MN Lec 9 Mobile IP

8/13/2019 MN Lec 9 Mobile IP

1/48

Mobile IP

Lec#9


2/48

Lecture Objectives

Present the basic principles of addressing in IPnetworks

Describe the problem of mobility with IP andconsider alternative solutions

Describe the operation of Mobile IP


3/48

Agenda

IP addressing Node mobility and IP Mobile IP

o Foreign agent discoveryo Home agent registrationo Packet delivery through tunnelingo Route optimization


4/48

IP Addressing

IPv4 addresseso Uniquely identify an interfaceo 32 bits longo Consist of a network identifier and a host identifier

Routing outside of the destination hosts subnet isusually based on the network identifier, while thehost identifier is only used within the destinationssubnet

IPv6 uses 128-bit addresses

Network Identifier Host Identifier

0 31


5/48

Five Classes of IP Addresses

IP addressing was originally based on five classes ofaddresseso A router can interpret the network and host fields by

examining the first few bits of the IP address

Class B 1 0 netid hostid

Class C 1 1 0 hostidnetid

Class D 1 1 1 0 multicast address

Class E 1 1 1 1 reserved for future use

Class A 0 netid0 1 2 3 4 8

16

24

31

hostid


6/48

CIDR

Classless Inter-Domain Routing (CIDR) wasintroduced to remedy problems with the rigidclasses of IP addresseso Defined in RFCs 1517-1520

Generalize the notion of subnet addressing Allows a flexible definition of the boundary between

the network identifier and the host identifier Example

o IP address: 10.1.9.52o Subnet mask: 255.255.252.0 (22-bit network identifier)o Network: 10.1.8.0/22o Packets with address in the range 10.1.8.0-10.1.11.255 will be

routed to network 10.1.8.0/22 based on the first 22 bits


7/48

A Problem With IP Addressing

An IP address serves two different functionso The namefor an interface (host) ando The locat ion(subnet) of the interface (host) in the network

IP address is the only name carried in an IPdatagramo DNS can be used to map one or more symbolic names to one or

more IP addresses, but a symbolic name is not carried in thedatagram and has no meaning once the DNS lookup iscompleted

Network identifier in the IP address is used by routers

to deliver to the destination subnet

o The IP address is associated with the location or subnet of thedestination host

IP address used by the applications to identify theendpoints


8/48

IP Routing

Router uses routing table to direct packets to theappropriate interface

a

b

c

3.0.0.2 3.0.0.3 3.0.0.4

4.0.0.5 4.0.0.6

Router

Dest = 3.0.0.4

Target Interface2.0.0.0/24 a3.0.0.0/24 b4.0.0.0/24 c


9/48

Traditional Routing for a Mobile Host

Host moving to another network is unreachable

a

b

c

3.0.0.2 3.0.0.3 3.0.0.4

4.0.0.5 4.0.0.6

Router

Dest = 3.0.0.4

3.0.0.4

X

Mobi le

Host

Target Interface2.0.0.0/24 a3.0.0.0/24 b4.0.0.0/24 c


10/48

Definitions

Home l ink Link assigned the same network prefixas the prefix of the hosts IP addresso For example, link 3.0.0.0/24

Foreign l inkAny link where the network prefixdiffers from the prefix of the hosts IP addresso For example, link 4.0.0.0/24

Mobi l i tyThe ability of a host to change itsattachment from one link to another whilemaintaining communications and not changing its IPaddress (transparently to corresponding host)o Host can change from home link to foreign link (or foreign

link to another foreign link) without a change in IP addressand without a disruption in communication


11/48

Solutions for Mobile Hosts (1)

Host-specific routingo Add routes for the mobile host to routing tables at routerso Solution is not scalable since updates and unique entries

would be needed for every mobile host Change IP address

o

Mobile host can change its address to the foreign linksnetwork prefixo Need to register new IP address with DNS, resulting in added

load on the DNS server and networko Communications, e.g., TCP connections, would be disruptedo Changing host IP address does not enable mobi l i ty, but it

does enable nomadic i ty


12/48

Solutions for Mobile Hosts (2)

