Mobile IP by yaofenjin


									Mobile IP

                    SEMINAR TITLE                   Page 1
Mobile IP

                    Many organizations utilize traditional wire-based networking technologies to
            establish connections among computers. These technologies fall into the following three
            main categories namely LAN, MAN & WAN.
                     These traditional networking technologies offer tremendous capabilities from an
            office, hotel room, or home. Activities such as communicating via e-mail with someone
            located in a faraway town or conveniently accessing product information from the World
            Wide Web are the result of widespread networking. But limitations to networking
            through the wire-based system exist because you can not utilize these network services
            unless you are physically connected to a LAN or a telephone system.
                     Wireless networks are stretching their legs day by day. With the increasing no. of
            mobile users wireless technology has become inevitable. Wireless networking is the first
            step towards the mobile communication system. As for wireless networking we use
            certain protocols for the communication thus definitely we need protocols for mobile
            communication. These protocols as in wireless networks are called Mobile IP or Mobile
            Internet Protocol.
                    The day will arrive, hastened by Mobile IP, when no person will ever feel ―lost‖
            or out of touch. As people move from place to place with their laptop, keeping connected
            to the network can become a challenging and sometimes frustrating and expensive
            proposition. The goal is that with widespread deployment of the mobile networking
            technologies described here automatic communications with globally inter-connected
            computing resources will be considered as natural for people on the move as it is for
            people sitting at a high performance workstation in their office. In the near future
            communicating via laptop should be as natural as using telephone.
                    Although the Internet offers access to information sources worldwide, typically
            we do not expect to benefit from that access until we arrive at some familiar point --
            whether home, office, or school. However, the increasing variety of wireless devices
            offering IP connectivity, such as personal digital assistants, handhelds, and digital cellular
            phones, is beginning to change our perceptions of the Internet.

                   Mobile IP is a proposed standard protocol that builds on the Internet Protocol by
            making mobility transparent to applications and higher-level protocols like TCP. This
            paper aims at discussing the design principles of Mobile IP and how it can be
            incorporated with the already existing Internet architecture.
                    Mobile Internet Protocol is a new recommended Internet protocol designed to
            support the mobility of a user (host). Host mobility is becoming important because of the
            recent blossoming of laptop computers and the high desire to have continuous network
            connectivity anywhere the host happens to be. The development of Mobile IP makes this
                   There are mainly three processes in Mobile IP:                                                                                            Page 2
Mobile IP

            1. Agent Discovery: The process by which a Mobile node determines its current location
               and obtains the care of address.
            2. Registration: The process by which a Mobile node request service from a foreign
               agent on foreign link and informs its home agent of its current care-off address.
            3. Tunneling: The specific mechanism by which packets are routed to and from a
               Mobile node that is connected to a foreign link.
                    Mobile Computing is becoming increasingly important due to the rise in the
            number of portable computers and the desire to have continuous network connectivity to
            the Internet irrespective of the physical location of the node. The Internet infrastructure is
            built on top of a collection of protocols, called the TCP/IP protocol suite. Transmission
            Control Protocol (TCP) and Internet Protocol (IP) are the core protocols in this suite. IP
            requires the location of any host connected to the Internet to be uniquely identified by an
            assigned IP address. This raises one of the most important issues in mobility, because
            when a host moves to another physical location, it has to change its IP address. However,
            the higher level protocols require IP address of a host to be fixed for identifying
                   The Mobile Internet Protocol (Mobile IP) is an extension to the Internet Protocol
            proposed by the Internet Engineering Task Force (IETF) that addresses this issue. It
            enables mobile computers to stay connected to the Internet regardless of their location
            and without changing their IP address.
                    Mobile IP specifies enhancements that allow transparent routing of IP datagrams
            to mobile nodes in the Internet. Each mobile node is always identified by its home
            address, regardless of its current point of attachment to the Internet. While situated away
            from its home, a mobile node is also associated with a care-of address, which provides
            information about its current point of attachment to the Internet. The protocol provides
            for registering the care-of address with a home agent. The home agent sends datagrams
            destined for the mobile node through a tunnel to the care-of address. After arriving at the
            end of the tunnel, each datagram is then delivered to the mobile node.
                    Regardless of the movement between different networks connectivity at the
            different points is achieved easily. Roaming from a wired network to wireless or wide
            area network is also done with ease. Mobile IP is a part of both IPV4 and IPV6.
                    The description of the core differences between the present protocol Ipv4 and the
            future protocol Ipv6 such as scalability, security, realtimeness, Plug and Play, Clear spec.
            and optimizations are looked. Covered next is the difference between the headers
            schemes of the IPV4 the currently used Protocol Vs IPV6 the up-coming sensation in the
            Internet World. Well you are using it then you should be aware of what are the
            advantages of the thing and thus here it covers the Advantages of IPV6 over IPV4.                                                                                            Page 3
Mobile IP


            TOPIC                                   PAGE NO

            1. INTRODUCTION                             1

            2. MOBILE IP OVERVIEW                       3

            3. TERMINOLOGY                              5

            4. PROTOCOL OVERVIEW                        6

            5. RELATIONSHIPS OF THE COMPONENTS          10

            6. HOW MOBILE IP WORKS                      11

              6.1 AGENT DISCOVERY                       11
              6.2 REGISTRATION                          12
              6.3 TUNNELING                             13

