 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

External Host

GW2(NAT)

MANETSource Node

RREQ: Route RequestRREP: Route ReplyXH: External HostGW: Gateway

RREQ: Route RequestRREP: Route ReplyXH: External HostGW: Gateway

GW1(NAT)

?

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Test bed experiment (1)

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

External Host

GW2(NAT)

MANET

Source Node

GW1(NAT)

Intermediate Node

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Test bed experiment (2)

0 %

50 %

100 %

0 1 2 3 4 5

Tmax (ms)

From GW1

From GW2

Sha

re o

f RR

EP

s re

ceiv

ed

14

Tmax [ms]

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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

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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.).

Variable Packet Transmission Interval (with fixed route timeout, fixed terrain size and no mobility)

0 %

25 %

50 %

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Packet Transmission Interval (ms)

Ses

sio

n b

reak

ages

/Dat

a P

acke

t

Range 10

Range 50

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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 configurations (with fixed terrain size and no mobility)

0 %

5 %

10 %

15 %

20 %

25 %

30 %

35 %

40 %

45 %

50 %

0 % 20 % 40 % 60 % 80 %

Session Breaks/Packet for different Network Configurations

Sh

are

of

Ne

two

rk C

on

fig

ura

tio

ns

Range 10m

Range 50m

Distribution of different network with bad performance

Pe

rce

nta

ge

of

ne

two

rks

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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.

Variable Terrain Size(with fixed route timeout, 2Kbps CBR and no mobility)

0 %

10 %

20 %

30 %

40 %

50 %

60 %

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Size of Sides of Terrain Square (m)

Se

ss

ion

bre

ak

ag

es

/Da

ta P

ac

ke

t

Range 10

Range 50

(50) (400)(100) (350)(150) (200) (250) (300)

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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

Variable Mobility(with fixed route timeout, CBR 8 Kbps - i.e.1pkt/sec - and fixed terrain size)

0 %

5 %

10 %

15 %

20 %

25 %

30 %

35 %

40 %

45 %

50 %

0 1 2 3 4 5 6 7 8

Max Random Speed (m/sec)

Ses

sio

n b

reak

ages

/Pac

ket

Range 10

Range 50

(5) (40)(35)(30)(10)(0) (20)(15) (25)

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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.

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Proposed working solution

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

External Host

GW2(NAT)

MANET

Source Node

GW1(NAT)

Intermediate Nodesrc=SNdst=XH

Inner IP-header

Outer IP-header

IP-payloadsrc=SNdst=GW1

src=SNdst=XH

Inner IP-header

IP-payload

RREQ: Route RequestRREP: Route ReplyXH: External HostSN: Source Node

RREQ: Route RequestRREP: Route ReplyXH: External HostSN: Source Node

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Route discovery in AODV

A

B

H

S

C

EF

I

G

K

ML

N

J

D

Represents a node that has received RREQ for D from S

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A

B

H

S

C

EF

I

G

K

ML

N

J

D

Represents transmission of RREQ

Broadcast transmission

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A

B

H

S

C

EF

I

G

K

ML

N

J

D

Represents links on Reverse Path

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A

B

H

S

C

EF

I

G

K

ML

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

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A

B

H

S

C

EF

I

G

K

ML

N

J

D

24


A

B

H

S

C

EF

I

G

K

ML

N

J

D

25


A

B

H

S

C

EF

I

G

K

ML

N

J

D

Routing table entries used to forward data packetRoute is not included in packet

Documents

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