Source routingo Use loose source routing to specify a path to the foreign link

(router interface) and then to the mobile nodes interfaceo Source host must determine address of foreign link, which is

not a standard function for a host

Use link level (Layer 2) mobility

o Some Layer 2 protocols support mobility (e.g., betweenaccess points in IEEE 802.11 infrastructure networks)

o Requires that the mobile host not leave the local IP subnet Mobile IP

o Extension to IP routing to support mobile nodes in a

scaleable and secure mannero Mobile IP allows a host to move to a foreign network, but still

maintain its home IP address


13/48

Abstract Functions Needed to SupportMobility

Readdressing at the home network Associating (in the location directory) the home

address and the care-of-address of the mobile nodeand maintaining up-to-date values for the

association

Delivering the datagram to the care-of-address Inverting the readdressing operation once the

datagram arrives at the care-of-address


14/48

Mobile IP Addressing

Really need two addresses o One address for locat ing(routing to) the hosto Another address for ident i fy ing(naming) a communications

end-pointo Standard IP uses one address for both functions

Addresses in Mobile IPo Home addressKnown IP address for the hosto Home network(home link)Destination network associated

with the home addresso Foreign netwo rk(foreign link)Network associated with the

visited or foreign linko Care-of add ressIP address on the foreign link used to

locate the host


15/48

Mobile IP Overview: Data Flow

Home

Agent

ForeignAgent

CorrespondentNode (Host)

10.0.8.0/24

10.4.5.0/24

10.0.8.510.0.8.5

10.4.5.43

10.4.5.43

MobileHost

10.0.8.5

10.0.8.5

10.92.2.3

10.92.2.3


16/48

Mobile IP Elements

Mob ile Host (MH)Host that changes its attachment point fromone network or subnetwork to another Home Agent (HA)

o Specialized router on mobile nodes home network that tunnelsdatagrams for delivery to the mobile host

o Maintains current location information for the mobile nodeo Implements the readdressing function

Foreign Agent (FA)o Specialized router on foreign network that provides routing services to

the mobile host while registeredo May serve as default router for registered mobile hostso Implements the reverse readdressing function when the datagram is

delivered to the care-of-address Correspondent Node (CN)Communicates with mobile host


17/48

Mobile IP Operation (1)

Mobile (foreign and home) agents advertise theiravailability using agent-advertisement messageso Mobile host may optionally solicit an agent-advertisement

message Mobile host receives agent-advertisement message

and decides if it is on a foreign or home network If the mobile node is returning to its home network, it

deregisters with its home agent If the mobile host is on a foreign network, it obtains

a care-of address on the foreign networko Foreign agent care-of addresso Colocated care-of address


18/48


Mobile host registers new care-of address with homeagent, possibly via a foreign agento Registration requesto Registration reply

Home agent intercepts datagrams sent to the mobile

nodes home address and tunnels datagrams to theregistered care-of address

Tunneled datagram receivedo At foreign agent and delivered to mobile node, oro Directly at the mobile node (colocated)

Mobile host can usually send datagrams directlyback to the correspondent node


19/48


Datagrams sent by the mobile node are delivereddirectly to the destinationo No need to pass through the home agent


20/48

Mobile IP Procedures

Fall into following areaso Agent Advertisement/discovery HA and FA may advertise their availability on each link for

which they provide service (advertisement) A newly arrived mobile node can send a solicitation on the link

to learn if any prospective agents present (discovery)o Registration

When the MN is away from home, it registers its care-of-addresswith it HA Either directly with its HA Through a FA, which forwards the registration to the HA

o

Tunneling

HA tunnels the datagram to the care-of-address to deliver to MN


21/48


Two ways to acquire care-of-address1. Provides by the FA through its agent advertisementmessages Care-of-address is an IP address of the FA Many MNs share the same care-of-address

2. A co-located care-of-address acquired by the MN through

some external means, and associates with one of its networkinterfaces DHCP Preconfigured in MN


22/48


1. Mobile agents (HA or FA) advertise their presence via agentadvertisement messageso A MN can also solicit an agent advertisement message from any local

agent2. MN receives an agent advertisement message and determines

whether it is on its home network or a foreign networko At home networks MN operates without mobility services

o Deregisters it self from HA when returning home from some FA

3. When MN detects an FA, it obtains a care-of-address (either of FA orco-located)

4. MN, away from home registers its new care-of-address with HAthrough registration requests/reply messages possible through FA

5. HA tunnels the datagrams to MN6. Datagrams sent by MN may be delivered to their destination using

standard IP routing mechanisms, without necessarily passingthrough the HA


23/48

Mobile IP Details (1)

Agent advertisement/discoveryo ICMP router discoveryo Mobility agent discovery operationo Agent advertisement and solicitation messages

Registrationo

Registration operation

o Authenticationo Registration request and reply messageso Securityo Example

Datagram delivery (Tunneling)o Encapsulation principles and schemeso ARP issues

1

2

3


24/48

Agent Advertisement/Discovery

Process by which a mobile host o Determines if it is connected to its home network or to a foreign networko Determines when it has moved from one network to anothero Learns the care-of address provided by a foreign agent

Based on extensions to Internet Control Message Protocol (ICMP)router discovery mechanismo Agent advertisementis formed by including a mobility agent

advertisement extension in an ICMP router advertisement messageo Agent sol ic i tat ionmessage is similar to an ICMP Router solicitation

Both messages may not necessary for link layers that alreadyprovide this functionalityo Different for each kind of link layer