            7. SECURITY                                 16

            8. ONGOING WORK & OPEN QUESTIONS            17

            9. CHANGES WITH IPV6                        21

               9.1 ROUTE OPTIMIZATION
               9.2 SECURITY
               9.3 SOURCE ROUTING

                IN MOBILE IP

            12. CONCLUSION                               26

             13. REFERENCES AND BIBLIOGRAPHY            26                                             Page 4
Mobile IP

                   1. INTRODUCTION

                    The exponential growth of the Internet and the inexorable increase in native
            computing power of laptop computers and other digital wireless data communication
            devices has brought the need for mobile networking into sharp focus. As network
            services proliferate and become available ubiquitously, every network device will take
            advantage of mobile networking technology to offer maximum flexibility to the
            customers needing those devices.
                    To understand the contrast between the current realities of IP connectivity and
            future possibilities, consider the transition toward mobility that has occurred in telephony
            over the past 20 years. An analogous transition in the domain of networking, from
            dependence on fixed points of attachment to the flexibility afforded by mobility, has just
                    As PDAs and the next generation of data-ready cellular phones become more
            widely deployed, a greater degree of connectivity is almost becoming a necessity for the
            business user on the go. Data connectivity solutions for this group of users are a very
            different requirement than it is for the fixed dialup user or the stationary wired LAN user.
            Solutions here need to deal with the challenge of movement during a data session or
            conversation. Cellular service providers and network administrators wanting to deploy
            wireless LAN technologies need to have a solution which will grant this greater freedom
                    Cisco IOS has integrated new technology into our routing platforms to meet these
            new networking challenges. Mobile IP is a tunneling-based solution which takes
            advantage of the Cisco-created GRE tunneling technology, as well as simpler IP-in-IP
            tunneling protocol. This tunneling enables a router on a user’s home subnet to intercept
            and transparently forward IP packets to users while they roam beyond traditional network
            boundaries. This solution is a key enabler of wireless mobility, both in the wireless LAN
            arena, such as the 802.11 standard, and in the cellular environment for packet-based data
            offerings which offer connectivity to a user’s home network and the Internet.
                    Mobile IP provides users the freedom to roam beyond their home subnet while
            consistently maintaining their home IP address. This enables transparent routing of IP
            data grams to mobile users during their movement, so that data sessions can be initiated
            to them while they roam; it also enables sessions to be maintained in spite of physical
            movement between points of attachment to the Internet or other networks. Cisco’s
            implementation of Mobile IP is fully compliant with the Internet Engineering Task
            Force’s (IETF’s) proposed standard defined in Request for Comments.
                    Mobile computing and networking should not be confused with the portable
            computing and networking we have today. In mobile networking, computing activities
            are not disrupted when the user changes the computer's point of attachment to the
            Internet. Instead, all the needed reconnection occurs automatically and non-interactively.                                                                                          Page 5
Mobile IP

                     Truly mobile computing offers many advantages. Confident access to the Internet
            anytime, anywhere will help free us from the ties that bind us to our desktops. Consider
            how cellular phones have given people new freedom in carrying out their work. Taking
            along an entire computing environment has the potential not just to extend that flexibility
            but to fundamentally change the existing work ethic.
                    The evolution of mobile networking will differ from that of telephony in some
            important respects. The endpoints of a telephone connection are typically human;
            computer applications are likely to involve interactions between machines without human
            intervention. Obvious examples of this are mobile computing devices on airplanes, ships,
            and automobiles. Mobile networking may well also come to depend on position-finding
            devices, such as a satellite global positioning system, to work in tandem with wireless
            access to the Internet.
                     However, there are still some technical obstacles that must be overcome before
            mobile networking can become widespread. The most fundamental is the way the
            Internet Protocol, the protocol that connects the networks of today's Internet, routes
            packets to their destinations according to IP addresses. These addresses are associated
            with a fixed network location much as a non-mobile phone number is associated with a
            physical jack in a wall. When the packet's destination is a mobile node, this means that
            each new point of attachment made by the node is associated with a new network number
            and, hence, a new IP address, making transparent mobility impossible.
                   Network mobility is enabled by Mobile IP, which provides a scalable, transparent,
            and secure solution. It is scalable because only the participating components need to be
            Mobile IP aware—the Mobile Node and the endpoints of the tunnel. No other routers in
            the network or any hosts with which the Mobile Node is communicating need to be
            changed or even aware of the movement of the Mobile Node. It is transparent to any
            applications while providing mobility. Also, the network layer provides link-layer
            independence; interlink layer roaming, and link-layer transparency. Finally, it is secure
            because the set up of packet redirection is authenticated.                                                                                         Page 6
Mobile IP

                   2. Mobile IP Overview
                    In IP networks, routing is based on stationary IP addresses, similar to how a postal
            letter is delivered to the fixed address on the envelope. A device on a network is
            reachable through normal IP routing by the IP address it is assigned on the network.
                    The problem occurs when a device roams away from its home network and is no
            longer reachable using normal IP routing. This results in the active sessions of the device
            being terminated. Mobile IP was created to enable users to keep the same IP address
            while traveling to a different network (which may even be on a different wireless
            operator), thus ensuring that a roaming individual could continue communication without
            sessions or connections being dropped. Because the mobility functions of Mobile IP are
            performed at the network layer rather than the physical layer, the mobile device can span
            different types of wireless and wire line networks while maintaining connections and
            ongoing applications. Remote login, remote printing, and file transfers are some
            examples of applications where it is undesirable to interrupt communications while an
            individual roams across network boundaries. Also, certain network services, such as
            software licenses and access privileges, are based on IP addresses. Changing these IP
            addresses could compromise the network services.
                   This section discusses the main concepts and operations of the IETF Mobile IP
            protocol. The basic protocol procedures fall into the following areas:
                    Mobile IP is a modification to IP that allows nodes to continue to receive
            datagrams no matter where they happen to be attached to the Internet. It involves some
            additional control messages that allow the IP nodes involved to manage their IP routing
            tables reliably. Scalability has been a dominant design factor during the development of
            Mobile IP, because in the future a high percentage of the nodes attached to the Internet
            will be capable of mobility.
                    As explained in the previous section, IP assumes that a node’s network address
            uniquely identifies the node’s point of attachment to the Internet. Therefore, a node must
            be located on the network indicated by its IP address to receive datagrams destined to it;
            otherwise, datagrams destined to the node would be undeliverable. Without Mobile IP,
            one of the two following mechanisms must be typically employed for a node to change
            its point of attachment without losing the ability to communicate:

            The node must change its IP address whenever it changes its point of attachment.
            Host-specific routes must be propagated throughout the relevant portion of the Internet
            routing infrastructure.
                  Both these alternatives are plainly unacceptable in the general case. The first
            makes it impossible for a node to maintain transport and higher layer connections when                                                                                          Page 7
Mobile IP

            the node changes location. The second has obvious and severe scaling problems that are
            especially relevant considering the explosive growth in sales of notebook (mobile)
                     Mobile IP was devised to meet the following goals for mobile nodes that move
            (that is, change their point of attachment to the Internet) more frequently than once per
            second. The following five characteristics should be considered baseline requirements to
            be satisfied be any candidate for a mobile IP protocol:

            A mobile node must be able to communicate with other nodes after changing its link-
            layer point of attachment to the Internet, yet without changing its IP address.

