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ABSTRACT
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 possible.
There are mainly three processes in 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 connections.
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.
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
begun.
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.
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.
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:
· Advertisement.
· Registration
· Tunneling
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 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) computers.
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.
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.
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.
With these operations in mind, a rough
outline of the operation of the Mobile IP protocol follows:
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 message.
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
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.
· MESSASGE FORMAT AND PROTCOL EXTENSIBILITY:
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 defined:
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)
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 extensions:
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.
5.
RELATIONSHIP OF THE COMPONENTS OF 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 network.)
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
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 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.
Figure 5. Packet
Forwarding
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.
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.
8. ONGOING WORK AND OPEN QUESTIONS
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 involved.
·
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, 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 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 resolved.
·
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.
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.
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.
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.
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.
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 optimization;
·
renumbering of home networks;
and Automatic home agent discovery.
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 demands:
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 location.
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 3).
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
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.
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.
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