Mobile IP –
Overview
Chuan-Ming Liu
Computer Science and Information Engineering
National Taipei University of Technology
Spring‘04
Mobile IP Discussion Overview
Will cover:
Why IP routing breaks under mobility
Mobile IPv4 basics
Some low-level protocol details (message
formats,headers,etc.)
Lots more detail in the specifications (see
RFC)
Why Mobile IP?
Laptop Computing
Wireless Technologies
Mobility v.s,Portability
Making mobility transparent to
applications
IP Addresses
Two parts:
Routing prefix (determined by the netmask)
network on which the address resides
Host number
host on the network
routing prefix host number
32 bits
Two-level Addressing
Applications use IP addresses to identify
routes by which datagrams may be
exchanged between network nodes
Applications also use IP addresses to find
the endpoints
The delivery of packets consists of
Routing to the destination network
Sending to the host
Two-level Addressing
Things are different when changing one’s
point of attachment to the internet.
Mobile node (MN),or mobile host
(MH),in the mobile computing
environment may change its point of
attachment to the internet,say from
140.124.182.X to 128.10.7.Z
R
R
140.124.182
128.10.7Internet
140.124.182.XMN
140.124.182.XMN
128.10.7.Z
What is Mobile IP
Modification to IP that allows nodes to
continue to receive datagrams no matter
where they happen to be attached to the
internet
Scalability has been a dominant design
factor
Recall that IP can identify a node on the
internet uniquely
If no Mobile IP
Two ways to support mobility
Change IP address whenever it changed its
point of attachment
Host-specific routes must be propagated
throughout the relevant portion of the
Internet routing infrastructure
Above two approaches are not acceptable
Two Addresses for Mobile IP
Mobile IP solves this by maintaining two
addresses:
One identifies a communication endpoint
(home address)
The other locates the mobile computer
(care-of address)
Abstract Mobility
Management Model
Two IP addresses are associated with a
mobile node (MN)
Identifying and locating
Directory to store the association
The IP used to identify the endpoint is used
as an index in the directory – home address
The other IP in an entry is used to locate the
mobile node – care-of address
Abstract Mobility
Management Model
The network on which as if the mobile
nodes were actually located is known as
home network
If the mobile node is attached to its home
network,nothing special
If the mobile node is not attached to its
home network,a datagram sent to the
mobile node should be delivered to its care-
of address
f g
LD
source
dest.
Internet Routing
LD,Location directory
Abstract Mobility
Management Model
To deliver the datagram from the home
network to the care-of address,one needs
readdressing
Changing the original destination IP address
(home address) into a different IP address
(care-of address)
On the site of care-of address,the care-of
address needs to be readdressed
inversely by the home address
Abstract Mobility
Management Model
Abstract functions to support mobility
Readdressing at the home network
Associate the home address and the care-of
address
Delivering the datagram to the care-of
address
Inverting the readdressing operation on the
care-of address
f g
LD
source
dest.
Internet Routing
LD,Location directory
Abstract Model for Mobile IP
IETF Mobile IP Protocol
Defined by the Internet Engineering Task
Force (IETF) in 1996
Previous version of Mobile IP Protocol is
Columbia Mobile IP
IETF Mobile IP Protocol
The LD (location directory) is present at
the same node on the home network that
implements the readdressing function
The readdressing node on the home
network is called the home agent
A foreign agent fulfills the inverse
readdressing function
IETF Mobile IP Protocol
Foreign agents can
use a single care-of address to serve a
number of mobile nodes,or
acquire their own care-of address with
distinct addresses
Agents
Home agent (HA),router on a MN’s home
network that
readdresses and delivers the datagram to the
MN’s when it is away from home
maintains current location information for the
mobile node
Foreign agent (FA),router on a MN’s
visited network that provides routing
services to the MN while registered
Protocol Overview
Mobile IP is a way of doing three functions:
Agent discovery
HA and FA advertise their availability
Newly arrived MN can send solicitation to learn if any
prospective agents are present
Registration – MN registers its care-of address with
its HA
Directly,or
Through a FA
Tunneling – delivers datagram from HA to MN
when MN is away from home
Care-of Address
Mobile IP provides two ways to obtain a
care-of address
Provided by a foreign agent through its
agent advertisement messages
Colocated care-of address acquired by the
some external means as a local IP address
Outline of the Operation of
Mobile IP
Mobility agents (FA and MA) advertise
their presence via advertisement message;
