Lecture 9 Mobile Networks: IP Addressing and Mobile IP Wireless Networks and Mobile Systems

Lecture 9Mobile Networks:

IP Addressing and Mobile IP

Wireless Networks and Mobile Systems

Mobile Networks: IP Addressing and Mobile IP 2

Lecture Objectives

● Present the basic principles of addressing in IP networks

● Describe the problem of mobility with IP and consider alternative solutions

● Describe the operation of Mobile IP


Agenda

● IP addressing● Node mobility and IP● Mobile IP

■ Foreign agent discovery■ Home agent registration■ Packet delivery through tunneling■ Route optimization


IP Addressing

● IPv4 addresses…■ Uniquely identify an interface ■ 32 bits long■ Consist of a network identifier and a host identifier

● Routing outside of the destination host’s subnet is usually based on the network identifier, while the host identifier is only used within the destination’s subnet

● IPv6 uses 128-bit addresses

Network Identifier Host Identifier

0 31


Five Classes of IP Addresses

● IP addressing was originally based on five classes of addresses■ 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


CIDR

● Classless Inter-Domain Routing (CIDR) was introduced to remedy problems with the rigid classes of IP addresses■ Defined in RFCs 1517-1520

● Allows a flexible definition of the boundary between the network identifier and the host identifier

● Example■ IP address: 10.1.9.52■ Subnet mask: 255.255.252.0 (22-bit network

identifier)■ Network: 10.1.8.0/22■ 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


A Problem With IP Addressing

● An IP address serves two different functions…■ The name for an interface (host) and■ The location (subnet) of the interface (host) in the network

● The IP address is the only “name” carried in an IP datagram■ 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 the datagram and has no meaning once the DNS lookup is completed

● The network identifier in the IP address is used by routers to deliver to the destination subnet■ The IP address is associated with the location or subnet of

the destination host


IP Routing

● Router uses routing table to direct packets to the appropriate interface

ab

c

3.0.0.2 3.0.0.3 3.0.0.4

4.0.0.5 4.0.0.6

RouterDest = 3.0.0.4

Target Interface 2.0.0.0/24 a 3.0.0.0/24 b 4.0.0.0/24 c


Traditional Routing for a Mobile Host

● Host moving to another network is unreachable

ab

c

3.0.0.2 3.0.0.3 3.0.0.4

4.0.0.5 4.0.0.6

RouterDest = 3.0.0.4

3.0.0.4

X

MobileHost

Target Interface 2.0.0.0/24 a 3.0.0.0/24 b 4.0.0.0/24 c


Definitions

● Home link – Link assigned the same network prefix as the prefix of the host’s IP address■ For example, link 3.0.0.0/24

● Foreign link – Any link where the network prefix differs from the prefix of the host’s IP address■ For example, link 4.0.0.0/24

● Mobility – The ability of a host to change its attachment from one link to another while maintaining communications and not changing its IP address (transparently to corresponding host)■ Host can change from home link to foreign link (or foreign

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


Solutions for Mobile Hosts (1)

● Host-specific routing■ Add routes for the mobile host to routing tables at routers■ Solution is not scaleable since updates and unique entries

would be needed for every mobile host

● Change IP address■ Mobile host can change its address to the foreign link’s

network prefix■ Need to register new IP address with DNS (if it is to maintain

identity), resulting in added load on the DNS server and network

■ Communications, e.g., TCP connections, would be disrupted■ Changing host IP address does not enable mobility, but it

does enable nomadicity


Solutions for Mobile Hosts (2)

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

(router interface) and then to the mobile node’s interface■ Source host must determine address of foreign link, which is

not a standard function for a host

● Use link level (Layer 2) mobility■ Some Layer 2 protocols support mobility (e.g., between

access points in IEEE 802.11 infrastructure networks)■ Requires that the mobile host not leave the local IP subnet

● Mobile IP■ Extension to IP routing to support mobile nodes in a

scaleable and secure manner


Mobile IP

● Mobile IP allows a host to move to a foreign network, but still maintain its home IP address

● References■ C. E. Perkins, editor, “IP Mobility Support for IPv4, RFC 3344,

August 2002.■ C. E. Perkins, Mobile IP: Design Principles and Practices,

Addison-Wesley, Reading, MA, 1998.■ J. D. Solomon, The Internet Unplugged, Prentice Hall PTR,