            A mobile node must be able to communicate with other nodes that do not implement
            Mobile IP.
            All messages used to transmit information to another node about the location of a
            mobile node must be authenticated to protect against remote redirection attacks.
            The link by which a mobile node is directly attached to the Internet may often be a
            wireless link. This link may thus have a substantially lower bandwidth and higher error
            rate than the traditional wired networks. Moreover, mobile nodes are likely to be battery
            powered, and minimizing power consumption is important. Therefore, the number of
            administrative messages sent over the link by which a mobile node is directly connected
            to the Internet should be minimized, and the size of these messages should be kept as
            small as possible.
            Mobile IP must place no additional constraints on the assignment of IP addresses.                                                                                       Page 8
Mobile IP

                   3. Terminology

                   Mobile IP introduces the following new functional entities:
                   Mobile node – A mobile node is a host or a router that changes its point of
            attachment from one network or sub network to another. A mobile node may change its
            location without changing its IP address. It may continue to communicate with other
            Internet nodes at any location using its (constant) IP address, assuming link-layer
            connectivity to a point of attachment is available.
                   Home agent – A home agent is a router on a mobile node’s home network that
            tunnels datagrams for delivery to the mobile node when it is away from home and
            maintains current location information for the mobile node.
                   Foreign agent – A foreign agent is a router on a mobile node’s visited network
            that provides routing services to the mobile node while registered. The foreign agent
            detunnels and delivers datagrams to the mobile node that were tunneled by the mobile
            node’s home agent. The foreign agent may always be selected as a default router by
            registered mobile nodes.
                    A mobile node is given a long term IP address on a home network. When away
            from its home network, a care-of address is associated with the mobile node and reflects
            the mobile node’s current point of attachment. The mobile node uses its home address as
            the source address of all IP datagrams that it sends, except during registration if it
            happens to acquire another IP address.

            Figure 1. Functional Entities of Mobile IP                                                                                      Page 9
Mobile IP

                   4. Protocol Overview

                   Mobile IP is, in essence, a way of doing three relatively separate functions:
            1. Agent Discovery – Home agents and foreign agents may advertise their availability
            on each link for which they provide service. A newly arrived mobile node can send a
            solicitation on the link to learn if any prospective agents are present.
            2. Registration – When the mobile node is away from home, it registers its care of
            address with its home agent. Depending upon its method of attachment, the mobile node
            will register either directly with its home agent or through a foreign agent, which
            forwards the registration to the home agent.
            3. Tunneling – In order for datagrams to be delivered to the mobile node when it is
            away from home, the home agent has to tunnel the datagrams to the care-of-address.
            When away from home, Mobile IP uses protocol tunneling to hide a mobile node’s home
            address from intervening routers between its home network and current location. The
            tunnel terminates at the node’s care-of-address. The care-of-address must be an address
            to which datagrams can be delivered via conventional IP routing. At the care-of address,
            the original datagram is removed from the tunnel and delivered to the mobile node.
            Mobile IP provides two ways to acquire a care-of address:
            1. A foreign agent care-of address is a care-of address provided by a foreign agent
            through its agent advertisement messages. In this case, the care-of address is an IP
            address of the foreign agent. In this mode, the foreign agent is the endpoint of the tunnel
            and, on receiving tunneled datagrams, decapsulates them and delivers the inner datagram
            to the mobile node. This mode of acquisition is advantageous because it allows many
            nodes to share the same care-of address and therefore does not place unnecessary
            demands on the already limited Internet Protocol version 4 (Ipv4) address space.
            2. A collocated care-of address is a care-of address acquired by the mobile node as a local
            IP address through some external means, which the mobile node then associates with one
            of its own network interfaces. The address may be dynamically acquired as a temporary
            address by the mobile node, such as through DHCP, or it may be owned by the mobile
            node as a long-term address for its use only while visiting some foreign network. When
            using a collocated care-of address, the mobile node serves as the end point of the tunnel
            and performs decapsulation of the datagrams tunneled to it. An additional advantage of a
            collocated address for mobile nodes that are equipped to use the address in this fashion is
            that they can be used for connections that are not long lived and thus will never need the
            services of any home agent.                                                                                         Page 10
Mobile IP

            With these operations in mind, a rough outline of the operation of the Mobile IP protocol
            1. Mobility agents (that is, foreign agents and home agents) advertise their presence via
            agent advertisement messages. A mobile node may optionally solicit an agent
            advertisement message from any local mobility agents by using an agent solicitation
            2. A mobile node receives an agent advertisement and determines whether it is on its
            home network or a foreign network.
            3. When the mobile node detects that it is located on its home network, it operates
            without mobility services. If returning to its home network from being registered
            elsewhere, the mobile node deregisters with its home agent through a variation of the
            normal registration process.
            4. When the mobile node detects that it has moved to a foreign network, it obtains a care
            of address on the foreign network. The care-of address can either be a foreign agent care-
            of address or a collocated care-of address.
            5. The mobile node, operating away from home, then registers its new care-of address
            with its home agent through the exchange of a registration request and registration reply
            message, possibly by way of a foreign agent.

            Figure 2. Mobile IP datagram flow                                                                                        Page 11
Mobile IP

            6. Datagrams sent to the mobile node’s home address are intercepted by its home agent,
            tunneled by the home agent to the mobile node’s care-of address, received at the tunnel
            endpoint (either at a foreign agent or at the mobile node itself), and finally delivered to
            the mobile node.

            7. In the reverse direction, datagrams sent by the mobile node may be delivered to their
            destination using standard IP routing mechanisms, without necessarily passing through
            the home agent.
                  Figure 2 illustrates the routing of datagrams to and from a mobile node away from
            home, once the mobile node has registered with its home agent. In this figure, the mobile
            node is using a foreign agent care-of address as follows:
            1. A datagram to the mobile node arrives on the home network via standard IP routing.
            2. The datagram is intercepted by the home agent and is tunneled to the care-of address.
            3. The datagram is detunneled and delivered to the mobile node.
            4. For datagrams sent by the mobile node, standard IP routing delivers each datagram to
            its destination. In Figure 2, the foreign agent is the mobile node’s default router.

