mobile ip, Mobile COmmunication Internet Protocol

EPL476 Mobile Networks
Mobile Network Protocols
Instructor: Dr. Vasos Vassiliou
Slides adapted from Prof. Dr.-Ing. Jochen H. Schiller and W. Stallings

2
MOBILE NETWORK LAYER
Mobile IP

3
Mobile IP (I)
Mobile IP adds mobility support to the Internet network
layer protocol IP.
 The Internet started at a time when no-one had a concept of
mobile computers.
• The Internet of today lacks mechanisms for the support of users
traveling through the world.
– IP is the common base for thousands of applications and runs over dozens of
different networks; this is the reason for supporting mobility at the IP layer.
Motivation for Mobile IP:
 Routing
• based on IP destination address, network prefix 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

4
Mobile IP (II)
 Create specific routes to end-systems – mobile nodes?
• 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
 Changing the IP address?
• adjust the host IP address depending on the current location
• almost impossible to find a mobile host, DNS has not been built
for frequent updates
• TCP connection break

5
Mobile IP (III)
Requirements to 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 does
• no changes to current end-systems and routers required
• Mobile end-systems can communicate with fixed systems

6
Mobile IP (IV)
 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

7
Real-life Solution
Take up the analogy of you moving from one
apartment to another. What do you do?
 Leave a forwarding address with your old post-
office
 The old post-office forwards mail to your new
post-office, which then delivers it to you

8
Mobile IP - Definition
“Mobile IP (MIP) is a modification to IP
that allows nodes to continue to receive
datagrams no matter where they happen to
be attached to the Internet”

9
Mobile IP (V)
Terminology:
 Mobile Node (MN)
• system (node) that can change the point of connection to the network
without changing its IP address
 Home Agent (HA)
• system in the home network of the MN, typically a router
• registers the location of the MN, tunnels IP datagrams to the COA
 Foreign Agent (FA)
• system in the current foreign network of the MN, typically a router
• forwards the tunneled datagrams to the MN, typically also the default
router of the MN

10
Mobile IP (VI)
 Care-of Address (COA)
• address of the current tunnel end-point for the MN (at FA or
MN)
• actual location of the MN from an IP point of view
• can be chosen, e.g., via DHCP
 Correspondent Node (CN)
• communication partner

11
Mobile IP in detail …
Combination of 3 separable mechanisms:
 Discovering the care-of address
 Registering the care-of address
 Tunneling to the care-of address

12
CN
2. HA Discovery Request
3. HA Discovery Reply
4. HA Registration through FA
5. HA Registration Ack.
1. CoA Discovery
MN HA
1
2
3
-- MN is Registered with HA --
4
55
-- CoA and HA Discovery --
-- Registration Procedure --
-- CN starts communication with MN --
6. Data Packet
7. IP-in-IP Encapsulation
8. Tunneled Data
-- Signals 6-10a as above --
8 77
6a. Data Packet
-- MN starts communication with CN --
8a Detunnelled Data
9. Binding Update
6a6a
-- Discovery and Registration as above --
FA
8a
66
10
10. IP-in-IP tunneling
99
10a 10a. Detunnelled Data
CN
2. HA Discovery Request
3. HA Discovery Reply
4. HA Registration BU
5. HA Registration BU Ack.
1. CoA Discovery
MN HA
1
2
3
-- MN is Registered with HA --
4
55
-- CoA and HA Discovery --
-- Registration Procedure --
-- CN starts communication with MN --
6. Data Packet
7. IP-in-IP Encapsulation
8. Tunneled Data
-- Signals 6-10 as above --
8
77
6a. Data Packet
-- MN starts communication with CN --
9. Binding Update
6a6a
-- Discovery and Registration as above --
FA
66
10
10. Binding Ack
99
MIPv4 MIPv6
Mobile IP in detail

13
Discovering the care-of address
Discovery process built on top of an existing
standard protocol: router advertisements
Router advertisements extended to carry available
care-of addresses called: agent advertisements
Foreign agents (and home agents) send agent
advertisements periodically
A mobile host can choose not to wait for an
advertisement, and issue a solicitation message

14
Agent advertisements
Foreign agents send advertisements to advertise
available care-of addresses
Home agents send advertisements to make
themselves known
Mobile hosts can issue agent solicitations to
actively seek information
If mobile host has not heard from a foreign agent
its current care-of address belongs to, it seeks
for another care-of address

15
Registering the Care-of
Address
Once mobile host receives care-of address, it
registers it with the home agent
A registration request is first sent to the home
agent (through the foreign agent)
Home agent then approves the request and sends a
registration reply back to the mobile host
Security?