Upper Saddle River, NJ, 1998.■ IETF Working Groups

○ Mobility for IPv4:http://www.ietf.org/html.charters/mip4-charter.html

○ Mobility for IPv6:http://www.ietf.org/html.charters/mip6-charter.html


Mobile IP Addressing

● Really need two addresses … ■ One address for locating (routing to) the host■ Another address for identifying (naming) a communications

end-point■ Standard IP uses one address for both functions

● Addresses in Mobile IP■ Home address – Known IP address for the host■ Home network (home link) – Destination network associated

with the home address■ Foreign network (foreign link) – Network associated with the

visited or foreign link■ Care-of address – IP address on the foreign link used to

locate the host


Mobile IP Overview: Data Flow

HomeAgent

ForeignAgent

CorrespondentNode (Host)

10.0.8.0/24

10.4

.5.0/2

4

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


Mobile IP Elements

● Mobile Host (MH) – Host that changes its attachment point from one network or subnetwork to another

● Home Agent (HA) – Specialized router on mobile node’s home network that tunnels datagrams for delivery to the mobile host and maintains current location information for the mobile node

● Foreign Agent (FA) – Specialized router on foreign network that provides routing services to the mobile host while registered and may serve as default router for registered mobile hosts

● Correspondent Node (CN) – Communicates with mobile host


Mobile IP Operation (1)

● Mobile (foreign and home) agents advertise their availability using agent-advertisement messages■ 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 network■ Foreign agent care-of address■ Colocated care-of address



● Mobile host registers new care-of address with home agent, possibly via a foreign agent■ Registration request■ Registration reply

● Home agent intercepts datagrams sent to the mobile node’s home address and tunnels datagrams to the registered care-of address

● Tunneled datagram received■ At foreign agent and delivered to mobile node, or■ Directly at the mobile node (colocated)

● Mobile host can usually send datagrams directly back to the correspondent node



● Datagrams sent by the mobile node are delivered directly to the destination■ No need to pass through the home agent


Mobile IP Details (1)

● Agent discovery■ ICMP router discovery■ Mobility agent discovery operation■ Agent advertisement and solicitation messages

● Registration■ Registration operation■ Authentication■ Registration request and reply messages■ Security■ Example

1

2


Mobile IP Details (2)

● Datagram delivery■ Encapsulation principles and schemes■ ARP issues

3


Agent Discovery

● Process by which a mobile host …■ Determines if it is connected to its home network or to a

foreign network■ Determines when it has moved from one network to another■ Learns the care-of address provided by a foreign agent

● Based on extensions to Internet Control Message Protocol (ICMP) router discovery mechanism■ Router advertisement message■ Router solicitation message

● Mobile IP assumes link level connectivity is established by some other means, e.g., association in IEEE 802.11b

1


Router Discovery Operation

● Router discovery message is multicast by routers to hosts on the subnet■ Normally, the all-systems multicast address (224.0.0.1) is the

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

solicitation message

● Systems on the subnet receive the discovery message and process

1


Router Discovery Message (1)

IP Header

ICMP Message

0 8 16 24 31

num addrs

router address (1)

...

addr entr sz lifetime

preference (1)

type code checksum

ICMPMessage

ICMPHeader

1



● Type: Type of ICMP message (9)● Code: Used by some types to indicate a specific

condition (0)● Checksum: Checksum over full message● Num addrs: Number of 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

addresses may be considered valid

1



● Router address (i), i=1…num addrs: Sending router’s IP address on the interface from which this message is sent

● Preference level (i), i=1…num addrs: Preference of this router address relative to other routers on this subnet (higher values are more preferable)

1


Router Solicitation Operation

● Host can send router solicitation message for immediate information

● Solicitation message can be broadcast or multicast■ Broadcast to the limited-broadcast address

(255.255.255.255)■ Multicast to the all-routers multicast address (224.0.0.2) with

TTL = 1

● Routers reply with a router advertisement■ Unicast to the host sending the solicitation

● Host processes advertisement in standard way

1


Router Solicitation 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


Agent Advertisement

● Extend router advertisement messages■ Mobility agent advertisement extension■ Prefix-length extension■ One-byte padding extension■ Future extensions

● Important fields for …■ Link layer■ IP■ ICMP (router discovery)

1


Advertising by Mobility Agents

● If link-layer protocol does not provide agent discovery, mobility agent (HA and FA) must…■ Send agent advertisement messages (at some maximum

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

● If link-layer protocol does provide agent discovery, mobility agent must…■ Respond to agent solicitation messages■ Send agent advertisement messages if site policy requires

additional registration

1


Agent Discovery by Mobile Hosts

● MH sends solicitation only if… ■ There is no agent advertisement message■ Care-of address not established by link-layer protocol