                To handle registration. Mobile IP defines a set of new control messages sent with
            UDP using well-known port number 434. Currently, the following two message types are
                1 Registration request
                2 Registration reply
            Up-to-date values for the message types for mobile IP control messages are specified in
            the most recent Assigned Numbers.
            For agent discovery, Mobile IP modifies the existing router advertisement and router
            solicitation messages defined for ICMP router discovery.
                    Mobile IP defines a general extension mechanism to allow optional information to
            be carried by Mobile IP control messages or by ICMP router discovery messages. Each
            of these extensions (with one exception, the pad extension) is encoded in what is
            conventionally called the type-length-value (TLV) format shown in figure, where the
            value is the data following the length.

                  type                           length                         Data(value)

                                                 (TLV extension format)                                                                                         Page 12
Mobile IP

                     The type indicates the particular type of extension. The length of the extension,
            counted in bytes – or, more technically in octets, which are groups of 8 bits – does not
            include the type and length bytes, and may be zero or greater. The type and length fields
            determine the format of the data field. Extensions allow variable amounts of information
            to be carried within each message. The total length of IP datagram determines the end of
            the list of extensions.

                    Two separately maintained sets of numbering spaces, from which extension type
            values are allocated, are used in Mobile IP. The first set consists of those extensions that
            may appear in Mobile IP control messages (those sent to and from UDP port number
            434). Currently, the following types are defined for extensions appearing in Mobile IP
            registration messages:

                   32 Mobile – home authentication
                   33 Mobile – foreign authentication
                   34 Foreign – home authentication

                   The second set consists of those extensions that may appear in ICMP router
            discovery messages. Currently, Mobile IP defines the following types for such

                    0 One byte padding (encoded with no length or data field)
                   16 Mobility agent advertisements
                   19 Prefix lengths

                    Up-to-date values for these extension type numbers are specified in the most
            recent list of Assigned Numbers form the Internet Assigned Numbers Authority (IANA).

                   Since these sets of extensions are independent, it is conceivable that two unrelated
            extensions that are defined at a later date could have identical type values. One of the
            extensions could have identical type values. One of the extensions could be used only in
            Mobile IP control messages and the other only in ICMP router discovery messages.

                    The value of the extension number is important when trying to determine the
            correct disposition of unrecognized extensions. When an extension numbered in either of
            these sets within the range 0 through 127 is encountered but not recognized, the message
            containing that extension is required to be silently discarded. When an extension
            numbered in the range 128 through 255 is encountered but unrecognized, that particular
            extension is ignored, but the rest of the extensions and message data are still required to
            be processed. The length field of the extension is used to skip the data field in searching
            for the next extension.                                                                                          Page 13
Mobile IP

                      MOBILE IP

                   The Mobile Node is a device such as a cell phone, personal digital assistant, or
            laptop whose software enables network roaming capabilities.
                    The Home Agent is a router on the home network serving as the anchor point for
            communication with the Mobile Node; it tunnels packets from a device on the Internet,
            called a Correspondent Node, to the roaming Mobile Node. (A tunnel is established
            between the Home Agent and a reachable point for the Mobile Node in the foreign
                   The Foreign Agent is a router that may function as the point of attachment for the
            Mobile Node when it roams to a foreign network, delivering packets from the Home
            Agent to the Mobile Node.
                    The care-of address is the termination point of the tunnel toward the Mobile Node
            when it is on a foreign network. The Home Agent maintains an association between the
            home IP address of the Mobile Node and its care-of address, which is the current location
            of the Mobile Node on the foreign or visited network

            Figure 3. Mobile IP Components and Relationships                                                                                       Page 14
Mobile IP

                   6. How Mobile IP Works

                   6.1 Agent Discovery
                    During the agent discovery phase, the Home Agent and Foreign Agent advertise
            their services on the network by using the ICMP Router Discovery Protocol (IRDP). The
            Mobile Node listens to these advertisements to determine if it is connected to its home
            network or foreign network.
                    The IRDP advertisements carry Mobile IP extensions that specify whether an
            agent is a Home Agent, Foreign Agent, or both; its care-of address; the types of services
            it will provide such as reverse tunneling and generic routing encapsulation (GRE); and
            the allowed registration lifetime or roaming period for visiting Mobile Nodes. Rather
            than waiting for agent advertisements, a Mobile Node can send out an agent solicitation.
            This solicitation forces any agents on the link to immediately send an agent
            advertisement. If a Mobile Node determines that it is connected to a foreign network, it
            acquires a care-of address.
            Two Types of care-of addresses exist:
            • Care-of address acquired from a Foreign Agent
            • Collocated care-of address
                          A Foreign Agent care-of address is an IP address of a Foreign Agent that
            has an interface on the foreign network being visited by a Mobile Node. A Mobile Node
            that acquires this type of care-of address can share the address with other Mobile Nodes.
            A colocated care-of address is an IP address temporarily assigned to the interface of the
            Mobile Node itself. A collocated care-of address represents the current position of the
            Mobile Node on the foreign network and can be used by only one Mobile Node at a time.
                    When the Mobile Node hears a Foreign Agent advertisement and detects that it
            has moved outside of its home network, it begins registration.

                   6.2 Registration
                   The Mobile Node is configured with the IP address and mobility security
            association (which includes the shared key) of its Home Agent. In addition, the Mobile
            Node is configured with either its home IP address, or another user identifier, such as a
            Network Access Identifier.
                   The Mobile Node uses this information along with the information that it learns
            from the Foreign Agent advertisements to form a Mobile IP registration request. It adds
            the registration request to its pending list and sends the registration request to its Home
            Agent either through the Foreign Agent or directly if it is using a colocated care-of
            address and is not required to register through the Foreign Agent. If the registration
            request is sent through the Foreign Agent, the Foreign Agent checks the validity of the
            registration request, which includes checking that the requested lifetime does not exceed
            its limitations, the requested tunnel encapsulation is available, and that reverse tunnel is
            supported. If the registration request is valid, the Foreign Agent adds the visiting Mobile                                                                                          Page 15
Mobile IP

