lec6 mobile ip - wireless and mobile networking laboratorywmnlab.ee.ntu.edu.tw/951cross/lec6 mobile...

Lecture 6: Mobile IPLecture 6: Mobile IP

Hung-Yu WeiNational Taiwan University

2

Network Layer (LayerNetwork Layer (Layer--3)3)• Routing

– Important issue in “mobile” network• IP-based network solution

– IP dominates the networking world!• Mobile network routing

– Mobility management protocols• Global mobility management protocols

– Mobile IP• Local mobility management protocols

– Cellular IP, HAWAII– Ad hoc network routing protocols

• AODV, DSR, OLSR, DSDV…etc

3

IPIP--based Mobilitybased Mobility• Mobile IP

– IETF (www.ietf.org) Internet Engineering Task Force • Mobile IP working group

– RFCs (Request for Comments)

– Mobile IPv4• RFC 3344

– Mobile IPv6• RFC 3775

4

What is Mobile IP?What is Mobile IP?• Basic Mobile IP protocol

– Advertisement– Registration– Tunneling datagrams

• Extensions– Route optimizations– Movement detection issues

• Support protocols– DHCP, AAA, micro-mobility

5

The IP Addressing ProblemThe IP Addressing Problem

• IP address address allocation and administration have historically assumed that there is a close relationship between a computer’s IP address and its physical location

6

IP Address StructureIP Address Structure• Routing prefix

– defines the network on which the address resides

– often determined the netmask– usually subnet prefix

• Host number– fits in the least significant remaining bits of

the IP address following the routing prefix

Routing prefix Host number

32 bits

7

IP Subnet Model vs. MobilityIP Subnet Model vs. Mobility

Router

132.4.16

…2 …3

Router128.8.128

128.8.128.Y132.4.16.Z

Internet

8

The Transport ProblemThe Transport Problem• TCP uses ports and the IP addresses of the

network endpoints to identify a communication channel used for data transfer

SHfloss.watson.ibm.com

MHtapti.cs.umd.edu

9

Problems with Dual use of IP AddressesProblems with Dual use of IP Addresses• Applications use IP addresses

– to identify routes by which datagrams my be exchanged between two network nodes

• Applications use IP addresses– to identify the endpoints themselves

• Dual usage – causes problems when trying to uses

applications (e.g., TCP) when changing the hosts point of attachment

10

SolutionSolution• We observe that

– Applications need an unchanging way to identify the network endpoints

– Routes between the endpoints must change as they move

• Mobile IP solves this issue– by maintaining two addresses; one for each of

the dual usage• Identification• Routing

– one IP address is used to “locate” the mobile host

– the other IP address for “identifying” a communications endpoint on the mobile host

11

““LocatingLocating”” and and ““IdentifyingIdentifying””: : twotwo--tier addressing for mobile nodestier addressing for mobile nodes

Router

132.4.16

…2 …3

Router 128.8.128

128.8.128.Y

132.4.16.Z

Internet

FOO

128.8.128.X

128 8 128 Y 132 4 16 ZFOO

Topologically Significant Address Static Address

12

Concept: home network and foreign Concept: home network and foreign networknetwork

• Home network– Home address: home network should have the

same prefix for mobile nodes’ home addresses• Foreign network

– A network that is not home network• Mobility agents

– Agents that handle IP-mobility• Home Agent• Foreign Agent

13

Mobility Management ModelMobility Management Model• Home network

– datagrams are routed toward the home address– source nodes is unaware of whether the destination is mobile

or not; it simply sends to the home address• Care-of-address (CoA)

– address used to locate the mobile host’s current position– if mobile host is away from home then packets can only be

delivered using Internet routing based on position in the infrastructure

– “readdressing” is the operation used to change the destination address (home address) to the care-of-address

14

Abstract ModelAbstract Model• Two mapping functions

– f(home address) (forwarding address)– g(forwarding address) (home address)

• Readdressing (f) at the home network– associating (in the location directory - LD) the home address and

the care-of-address of the mobile host and maintaining up to date values for this association