● Agent advertisement provides…■ Care-of address■ Foreign agent address

● Mobile host knows it is on its home link when it sees advertisement messages from its home agent■ Mobile host reconfigures routing for home network

operation■ Issues gratuitous ARP to update any cached ARP entries■ Deregisters with home agent

1


Advertisement Features (1)

● Link layer■ Destination address should match link layer source address

for agent solicitation

● IP■ TTL = 1 (local subnet only)■ Destination address is …

○ All-systems multicast address (224.0.0.1), or○ Limited-broadcast address (225.225.225.225)

1


Advertisement Features (2)

● ICMP■ Type = 9 (router advertisement message)■ Code

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

○ Code = 16 if mobility agent does not route common traffic (but it must route datagrams from a registered mobile host)

■ Lifetime is maximum time this advertisement is considered valid

■ Router addresses are usual router addresses that are advertised (preference may be low)

■ Num addrs is the number of advertised router addresses

1


Agent Advertisement Extension (1)

0 8 16 24 31

registration lifetime

type length sequence number

reservedRBHFMGV

zero or more care-of addresses

● Type: 16● Length: 6 + 4N, where N is the number of advertised

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

messages since agent was initialized

(follows ICMP router discovery)

1



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

● Bit fields■ R: Foreign agent requires registration rather than using

colocated care-of address (e.g., for accounting or other policies)

■ B: Busy -- foreign agent will not accept registrations from new mobile hosts if set

■ H: Home agent -- agent offers home agent services on this link

■ F: Foreign agent -- agent offers foreign agent services on this link

1



● Bit fields (continued)■ M: Minimal encapsulation -- agent can receive datagrams

that contain minimal encapsulation■ G: Generic routing encapsulation (GRE) -- agent can receive

datagrams that use GRE■ 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 agent■ Must provide at least one if F = 1■ Number of addresses determined by length field

1


Agent Solicitation Message

● Same as ICMP router solicitation message■ TTL = 1 required

● Used in a slightly different way■ Frequency■ Number of attempts

1


Registration

● Mobile IP registration allows mobile hosts to communicate their location (reachability) information to their home agent■ Request forwarding services on a foreign network■ Inform home agent of care-of address■ Renew a binding that is due to expire■ Deregister upon return to the home network

● Creates or modifies a mobility binding at home agent and allows foreign agent to begin or renew service for the mobile host■ Binds mobile host’s care-off address to its home address■ Binding is valid for a registration lifetime

2


Registration Preliminaries (1)

● Preconfigured in mobile host…■ Home IP address and subnet mask■ Mobility security association for each home agent (for

authentication)■ Optionally, IP address of one or more home agents

● Two forms of registration■ Foreign agent acts as an intermediary■ Mobile host registers directly with home agent

● Both procedures consist of exchange of registration request and reply messages

2


Registration Preliminaries (2)

● Registration via foreign agent if …■ Mobile host registers foreign agent care-off address■ Foreign agent registration is required (R = 1 in

advertisement)

● Registration directly with home agent if …■ Mobile host is using a colocated care-of address■ Mobile host returns home and deregisters

2


Registration Via Foreign Agent

(2)

(5)

(1)

(3)

(4)

1. FA advertises service2. MH requests service3. FA relays request to HA4. HA accepts (or denies) request and replies5. FA relays reply to MH

MH FA HA

MobileHost

HomeAgent

ForeignAgent

2


Authentication (1)

● Without security, a “bad guy” host on any network (with a FA) could issue a registration request for a host on any network (with a HA)■ HA would begin to forward datagrams to the bad guy host

● So, registration messages between a mobile host and its home agent must be authenticated■ Uses mobile-home authentication extension

● Mobile hosts, home agents, and foreign agents must maintain a mobility security association for mobile hosts, indexed by…■ Security Parameter Index (SPI)■ IP address (home address for mobile host)

2


Authentication (2)

● Identification field in registration request changes with each new registration to prevent malicious snooping agent from replaying request■ Provides replay protection

● Identification field in reply based on identification field in request

2


Registration Message Format

● Carried in UDP datagrams● Non-zero checksum in UDP

header (receiver should check)

● Mobile IP implements its own retransmission scheme

● TCP overhead not needed, especially beneficial for high packet loss rates

● Include a lifetime value

IP Header

UDP Header

Mobile IPMessage Header

Extensions …

2


extensions ...