17
Home agent discovery
If the mobile host is unable to
communicate with the home agent, a home
agent discovery message is used
The message is sent as a broadcast to the
home agents in the home network

18
Tunneling to the Care-of address
When home agent receives packets addressed to
mobile host, it forwards packets to the care-of
address
How does it forward it? - encapsulation
The default encapsulation mechanism that must
be supported by all mobility agents using mobile IP
is IP-within-IP
Using IP-within-IP, home agent inserts a new IP
header in front of the IP header of any datagram

19
Tunneling (contd.)
Destination address set to the care-of
address
Source address set to the home agent’s
address
After stripping out the first header, IP
processes the packet again

21
(current physical network
for the MN)
home network
(physical home network
for the MN)
Mobile IP (VII)
Example network
Internet
router
HA
MN
router
FA foreign
network
routerend-system
CN

22
Mobile IP (VIII)
Data transfer to the mobile system
Internet
home network
foreign
network
FA
HA
MN
receiver
1
2
3
sender
CN
1. Sender sends to the IP address of MN,
HA intercepts packet
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet to the MN

23
foreign
network
home network
Mobile IP (IX)
Data transfer from the mobile system
Internet
HA
MN
sender
receiver
CN
1. Sender sends to the IP address
of the receiver as usual,
FA works as default router
FA
1

24
Mobile IP (XIII)
Optimization of packet forwarding:
 Triangular routing
• sender sends all packets via HA to MN
• higher latency and network load
 Solutions – optimization
• HA informs a sender about the location of MN
• sender learns the current location of MN
• direct tunneling to this location
• big security problems!

25
Mobile IP (XIV)
 Change of FA
• Packets on-the-fly during the change can be lost
• new FA informs old FA to avoid packet loss, old FA forwards
remaining packets to new FA
• this information also enables the old FA to release resources
for the MN

26
Mobile IP (XV)
 Change of the foreign agent with the optimized mobile
IP
CN HA FAold FAnew MN
t
request
update
ACK
data data
MN changes
locationregistration
update
ACKdata
data data
warning
update
ACK
data
data
registration

27
Mobile IP (XVI)
Reverse tunneling:
Internet
receiver
FA
HA
MN
home network
foreign
network
sender
3
2
1
1. MN sends to FA
2. FA tunnels packets to HA
by encapsulation
3. HA forwards the packet to the
receiver (standard case)
CN

28
Mobile IP (XVII)
Mobile IP with 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)
 The standard is backwards compatible
• the extensions can be implemented easily and cooperate with
current implementations without these extensions
• Agent Advertisements can carry requests for reverse tunneling

29
[modified from Ericsson Tech. Rep. 11/0362-FCB, Dec
Mobile IP in detail

type = 16
length = 6 + 4 * #COAs
R: registration required
B: busy, no more registrations
H: home agent
F: foreign agent
M: minimal encapsulation
G: GRE encapsulation
r: =0, ignored (former Van Jacobson compression)
T: FA supports reverse tunneling
reserved: =0, ignored
Agent advertisement
preference level 1
router address 1
#addresses
type
addr. size lifetime
checksum
COA 1
COA 2
type = 16 sequence numberlength
0 7 8 15 16 312423
code
preference level 2
router address 2
. . .
registration lifetime
. . .
R B H F M G r reservedT

Registration
t
MN HAregistrationrequest
registration
reply
t
MN FA HAregistrationrequest
registrationrequest
registration
reply
registration
reply

