MC-6 Mobile IP
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Transcript of MC-6 Mobile IP
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Mobile IP
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MOBILE IP
Mobile computing in a true sense will be able to provide an environment where auser will be able to continuously access data and services in a state of mobility.
A data connection between two end-points through TCP lIP network requires a
source IP address, source TCP port and a target IP address with a target TCP
port.
The combination of one IP address of the host system combined with a TCP
port as the identification of a service becomes a point of attachment for an
end-point. TCP port number is application-specific and remains constant. IP
address, on the other hand, is network specific and varies from network to
network.
IP addresses are assigned to a host from a set of addresses. This structure
works well as long as the client is static and is using a desktop computer.
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Let us assume that the user is mobile and is using a laptop with WiFi
As the user moves, the point of attachment will change from one subnet to another
subnet resulting in a change of IP address.
This will force the connection to terminate. Therefore, the question is how do we
allow mobility while a data connection is alive.
The technology to do so is 'Mobile IP,and signifies that, while a user is connected to
applications across the Internet and the user's point of attachment changes
dynamically, all connections are maintained despite the change in underlying network
properties. This is similar to the handoff roaming situation in cellular network.
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Internet Protocal routes packets from a source endpoint to a destination endpoint
through various routers. An IP address of a host can be considered to be a combinationof network address (most significant 24 bits) and the node address (least significant 8
bits).
The network portion of an IP address is used by routers to deliver the packet to the last
router in the chain to which the target computer is attached. This last router then uses
the host portion of the IP address to deliver the IP packet to the destination computer.
The port number is used by the host to deliver the packet to the appropriate
application.
To ensure that an active TCP connection is not terminated while the user is mobile, it is
essential that all of these four identities remain constant.
The TCP ports are application specific and generally constant. However, the IP address
changes from subnet to subnet.
MOBILE IP
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Therefore, to fix this problem mobile IP allows the mobile node to use two IP addresses.
These IP addresses are called home addressand care-of address.
The home address is static and known to everybody as the identity of the host. The
care-of address changes at each new point of attachment and can be thought of as the
mobile node's location specific address.
This is similar to the concept of HLR (Home Location Register) and VLR (Visitor Location
Register) in cellular networks.
When the mobile node is roaming and is attached to a foreign network, the home agent
receives all the packets for the mobile node and arranges to forward them to the mobile
node's current point of attachment.
The network node that is responsible for forwarding and managing this transparency is
known as the home agent.
MOBILE IP
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MobileIP Mobile IP was developed as a means for transparently dealing with problems of mobile
users Enables hosts to stay connected to the Internet regardless of their location
Enables hosts to be tracked without needing to change their IP address
Requires no changes to software of non-mobile hosts/routers
Requires addition of some infrastructure
Has no geographical limitations
Requires no modifications to IP addresses or IP address format
Supports security
Could be even more important than physically connected routing
IETF standardization process is still underway
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Definitions Home Network: Network where the mobile node belongs originally
Home Address: IP address of the mobile node in the home network
(static)
Home Agent: Typically a router on the home network that controls
traffic in that network
Foreign Network: Network different from the home where the
mobile node is connected at the moment.
Foreign Agent: Typically a router on the foreign network. It controls
traffic in that network.
Care-of Address: Temporary IP address assigned to the mobile unit
by the foreign network
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Permanent Address: IP address permanently assigned to the Mobile node
Care-of address: Temporary IP address assigned to Mobile node by
Foreign agent
Correspondent: Node wishing to communicate with Mobile node
Functionality:
Correspondent sends a message addressed to the Permanent address.
This message will arrive to the Home agent. Home agent forwards the
message to Foreign agent.
Foreign agent forwards it to Mobile node.
Mobile node replies directly to Correspondent.
Mobile IP - cont
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Mobile IP -cont
Additional protocols required:
Agent discovery:Mobile node finds the Foreign agent or Home agent
Registration with Home agent: Foreign agent sends Home agent Care-of
address
Indirect routing of Correspondents datagrams:Rules about encapsulating
datagrams forwarded to Mobile node by Home agent
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Mobile IP Entities
Mobile Node (MN) The entity that may change its point of attachment from network to network in the
Internet
Detects it has moved and registers with best FA
Assigned a permanent IP called its home address to which other hosts send packetsregardless of MNs location
Since this IP doesnt change it can be used by long-lived applications as MNslocation changes
Home Agent (HA)
This is router with additional functionality
Located on home network of MN
Does mobility binding of MNs IP with its COA Forwards packets to appropriate network when MN is away
Does this through encapsulation
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Mobile IP Entities contd.