Mobile IP assumes link level connectivity is established by some

other means, e.g., association in IEEE 802.11b No authentication is required for agent advertisement and agent

solicitation messages

1


25/48

Router Discovery ICMP Operation

Mobile IP extend ICMP router discovery as its primarymechanism for agent discovery Host determines the local router IP address to deliver its

datagrams to hosts on any other link and can monitor theircontinued presence

Involves two ICMP messageso One transmitted by the routero Other transmitted by the hosts themselves

Router discovery message is multicast/broadcast by routers tohosts on the subnet/networko Preceded by an IP headero Normally, the all-systems multicast address (224.0.0.1) is the IP

destination address with IP Time-To-Live (TTL) of 1o Can be unicast directly to a host that sent a router solicitation

message

1


26/48

Router Discovery ICMP Operation

A MN can also be configured with router addresses by usingDHCPo Not recommended, DHCP is quite a complex protocol

Router discovery messages do not constitute a routingprotocolo Enable hosts to discover the existence of neighboring routers, but

not which router is best used to reach the destination If a host chooses a poor first-step router for a particular

destination, it should receive an ICMP redirect from that router,which identifies a better one

In fact, it is quite often the case that hosts send all such

datagram traffic through a single routerthe default router Router preference level - how eager a router is to have new

hosts using its services

1

1


27/48

Router Discovery ICMP Message (1)

IP Header

ICMP Message

0 8 16 24 31

num addrs

router address (1)..

.

addr entrysz

lifetime

preference (1)

type code checksum

ICMPMessage

ICMPHeader

Router Advertisement

1


28/48


Type: Type of ICMP message (9)

Code: Used by some types to indicate a specificcondition (0)

Checksum: Checksum over full message Num addrs: Number of router addresses advertised

in this message Addr entry size: The number of 32-bit words of

information for each router address (two words here) Lifetime: Maximum number of seconds that the

router addresses may be considered valid

1


29/48


Router address (i), i = 1num addrs: Sendingrouters IP addresses on the interface from whichthis message is sent

Preference level (i), i = 1num addrs: Preference ofthis router address relative to other routers on this

subnet (higher values are more preferable)

1


30/48

Router Solicitation ICMP Operation

Host can send router solicitation message forimmediate information Solicitation message can be broadcast or multicast

o Broadcast to the limited-broadcast address (255.255.255.255)o Multicast to the all-routers multicast address (224.0.0.2) with

TTL = 1

Routers reply with a router advertisemento Unicast to the host sending the solicitation

Host processes advertisement in standard way

1


31/48

Router Solicitation ICMP Message

Type: ICMP type (10) Code: code for this type (0) Checksum: checksum over full message Reserved: sent as 0; ignored by receiver

0 8 16 24 31

reserved

type code checksum

1

ChecksumCodeType

1


32/48

Agent Advertisement

An ICMP Router Advertisement that has beenextended also to carry mobility agent advertisementextension

Mobility agent transmits agent advertisements toadvertise its services on a linko Mobile nodes use these advertisements to determine their

current point of attachment to the Internet

Extend router advertisement messages may also carryother extensionso Mobility agent advertisement extensiono Prefix-length extensiono One-byte padding extensiono Future extensions

1

1


33/48

Agent Advertisement

Within an agent advertisement message, ICMP routeradvertisements include the following link layer, IP,and ICMP header fieldso Link layerdestination address

Link layer destination address of a unicast agentadvertisement is required to be the same as the sourcelink-layer address of the agent solicitation that promptedthe advertisement

o IP TTL - requires to be set to 1 for all agent advertisements Destination addressall systems on this link mulicast

address (224.0.0.1) or the limited broadcast address(255.255.255.255)

o ICMP (router discovery fields)

1

Ad i F (2)1


34/48

Advertisement Features (2)

ICMP

o Type = 9 (router advertisement message)o Code

Code = 0 if mobility agent handles common traffic, i.e. it isa router for general IP traffic

Code = 16 if mobility agent does notroute common traffic

(but it must route datagrams from a registered mobilehost)

o Lifetime is maximum time this advertisement is consideredvalid

o Router addresses are usual router addresses that areadvertised (preference may be low)

o Num addrs is the number of advertised router addresses

1

M bili A Ad i E i (1)

1


35/48

Mobility Agent Advertisement Extension (1)

0 8 16 24 31

registration lifetime

type length sequence number

reservedRBHFMG

V

zero or more care-of addresses

Type: 16 Length: 6 + 4*N, where Nis the number of advertised

care-of addresses (4 bytes each) Sequence number: Count of advertisement messages

since agent was initialized

( fol low s ICMP rou ter advert isement f ield

A t Ad ti t E t i (2)1


36/48

Agent Advertisement Extension (2)