a MN may optionally solicit an agent
advertisement message from any local
mobility agent using an agent solicitation
message
Outline of the Operation of
Mobile IP
MN receives an agent advertisement and
decide it is on its home network or not
If the MN is on the home network,it
operates without mobility services,(If
returning to its home network from being
registered elsewhere,the MN deregisters
with its home agent)
Outline of the Operation of
Mobile IP
If the MN detects it has moved to a foreign
network,it obtains a care-of address on the
foreign network,( the care-of address can
be a foreign agent care-of address or a
colocated care-of address)
The MN away from home registers its new
care-of address with its home agent through
the exchange of registration request and
reply messages
Outline of the Operation of
Mobile IP
Datagram sent to the MN’s home address
are intercepted by its HA,tunneled by the
HA to the MN’s care-of address,received at
the tunnel endpoint,and finally delivered to
the MN
Datagram sent by the MN may be delivered
to their destination using standard IP
routing mechanisms (not necessarily
passing through the HA)
More on Care-of Address
Using colocated care-of address
has the advantage of allowing a MN to
function without a FA
Place an additional burden on the IPv4 address
space
Care-of address is simply the endpoint of a
tunnel
FA is a mobility agent which provides
service to MN’s
Placement of the HA
Protocol Messages
Agent discovery
Extension to ICMP (router advertisement
and router solicitation messages)
Care-of address registration
Message sent with UDP using port 434
Two message types
Registration request
Registration reply
IP header
IP-in-IP Tunneling
Packet to be forwarded is encapsulated in a new
IP packet
See RFC 2003 for details
In the new header:
Destination = care-of-address
Source = address of home agent
Protocol number = IP-in-IP
IP header
data IP header
data
data area
Data Transfer
Mobile IP,Conclusions...
Great potential for mobile application
deployment using Mobile IP
Minimizes impact on existing Internet
infrastructure
Security issues are important
(Complicated) firewall solutions proposed
Several working implementations (e.g.,
Monarch project at CMU)
Some things still need work,e.g.,integration of
Mobile IP and 802.11 wireless LANs
Inefficiency in Mobile IP
Overview
Chuan-Ming Liu
Computer Science and Information Engineering
National Taipei University of Technology
Spring‘04
Mobile IP Discussion Overview
Will cover:
Why IP routing breaks under mobility
Mobile IPv4 basics
Some low-level protocol details (message
formats,headers,etc.)
Lots more detail in the specifications (see
RFC)
Why Mobile IP?
Laptop Computing
Wireless Technologies
Mobility v.s,Portability
Making mobility transparent to
applications
IP Addresses
Two parts:
Routing prefix (determined by the netmask)
network on which the address resides
Host number
host on the network
routing prefix host number
32 bits
Two-level Addressing
Applications use IP addresses to identify
routes by which datagrams may be
exchanged between network nodes
Applications also use IP addresses to find
the endpoints
The delivery of packets consists of
Routing to the destination network
Sending to the host
Two-level Addressing
Things are different when changing one’s
point of attachment to the internet.
Mobile node (MN),or mobile host
(MH),in the mobile computing
environment may change its point of
attachment to the internet,say from
140.124.182.X to 128.10.7.Z
R
R
140.124.182
128.10.7Internet
140.124.182.XMN
140.124.182.XMN
128.10.7.Z
What is Mobile IP
Modification to IP that allows nodes to
continue to receive datagrams no matter
where they happen to be attached to the
internet
Scalability has been a dominant design
factor
Recall that IP can identify a node on the
internet uniquely
If no Mobile IP
Two ways to support mobility
Change IP address whenever it changed its
point of attachment
Host-specific routes must be propagated
throughout the relevant portion of the
Internet routing infrastructure
Above two approaches are not acceptable
Two Addresses for Mobile IP
Mobile IP solves this by maintaining two
addresses:
One identifies a communication endpoint
(home address)
The other locates the mobile computer
(care-of address)
Abstract Mobility
Management Model
Two IP addresses are associated with a
mobile node (MN)
Identifying and locating
Directory to store the association
The IP used to identify the endpoint is used
as an index in the directory – home address
The other IP in an entry is used to locate the
mobile node – care-of address
Abstract Mobility
Management Model
The network on which as if the mobile
nodes were actually located is known as
home network
If the mobile node is attached to its home
network,nothing special
If the mobile node is not attached to its
home network,a datagram sent to the
mobile node should be delivered to its care-
of address
f g
LD
source
dest.