Foreign Agent (FA)
Another router with enhanced functionality
If MN is away from HA the it uses an FA to send/receive data to/from HA
Advertises itself periodically
Forwards MNs registration request Decapsulates messages for delivery to MN
Care-of-address (COA)
Address which identifies MNs current location
Sent by FA to HA when MN attaches
Usually the IP address of the FA
Correspondent Node (CN)
End host to which MN is corresponding (eg. a web server)
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Mobile IP Support Services
Agent Discovery
HAs and FAs broadcast their presence on each network to which they areattached
Beacon messages via ICMP Router Discovery Protocol (IRDP)
MNs listen for advertisement and then initiate registration
Registration When MN is away, it registers its COA with its HA
Typically through the FA with strongest signal
Registration control messages are sent via UDP to well known port
Encapsulationjust like standard IP only with COA
Decapsulationagain, just like standard IP
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Mobile IP Operation
A MN listens for agent advertisement and then initiates registration If responding agent is the HA, then mobile IP is not necessary
After receiving the registration request from a MN, the HA acknowledges and
registration is complete
Registration happens as often as MN changes networks
HA intercepts all packets destined for MN This is simple unless sending application is on or near the same network as the MN
HA masquerades as MN
There is a specific lifetime for service before a MN must re-register
There is also a de-registration process with HA if an MN returns home
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Registration Process
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Mobile IP Operation contd.
HA then encapsulates all packets addressed to MN and forwards them to FA
IP tunneling
FA decapsulates all packets addressed to MN and forwards them via hardware address(learned as part of registration process)
NOTE that the MN can perform FA functions if it acquires an IP address eg. via DHCP
Bidirectional communications require tunneling in each direction
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Home Network and Home Agent
Home network:permanenthome of mobile(e.g., 128.119.40/24)
Permanent address:address in home network,can alwaysbe used toreach mobilee.g., 128.119.40.186
Home agent: entity that willperform mobility functions onbehalf of mobile, when mobile isremote
wide areanetwork
correspondent
Correspondent:wants to
communicate with mobile
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Visited Network and Care-of Address
Care-of-address:address in
visited network.(e.g., 79,129.13.2)
wide areanetwork
Visited network:network inwhich mobile currentlyresides (e.g., 79.129.13/24)
Permanent address:remainsconstant (e.g., 128.119.40.186)
Home agent: entity invisited network thatperforms mobilityfunctions on behalf ofmobile.Correspondent:wants to
communicate with mobile
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IP Mobile Basic Capabilities
Discovery: A mobile unit uses a discovery procedureto identify prospective home agents and foreignagents.
Registration: A mobilenode uses an authenticatedregistration procedure to inform its home agent of itscare-of address
Tunnelling: Tunnelling is used to forward IP
datagrams from a home address to a care-ofaddress.
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Discovery
Need to determine if the node is in its home network
or on a foreign network. This is done through
Advertisement.
A transmission from the home network to a foreignnetwork can occur at any time without notification
to the network layer (IP layer)
discovery for a mobile node is a continuous process.
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Lecture 5: Mobility
Mobile IP: agent discovery
agent advertisement:foreign/home agents advertise serviceby broadcasting ICMP messages(typefield = 9)
RBHFMGVbits
reserved
type = 16
type = 9 code = 0 checksum
router address
standardICMP fields
mobility agentadvertisement
extension
length sequence #
registration lifetime
0 or more care-of-addresses
0 8 16 24
R bit: registrationrequired
H,F bits: homeand/or foreign agent
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DiscoveryMove Detection
Mobile nodes may move between networksdue to some handoff mechanism without theIP level being aware of it.
Agent Discovery Process is intended to enablethe agent to detect such move. There are twoalgorithms used for this:
Use of Lifetime Field
Use of Network Prefix
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Move Detection Algorithms
Lifetime Filed:When a mobile node(MN) receives an agent
advertisement from a foreign agent that it is currently using or
that it is now going to register with, it records the lifetime
field as a timer
If the timer expires before the MN receives another agent advertisement fromthe agent, then the node assumes that it lost contact with that agent.
If the MN has received an agent advertisement from another agent, and that
advertisement has not yet expired, the MN can register with this new agent.
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Move Detection Algorithms
Network Prefix: The mobile node (MN) checks
whether any newly received agent advertisement is
on the same network as the nodes current care-of-
address. If it is not, the MN assumes that it has moved and may
register with the agent whose advertisement the mobile
node has just received.
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Registration
Once a mobile node has recognized that it is
on a foreign network and has acquired a care-
of address, it needs to alert a home agent on
its home network and request that the homeagent forward its IP traffic
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Registration
The registration process involves four steps:
1. The mobile node requests the forwarding service by sendinga registration request to the foreign agent that the mobile
node wants to use.2. The foreign agent relays this request to the mobile nodes
home agent.
