Mobile IP
3/20/2006
Modified based on
http://zoo.cs.yale.edu/classes/cs434/lectures/MobileIP.ppt
1
Mobile IP
Incorporation of mobile users in the network.
Cellular system (e.g., GSM) started with
mobility in mind.
The internet started with no thought of
mobile computers.
IP: a unified networking layer supporting
heterogeneous networks.
2
Outline
Network layer service
Mobile IP
Network Layer Service
Transport packet from
source to dest.
Network layer protocol in
every host, router
application
transport
network
data link
physical
network
data link
physical
network
data link
physical
Basic functions:
Control path: route
determination
route taken by packets from
source to destination
Data path: forwarding
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
application
transport
network
data link
physical
move packets from routers
input to appropriate router
output
Question: what are the crucial components to
implement the above services?
IP Datagram Format
IP protocol version
number
header length
(bytes)
type of data
max number
remaining hops
(decremented at
each router)
upper layer protocol
to deliver payload to
32 bits
type of
ver head.
len service
length
fragment
16-bit identifier flgs
offset
time to upper
Internet
layer
live
checksum
total datagram
length (bytes)
for
fragmentation/
reassembly
32 bit source IP address
32 bit destination IP address
Options (if any)
data
(variable length,
typically a TCP
or UDP segment)
E.g. timestamp,
record route
taken, specify
list of routers
to visit.
IP Addresses
The way we assign IP address will affect the
efficiency of the routing protocols
Addressing from daily life:
Postal address, e.g.,
150 Main Street
Stony brook, NY 11790
Telephone address, e.g.,
631-751-0555
6
IP Address: An IP Address Identifies an Interface
IP address: 32-bit
identifier for host,
router interface
interface: connection
between host, router
and physical link
routers typically have
multiple interfaces
host may have multiple
interfaces
IP addresses
associated with
interface
%/sbin/ifconfig -a
223.1.1.1
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
223.1.3.1
223.1.3.2 = 11011111 00000001 00000011 00000010
223
2
7
IP Addressing
IP address:
network part (high
order bits)
host part (low order
bits)
223.1.1.2
223.1.1.1
223.1.1.4
223.1.1.3
223.1.9.2
223.1.7.0
Whats a network?
(from IP address
perspective)
223.1.9.1
223.1.8.1
device interfaces with
same network part of
223.1.2.6
IP address
can physically 223.1.2.1
223.1.2.2
reach each other
without intervening
router
223.1.7.1
223.1.8.0
223.1.3.27
223.1.3.1
223.1.3.2
IP hierarchy
The hierarchical nature of IP addresses
enables compression at routers.
In routing tables, only prefixes are stored.
This also allows the smooth integration of
heterogeneous networks into the Internet.
Inside each network different architectures can
be adopted.
In-between networks a unifying networking layer
allow their cooperation.
Network Layer in Internet:
Big Picture
Host, router network layer functions:
Transport layer: TCP, UDP
Network layer protocol (e.g., IP)
routing protocols
path selection
Network
layer
addressing conventions
packet format
packet handling conventions
forwarding
Control protocols (e.g. ICMP)
error reporting
router signaling
Link layer
physical layer
10
Outline
Network layer services
Mobile IP
11
Discussion
IP works fine for the Internet
it has problems; but during vast majority of the
time it gets its job done efficientlymoving a
packet from a src. to a dest.
What problem can mobility cause?
How do you solve the problem?
12
Mobile IP
Routing
based on IP destination address, network prefix
(e.g. 129.13.42) determines physical subnet
change of physical subnet implies change of IP
address to have a topological correct address
(standard IP) or needs special entries in the
routing tables
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Mobile IP
Specific routes to end-systems?
change of all routing table entries to forward
packets to the right destination
does not scale with the number of mobile hosts
and frequent changes in the location
IP hierarchies can not be used.
14
Mobile IP
Changing the IP-address?
adjust the host IP address depending on the
current location
DHCP (dynamic host configuration protocol): reassign a new IP address.
almost impossible to find a mobile system, DNS
updates take to long time
Limited in local use.
TCP connections break, security problems
15
Mobile IP
Transparency
mobile end-systems keep their IP address
continuation of communication after interruption
of link possible
point of connection to the fixed network can be
changed
Compatibility
support of the same layer 2 protocols as IP
no changes to current end-systems and routers
required
mobile end-systems can communicate with fixed
systems
16
Mobile IP
Security
authentication of all registration messages
Efficiency and scalability
only little additional messages to the mobile
system required (connection typically via a low
bandwidth radio link)
world-wide support of a large number of mobile
systems in the whole Internet
17
Mobile IP: Terminology
Mobile Node (MN)
the node under consideration
Home Agent (HA)
a stationary network node (e.g., a router) at the home network
Foreign Agent (FA)
A network node (e.g. a router) in the foreign network
Care-of Address (COA)
The address in the foreign network
Correspondent Node (CN)
communication partner
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Illustration
HA
MN
router
home network
mobile node
Internet
(physical home network
for the MN)
FA
foreign
network
router
(current physical network
for the MN)
CN
end-system
router
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Data transfer
HA
MN
home network
Internet
receiver
3
FA
CN
sender
foreign
network
1. Sender sends to the IP address of MN,
HA intercepts packet (proxy ARP)
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet
to the MN
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Data transfer
HA
home network
MN
sender
Internet
FA
foreign
network
1. Sender sends to the IP address
of the receiver as usual,
FA works as default router
CN
receiver
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Overview
COA
home
network
router
FA
router
HA
MN
foreign
network
Internet
CN
router
home
network
router
HA
router
FA
2.