Registration Request Message (1)

0 8 16 24 31

type SBDMGVrsv lifetime

home address

home agent

care-of address

identification

2



● Type: 1 (indicates registration request)● Bit fields

■ S: Simultaneous bindings -- set if mobile host wants home agent to keep its current bindings

■ B: Broadcast datagrams -- set if mobile host wants to receive broadcasts on its home network

■ D: Decapsulation -- set to indicate that mobile host will decapsulate datagrams sent to care-of address (mobile node is using colocated care-of address)

2



● Bit fields (continued)■ M: Minimal encapsulation -- set to request home agent use

minimal encapsulation for tunneled datagrams■ G: Generic routing encapsulation -- set to request home

agent use GRE for tunneled datagrams■ V: Van Jacobson header compression -- set to request that

mobility agent use of this header compression scheme over its link with mobile host

■ rsv: Two reserved bits -- sent as 0; ignored on reception

2



● Lifetime: Number of seconds before registration should be considered to expire■ Should not exceed that advertised by the foreign agent■ Set to 0 to delete the registration

● Home address: Home IP address of the mobile host● Home agent: IP address of the mobile host’s home

agent

2



● Care-of address: IP address of the tunnel endpoint■ Colocated (e.g., obtained using DHCP)■ Foreign agent (e.g., obtained through agent discovery)■ Home address to deregister all (return to home)

● Identification: 64-bit identification number constructed by mobile host■ Associates registration requests with registration replies■ Protects against replay attacks of registration messages

2


IP for Registration Requests

● Source address■ Care-of address if colocated care-of address■ Otherwise, mobile host’s home address

● Destination address■ IP address of foreign agent learned through advertisement

message if registering through foreign agent■ If IP address not known, all-mobility-agents multicast

address (224.0.0.11) with TTL = 1 and link-layer address set to agent’s address

■ IP address of home agent if registering directly with home agent

■ Subnet-directed broadcast of home agent if IP address not known

2


UDP for Registration Requests

● Source port: Variable (dynamically assigned by operating system, for example)

● Destination port: 434 (well-known port number)

2


Registration Reply Message (1)

extensions ...

0 8 16 24 31

type code lifetime

home address

home agent

identification

2



● Type: 3 (indicates registration reply)● Code: Indicates result of registration request

(defined in Assigned Numbers)■ Registration successful

○ 0: Registration accepted○ 1: Registration accepted, simultaneous

registration not supported■ Registration denied by foreign agent

○ Codes 64-88■ Registration denied by home agent

○ Codes 128-136

2



● Lifetime: Duration for which binding is valid● Home address: IP address of the mobile host● Home agent: IP address of mobile host’s home agent● Identification: 64-bit identification field

■ Low 32 bits matched to identification sent in request■ Used for authentication

2


IP for Registration Replies

● Source address■ Typically copied from the destination address of associated

registration request■ If request sent to a multicast or broadcast address, source

address is set to home agent’s preferred unicast address

● Destination address: Copied from the source address of the associated registration request

2


UDP for Registration Replies

● Source port: Variable● Destination port: Copied from the source port of the

associated registration request

2


Security Parameter Index

● SPI defines the security context used to compute the authenticator value■ Authentication algorithm■ Mode■ Shared secret

● Shared secret■ Shared private key, or■ Public/private key pair

2


Authentication Extension

0 8 16 24 31

authenticator …

type code SPI (first two bytes)

SPI (second two bytes)

● Type: 32 Mobile-home authentication33 Mobile-foreign authentication34 Foreign-home authentication

● Length: 4 plus length of authenticator● SPI: 4-byte SPI● Authenticator: Variable length (SPI)

2


Order of Extensions

IP header

UDP header

Fixed part of registration request

Nonauthentication extensions for home agent

Mobile-home authentication extension

Nonauthentication extensions for foreign agent

Mobile-foreign authentication extension

● Example -- registration request from mobile host to home agent via foreign agent

2


Registration Information (1)

● Maintained at the mobile host for each pending registration■ Link-layer address of foreign agent (if applicable)■ IP destination address of the registration request■ Care-of address used in registration■ Identification value sent in registration■ Originally requested lifetime■ Remaining lifetime of pending registration

2



● Information in visitor’s log at foreign agent■ Link-layer source address of mobile host■ IP source address (the mobile host’s home address)■ IP destination address (the foreign agent address used by

the mobile host)■ UDP source port (UDP port used at the mobile host)■ Home agent address■ Identification field (for authentication)■ Requested registration lifetime■ Remaining lifetime of the pending or current registration

2



● Information in mobility binding (indexed by home address of mobile host) at home agent■ Mobile host’s care-of address■ Identification field from registration reply■ Remaining lifetime of the registration

2


FA Care-of Address Example

● Example values■ Mobile host’s home address 129.34.78.5■ Mobile host’s home agent 129.34.78.254■ Foreign agent’s link address 137.0.0.11■ Foreign agent’s care-of address 9.2.20.11■ Mobile node’s source port 1094■ Foreign agent’s source port 1105■ Care-of registration lifetime 60,000 s■ Home agent-granted lifetime 35,000 s■ SPI (mobile node/home agent) 302/303

From C. E. Perkins, Mobile IP: Design Principles and Practices, Addison-Wesley, Reading, MA, 1998.

