NIJO JOB

CS-B S7

54

ACN Seminar Mobile IP

Mobile IP- Mobile IP is a standard that allows users to move from one network

to another without loosing connectivity.

- It is a modification to IP that allows nodes to continue to receive

datagrams no matter where they happen to be attached to the

Internet

- The network is updated with the new location every time the user

changes the computer's point of attachment to the Internet.

- Mobile IP basically adds mobility support to the Internet network

layer protocol IP.

RequirementsCompactability:- A new standard cannot introduce changes for

applications or network protocols already in use. Mobile IP has to

remain compatible with all lower layers used for the standard, non-

mobile, IP. End-systems enhanced with a mobile IP implementation

should still be able to communicate with fixed systems without

mobile IP. Mobile IP has to ensure that users can still access all the

other servers and systems in the internet using the same address

format and routing mechanisms.

RequirementsTransparency:- Mobility should remain ‘invisible’ for many higher

layer protocols and applications. Besides maybe noticing a lower

bandwidth and some interruption in service, higher layers should

continue to work even if the mobile computer has changed its point

of attachment to the network. Many of today’s applications have not

been designed for use in mobile environments, so the only effects of

mobility should be a higher delay and lower bandwidth. However,

there are some applications for which it is better to be ‘mobility

aware’. Examples are cost-based routing or video compression.

RequirementsScalability and efficiency:- Introducing a new mechanism to the

internet must not jeopardize its efficiency. Enhancing IP for mobility

must not generate too many new messages flooding the whole

network. Also, it is crucial for a mobile IP to be scalable over a large

number of participants in the whole internet, worldwide.

Security:- The minimum requirement is that of all the messages

related to the management of Mobile IP are authenticated. The IP

layer must be sure that if it forwards a packet to a mobile host that

this host receives the packet.

Terminologies

Mobile node:- A mobile node is an end-system or router that can

change its point of attachment to the internet using mobile IP.

Home network:- The home network of a mobile device is the

network within which the device receives its identifying IP address.

Correspondent node:- At least one partner is needed for

communication. The CN can be a fixed or mobile node.

Home address:- The home address of a mobile device is the IP

address assigned to the device within its home network.

Foreign network:- A foreign network is the network in which a mobile

node is operating when away from its home network.

Terminologies

Care-of address:- The care-of address of a mobile device is the

network-native IP address of the device when operating in a foreign

network.

Home agent:- A home agent is a router on a mobile node’s home

network which tunnels datagrams for delivery to the mobile node

when it is away from home. It maintains current location information

for the mobile node. It is used with one or more foreign agents.

Foreign agent:- A foreign agent is a router that stores information

about mobile nodes visiting its network. Foreign agents also

advertise care-of-addresses which are used by Mobile IP.

Agent DiscoveryA mobile node discovers its foreign agents and home agents during

agent discovery.

In mobile IP, both a foreign agent and a home agent periodically

broadcast agent advertisement messages.

A mobile host must discover(learn the address of) a home agent

before it leaves the home agent.

A mobile host must also discover a foreign agent after it moved to a

foreign network.

It allows mobile nodes to discover foreign agents and get care-of

addresses, to know the services provided by the foreign agent and to

determine whether an agent is its home agent or a foreign agent

When an mobile host has moved to a new network and has not

received agent advertisements,it can initiate an agent solicitation.

A mobile node can generate agent solicitation messages when it is

looking for a foreign agent.

Agent Solicitation

When a mobile node receives a care-of address from a foreign

agent, its home agent needs to be informed.

The mobile node sends a registration request to its home agent

through the foreign agent who has provided the new care-of

address.

When the home agent receives the request, it updates its routing

table and sends a registration reply back to the foreign agent.

Registration

The transfer of the packet from the home agent to the care-of

address is called tunnelling

The home agent is the source of the tunnel. The home agent inserts

a new tunnel header in front of the IP header of a packet addressed

to the mobile agent and received by the home agent

The tunnel header is the care-of IP address of the mobile node. The

old header is preserved as it was in the original packet.

The foreign agent is the receiver of the tunnel

When the foreign agent receives the tunnelled packet, it has to

delete the tunnel header to recover the original packet.

The foreign agent delivers the packet to the mobile node after

removing the tunnel header

Tunnelling

When a remote host wants to send a packet to the mobile host, it

uses its address as the source address and the home address of

the mobile host as the destination address .

After receiving the packet, the home agent sends the packet to the

foreign agent . The home agent encapsulates the whole IP packet

inside another IP packet using its address as the source and the

foreign agent’s as the destination address.

When the foreign agent receives the packet, it removes the original

packet. Since, the destination address is the home address of the

mobile host, the foreign agent consults a registry table to find the

CAO.

Data Transfer

•13

(current physical network

•for the MN)

•home network

•(physical home network

•for the MN)

•Internet

•router

•HA

•MN

•router

•FA foreign

•network

•router•end-system

•CN

Sample network

•14

•TunnelingData transfer to the mobile system

•Internet•home network

•foreign

•network•FA

•HA

•MN

•receiver

•1

•2

•3

•sender

•CN

•1. Sender sends to the IP address of MN,

• HA intercepts packet

•2. HA tunnels packet to COA, here FA,

• by encapsulation

•3. FA forwards the packet to the MN

•15

•foreign

•network

•home network

Data transfer from the mobile system

•Internet

•HA

•MN

•sender

•receiver

•CN

•1. Sender sends to the IP address

• of the receiver as usual,

• FA works as default router

•FA

•1

•Tunneling

Optimization

An inefficient behavior of a non-optimized mobile IP is called

triangular routing. The triangle is made of the three segments, CN

to HA, HA to COA/MN, and MN back to CN.

The current location of the MN is informed to CN. The CN can learn

the location by caching it in a binding cache which is a part of the

local routing table for the CN.

- Binding request: Any node that wants to know the current location

of an MN can send a binding request to the HA.

- Binding update: This message sent by the HA to CNs reveals the

current location of an MN.

- Binding acknowledgement: If requested, a node returns this

acknowledgement after receiving a binding update message.

- Binding warning: If a node decapsulates a packet for an MN, but it

is not the current FA for this MN, this node sends a binding warning.

Optimization

Reverse Tunneling

The return path from the MN to the CN looks quite simple. The MN

can directly send its packets to the CN as in any other standard IP

situation. The destination address in the packets is that of CN.

Quite often firewalls only allow packets with topologically correct

addresses to pass. However, MN still sends packets with its fixed IP

address as source which is not topologically correct in a foreign

network. Firewalls often filter packets coming from outside

containing a source address from computers of the internal network.

•19

Reverse Tunneling

•Internet

•receiver

•FA

•HA

•MN

•home network

•foreign

•network

•sender

•3

•2

•1

•1. MN sends to FA

•2. FA tunnels packets to HA

• by encapsulation

•3. HA forwards the packet to the

• receiver (standard case)

•CN

THANK YOU