Mobile IP registration request
home agent
home address
type = 1 lifetime
0 7 8 15 16 312423
T x
identification
COA
extensions . . .
S B DMG r
S: simultaneous bindings
B: broadcast datagrams
D: decapsulation by MN
M mininal encapsulation
G: GRE encapsulation
r: =0, ignored
T: reverse tunneling requested
x: =0, ignored

Mobile IP registration reply
home agent
home address
type = 3 lifetime
0 7 8 15 16 31
code
identification
extensions . . .Example codes:
registration successful
0 registration accepted
1 registration accepted, but simultaneous mobility bindings unsupported
registration denied by FA
65 administratively prohibited
66 insufficient resources
67 mobile node failed authentication
68 home agent failed authentication
69 requested Lifetime too long
registration denied by HA
129 administratively prohibited
131 mobile node failed authentication
133 registration Identification mismatch
135 too many simultaneous mobility bindings

Encapsulation
original IP header original data
new datanew IP header
outer header inner header original data

Encapsulation I
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)
IP-in-IP-encapsulation (mandatory, RFC 2003)
 tunnel between HA and COA
Care-of address COA
IP address of HA
TTL
IP identification
IP-in-IP IP checksum
flags fragment offset
lengthDS (TOS)ver. IHL
IP address of MN
IP address of CN
TTL
IP identification
lay. 4 prot. IP checksum
TCP/UDP/ ... payload

Encapsulation II
Minimal encapsulation (optional)
 avoids repetition of identical fields
 e.g. TTL, IHL, version, DS (RFC 2474, old: TOS)
 only applicable for non fragmented packets, no space left for fragment
identification
care-of address COA
IP address of HA
TTL
IP identification
min. encap. IP checksum
IP address of MN
original sender IP address (if S=1)
Slay. 4 protoc. IP checksum
reserved

Generic Routing Encapsulationoriginal
header
original data
new datanew header
outer header
GRE
header
original data
original
header
Care-of address COA
IP address of HA
TTL
IP identification
GRE IP checksum
IP address of MN
IP address of CN
TTL
IP identification
lay. 4 prot. IP checksum
routing (optional)
sequence number (optional)
key (optional)
offset (optional)checksum (optional)
protocolrec. rsv. ver.CRK S s
RFC 1701
RFC 2784 (updated by 2890)
reserved1 (=0)checksum (optional)
protocolreserved0 ver.C

38
Route Optimizations
Enable direct notification of the
corresponding host
Direct tunneling from the corresponding
host to the mobile host
Binding cache maintained at corresponding
host

39
Route optimizations (contd.)
4 types of messages
 Binding update
 Binding request
 Binding warning
 Binding acknowledge

40
Binding Update
When a home agent receives a packet to be
tunneled to a mobile host, it sends a binding
update message to the corresponding host
When a home agent receives a binding request
message, it replies with a binding update message
Also used in the the smooth-handoffs optimization

41
Binding Update (Contd.)
Corresponding host caches binding and uses it for
tunneling subsequent packets
Lifetime of binding?
Corresponding host that perceives a near-expiry
can choose to ask for a binding confirmation using
the binding request message
Home agent can choose to ask for an
acknowledgement to which a corresponding host
has to reply with a binding ack message

42
Binding warning
When a foreign agent receives a tunneled
message, but sees no visitor entry for the mobile
host, it generates a binding warning message to
the appropriate home agent
When a home agent receives a warning, it issues an
update message to the corresponding host
What if the foreign agent does not have the home
agent address (why?) ?