– delivering the datagram to the care-of-address• Inverting (g) the readdressing operation once the

datagram arrives at the care-of-address

f gInternetRouting

LD

Source Destination

15

Remote Redirection IssuesRemote Redirection Issues• Updating LD raises a number of technical

challenges– the mobile host should drive this update– need security, authentication of control

messages to eliminate well known problems of malicious location updates

16

IETF Mobile IPIETF Mobile IP• The exact ways in which the f, g and LD

functions are located in various nodes and networks distinguishes the various approaches

Mobile Host 2Source

f

LDHome Agent

Mobile Host 1

g

g

Home Network

S

Foreign Agent

Mobile Host, Using DHCP

17

Basic Mobile IP Basic Mobile IP • Operations

– advertisement, registration, tunneling • Mobile host• Home agent

– is a router that tunnels datagarms to a mobile node when it is away from its home network and maintains current location information

• Foreign agent– is a router on the visited network that provides

routing services to the mobile node while registered. Detunnels datagrams

18

Agent DiscoveryAgent Discovery• Agent discovery

– home agent and foreign agents may advertise their availability on each link for which they provide services

– a newly arrived mobile node can send a solicitation on the link to learn if any prospective agents are present

19

Mobile IPMobile IP

HA

Subnet C

FA C

Mobile Node

Subnet B

FA FA

HA

Global Internet

Subnet D

(Home agent for a virtual home network)

HA = home agent

FA = foreign agent

Mobile Nodes

20

Registration Registration • Registration

– when the mobile node is away from home, it registers its care of address with its home agent

– depending on its method of attachment, the mobile node will register either directly with its home agent or though a foreign agent, which forwards the registration to the home agent

21

Registration Registration

FA

FA

FA

FA

FA

MHMHrequestsservice

FA relaysstatus to MH

MH

HAFA relaysrequest to HA

HAHA acceptsor denies

FA = foreign agentMH = mobile hostHA = home agent

FAadvertisesservice

22

TunnelingTunneling• Tunneling datagrams

– in order for datagrams to be delivered to the mobile node when it is away from home, the home agent has to tunnel the datagram to the care-of-address

23

DatagramDatagram

Home agent Foreign agent Mobile node

IP host

GlobalInternet

2

14

3

24

Getting a careGetting a care--ofof--address (COA)address (COA)• Two ways to acquire a care-of-address

(COA)– a foreign agent COA is a COA provided by the

foreign agent through its agent advertisement messages

• many modes can use a single FA COA– a colocated COA is a COA acquired by the

mobile node as a local IP address through some external means, which the mobile node then associates with its own network - the address may be dynamic, e.g., DHCP

• only a single mobile can use this address

25

Protocol Operations Protocol Operations • Mobility agent (foreign and home agents)

advertise their presence via agent advertisement messages

• A mobile may optionally solicit an agent advertisement message from any local mobility agent by using an agent solicitation message

• A mobile node receives an agent advertisement and determines whether it is on its home network or a foreign network

• When the mobile detects that it is located on its home network, it operates without mobility services.

26

Protocol OperationsProtocol Operations• If returning to its home network from being

registered elsewhere, the mobile node degregisters with its home agent through a variation of the normal registration process

• When MN detects that it has moved to a foreign network– MN obtains a care-of-address on the foreign network.

• The COA can either be a foreign agent COA• Or a co-located COA

• MN then registers its new COA with its home agent through the – exchange of registration request and registration reply

messages (might through FA or not)

27

Protocol OperationsProtocol Operations• 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 COA, received at the tunnel endpoint (either at the foreign agent or at the mobile node itself) and finally delivered to the mobile node.

