Transcript Analysis of NAT-Based Internet Connectivity for Multi

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, Norway
Presented by: Geir Egeland
http://www.unik.no/~paalee/research.htm
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 Adhoc 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
2
Background (1):
Ad-hoc on demand Distance Vector (AODV)
External Host

Reactive ad-hoc routing
protocol
Internet
– Generates routes only when
needed
Gateway

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

Gateway
MANET
A node in a MANET may want
to connect to a host on the
Internet
3
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

Gateway
Drawbacks
– High complexity
– MIP and AODV makes unsynchronized
modifications to routing table
– MIP requires global IPv4 addresses

Internet
Foreign Agent
Source Node
MANET
Advantages
– MANET nodes can use its Home Address and
be globally routable
4
Background (3): NAT
External Host

Overview
– A gateway uses NAT to hide non-routable
addresses in MANET

3
2
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)

Internet
Advantages
Gateway
1
Network
Address Translator
4
Source Node
– Less complex, easy to implement and
deploy
– Does not rely on MIPv4 deployment and
fixed IPv4 address
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MANET
Route Discovery with Proxy RREP
External Host

How gateways discover that the XH is
present on the Internet
Internet
– MIP-FA Gateway (Belding-Royer et.al.): Source
Node sets F-bit in RREQ
– AODV-UU NAT-solution: Require different IP
address spaces
F

Source Node (SN) broadcasts a RREQ to
establish route to External Host (XH)
F

Gateway impersonates XH, by sending a
RREP on behalf of XH. This is a “Proxy
RREP”
F
F


SN forwards packets to XH using the
route established by the Proxy RREP.
The gateway forwards the packet to XH
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Gateway
Gateway (NAT)
Source Node
MANET
RREQ: Route Request
RREP: Route Reply
XH: External Host
NAT: Network Address Translation
Proxy RREPs and Multi Homing
F
External Host

F

F

F

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
7
Internet
NAT
NAT
Source Node
MANET
RREQ: Route Request
RREP: Route Reply
XH: External Host
NAT: Network Address Translation
Race Conditions – a route needs to
be re-discovered
?
F
F
F
F
F
F
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
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Internet
GW1
(NAT)
GW2
(NAT)
Source Node
MANET
RREQ: Route Request
RREP: Route Reply
XH: External Host
GW: Gateway
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
Internet
GW1
(NAT)

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%
9
GW2
(NAT)
Intermediate
Node
MANET
Source Node
Share of RREPs received
Test bed experiment (2)
14
Tmax [ms]
10
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
11
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)
50 %
Session breakages/Data Packet

Range 10
25 %
0%
500
Range 50
1000
1500
2000
2500
3000
3500
4000
Packet Transmission Interval (ms)
12
4500
5000
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
Distribution
of different
network
configurations
(with fixed terrain size and no mobility)
50 %
45 %
Share of Network Configurations

40 %
35 %
30 %
Range 10m
25 %
Range 50m
20 %
15 %
10 %
5%
0%
0%
20 %
40 %
60 %
80 %
Session Breaks/Packet for different Network Configurations
13
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)
60 %
Session breakages/Data Packet

50 %
40 %
Range 10
30 %
Range 50
20 %
10 %
0%
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
(50)
(100)
(150)
(200)
(250)
(300)
(350)
(400)
Size of Sides of Terrain Square (m)
14
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)
50 %
45 %
Session breakages/Packet

40 %
35 %
30 %
25 %
Range 10
20 %
Range 50
15 %
10 %
5%
0%
0
(0)
1
(5)
2
(10)
3
(15)
4
(20)
5
(25)
Max Random Speed (m/sec)
15
6
(30)
7
(35)
8
(40)
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
External Host
F
F
F
F
F
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)

src=SN IP-payload
dst=XH
Inner IPheader
GW1
(NAT)
src=SN
src=SN IP-payload
dst=GW1 dst=XH
Outer IP- Inner IPheader
header
Intermediate Node
MANET
SN tunnels traffic to selected GW
– GW decapsulates and forwards to XH

GW2
(NAT)
RREP contains extensions with
– XH’s destination IP-address
– The functionality/capabilities of the gateway

Internet
Source Node
GW tunnels return traffic from XH to
SN
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RREQ: Route Request
RREP: Route Reply
XH: External Host
SN: Source Node
Route discovery in AODV
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
Represents a node that has received RREQ for D from S
19
Route discovery in AODV
Broadcast transmission
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
Represents transmission of RREQ
20
Route discovery in AODV
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
Represents links on Reverse Path
21
Route discovery in AODV
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
Node C receives RREQ from G and H, but does not
forward it again, because node C has already forwarded
RREQ once
22
Route discovery in AODV
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
23
Route discovery in AODV
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
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Route discovery in AODV
S
F
C
B
A
E
H
J
G
K
M
L
D
I
N
Routing table entries used to forward data packet
Route is not included in packet
25