43
Binding Update and Warning
Home Agent
Foreign AgentCorresponding Host
Mobile Host
BU BW
BW
BR
BA

Optimization of packet
forwarding
Problem: Triangular Routing
 sender sends all packets via HA to MN
 higher latency and network load
“Solutions”
 sender learns the current location of MN
 direct tunneling to this location
 HA informs a sender about the location of MN
 big security problems!
Change of FA
 packets on-the-fly during the change can be lost
 new FA informs old FA to avoid packet loss, old FA now
forwards remaining packets to new FA
 this information also enables the old FA to release resources
for the MN

Change of foreign agent
CN HA FAold FAnew MN
MN changes
location
t
Data Data Data
Update
ACK
Data Data
RegistrationUpdate
ACK
Data
Data Data
Warning
Request
Update
ACK
Data
Data

Reverse tunneling (RFC 3024, was: 2344)
Internet
receiver
FA
HA
MN
home network
foreign
network
sender
3
2
1
1. MN sends to FA
2. FA tunnels packets to HA
by encapsulation
3. HA forwards the packet to the
receiver (standard case)
CN

Mobile IP with 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)
The standard is backwards compatible
 the extensions can be implemented easily and cooperate with current
implementations without these extensions
 Agent Advertisements can carry requests for reverse tunneling

48
Mobile IP and IPv6
Mobile IP was developed for IPv4, but IPv6 simplifies the
protocols
 security is integrated and not an add-on, authentication of
registration is included
 COA can be assigned via auto-configuration (DHCPv6 is one
candidate), every node has address autoconfiguration
 no need for a separate FA, all routers perform router
advertisement which can be used instead of the special agent
advertisement; addresses are always co-located
 MN can signal a sender directly the COA, sending via HA not
needed in this case (automatic path optimization)
 „soft“ hand-over, i.e. without packet loss, between two subnets
is supported
• MN sends the new COA to its old router
• the old router encapsulates all incoming packets for the MN and
forwards them to the new COA
• authentication is always granted

49
Problems with mobile IP
Security
 authentication with FA problematic, for the FA typically
belongs to another organization
 no protocol for key management and key distribution has been
standardized in the Internet
 patent and export restrictions
Firewalls
 typically mobile IP cannot be used together with firewalls,
special set-ups are needed (such as reverse tunneling)
QoS
 many new reservations in case of RSVP
 tunneling makes it hard to give a flow of packets a special
treatment needed for the QoS
Security, firewalls, QoS etc. are topics of current research
and discussions!

50
Security in Mobile IP
Security requirements (Security Architecture for the
Internet Protocol, RFC 1825)
 Integrity
any changes to data between sender and receiver can be
detected by the receiver
 Authentication
sender address is really the address of the sender and all data
received is really data sent by this sender
 Confidentiality
only sender and receiver can read the data
 Non-Repudiation
sender cannot deny sending of data
 Traffic Analysis
creation of traffic and user profiles should not be possible
 Replay Protection
receivers can detect replay of messages

not encrypted encrypted
IP security architecture I
Two or more partners have to negotiate security mechanisms
to setup a security association
 typically, all partners choose the same parameters and
mechanisms
Two headers have been defined for securing IP packets:
 Authentication-Header
• guarantees integrity and authenticity of IP packets
• if asymmetric encryption schemes are used, non-repudiation can
also be guaranteed
 Encapsulation Security Payload
• protects confidentiality between communication partners
Authentification-HeaderIP-Header UDP/TCP-Paketauthentication headerIP header UDP/TCP data
ESP headerIP header encrypted data

Mobile Security Association for registrations
 parameters for the mobile host (MH), home agent (HA), and
foreign agent (FA)
Extensions of the IP security architecture
 extended authentication of registration
 prevention of replays of registrations
• time stamps: 32 bit time stamps + 32 bit random number
• nonces: 32 bit random number (MH) + 32 bit random number (HA)
registration reply
registration request
registration request
IP security architecture II
MH FA HA
registration reply
MH-HA authentication
MH-FA authentication FA-HA authentication

Key distribution
Home agent distributes session keys
foreign agent has a security association with the home agent
mobile host registers a new binding at the home agent
home agent answers with a new session key for foreign agent
and mobile node
FA MH
HA
response:
EHA-FA {session key}
EHA-MH {session key}

54
Recap
Host mobility and Internet addresses
Post-office analogy
Home agent, foreign agent, care-of address, home
address
Registration and Tunneling
Mobile IP problems
Mobile IP Optimizations
Other options

mobile ip, Mobile COmmunication Internet Protocol

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