• In the reverse direction, datagram sent by the mobile node may be delivered to their destination using standard IP routing mechanisms, without the necessarily passing through the home agent

28

Protocol ExtensionsProtocol Extensions• Mobile IP defines a set of new control

messages sent with UDP (using well-known port number 434)– registration request – registration reply

• For agent discovery, Mobile IP modifies the existing “router advertisement” and “router solicitation” messages defined for ICMP (Internet Control Message Protocol)

AdvertisementAdvertisement

30

AdvertisementAdvertisement• Agent discovery is the method by which a mobile

host– determines whether it is currently connected to its

home network or a foreign network; and– detects when it has moved from one network to

another• Agent solicitation and discovery mechanisms• Router discovery protocol• Agent advertisement• Agent solicitation• Agent discovery by mobile nodes

31

Router Discovery ProtocolRouter Discovery Protocol• Router discovery

– provides the means by which IP hosts can determine automatically the local router’s IP address and monitor their continued presence

• This is done by using two simple ICMP messages– one transmitted by the routers and another that may

be transmitted by the hosts themselves• Historical choice of using this protocol for agent

discovery that may have been a poor choice with hindsight

32

Router DiscoveryRouter Discovery• Router advertisements

– are periodically multicast or broadcast to those links that the router is connected with which it wishes to offer routing services to

• Hosts listen to the advertisements and select a router address

• The speed at which a host can select a default router is determined by the advertisement period

33

Router Advertisement MessageRouter Advertisement Message

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2

type code checksum

num addrs addr entry size lifetime

preference level (1)

router address (1)

34

Router Solicitation (MH initiated)Router Solicitation (MH initiated)• When an IP host needs timely information

about local default routers, it can multicast or broadcast a router solicitation message– Any router in the vicinity will respond with a

unicast router advertisement sent directly to the soliciting host

– After receiving the advertisement the host then responds just as if the advertisement were unsolicited

35

Router Solicitation MessageRouter Solicitation Message

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2

type code checksum

reserved

36

Agent AdvertisementAgent Advertisement• An agent advertisement is an ICMP router

advertisement that has been extended to also carry mobility advertisements extensions– A mobility agent transmits agent

advertisements to advertise its service on a link

– Mobile hosts use these advertisements to determine their current point of attachment to the Internet

37

Agent AdvertisementAgent Advertisement• Within an agent advertisement, ICMP

router advertisement include the following link-layer, IP and ICMP header information

• Link-layer – destination address

• IP fields– TTL, destination address

• ICMP fields– type (9), code (0 and 16), lifetime, router

addresses, number of addresses

38

Agent Advertisement ExtensionAgent Advertisement Extension

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2

type length sequence number

registration lifetime R B H F M G V reservedzero or more care-of address

39

Important FieldsImportant Fields• R (registration required)

– registration with the FA is required rather than collocated care-of address

• B (busy)– if this bit is set the FA will not accept any

registrations from additional mobile hosts• H (home agent)

– if this bit is set the agent offers home agent services on the link which the advertisement is sent

40

Important FieldsImportant Fields• F (foreign agent)

– this agent offers service as a foreign agent on the link on which the advertisement if sent

• M (minimal encapsulation)• G (generic record encapsulation)• V (VJ header compression)• care-of addresses (COA)

– the advertised FA care-of address provided by the FA. Must include at least one COA if the F bit is set. More than one COA can be advertised

41

Agent SolicitationAgent Solicitation• The format of the agent solicitation is the same

as the ICMP router solicitation. Agent solicitation do, however, always set the TTL to one.

• Advertisements only need to be sent when the site policy requires registration with the agent (R-bit is set) or as a response to a specific agent solicitation

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2

type code checksum

reserved

42

Mobile Agent OperationsMobile Agent Operations• A mobility agent should limit the rate of sending

agent advertisements. – recommended maximal rate = 1/second.

• A FA must accept router solicitations even when the IP source address appears to reside on a different subnet

• A mobility agent “may” be configured to send agent advertisements only in response to an agent solicitation

43

Agent Discovery by Mobile NodesAgent Discovery by Mobile Nodes• Agent solicitations should only be sent in the

absence of agent advertisements and when the care-of address can not be determined through a link-layer protocol or other means

• Operational differences to the router solicitation– mobile nodes may solicit more often than once every

three – mobile node that is currently not connected to any FA

may solicit more times than currently configured.