            Node to its pending list before relaying the request to the Home Agent. If the registration
            request is not valid, the Foreign Agent sends a registration reply with appropriate error
            code to the Mobile Node.
                      The Home Agent checks the validity of the registration request, which includes
            authentication of the Mobile Node. If the registration request is valid, the Home Agent
            creates a mobility binding (an association of the Mobile Node with its care-of address), a
            tunnel to the care-of address, and a routing entry for forwarding packets to the home
            address through the tunnel.
                      The Home Agent then sends a registration reply to the Mobile Node through the
            Foreign Agent (if the registration request was received via the Foreign Agent) or directly
            to the Mobile Node. If the registration request is not valid, the Home Agent rejects the
            request by sending a registration reply with an appropriate error code.
            The Foreign Agent checks the validity of the registration reply, including ensuring that an
            associated registration request exists in its pending list. If the registration reply is valid,
            the Foreign Agent adds the Mobile Node to its visitor list, establishes a tunnel to the
            Home Agent, and creates a routing entry for forwarding packets to the home address. It
            then relays the registration reply to the Mobile Node.
                    Finally, the Mobile Node checks the validity of the registration reply, which
            includes ensuring an associated request is in its pending list as well as proper
            authentication of the Home Agent. If the registration reply is not valid, the Mobile Node
            discards the reply. If a valid registration reply specifies that the registration is accepted,
            the Mobile Node is confirmed that the mobility agents are aware of its roaming. In the
            colocated care-of address case, it adds a tunnel to the Home Agent. Subsequently, it
            sends all packets to the Foreign Agent.
                    The Mobile Node reregisters before its registration lifetime expires. The Home
            Agent and Foreign Agent update their mobility binding and visitor entry, respectively,
            during registration. In the case where the registration is denied, the Mobile Node makes
            the necessary adjustments and attempts to register again.
            For example, if the registration is denied because of time mismatch and the Home Agent
            sends back its time stamp for synchronization, the Mobile Node adjusts the time stamp in
            future registration requests.
                   Thus, a successful Mobile IP registration sets up the routing mechanism for
            transporting packets to and from the Mobile Node as it roams.

                   6.3 Tunneling
                   Mobile IP requires the use of encapsulation to deliver datagrams from the home
            network to the current location of the mobile node (its care-of address). In the most
            general encapsulation (tunneling) case, illustrated in Figure 4. The source, encapsulator,
            decapsulator, and destination are separate nodes. The encapsulator node is considered the
            entry point of the tunnel, and the decapsulator node is considered the exit point of the
            tunnel. Multiple source-destination pairs can use the same tunnel between the
            encapsulator and the decapsulator.                                                                                             Page 16
Mobile IP

                   Mobile IP requires each agent and foreign agent to support tunneling datagrams
            using IP-in-IP encapsulation. Any mobile node that uses a collocated care-of address is
            required to support receiving datagrams tunneled using IP-in-IP encapsulation.

            Figure 4. General Tunneling

                    The Mobile Node sends packets using its home IP address, effectively
            maintaining the appearance that it is always on its home network. Even while the Mobile
            Node is roaming on foreign networks, its movements are transparent to correspondent
            nodes. Data packets addressed to the Mobile Node are routed to its home network, where
            the Home Agent now intercepts and tunnels them to the care-of address toward the
            Mobile Node. Tunneling has two primary functions: encapsulation of the data packet to
            reach the tunnel endpoint, and encapsulation when the packet is delivered at that
            endpoint. The default tunnel mode is IP Encapsulation within IPEncapsulation.
            Optionally, GRE and minimal encapsulation within IP may be used. Typically, the
            Mobile Node sends packets to the Foreign Agent, which routes them to their final
            destination, the Correspondent Node, as shown in Figure 5.                                                                                     Page 17
Mobile IP

            Figure 5. Packet Forwarding

                 However, this data path is topologically incorrect because it does not reflect the true
            IP network source for the data—rather; it reflects the home network of the Mobile Node.
            Because the packets show the home network as their source inside a foreign network, an
            access control list on routers in the network called ingress filtering drops the packets
            instead of forwarding them. A feature called reverse tunneling solves this problem by
            having the Foreign Agent tunnel packets back to the Home Agent when it receives them
            from the mobile node see figure 6.                                                                                          Page 18
Mobile IP

            Figure 6. Reverse Tunnel

                    Tunnel MTU (Maximum Transmission Unit) discovery is a mechanism for a
            tunnel encapsulator such as the Home Agent to participate in path MTU discovery to
            avoid any packet fragmentation in the routing path between a Correspondent Node and
            Mobile Node. For packets destined to the Mobile Node, the Home Agent maintains the
            MTU of the tunnel to the care-of address and informs the Correspondent Node of the
            reduced packet size. This improves routing efficiency by avoiding fragmentation and
            reassembly at the tunnel endpoints to ensure that packets reach the Mobile Node.                                                                                 Page 19
       7. Security

        Mobile IP uses a strong authentication scheme for security purposes. All
registration messages between a Mobile Node and Home Agent are required to contain
the Mobile-Home Authentication Extension (MHAE).
       The integrity of the registration messages is protected by a preshared 128-bit key
between a Mobile Node and Home Agent. The keyed message digest algorithm 5 (MD5)
in ―prefix + suffix‖ mode is used to compute the authenticator value in the appended
MHAE, which is mandatory. Mobile IP also supports the hash-based message
authentication code (HMAC-MD5). The receiver compares the authenticator value it
computes over the message with the value in the extension to verify the authenticity.
       Optionally, the Mobile-Foreign Authentication Extension and Foreign-Home
Authentication Extension are appended to protect message exchanges between a Mobile
Node and Foreign Agent and between a Foreign Agent and Home Agent, respectively.
Replay protection uses the identification field in the registration messages as a timestamp
and sequence number. The Home Agent returns its time stamp to synchronize the Mobile
Node for registration.
       Cisco IOS software allows the mobility keys to be stored on an authentication,
authorization, and accounting (AAA) server that can be accessed using TACACS+ or
RADIUS protocols. Mobile IP in Cisco IOS software also contains registration filters,
enabling companies to restrict who is allowed to register.
       Mobility security association- A collection of security contexts between a pair of
nodes, which may be applied to Mobile IP protocol messages exchanged between them.
Each context indicates an authentication algorithm and mode, a secret (a shared key or
appropriate public/private key pair), and a style of replay protection in use.

