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

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lecture objectives
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

Mobile Networks: IP Addressing and Mobile IP 2

agenda
Agenda
  • IP addressing
  • Node mobility and IP
  • Mobile IP
    • Foreign agent discovery
    • Home agent registration
    • Packet delivery through tunneling
    • Route optimization

Mobile Networks: IP Addressing and Mobile IP 3

ip addressing
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

0

31

Network Identifier

Host Identifier

Mobile Networks: IP Addressing and Mobile IP 4

five classes of ip addresses
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

0

1

2

3

4

8

16

24

31

Class A

0

netid

hostid

Class B

1

0

netid

hostid

Class C

1

1

0

netid

hostid

Class D

1

1

1

0

multicast address

Class E

1

1

1

1

reserved for future use

Mobile Networks: IP Addressing and Mobile IP 5

slide6
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

Mobile Networks: IP Addressing and Mobile IP 6

a problem with ip addressing
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

Mobile Networks: IP Addressing and Mobile IP 7

ip routing
IP Routing
  • Router uses routing table to direct packets to the appropriate interface

TargetInterface

2.0.0.0/24 a

3.0.0.0/24 b

4.0.0.0/24 c

3.0.0.2

3.0.0.3

3.0.0.4

b

a

Router

Dest = 3.0.0.4

c

4.0.0.5

4.0.0.6

Mobile Networks: IP Addressing and Mobile IP 8

traditional routing for a mobile host
Traditional Routing for a Mobile Host
  • Host moving to another network is unreachable

TargetInterface

2.0.0.0/24 a

3.0.0.0/24 b

4.0.0.0/24 c

3.0.0.2

3.0.0.3

3.0.0.4

b

X

a

Router

Dest = 3.0.0.4

c

MobileHost

3.0.0.4

4.0.0.5

4.0.0.6

Mobile Networks: IP Addressing and Mobile IP 9

definitions
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

Mobile Networks: IP Addressing and Mobile IP 10

solutions for mobile hosts 1
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

Mobile Networks: IP Addressing and Mobile IP 11

solutions for mobile hosts 2
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 Networks: IP Addressing and Mobile IP 12

mobile ip
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 Networks: IP Addressing and Mobile IP 13

mobile ip addressing
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 Networks: IP Addressing and Mobile IP 14

mobile ip overview data flow
Mobile IP Overview: Data Flow

Home

Agent

10.92.2.3

CorrespondentNode (Host)

10.0.8.5

10.0.8.5

10.92.2.3

10.0.8.0/24

10.4.5.43

Foreign

Agent

10.4.5.43

10.4.5.0/24

10.0.8.5

MobileHost

10.0.8.5

Mobile Networks: IP Addressing and Mobile IP 15

mobile ip elements
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 Networks: IP Addressing and Mobile IP 16

mobile ip operation 1
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 Networks: IP Addressing and Mobile IP 17

mobile ip operation 2
Mobile IP Operation (2)
  • 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

Mobile Networks: IP Addressing and Mobile IP 18

mobile ip operation 3
Mobile IP Operation (3)
  • Datagrams sent by the mobile node are delivered directly to the destination
    • No need to pass through the home agent

Mobile Networks: IP Addressing and Mobile IP 19

mobile ip details 1
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 Networks: IP Addressing and Mobile IP 20

mobile ip details 2
Mobile IP Details (2)
  • Datagram delivery
    • Encapsulation principles and schemes
    • ARP issues

3

Mobile Networks: IP Addressing and Mobile IP 21

agent discovery
Agent Discovery

1

  • 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

Mobile Networks: IP Addressing and Mobile IP 22

router discovery operation
Router Discovery Operation

1

  • 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

Mobile Networks: IP Addressing and Mobile IP 23

router discovery message 1
Router Discovery Message (1)

1

IP Header

ICMPHeader

ICMPMessage

ICMP Message

0

8

16

24

31

type

code

checksum

num addrs

addr entr sz

lifetime

router address (1)

preference (1)

...