44

Limiting Signaling OverheadLimiting Signaling Overhead• MN should limit the rate at which its sends

solicitations. – 3 initial solicitations at the max rate(1/second) while

searching for an agent.– Subsequent solicitations are required to be sent using

a binary exponential backoff mechanism up to a maximal interval (one minute).

• While searching for an agent the mobile node is not allowed to increase the rate at which it sends solicitations unless it knows it has moved to a new link

45

Agent DiscoveryAgent Discovery• Mobile nodes process agent advertisements to

discover a care-of address and FA. This is to for the registration phase

• Foreign networks can enforce visiting policy. – E.g Set R bit in agent advertisements

• Force mobile nodes to register with FA( when when the mobile might be able to acquire its own COA.)

• Detect returning to home network– MN receives an agent advertisement from its own home

agent

46

DrawbacksDrawbacks• Piggybacking the agent discovery scheme on the

existing route advertisement method is restrictive– E.g. suppose a mobile node makes a cell switch. To

detect the movement at the network layer the mobile node has to hear a mobility agent advertisement

– If the mobile node has to wait three seconds to discover that its previous FA is out of reach and unacceptable response time is observed

• Worse performance can be experienced if multiple advertisements are lost before initiating handoff

Mobile IP Registration and Mobile IP Registration and TunnelingTunneling

48

Mobile IP MechanismsMobile IP Mechanisms• Advertisement• Registration• Tunneling datagrams

49

Mobile IP RegistrationMobile IP Registration

Mobile Host

FAMH = mobile host

HA = home agent

FA = foreign agent

Mobile Host

FA

FA

FA

FA

MH requests service

FA relays status to

MH

HA

HA Tim

e

FA advertises

service

HA accepts or denies

MH requests service

50

OperationsOperations• Request forwarding services when visiting a

foreign network• Inform their home agent of their current

care-of address• Renew a binding that is due to expire• Deregister when they return home

51

RegistrationRegistration• Registration messages exchange the mobile

node’s current binding information among a mobile node (possibly a FA) and its home network

• Registration creates or modifies a mobility binding at the home agent, associating the mobile node’s home address with its COA for a certain length of time called the registration lifetime

52

Movement DetectionMovement Detection• Important issue for handoff performance• How does the mobile device know its moved to a

new cell?– Handoff initiation (criteria and procedures)

• When the mobile node determines that it has moved it should register with a suitable care-of address (COA) on the new foreign network

• Limitations: can’t register more that once per-second on average– Mobile IP is designed to support mobility with handoff

rate less than once per second• Mobile IP supports three types of movement

detection schemes– Room for improvement research in fast handoff

53

Lazy Cell SwitchingLazy Cell Switching• Lazy Cell Switching

– MH waits to hear new agent advertisement based on the lifetime timeout. If it receives one then it knows its still taking to the current BS

– If advertisements are missed then it attempts to register with a possibly new cell using agent solicitation.

– MHs typically try to receive two or more advertisements before expiring any advertisement before attempting to find a new foreign agent (FA)

54

Prefix MatchingPrefix Matching• MH uses the “prefix extension” to

determine whether a newly received agent advertisement is from the same subnet– If the prefix is different it knows its

connected to a new cell and registers

• Downside: the prefix-extension in agent advertisements is optional

55

Eagar Cell SwitchingEagar Cell Switching• Based on the mobile host hearing beacons

from multiple FAs simultaneously. Also make some assumptions about mobility patterns which may not hold – traveling in a straight line.– Maintains list of FAs and their COAs; and the

current FA/COA– Once the current FA is no longer available (e.g.,

because the mobile has moved) then it selects a new one form this list

• Faster than Lazy Cell Switching but makes a number of assumptions

56

Movement Detection without FAsMovement Detection without FAs• All the schemes depend on FA

advertisements – what happens when there are no FAs?– The collocated COA is invalid once a mobile

host has moved• No good solution

– try to detect a lack of traffic but that may not indicate movement to a new cell

57

UDP Registration MessagingUDP Registration Messaging• Mobile IP registration messages use UDP.