Mobile IP

                    The most pressing outstanding problem facing Mobile IP is that of security, but
            other technical as well as practical obstacles to deployment exist. Work is also continuing
            to refine and extend the protocol within the academic and commercial communities and
            within the IETF. This section surveys the state of implementation of Mobile IP and
            speculates on a possible timetable for deployment.

                    Routing inefficiencies.

                   The base Mobile IP specification has the effect of introducing a tunnel into the
            routing path followed by packets sent by the correspondent node to the mobile node.
            Packets from the mobile node, on the other hand, can go directly to the correspondent
            node with no tunneling required. This asymmetry is captured by the term triangle routing,
            where a single leg of the triangle goes from the mobile node to the correspondent node,
            and the home agent forms the third vertex controlling the path taken by data from the
            correspondent node to the mobile node. Triangle routing is alleviated by use of
            techniques in the route optimization draft, but doing so requires changes in the
            correspondent nodes that will take a long time to deploy for IPv4. It is hoped that triangle
            routing will not be a factor for IPv6 mobility.

                      Security issues.
                    A great deal of attention is being focused on making Mobile IP coexist with the
            security features coming into use within the Internet. Firewalls in particular, cause
            difficulty for Mobile IP because they block all classes of incoming packets that do not
            meet specified criteria. Enterprise firewalls are typically configured to block packets from
            entering via the Internet that appear to emanate from internal computers. Although this
            permits management of internal Internet nodes without great attention to security, it
            presents difficulties for mobile nodes wishing to communicate with other nodes within
            their home enterprise networks. Such communications, originating from the mobile node,
            carry the mobile node's home address, and would thus be blocked by the firewall.
                   Mobile IP can be viewed as a protocol for establishing secure tunnels. Gupta and
            Glass have proposed a firewall traversal solution. Efforts along these lines are also being
            made at BBN as part of the MOIPS (Managed Objects for IP Mobility Support) project to
            extend Mobile IP operation across firewalls, even when multiple security domains are

                    Ingress filtering.

                   Ingress Filtering involves routers dropping packets that do not have a source IP
            address consistent with the network address of the network it is being sent from. This
            presents a major problem to the operation of Mobile IP. As was described in above topic,                                                                                          Page 16
Mobile IP

            a mobile node attached to a foreign network sends packets using its home address as the
            packet source. Hence the packet source will have a different network prefix to the foreign
            network address. Routers in the foreign network that employ ingress filtering will drop
            this packet.
                    Complications are also presented by ingress filtering operations. Many border
            routers discard packets coming from within the enterprise if the packets do not contain a
            source IP address configured for one of the enterprise's internal networks. Because
            mobile nodes would otherwise use their home address as the source IP address of the
            packets they transmit, this presents difficulty. Solutions to this problem in Mobile IPv4
            typically involve tunneling outgoing packets from the care-of address, but then the
            difficulty is how to find a suitable target for the tunneled packet from the mobile node.
            The only universally agreed on possibility is the home agent, but that target introduces
            yet another serious routing anomaly for communications between the mobile node and
            the rest of the Internet. Montenegro has proposed the use of reverse tunnels to the home
            agent to counter the restriction imposed by ingress filtering. Mobile IPv6 also offers a
            solution in the home address destination option.

                    User perceptions of reliability.
                     The design of Mobile IP is founded on the premise that connections based on TCP
            should survive cell changes. However, opinion is not unanimous on the need for this
            feature. Many people believe that computer communications to laptop computers are
            sufficiently bursty that there is no need to increase the reliability of the connections
            supporting the communications. The analogy is made to fetching Web pages by selecting
            the appropriate URLs. If a transfer fails, people are used to trying again. This is
            tantamount to making the user responsible for the retransmission protocol and depends
            for its acceptability on a widespread perception that computers and the Internet cannot be
            trusted to do things right the first time. Naturally, such assumptions are strongly
            distasteful to many Internet protocol engineers, myself included. Nevertheless, the fact
            that products exhibiting this model are currently economically viable cannot be denied.
            Hopefully in the near future better engineering will counter this perception and increase
            the demand for Internet reliability.

                    Issues in IP addressing.

                    Mobile IP creates the perception that the mobile node is always attached to its
            home network. This forms the basis for the reachability of the mobile node at an IP
            address that can be conventionally associated with its fully qualified domain name
            (FQDN). If the FQDN is associated with one or more other IP addresses, perhaps
            dynamically, then those alternative IP addresses may deserve equal standing with the
            mobile node's home address. Moreover, it is possible that such an alternative IP address
            would offer a shorter routing path if, for instance, the address were apparently located on
            a physical link nearer to the mobile node's care-of address, or if the alternative address
            were the care-of address itself. Finally, many communications are short-lived and depend
            on neither the actual identity of the mobile node nor its FQDN, and thus do not take                                                                                         Page 17
Mobile IP

            advantage of the simplicity afforded by use of the mobile node's home address. These
            issues surrounding the mobile node's selection of an appropriate long-term (or not-so-
            long-term) address for use in establishing connections are complex and are far from being

                      Slow growth in the wireless LAN market.
                    Mobile IP has been engineered as a solution for wireless LAN location
            management and communications, but the wireless LAN market has been slow to
            develop. It is difficult to make general statements about the reasons for this slow
            development, but with the recent ratification of the IEEE 802.11 MAC protocol, wireless
            LANs may become more popular. Moreover, the bandwidth for wireless devices has been
            constantly improving, so that radio and infrared devices on the market today offer
            multimegabyte-per-second data rates. Faster wireless access over standardized MAC
            layers could be a major catalyst for growth of this market.

                    Competition from other protocols.
                    Mobile IP may well face competition from alternative tunneling protocols such as
            PPTP and L2TP. These other protocols, based on PPP, offer at least portability to mobile
            computers. Although I believe portable operation will ultimately not be a long-term
            solution, it may look quite attractive in the short term in the absence of full Mobile IP
            deployment. If these alternative methods are made widely available, it is unclear if the
            use of Mobile IP will be displaced or instead made more immediately desirable as people
            experience the convenience of mobile computing. In the future, it is also possible that
            Mobile IP could specify use of such alternative tunneling protocols to capitalize on their
            deployment on platforms that do not support IP-within-IP encapsulation.