Internet Routing
LD,Location directory
Abstract Mobility
Management Model
To deliver the datagram from the home
network to the care-of address,one needs
readdressing
Changing the original destination IP address
(home address) into a different IP address
(care-of address)
On the site of care-of address,the care-of
address needs to be readdressed
inversely by the home address
Abstract Mobility
Management Model
Abstract functions to support mobility
Readdressing at the home network
Associate the home address and the care-of
address
Delivering the datagram to the care-of
address
Inverting the readdressing operation on the
care-of address
f g
LD
source
dest.
Internet Routing
LD,Location directory
Abstract Model for Mobile IP
IETF Mobile IP Protocol
Defined by the Internet Engineering Task
Force (IETF) in 1996
Previous version of Mobile IP Protocol is
Columbia Mobile IP
IETF Mobile IP Protocol
The LD (location directory) is present at
the same node on the home network that
implements the readdressing function
The readdressing node on the home
network is called the home agent
A foreign agent fulfills the inverse
readdressing function
IETF Mobile IP Protocol
Foreign agents can
use a single care-of address to serve a
number of mobile nodes,or
acquire their own care-of address with
distinct addresses
Agents
Home agent (HA),router on a MN’s home
network that
readdresses and delivers the datagram to the
MN’s when it is away from home
maintains current location information for the
mobile node
Foreign agent (FA),router on a MN’s
visited network that provides routing
services to the MN while registered
Protocol Overview
Mobile IP is a way of doing three functions:
Agent discovery
HA and FA advertise their availability
Newly arrived MN can send solicitation to learn if any
prospective agents are present
Registration – MN registers its care-of address with
its HA
Directly,or
Through a FA
Tunneling – delivers datagram from HA to MN
when MN is away from home
Care-of Address
Mobile IP provides two ways to obtain a
care-of address
Provided by a foreign agent through its
agent advertisement messages
Colocated care-of address acquired by the
some external means as a local IP address
Outline of the Operation of
Mobile IP
Mobility agents (FA and MA) advertise
their presence via advertisement message;
a MN may optionally solicit an agent
advertisement message from any local
mobility agent using an agent solicitation
message
Outline of the Operation of
Mobile IP
MN receives an agent advertisement and
decide it is on its home network or not
If the MN is on the home network,it
operates without mobility services,(If
returning to its home network from being
registered elsewhere,the MN deregisters
with its home agent)
Outline of the Operation of
Mobile IP
If the MN detects it has moved to a foreign
network,it obtains a care-of address on the
foreign network,( the care-of address can
be a foreign agent care-of address or a
colocated care-of address)
The MN away from home registers its new
care-of address with its home agent through
the exchange of registration request and
reply messages
Outline of the Operation of
Mobile IP
Datagram sent to the MN’s home address
are intercepted by its HA,tunneled by the
HA to the MN’s care-of address,received at
the tunnel endpoint,and finally delivered to
the MN
Datagram sent by the MN may be delivered
to their destination using standard IP
routing mechanisms (not necessarily
passing through the HA)
More on Care-of Address
Using colocated care-of address
has the advantage of allowing a MN to
function without a FA
Place an additional burden on the IPv4 address
space
Care-of address is simply the endpoint of a
tunnel
FA is a mobility agent which provides
service to MN’s
Placement of the HA
Protocol Messages
Agent discovery
Extension to ICMP (router advertisement
and router solicitation messages)
Care-of address registration
Message sent with UDP using port 434
Two message types
Registration request
Registration reply
IP header
IP-in-IP Tunneling
Packet to be forwarded is encapsulated in a new
IP packet
See RFC 2003 for details
In the new header:
Destination = care-of-address
Source = address of home agent
Protocol number = IP-in-IP
IP header
data IP header
data
data area
Data Transfer
Mobile IP,Conclusions...
Great potential for mobile application
deployment using Mobile IP
Minimizes impact on existing Internet
infrastructure
Security issues are important
(Complicated) firewall solutions proposed
Several working implementations (e.g.,
Monarch project at CMU)
Some things still need work,e.g.,integration of
Mobile IP and 802.11 wireless LANs
Inefficiency in Mobile IP