Mobile Networks: IP Addressing and Mobile IP 24

router discovery message 2
Router Discovery Message (2)

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

Mobile Networks: IP Addressing and Mobile IP 25

router discovery message 3
Router Discovery Message (3)

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)

Mobile Networks: IP Addressing and Mobile IP 26

router solicitation operation
Router Solicitation Operation

1

  • 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

Mobile Networks: IP Addressing and Mobile IP 27

router solicitation message
Router Solicitation Message

1

  • 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

type

code

checksum

reserved

Mobile Networks: IP Addressing and Mobile IP 28

agent advertisement
Agent Advertisement

1

  • 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)

Mobile Networks: IP Addressing and Mobile IP 29

advertising by mobility agents
Advertising by Mobility Agents

1

  • 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

Mobile Networks: IP Addressing and Mobile IP 30

agent discovery by mobile hosts
Agent Discovery by Mobile Hosts

1

  • 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

Mobile Networks: IP Addressing and Mobile IP 31

advertisement features 1
Advertisement Features (1)

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)

Mobile Networks: IP Addressing and Mobile IP 32

advertisement features 2
Advertisement Features (2)

1

  • 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

Mobile Networks: IP Addressing and Mobile IP 33

agent advertisement extension 1
Agent Advertisement Extension (1)

1

  • 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)

0

8

16

24

31

type

length

sequence number

registration lifetime

RBHFMGV

reserved

zero or more care-of addresses

Mobile Networks: IP Addressing and Mobile IP 34

agent advertisement extension 2
Agent Advertisement Extension (2)

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

Mobile Networks: IP Addressing and Mobile IP 35

agent advertisement extension 3
Agent Advertisement Extension (3)

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

Mobile Networks: IP Addressing and Mobile IP 36

agent solicitation message
Agent Solicitation Message

1

  • Same as ICMP router solicitation message
    • TTL = 1 required
  • Used in a slightly different way
    • Frequency
    • Number of attempts

Mobile Networks: IP Addressing and Mobile IP 37

registration
Registration

2

  • 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

Mobile Networks: IP Addressing and Mobile IP 38

registration preliminaries 1
Registration Preliminaries (1)

2

  • 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

Mobile Networks: IP Addressing and Mobile IP 39

registration preliminaries 2
Registration Preliminaries (2)

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

Mobile Networks: IP Addressing and Mobile IP 40

registration via foreign agent

(1)

(2)

(3)

(4)

(5)

Registration Via Foreign Agent

2

MobileHost

ForeignAgent

HomeAgent

MH

FA

HA

1. FA advertises service

2. MH requests service

3. FA relays request to HA

4. HA accepts (or denies) request and replies

5. FA relays reply to MH

Mobile Networks: IP Addressing and Mobile IP 41

authentication 1
Authentication (1)

2

  • 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)

Mobile Networks: IP Addressing and Mobile IP 42

authentication 2
Authentication (2)

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

Mobile Networks: IP Addressing and Mobile IP 43

registration message format
Registration Message Format

2

  • 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 …

Mobile Networks: IP Addressing and Mobile IP 44

registration request message 1
Registration Request Message (1)

2

0

8

16

24

31

type

SBDMGVrsv

lifetime

home address

home agent

care-of address

identification

extensions ...

Mobile Networks: IP Addressing and Mobile IP 45

registration request message 2
Registration Request Message (2)

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)

Mobile Networks: IP Addressing and Mobile IP 46

registration request message 3
Registration Request Message (3)

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

Mobile Networks: IP Addressing and Mobile IP 47

registration request message 4
Registration Request Message (4)

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

Mobile Networks: IP Addressing and Mobile IP 48

registration request message 5
Registration Request Message (5)

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

Mobile Networks: IP Addressing and Mobile IP 49

ip for registration requests
IP for Registration Requests

2

  • 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

Mobile Networks: IP Addressing and Mobile IP 50

udp for registration requests
UDP for Registration Requests

2

  • Source port: Variable (dynamically assigned by operating system, for example)
  • Destination port: 434 (well-known port number)

Mobile Networks: IP Addressing and Mobile IP 51

registration reply message 1
Registration Reply Message (1)

2

0

8

16

24

31

type

code

lifetime

home address

home agent

identification

extensions ...