Registration lifetime: Lifetime in seconds that thisagent is willing to accept a registration request(65,535 infinity)

Bit fieldso R: Registration required - Foreign agent requires registration

rather than using colocated care-of address (e.g., foraccounting or other policies)o B: Busy -- foreign agent will not accept registrations from new

mobile hosts if seto H: Home agent -- agent offers home agent services on this

linko F: Foreign agent -- agent offers foreign agent services on this

link

1



37/48


Bit fields (continued)

o M: Minimal encapsulation -- agent can receive datagrams thatcontain minimal encapsulation

o G: Generic routing encapsulation (GRE) -- agent can receivedatagrams that use GRE

o V: Van Jacobson header compression -- agent supports use

of header compression Reserved: sent as 0; ignored by receiver Care-of addresses: care-of addresses provided by

this agento Must provide at least one if F = 1o Number of addresses determined by length field

1



38/48


HA should never claim to be too busy to server MNs on itshome network

There can be multiple HAs However, an advertisement from any of the HA on the same

network will suffice to inform the MN that it is indeedattached to its home network

A FA may indicate that it is too busy to allow new MNs toregister with it, by setting the B bit in the agentadvertisementso However, it must continue to send agent advertisements so that

any MN already registered with it will know that they have not

moved out of the range of FA An agent advertisement message is not allowed to have a B

bit set if the F bit is not also set

Agent Ad ertisement E tension (5)1


39/48


Either the F bit or the H bit is required to be set in themobility agent advertisement extension When a FA wishes to require registration even from

those mobile nodes that have acquired colocatedcare-of-address, it sets R bit to one

Prefix Length Extension

1


40/48

Prefix-Length Extension

May follow the mobility agent advertisementextension Used to indicate the number of bits of network prefix

that apply to each router address listed in the ICMPRouter Advertisement portion of the agent

advertisement portion Type: 19 Length: N, where Nis the value of the num addrs

fields in the ICMP Router Advertisement portion of the

agent advertisement

0 8 16 24 31type length

Prefixlength

One byte Padding Extension

1


41/48

One-byte Padding Extension

Use to align ICMP to even number of bytes If present this extension should be the last extension

in the agent advertisement

0 8

type = 0

Mobile Agent Solicitation Message1


42/48

Mobile Agent Solicitation Message

Same as ICMP router solicitation messageo TTL = 1 required

Used in a slightly different wayo Frequencyo Number of attempts

Advertising by Mobility Agents1


43/48

Advertising by Mobility Agents

If link-layer protocol does notprovide agentdiscovery, mobility agent (HA and FA) musto Send agent advertisement messages (at some maximum rate

with 1 second maximum recommended rate)o Respond to agent solicitation messages

If link-layer protocol doesprovide agent discovery,mobility agent musto Respond to agent solicitation messageso Send agent advertisement messages if site policy requires

additional registration (when R bit is set or as a response to aspecific agent solicitation)

Agent Discovery by Mobile Hosts1


44/48

Agent Discovery by Mobile Hosts

MH sends solicitation only ifo There is no agent advertisement messageo Care-of address not established by link-layer protocol

Agent advertisement provideso Care-of addresso Foreign agent address

Mobile host knows it is on its home link when it seesadvertisement messages from its home agento Mobile host reconfigures routing for home network operationo Issues gratuitous ARP to update any cached ARP entrieso Deregisters with home agent



45/48


A MA is required to limit the rate at which it sendsbroadcast or multicast agent advertisementso A recommended maximal rate is once per second

A FA must accept router solicitation even when the IPsource address appears to reside on a different

subnet than the mobility agents interface on whichthe solicitation was received A MA may be configured to send agent

advertisements only in response to an agentsolicitation message



46/48


Solicitations should only be sent in the absence ofagent advertisements and when a care-of-address hasnot been determined through link-layer protocol orother means

A node may send three initial solicitations on a given

link, at a maximum rate of one per secondo After this, solicitation rate is required to be reduced (binary

exponential backoff mechanism) so as to limit the overhead onthe local link

In fact, a MN can continue to send out solicitation

indefinitely until a suitable FA finally comes withinrangeo With maximum interval of at least one min

Registration Requires1


47/48

Registration Requires

When a MN receives an agent advertisement with Rbit set, the MN should register through the FA, evenwhen the MN might be able to acquire its owncolocated care-of-addresso Intended to enforce visiting policies (such as accounting)

Returning Home1


48/48

Returning Home

A MN can detect that it has returned to its homenetwork when it receives as agent advertisement fromits own home agent

If so, it should deregister with its home agent Before attempting to deregister, the MN should

configure its routing table appropriately for its homenetwork

In addition, if the home network is using ARP, the MNis required to follow the procedures with regard toARP, proxy ARP, and gratuitous ARP

MN Lec 9 Mobile IP

Documents