3.
MN
4.
Internet
foreign
network
1.
CN
router
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Mobile IP Operations
Basic idea of Mobile IP: a MN acquires a COA in a
foreign network from a foreign agent and
registers to the home agent; all messages sent to
its home address is forwarded by its home agent
to its COA
Three steps
discovering home/foreign agents and the careof address (COA)
registering the care-of address
data transfer using the care-of address
23
Discovering the Agents and Careof Address
Mobile IP discovery process
(home or foreign) agent broadcasts
advertisements at regular intervals
announce the network
list one or more available care-of addresses
mobile node takes a care-of address
mobile node can also send solicitation to start
the process
24
Registering the Care-of Address
Once a mobile node has a care-of address,
its home agent must find out about it
Registration process
mobile node sends a registration request to its
home agent with the care-of address
information
home agent approves/disapproves the request
home agent adds the necessary information to
its routing table
home agent sends a registration reply back to
the mobile node
25
Registration Operations in Mobile IP
MH = Mobile Host
HA = Home Agent
FA = Foreign Agent
Discussion: what is the major challenge of the registration process? 26
Encapsulation
Tunneling
Encapsulation of one packet into another as
payload
e.g. IPv6 in IPv4 (6Bone), Multicast in Unicast
(Mbone)
here: e.g. IP-in-IP-encapsulation, minimal
encapsulation or GRE (Generic Record
Encapsulation)
original IP header
original data
new IP header
outer header
new data
inner header
original data
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Encapsulation I
IP-in-IP-encapsulation (mandatory, RFC
2003)
tunnel between HA and COA
ver.
IHL
DS (TOS)
length
IP identification
flags
fragment offset
TTL
IP-in-IP
IP checksum
IP address of HA
Care-of address COA
ver. IHL
DS (TOS)
length
IP identification
flags
fragment offset
TTL
lay. 4 prot.
IP checksum
IP address of CN
IP address of MN
TCP/UDP/ ... payload
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Encapsulation I
Minimal encapsulation (optional)
avoids repetition of identical fields
e.g. TTL, IHL, version, DS (RFC 2474, old: TOS)
only applicable for unfragmented packets, no
space left for fragment identification
ver.
IHL
DS (TOS)
length
IP identification
flags
fragment offset
TTL
min. encap.
IP checksum
IP address of HA
care-of address COA
lay. 4 protoc. S reserved
IP checksum
IP address of MN
original sender IP address (if S=1)
TCP/UDP/ ... payload
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Discussion
Any problems of the Mobile IP approach?
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Triangular Routing
Triangular Routing
CN sends all packets via HA to MN
higher latency and network load
Solution
CN learns the current location of MN
direct tunneling to this location
HA or MN informs a CN about the location of
MN
Problem of the solution
big security problems!
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Handoff
Change of FA (COA)
packets on-the-fly during the change can be lost
Solution
new FA informs old FA to avoid packet loss, old FA buffers and
then forwards remaining packets to new FA
this information also enables the old FA to release resources for
the MN
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Change of Foreign Agent
CN
HA
Data
Update
FAold
FAnew
Data
MN
Data
ACK
Data
Data
Update
ACK
Data
Data
Warning
MN changes
location
Registration
Data
Request
Update
ACK
Data
Data
t
33
Reverse tunneling
HA
MN
home network
Internet
sender
1
FA
CN
receiver
foreign
network
1. MN sends to FA
2. FA tunnels packets to HA
by encapsulation
3. HA forwards the packet to the
receiver (standard case)
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Reverse tunneling
Router accept often only topological correct
addresses (firewall!)
a packet from the MN encapsulated by the FA is now
topological correct
furthermore multicast and TTL problems solved (TTL in the
home network correct, but MN is to far away from the
receiver)
Reverse tunneling does not solve
problems with firewalls, the reverse tunnel can be abused
to circumvent security mechanisms (tunnel hijacking)
optimization of data paths, i.e. packets will be forwarded
through the tunnel via the HA to a sender (double
triangular routing)
35
Micro Mobility
A very typical scenario of Mobile IP is that a
MN visits a company or university
the MN may change foreign networks multiple
times in the foreign network, generating much
control traffic
Efficient local handover inside a foreign domain
without involving a home agent
Reduces control traffic on backbone
Especially needed in case of route optimization
36
Handoff Aware Wireless Access
Internet Infrastructure (HAWAII)
Operation:
MN obtains co-located
COA 1
and registers with HA 2
Handover: MN keeps
COA, 3
new BS answers Reg.
Request
and updates routers 4
MN views BS as foreign
agent
Internet
HA
Backbone
Router
Crossover
Router
4
BS
BS
Mobile IP
3
MN
2
Mobile IP
BS
MN
DHCP
Server
1
DHCP
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Summary
Mobile IP
Design focus: compatibility, transparency.
Big problem: security.
Next class: what problems will mobility
create in transport layer (TCP)?
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