Mobile Networks: IP Addressing and Mobile IP 52

registration reply message 2
Registration Reply Message (2)

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

Mobile Networks: IP Addressing and Mobile IP 53

registration reply message 3
Registration Reply Message (3)

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

Mobile Networks: IP Addressing and Mobile IP 54

ip for registration replies
IP for Registration Replies

2

  • 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

Mobile Networks: IP Addressing and Mobile IP 55

udp for registration replies
UDP for Registration Replies

2

  • Source port: Variable
  • Destination port: Copied from the source port of the associated registration request

Mobile Networks: IP Addressing and Mobile IP 56

security parameter index
Security Parameter Index

2

  • 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

Mobile Networks: IP Addressing and Mobile IP 57

authentication extension

type

code

SPI (first two bytes)

SPI (second two bytes)

authenticator …

Authentication Extension

2

  • Type: 32 Mobile-home authentication 33 Mobile-foreign authentication 34 Foreign-home authentication
  • Length: 4 plus length of authenticator
  • SPI: 4-byte SPI
  • Authenticator: Variable length (SPI)

0

8

16

24

31

Mobile Networks: IP Addressing and Mobile IP 58

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

Order of Extensions

2

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

Mobile Networks: IP Addressing and Mobile IP 59

registration information 1
Registration Information (1)

2

  • 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

Mobile Networks: IP Addressing and Mobile IP 60

registration information 2
Registration Information (2)

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

Mobile Networks: IP Addressing and Mobile IP 61

registration information 3
Registration Information (3)

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

Mobile Networks: IP Addressing and Mobile IP 62

fa care of address example
FA Care-of Address Example

2

  • 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.

Mobile Networks: IP Addressing and Mobile IP 63

example 1 agent advertisement
Example: 1) Agent Advertisement

2

  • Foreign agent discovery

Type=9

Code=16

IP Header

ICMP Header

Router Adv

Mobile Ext

Life=60,000

COA=9.2.20.11

S=137.0.0.11

D=255.255.255.255

F=1

Mobile Networks: IP Addressing and Mobile IP 64

example 2 mobile to foreign
Example: 2) Mobile to Foreign

2

  • Registration using the foreign agent

S=1094

D=434

SPI=302

IP Header

UDP Header

Mobile IP

Auth Ext

Type=1

Life=60,000

COA=9.2.20.11

HA=129.34.78.254

MH=129.34.78.5

S=129.34.78.5

D=137.0.0.11

TTL=64

Mobile Networks: IP Addressing and Mobile IP 65

example 3 foreign to home
Example: 3) Foreign to Home

2

S=1105

D=434

SPI=302

IP Header

UDP Header

Mobile IP

Auth Ext

Type=1

Life=60,000

COA=9.2.20.11

HA=129.34.78.254

MH=129.34.78.5

S=9.2.20.11

D=129.34.78.254

TTL=64

Mobile Networks: IP Addressing and Mobile IP 66

example 4 home to foreign
Example: 4) Home to Foreign

2

S=434

D=1105

SPI=303

IP Header

UDP Header

Mobile IP

Auth Ext

Type=3

Code=0

Life=35,000

HA=129.34.78.254

MH=129.34.78.5

S=129.34.78.254

D=9.2.20.11 TTL=64

Mobile Networks: IP Addressing and Mobile IP 67

example 5 foreign to mobile
Example: 5) Foreign to Mobile

2

  • Successful registration is complete

S=434

D=1094

SPI=303

IP Header

UDP Header

Mobile IP

Auth Ext

Type=3

Code=0

Life=35,000

HA=129.34.78.254

MH=129.34.78.5

S=137.0.0.11

D=129.34.78.5

TTL=1

Mobile Networks: IP Addressing and Mobile IP 68

datagram delivery
Datagram Delivery

3

  • 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)

Mobile Networks: IP Addressing and Mobile IP 69

tunneling basics
Tunneling Basics

3

Source

Destination

Tunnel

Encapsulation

Decapsulation

Mobile Networks: IP Addressing and Mobile IP 70

ip in ip encapsulation 1
IP-in-IP Encapsulation (1)

3

OriginalEndpoints

OriginalIP Header

Original IPPayload

TunnelEndpoints

OuterIP Header

OriginalIP Header

Original IPPayload

OtherOptionalHeaders

Mobile Networks: IP Addressing and Mobile IP 71

ip in ip encapsulation 2
IP-in-IP Encapsulation (2)

3

  • 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

Mobile Networks: IP Addressing and Mobile IP 72

special forms of arp
Special Forms of ARP

3

  • 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

Mobile Networks: IP Addressing and Mobile IP 73

route optimization 1
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

Mobile Networks: IP Addressing and Mobile IP 74

route optimization 2
Route Optimization (2)

Binding update

CorrespondingHost

Binding

Cache

HomeAgent

Datagram 1

Datagram 2

Tunnel

ForeignAgent

ACK

MobileHost

Mobile Networks: IP Addressing and Mobile IP 75

summary
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

Mobile Networks: IP Addressing and Mobile IP 76

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