                    Triangular Routing
                   Triangular routing is the situation where all traffic from the correspondent node to
            the mobile node is routed via the home agent. This method of routing increases the traffic
            on the network as the packets are first routed to the home agent and from here they are
            tunneled to the mobile node. In particular this increases the load on the home agent.                                                                                         Page 18
Mobile IP

                    Congestion

                   The Protocol Ipv4 is not the one which can accommodate and grow with the
               increasing number of users in the Mobile World. With its 32-bit addressing scheme
               there can be only 4 billion Mobile Devices which can be attached at a time. The
               Mobile devices grow with an average of 1000 per day only in India which of course is
               a large figure to suffice in the lesser device support by the Protocol. Thus the problem
               of congestion always happens during transmission. The core problem here is with
               clear hearing. You might have easily found transmission delays while you are talking
               which is in short the ratio of large devices using the same frequency with the fewer
               devices supported. As data is highly feed in the narrow channel bandwidth the delays
               and no signal issues arise within the network.

                    Current Development Efforts
                    Mobile IP has been studied in a number of wireless communication research
            projects. At the University of California at Berkeley, Mobile IP is being used to construct
            vertical handoffs between dissimilar media (for example, infrared, radio LANs, wide-area
            cellular, and satellite), depending upon error rates and bandwidth availability. Other
            factors such as cost and predictive service might also be taken into account. CMU's
            Monarch project has been the focus of investigation into campus wireless networks,
            Mobile IP, Mobile IPv6, and ad-hoc networking. Other academic efforts have been
            proceeding at the University of Portland, University of Alabama, University of Texas,
            UCLA, Macquarie University, SUNY Binghamton, University of Singapore, Swedish
            Royal Institute of Technology, and many others. Two books about Mobile IP have
            recently been published.                                                                                         Page 19
Mobile IP

                   9. CHANGES WITH IP VERSION 6
                    How will Mobile IP change when IP version 6 is adopted? IPv6 includes many
            features for streamlining mobility support that are missing in IP version 4 (current
            version), including Stateless Address Auto configuration and Neighbor Discovery. IPv6
            also attempts to drastically simplify the process of renumbering, which could be critical
            to the future rout ability of the Internet. Because the number of mobile computers
            accessing the Internet will likely increase, efficient support for mobility will make a
            decisive difference in the Internet's future performance. This, along with the growing
            importance of the Internet and the Web, indicates the need to pay attention to supporting
                   Mobility Support in IPv6, as proposed by the Mobile IP working group, follows
            the design for Mobile IPv4. It retains the ideas of a home network, home agent, and the
            use of encapsulation to deliver packets from the home network to the mobile node's
            current point of attachment. While discovery of a care-of address is still required, a
            mobile node can configure it’s a care-of address by using Stateless Address Auto
            configuration and Neighbor Discovery. Thus, foreign agents are not required to support
            mobility in IPv6. IPv6-within-IPv6 tunneling is also already specified.

               9.1     Route Optimization
                   Route optimization provides a means for any node to maintain a binding cache
            containing the care-of address of one or more mobile nodes. When sending an IP
            datagram to a mobile node, if the sender has a binding cache entry for the destination
            mobile node, it may tunnel the datagram directly to the care-of address indicated in the
            cached mobility binding.
                    In the absence of any binding cache entry, datagrams destined for a mobile node
            will be routed to a mobile node’s home network in the same way as any other IP
            datagram, and then tunneled to the mobile node’s current care-of address by the mobile
            node’s home agent. This is the only routing mechanism supported by the base Mobile IP
            protocol. As a side effect of this indirect routing of a datagram to a mobile node, it would
            be nice if the original sender of the datagram were informed of the mobile node’s current
            mobility binding, giving the sender an opportunity to cache the binding. In Figure 7., the
            Internet host is going to have to route each datagram for the mobile node indirectly,
            through its home agent. If the internet host had a binding cache entry for the mobile node,
            it would be able to send packets directly back to the mobile node without the services of
            the home agent.                                                                                          Page 20
Mobile IP

               Figure 7. Triangular Routing

               9.2 Security
                One of the biggest differences between IPv6 and IPv4 is that all IPv6 nodes are
            expected to implement strong authentication and encryption features to improve Internet
            security. This affords a major simplification for IPv6 mobility support, since all
            authentication procedures can be assumed to exist when needed and do not have to be
            specified in the Mobile IPv6 protocol. Even with the security features in IPv6, however,
            the current working group draft for IPv6 mobility support specifies the use of
            authentication procedures as infrequently as possible. The reasons for this are twofold.
            First, good authentication comes at the cost of performance and so should be required
            only occasionally. Second, questions about the availability of Internet-wide key
            management are far from resolved at this time.                                                                                      Page 21
Mobile IP

                9.3    Source Routing
                   In contrast to the way in which route optimization is specified in IPv4; in IPv6
            correspondent nodes do not tunnel packets to mobile nodes. Instead, they use IPv6
            routing headers, which implement a variation of IPv4's source routing option. A number
            of early proposals for supporting mobility in IPv4 specified a similar use of source
            routing options, but two main problems precluded their use:
               IPv4 source routing options require the receiver of source-routed packets to follow
                the reversed path to the sender back along the indicated intermediate nodes. This
                means that malicious nodes using source routes from remote locations within the
                Internet could impersonate other nodes, a problem exacerbated by the lack of
                authentication protocols.
               Existing routers exhibit terrible performance when handling source routes.
                Consequently, the results of deploying other protocols that use source routes have not
                been favorable.
            However, the objections to the use of source routes do not apply to IPv6, because IPv6's
            more careful specification eliminates the need for source-route reversal and lets routers
            ignore options that do not need their attention. Consequently, correspondent nodes can
            use routing headers without penalty. This allows the mobile node to easily determine
            when a correspondent node does not have the right care-of address. Packets delivered by
            encapsulation instead of by source routes in a routing header must have been sent by
            correspondent nodes that need to receive binding updates from the mobile node. It is a
            further point of contrast to route optimization in IPv4 that, in IPv6 mobility support, the
            mobile node delivers binding updates to correspondent nodes instead of to the home
            agent. In IPv6, key management between the mobile node and correspondent node is
            more likely to be available.
            Other features supported by IPv6 mobility include
             coexistence with Internet ingress filtering;
             smooth handoffs, which in Mobile IPv4 is specified for foreign agents as part of route
             renumbering of home networks; and Automatic home agent discovery.                                                                                         Page 22
Mobile IP