2


Example: 1) Agent Advertisement

IP Header ICMP Header Router Adv Mobile Ext

S=137.0.0.11D=255.255.255.255F=1

Type=9Code=16

Life=60,000COA=9.2.20.11

● Foreign agent discovery

2


Example: 2) Mobile to Foreign

IP Header UDP Header Mobile IP Auth Ext

S=129.34.78.5D=137.0.0.11TTL=64

S=1094D=434 SPI=302

Type=1Life=60,000COA=9.2.20.11HA=129.34.78.254MH=129.34.78.5

● Registration using the foreign agent

2


Example: 3) Foreign to Home


S=9.2.20.11D=129.34.78.254TTL=64

S=1105D=434 SPI=302

Type=1Life=60,000COA=9.2.20.11HA=129.34.78.254MH=129.34.78.5

2


Example: 4) Home to Foreign


S=129.34.78.254D=9.2.20.11 TTL=64

S=434D=1105 SPI=303

Type=3Code=0Life=35,000HA=129.34.78.254MH=129.34.78.5

2


Example: 5) Foreign to Mobile


S=137.0.0.11D=129.34.78.5TTL=1

S=434D=1094 SPI=303

Type=3Code=0Life=35,000HA=129.34.78.254MH=129.34.78.5

● Successful registration is complete

2


Datagram Delivery

● Mobile IP uses encapsulation to deliver datagrams from the home network to the current care-of address of the mobile host■ IP-in-IP encapsulation (must be supported)■ Minimal encapsulation (may be supported)■ Generic record encapsulation (may be supported)

3


Tunneling Basics

Source Destination

3

Encapsulation DecapsulationTunnel


IP-in-IP Encapsulation (1)

OriginalIP Header

Original IPPayload

OriginalIP Header

Original IPPayload

OuterIP Header

OtherOptionalHeaders

TunnelEndpoints

OriginalEndpoints

3


IP-in-IP Encapsulation (2)

● Encapsulation makes almost no change to original (or “inner”) IP header■ TTL is decremented by 1 (as in a router)

● Outer IP header■ Total length is length of entire encapsulated datagram■ TOS (DSCP) copied from inner header■ If DF flag is set in inner header, also set in outer■ Protocol = 4 (IP)■ Source address is address of encapsulator■ Destination address is address of decapsulator■ Optional header fields are generally not copied; others may

be added

3


Special Forms of ARP

● Proxy ARP■ An ARP reply sent by one node on behalf of another node■ ARP reply includes proxy’s link-layer address■ Future transmissions will be sent to the proxy■ Home agent can proxy ARP for mobile node

● Gratuitous ARP■ ARP request or reply sent in order to update ARP caches at

other nodes■ Nodes are required to update their caches■ Home agent does gratuitous ARP to update ARP caches on

local network after change in registration or deregistration■ Mobile host does gratuitous ARP when it returns home

3


Route Optimization (1)

● “Triangle routing” in basic Mobile IP is inefficient■ Traffic from correspondent host to mobile host traverses the

network twice

● Route optimization allows home agent to notify correspondent node of new location of the mobile host■ Requires enhanced capabilities at each correspondent node■ Requires security association between home agent and

correspondent node

● Route optimization approach is the only technique supported in IPv6■ IPv6 also uses only colocated care-of addresses


Tunnel

Binding update

Route Optimization (2)

ACK

Datagram 1

MobileHost

Datagram 2

HomeAgent

ForeignAgent

CorrespondingHost

BindingCache


Summary

● IP addressing presents problems for mobile hosts● Mobile IP is a solution for truly mobile operation

■ Home agents and foreign agents provide mobility support■ Dynamic Host Configuration Protocol (DHCP), Network

Address Translation (NAT), etc. can be used for nomadic operation

● Major operations■ Agent discover■ Registration■ Datagram delivery through tunneling

● Route optimization and IPv6 offer improvements on basic Mobile IP

Documents

Lecture 9 Mobile Networks: IP Addressing and Mobile IP Wireless Networks and Mobile Systems