– Mobile IP reg. does not need TCP (no need for congestion control and flow control)

IP header fields UDP header Mobile IP message header Extensions …

58

AuthenticationAuthentication• Each mobile node, FA and HA is required to be

able to support a mobility security association for mobile entities indexed by their security parameter index (SPI)

• Registration messages between a mobile node and its HA are required to be authenticated with the “mobile-home” authentication extension

• Replay protection is accomplished by using different values in each registration message to stop malicious users snooping the registration process and effectively replaying authenticated registration

59

RegistrationRegistration• Registration messages exchange the mobile

node’s current binding information among a mobile node (possibly a FA) and its home network

• Registration creates or modifies a mobility binding at the home agent, associating the mobile node’s home address with its COA for a certain length of time called the registration lifetime

60

Registration RequestRegistration Request

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

home address

care-of address

home agent

type S B D MG V rsv lifetime

identification

extensions …

61

Registration Request FieldsRegistration Request Fields• IP fields

– source address interface address– destination FA or HA

• UDP fields– source and destination ports

• Mobile IP fields– S simultaneous bindings.

• By setting the S-bit, the mobile node is requesting that the home agent retain its prior mobility bindings

62

Registration Request FieldsRegistration Request Fields• B broadcast datagram.

– By setting the B bit the mobile node is requesting that the home agent tunnel any packets broadcast on the home network

• D decapsulation. – By setting the D bit, the mobile node informs

the home agent that it will decapsulate datagrams that are sent to the COA. In this case the mobile node is using a collocated C OA

63

Registration Request FieldsRegistration Request Fields• Lifetime

– the number of seconds remaining before the registration is considered expired

• Home address• Home agent• COA

• The IP address for the end of the tunnel• Identification

– 64 bits used to match reg. Request and replay pairs and to solve the playback problem

64

Registration ReplyRegistration Reply• The HA can update some of the information

in the registration request• The FA is not allowed to modify the

lifetime selected by the mobile node in the registration request because the lifetime is covered by the “mobile-home”authentication extension

• Home agent can reduce the lifetime value

65

Registration ReplyRegistration Reply

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

home address

care-of address

home agent

type code lifetime

identification

extensions …

66

Registration Reply FieldsRegistration Reply Fields• IP Fields

– source address • typically copied from the destination address of the

registration request to which the agent is replying– destination address

• source address of the registration request• UDP Fields

– source port – destination port copied from the source port

67

Registration Reply FieldsRegistration Reply Fields• Type 3 (registration reply)• Code value indicating the result of reg. Request• Lifetime duration for which the binding is valid• Home address• Home agent• Identification

68

Return CodeReturn Code• Registration OK

– accepted– accepted but simultaneous binding not

supported• Registration denied by FA

– reasons unspecified– insufficient resources– mobile node failed authentication– requested encapsulation failed– home network unavailable

69

Registration Denied by the HARegistration Denied by the HA• Insufficient resources• mobile node failed authentication• FA failed authentication• Registration ID mismatch• Too many simultaneous bindings

70

Registration ExtensionsRegistration Extensions• There are three registration extensions

defined for Mobile IP all of which are associated with security to be applied to the registration process– Mobile-home authentication extension– Mobile-foreign authentication extension– Foreign-home authentication extension

• Each extension includes the SPI that indicates the mobility association that contains the secret and other information needed to compute the authenticator

71

Mobile Node Registration StateMobile Node Registration State• State maintained for each pending

registration– link layer address of the FA to which the

registration request was sent– IP destination address of the registration

request– COA used in registration– Original lifetime– Remaining lifetime of the pending registration