                   10. Improving the performance of handoff in mobile IP
            * Synopsis: Present implementations of mobile IP often fail to meet expectations of
            mobile applications when it comes to issues of packet loss and performance. We discuss
            various ways of moving closer to expectations.
                    The Internet suite of protocols (TCP/IP) assumes that the end-systems of an active
            networking session are stationary. If any of the end-points moves, the session breaks.
            This is a problem with mobile devices. Since redesigning the protocol suite is infeasible,
            the IETF mobile IP standard has taken the approach of providing additional support at the
            networking levels. Communication with a mobile device presents two conflicting
            a. To preserve active sessions, the device must retain its IP address.
            b. To route packets to a mobile device, its IP address should be dependent on its location.
            The IETF standard resolves this conflict by introducing multiple IP addresses for a
            mobile device. A mobile device retains its home address (see Note 1) irrespective of its
            Note 1. A mobile device (also called a mobile host) is identified by an IP address chosen
            from the address range of its starting network location, also called its home network. This
            address is called the home address of the mobile device.
            When the device is at the home network, packets can be delivered as usual. When the
            device moves to a foreign network (see Note 2) it acquires a care-of address (COA).
            Note 2. A network outside the home network of the mobile device is called a foreign
            network. Routing decisions are often made at the network level; thus, when a mobile host
            reaches a foreign network, there should a mechanism in place to forward packets meant
            for the mobile device from its home network to the foreign network. Packet redirection is
            accomplished using artifacts called home agents (HAs) and foreign agents (FAs; see Note
            Note 3. A home agent (HA) is a software module running on a host in the home network.
            The HA provides address translation so that a packet meant for a mobile device reaches
            its present point of attachment. The foreign agent (FA) is a software module running on a
            host in each foreign network that the mobile device needs to visit. There can be any
            number of foreign and home agents in a network. If there is any FA with which the
            mobile host has currently registered, the HA forwards the packet to this FA. Else it
            forwards the packet directly to the mobile device.
            The COA is either the address of a FA that can redirect packets to the device or the
            DHCP address of the device itself. The device registers with the HA and FA (if any) to
            ensure that packets are delivered to it at its new location. Unfortunately, these
            implementations suffer from poor performance during handoff. Suppose a mobile device
            moves from network A to network B. Packets sent to network A during this movement
            cannot be acknowledged by the device. This will be interpreted as packet loss due to
            congestion, and results in several problems including large retransmission intervals and
            reduced window size. Solutions involving hierarchical registration or multicasting have                                                                                         Page 23
Mobile IP

            often been used. Another solution is through active routers that intercept registration
            messages to update routing tables. Unfortunately, most real world networks lack support
            for these techniques. In yet another scheme packet are acknowledged and buffered at
            FAs. This eliminates the adverse effects that result from interpretation of
            unacknowledged packets as packet loss due to congestion. The obvious problem with this
            scheme is that it requires support for FAs. The performance problem is worse with
            implementations such as Mosquito Net, which do away with FAs altogether to make
            mobile IP usable on a wider set of networks. There is just one HA, in addition to mobile
            host (MH) software on the mobile device.
                    For such implementations, packet loss is significant as there is no entity to store
            the packets at network A as the device moves to B. The use of multicasting or active
            routers is also ruled out as these require special network support. How can we get
            reasonable performance with implementations such as Mosquito Net? One possible
            approach that we propose is to use smart buffering at the HA. In this scheme, the mobile
            device, in the process of moving from network A to B, initiates the process at the HA by
            sending it an ICMP request rather that a full-fledged registration message. The HA
            buffers unacknowledged packets sent to network A, as well as newly arriving packets.
            However, it forwards the packet only after the registration is complete. The HA adopts a
            small and accurate retransmission interval and normal window-size to avoid the problems
            discussed above arising due to misinterpreted congestion. This scheme requires changes
            only to the HA and MH, and hence can work with any foreign network. Smart buffering is
            best implemented in conjunction with a framework that dynamically discovers and
            leverages support for FAs, active routers, multicasting etc. in a given network, so that
            their performance advantages are realized. Designing such as architecture is of course an
            engineering challenge.                                                                                         Page 24
Mobile IP

                   11. CONCLUSION

                    As this brief introduction to mobile networking has shown, Mobile IP has great
            potential. Security needs are getting active attention and will benefit from the deployment
            efforts underway. Within the IETF, Mobile IP is likely to move from a proposed standard
            to a draft standard in the near future.
                    The IETF standardization process requires the working group to rigorously
            demonstrate interoperability among various independent implementations before the
            protocol can advance. FTP Software has hosted two interoperability testing sessions, and
            many vendors have taken advantage of the opportunity. Test results have given added
            confidence that the Mobile IP specification is sound, implementable, and of diverse
            interest throughout the Internet community. Only a few minor revisions have been
            needed to ensure the specification can be interpreted in only one way by the network
            protocol engineers and programmers who must implement it.
                    It is possible that the deployment pace of Mobile IP will track that of IPv6 or that
            the requirements for supporting mobility in IPv6 nodes will give additional impetus to the
            deployment of both IPv6 and mobile networking. The increased user convenience and the
            reduced need for application awareness of mobility can be a major driving force for
            adoption. Since both IPv6 and Mobile IP have little direct effect on the operating systems
            of mobile computers outside of the network layer of the protocol stack, application
            designers should find this to be an acceptable programming environment. Of course,
            everything depends heavily on the willingness of platform and router vendors to
            implement Mobile IP and/or IPv6, but indications are strong that most major vendors
            already have implementations either finished or underway.
                  The desire to improve the performance of mobile IP conflicts with the desire to
            use mobile IP on a wide set of networks. We have motivated one possible solution based
            on smart buffering and dynamic network service discovery.

                   12. References and Bibliography
            Mobile Computing – K.H.Wandra
            Data Communications and Networking – Behrouz Forouzen
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