3. The home agent either accepts or denies the request and
sends a registration reply to the foreign agent.4. The foreign agent relays this reply to the mobile node
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Mobility: Registration
Foreign agent knows about mobile
Home agent knows location of mobile
wide area
network
home networkvisited network
1
mobile contactsforeign agent onentering visitednetwork
2
foreign agent contacts home agenthome: this mobile is resident in mynetwork
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Mobility via Indirect Routing
wide areanetwork
home
network
visitednetwork
3
2
41
correspondentaddresses packetsusing home addressof mobile
home agent interceptspackets, forwards toforeign agent
foreign agentreceives packets,forwards to mobile
mobile repliesdirectly tocorrespondent
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Lecture 4: Mobility
Indirect Routing: comments
Mobile uses two addresses: permanent address:used by correspondent (hence
mobile location is transparentto correspondent)
care-of-address:used by home agent to forward
datagrams to mobile foreign agent functions may be done by mobile itself
triangle routing:correspondent-home-network-mobile
inefficient when
correspondent, mobile
are in same network
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Indirect Routing: Efficiency Issues
Mobile uses two addresses
Permanent address: used by correspondent (making
mobiles location is transparent to correspondent)
Care-of-address: used by the home agent to forwarddatagrams to the mobile
Mobile may perform the foreign agent functions
Triangle routing is inefficient E.g., correspondent and mobile in the same network
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Mobility via Direct Routing
wide areanetwork
home
network
visitednetwork
4
2
41correspondentrequests, receivesforeign address ofmobile
correspondent forwardsto foreign agent
foreign agentreceives packets,forwards to mobile
mobile repliesdirectly tocorrespondent
3
No longer transparent to the correspondent
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Lecture 5: Mobility
Mobile IP: indirect routing
Permanent address:128.119.40.186
Care-of address:79.129.13.2
dest: 128.119.40.186
packet sent bycorrespondent
dest: 79.129.13.2 dest: 128.119.40.186
packet sent by home agent to foreignagent: apacket within a packet
dest: 128.119.40.186
foreign-agent-to-mobile packet
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Tunnelling
Once a mobile node is registered with a home agent,the home agent must be able to intercept IPdatagrams sent to the mobile nodes home address
so that these datagrams can be forwarded viatunnelling
To forward an IP datagram to a care-of-address, the
home agent puts the entire IP datagram into anouter IP datagram. This is a form of encapsulation
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Tunnelling
Three options for encapsulation are allowed for
Mobile IP:
IP-within-IP encapsulation: IP datagram is inserted into a
new IP datagram with the care-of address.
Minimal Encapsulation:Less overhead, only a few fields
are added in the outer datagram.
Generic routing encapsulation (GRE): This is a generic
encapsulation procedure that was developed prior to the
development of Mobile IP
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Operation of Mobile IP
IP datagram to A
Encapsulation and Tunnelling
Network Level PDU
As response travels directly
to X due to fixed IP of X
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Lecture 5: Mobility
Mobile IP
RFC 3344
has many features weve seen:
home agents, foreign agents, foreign-agent
registration, care-of-addresses, encapsulation(packet-within-a-packet)
three components to standard:
indirect routing of datagrams
agent discovery
registration with home agent
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Features of Mobile IP
The mobile IP architecture comprises three functions:
1. A database that contains the most up-to-date mapping between the
two address spaces (home address to care-of-address)
2. The translation of the host identifier to the actual destination
address
3. Agents ensuring that the source and destination packets for arriving
and outgoing packets are updated properly so that routing of
packets are proper
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Mobile IP
Whenever the mobile host moves to a new subnet managed by a different
foreign agent, the dynamic care-of-address will change.
This changed care-of-address needs to be communicated to the home agent.
This process works for slowly moving hosts. For a high speed mobile host, therate of update of the addresses needs to match the rate of change of ddresses.
Otherwise, packets will be forwarded to the wrong (old) address.
Mobile IP fails to update the addressed properly for high speed mobility.
Cellular IP a new host mobility protocol has been designed to address this
issue.
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Mobile IP Vs Cellular IP
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Example: Boeing Connexion Service
Internet
12.78.3.0/24
http://www.freedigitalphotos.net/albums/userpics/10001/airplane6.jpghttp://www.lbisat.com/gallery/photos/New%20Skies%20Satellite.jpghttp://www.lbisat.com/gallery/photos/New%20Skies%20Satellite.jpghttp://www.esa.int/spacecraftops/Image/urlpicturelarge_id_1069167511889_NNO_new_l,2.jpghttp://www.esa.int/spacecraftops/Image/urlpicturelarge_id_1069167511889_NNO_new_l,2.jpg -
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Security in Mobile IP
Authentication can be performed by all parties
Only authentication between MN and HA is required
Keyed MD5 is the default
Replay protection
Timestamps are mandatory
Random numbers on request reply packets are optional
HA and FA do not have to share any security information.
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Problems with Mobile IP
Suboptimal triangle routing
What if MN is in same subnetwork as the node to which it is communicating andHA is on the other side of the world?
It would be nice if we could directly route packets
Solution: Let the CN know the COA of MN
Then the CN can create its own tunnel to MN
CN must be equipped with software to enable it to learn the COA
Initiated by HA who notifies CN via binding update
Binding table can become stale
Single HA model is fragile
Possible solutionhave multiple HA
Frequent reports to HA if MN is moving
Possible solutionsupport of FA clustering
Security
Connection hijacking, snooping
Many open research questions
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Mobility in IPv6
Route Optimization is a fundamental part of Mobile IPv6
Mobile IPv4 it is an optional set of extensions that may not be supported by allnodes
Foreign Agents are not needed in Mobile IPv6
MNs can function in any location without the services of any special router in thatlocation
Security
Nodes are expected to employ strong authentication and encryption
Other details