72

FA Registration StateFA Registration State• Link layer source address of the mobile

node• IP source address (the mobile node’s home

address)• IP destination address• UDP source port• Home agent address• Identification field• Request registration lifetime• Remaining lifetime of the pending or

current registration

73

HA Registration StateHA Registration State• The home agent is required to be

configured with the home address and mobility security association of each of its authorized mobile nodes

• When a registration request is accepted the HA creates or modifies the entry for the mobile in its mobility binding list– mobile nodes COA– Identification field from the registration reply– remaining lifetime of the registration

• The HA also maintains security associations with various FAs

74

Registering SecurelyRegistering Securely• HA and mobile nodes are required to be

able to perform authentication – Default algorithm: 128-bit MD5– The tunneling feature could be significantly

vulnerable if the registration were not authenticated

– Key management– Replay protection for registration requests

75

Example ScenariosExample Scenarios• Configuration

– mobile nodes home address 129.34.78.5– mobile node’s home agent 129.34.78.254– FA wireless address 137.0.0.11– FA COA 9.2.20.11– DHCP COA 9.2.43.94– mobile node’s source port 1094– FA source port 1105– COA reg. Lifetime 60,000 secs– HA granted lifetime 35,000 secs

76

Registration via a FARegistration via a FAIP header fields ICMP header Router Adv. fields Mobile Service Extension

Agent Advertisement

S = 137.0.0.11 type = 9 …… lifetime = 60,000D = 255.255.255.255 code = 16 COA = 9.2.20.11TTl = 1

IP header fields UDP header Mobile IP message fields Authentication ExtensionMobile Foreign

S = 129.34.78.5 S = 1094 type = 1 SPI = 302D = 137.0.0.11 D = 434 lifetime = 60,000TTL = 1 COA = 9.2.20.11

HA = 129.34.78.254MA = 129.34.78.5

IP header fields UDP header Mobile IP message fields Authentication ExtensionForeign Home


HA = 129.34.78.254MA = 129.34.78.5

IP header fields UDP header Mobile IP message fields Authentication ExtensionHome Foreign

S = 129.34.78.254 S = 434 type = 3 SPI = 303D = 9.2.20.11 D = 1105 lifetime = 35,000TTL = 64 HA = 129.34.78.254

MA = 129.34.78.5

IP header fields UDP header Mobile IP message fields Authentication ExtensionForeign Mobile

S = 137.0.0.11 S = 434 type = 3 SPI = 303D = 120.34.78.5 D = 1094 lifetime = 35,000TTL = 1 HA = 129.34.78.254

MA = 129.34.78.5

77

Registering with a Collocated Registering with a Collocated COACOA

IP header fields UDP header Mobile IP message fields Authentication Extension

Home Mobile Registration Reply


HA = 129.34.78.254MA = 129.34.78.5


Mobile Home Registration Request


HA = 129.34.78.254MA = 129.34.78.5D, M, G, B = 1, 1, 1, 1

78

Deregistering at the Home NetDeregistering at the Home Net


Mobile Home

S = 129.34.78.5 S = 1094 type = 1 SPI = 302D = 129.34.78.254 D = 434 lifetime = 0TTL = 1 COA = 129.34.78.5

HA = 129.34.78.254MA = 129.34.78.5


Home Mobile

S = 129.34.78.254 S = 434 type = 3 SPI = 303D = 129.34.78.5 D = 1094 lifetime = 0TTL = 1 COA = 129.34.78.5

HA = 129.34.78.254MA = 129.34.78.5

IP header fields ICMP header Router Adv. fields Mobile Service Extension

Agent Advertisement

S = 129.34.78.254 type = 9 …… … no COAs …D = 255.255.255.255 code = 16 lifetime = 35,000H = 1

79

TunnelingTunneling

80

What is Tunneling ?What is Tunneling ?

Encapsulation Decapsulation

Source Destination

81

Encapsulation ProcessEncapsulation Process• The original IP header is modified

– protocol field in IP header is replaced by the number 55 for min encapsulation protocol

– the dest. Address field in the IP header is replaced by the IP address of the exit point of the tunnel

– if the encapsulator is not the original source of the datagram, the source address field in the IP header is replaced by the IP address of the encapsulator

82

Encapsulation Process ContEncapsulation Process Cont’’dd• The original IP header is modified

– the total length field in the IP header is incremented by the size of the minimal forwarding header added to the datagram

– the header checksum field in the IP header is recomputed or updated to account for the change in the IP header

83

IPIP--inin--IPIP

Original IP header Inner IP header Original IP Payload

Other Headers (Optional)

Original IP header Original IP Payload

Tunnel Endpoints

84

Minimal EncapsulationMinimal Encapsulation



Tunnel Endpoints Destination IP

Address

Minimal encapsulated header

85

Minimal Encapsulation Minimal Encapsulation Header FormatHeader Format

original destination address

(if present) original source address

protocol S reserved header checksum

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

(optional) S-bit=1 if “original source address” is presented

86

Generic EncapsulationGeneric Encapsulation

key (optional)

rsv Protocol type

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

RKC S s recur ver

Checksum (optional) offset (optional)

sequence number (optional)

routing (optional)

Delivery Header GRE Header Packet Payload

87

Routing FailureRouting Failure• Common

– Destination unreachable– Source quench– Redirect– Time exceeded

88

Tunnel ManagementTunnel Management• Tunnel soft state

– MTU size– TTL– Ability to reach the end of the tunnel

• ICMP errors– datagram too big– time exceeded– destination unreachable– source quench

89

Broadcast DatagramsBroadcast Datagrams• Colocated COA

• FA COA

IP Destination = Care-of Address Broadcast IP Datagram

Broadcast IP DatagramIP Destination = Care-of Address IP Destination = Mobile Host

90

ARPARP• Address Resolution Protocol• ARP protocol maps IP address to link-layer

address– Request/Reply

91

Gratuitous ARP by Home AgentGratuitous ARP by Home Agent

ARP Reply : Z_IP Z_MAC

HomeAgent X Y

Router

Z

ARP Reply : Z_IP HA_MAC

HomeAgent X Y

Router

(a)

(b) Gratuitous ARP to update X,Y’s ARP cache

Proxy ARP to reply ARP request

92

ARP operation: MN leaves homeARP operation: MN leaves home1. MN is away from home and decides to register

with FA– Movement detection

2. Before MN transmits registration request, MN disables its ARP processing

3. MN transmits registration request4. After HA receives and accept registration

request– HA performs gratuitous ARP on behalf of MN– Afterwards, HA uses proxy ARP to relay ARP

requests (which requesting MN’s link address)

93

ARP operation: MN returns homeARP operation: MN returns home1. MN decides to deregister its CoA2. Before MN transmits registration request, MN

enables its future ARP processing3. MN performs gratuitous ARP4. MN transmits registration request5. After HA receives and accept registration

request• HA performs gratuitous ARP on behalf of MN

• Both MN and HA perform gratuitous ARP to make sure that wireless nodes receive the message

• HA stops proxy ARP operation

Other Mobile IP schemesOther Mobile IP schemes

95

IETF Mobile IPIETF Mobile IP• The exact ways in which the f, g and LD

functions are located in various nodes and networks distinguishes the various approaches

Mobile Host 2Source

f

LDHome Agent

Mobile Host 1

g

g

Home Network

S

Foreign Agent


96

Mobile IP with Route OptimizationMobile IP with Route Optimization

Mobile Host 2Source

f

LDHome Agent

Mobile Host 1

g

g

Home Network

S

Foreign Agent


f

Cache

97

Mobile IPv6Mobile IPv6

Mobile Host

Source

f

LDHome Agent

Home Network

S f

Cache

encapsulation

When LD cache entry is not available

98

Columbia Mobile IPColumbia Mobile IP

Source

f g

LD

S

cache

MSR

f g

LD

cache

MSR

f g

LD

cache

MSR

MH

Campus Network

MSR (mobile support routers)

J. Ioannidis et al, ACM Sigcomm 1991

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