wi - 6 – ip mobility - politecnico di milanohome.deib.polimi.it/capone/wn/wi-en-5-ip...

Politecnico di Milano Facoltà di Ingegneria dell’Informazione

WI - 6 – IP Mobility

Wireless Internet Prof. Antonio Capone

Introduction

o  Mobility management allows a terminal to change its point of access to the network : n  Without changing its address/identifier n  Keeping sessions active (at application level)

o  This is not always necessary n  Application clients do not need to be

reached with the same address/identifier n  They can change address/identifier

whenever they need and issue requests to servers as long as session continuity is not a problem

A. Capone: Wireless Internet 2

Client mobility


Change IP address Start new sessions

Mobility Management (MM) o  If you must be reached by other hosts with your

address/identifier: n  Server applications

o  And/or you want your sessions remain active n  Real time applications

o  Then you need some mobility management support by the network


Application layer

Transport layer

IP Layer

Link layer

Physical layer

Identifiers

Adresses

MM @ application layer

MM @ routing layer

MM @ Application Layer

o Change address and keep the same application layer identifier

o Manage sessions changing their description when address change

o  Examples: n  Dynamic DNS n  SIP



o Dynamic DNS


o  No session continuity o  Mainly devised for static servers with dynamic IP addresses

Dynamic DNS Server

Dynamic DNS Client

Name: myname.com Address: My_IP

DNS query

DNS reply



Foreign domain

Home domain

sip.polimi.it

sip.ucla.edu

3 - INVITE

4 - SIP/2.0 302 Moved Temp.

[email protected]

capone%[email protected]

o SIP mobility

o  Both pre-call and mid-call mobility can be provided with session continuity

MM @ routing layer: Link Layer

o We already analyzed the MM at layer 2 for WiFi:


A

R

AP2 AP1

A

AP3

Bridging tables updated

Broadcast Message (Gratuitous ARP reply)

MM @ routing layer: Link Layer

o  Let’s take a closer look: n  Bridging tables have an entry for each MAC

address n  When terminal changes its access point we

“just” need to update the corresponding entries in all bridging tables of the network

n  This approach is suitable for LANs n  It does not scale up to big networks


MM @ routing layer: IP Layer

o How to manage mobility at IP layer? n  IP routing is based on the network address

(prefix matching)

Network

Network address 131.175.21.0/24

Host address 131.175.21.58/24

Routing Table: … 0.0.0.0/0 è NH_a

Routing Table: … 131.175.0.0/16 è NH_b

Routing Table: … 131.175.21.0/24 è NH_c

131.175.21.0/24 è IF: local_IF



o How to manage mobility at IP layer?

Home Network

Foreign Network

Mobile Host (MH) 124.44.122.78/24



Mobile Host (MH) 124.44.122.78/24

Internet

Corresponding Host (CH)

?



o How to manage mobility at IP layer? n  Can we use the same approach for link

layer mobility è per host routes ?

Network


MH 124.44.122.78/32

Routing Table: … 0.0.0.0/0 è NH_a

Routing Table: … 131.175.0.0/16 è NH_b 124.44.122.78/32 è NH_b

Routing Table: … 131.175.21.0/24 è NH_c 124.44.122.78/32 è NH_c

131.175.21.0/24 è IF: local_IF 124.44.122.78/32 è IF: local_IF



o  Per host routes n  Large routing tables: potentially one entry

per mobile host n  Frequent routing updates that need to be

distributed on the whole network n  Even for a relatively small number of

mobile hosts, managing mobility with per host routes would not be easy


MOBILE IP


Mobile IP o  Mobile IP was developed as a means for

transparently dealing with problems of mobile users n  Enables hosts to stay connected to the Internet

regardless of their location n  Enables hosts to be tracked without needing to

change their IP address n  Requires no changes to software of non-mobile

hosts/routers n  Requires addition of some infrastructure n  Has no geographical limitations n  Requires no modifications to IP addresses or IP

address format n  Supports security


Mobile IP o  Mobile IP is an Internet Engineering Task Force

(IETF) standard communications protocol o  Mobile IP for IPv4 (MIPv4) is described in IETF

RFC 3344 and in RFC 4721


Basics o  Mobile IP allows a mobile host to move about

without changing its permanent IP address (PIP)

o  Each mobile host has a home agent (HA) on its home network (HN)

o  Mobile host establishes a care-of address (COA) when it's away from home


Basics o  Correspondent host is a host that wants to send

packets to the mobile host o  Correspondent host sends packets to the mobile

host’s IP permanent address o  These packets are routed to the mobile host’s

home network o  Home agent forwards IP packets for mobile host to

current care-of address o  Mobile host sends packets directly to

correspondent, using permanent home IP as source IP


Basics

Home Network

Foreign Network

Mobile Host (MH) 124.44.122.78/24


Network address 124.44.122.0/24 Internet



Home Agent

To: COA

Care-of address

o  MHs has two options for the care-of address: n  Foreign agent care-of address: care-of address can

be the address of a foreign agent on the remote network o  home agent tunnels packets to the foreign agent o  foreign agent delivers packets forwarded from home

agent to mobile host n  Co-located care-of address: care-of-address can be a

temporary IP address obtained through DHCP o  home agent tunnels packets directly to the

temporary IP address

o  In any case, care-of address must be registered with home agent


Foreign agent care-of address

Home Network

Foreign Network

Mobile Host (MH) 124.44.122.78/24





Home Agent

To: COA

Foreign Agent

Co-located care-of address

Home Network

Foreign Network

Mobile Host (MH) 124.44.122.78/24





Home Agent

To: COA

Tunneling

o  Packet is encapsulated in another IP packet


Payload Header

Source: CH Destination: PIP

Payload Header

Source: HA Destination: COA

Tables

o  Mobility Binding Table n  Maintained on HA n  Maps MH’s home address

with its current COA

o  Visitor List n  Maintained on FA serving

an MN n  Maps MN’s home address

to its MAC address and HA address

Home address

Care-Of Address

Lifetime (s)

124.44.122.78 131.175.21.78 300

124.44.122.49 197.23.62.34 100

…

Home address

Home Agent Address

Lifetime (s)

124.44.122.78 124.44.122.1 300

167.34.32.44 167.34.32.254 300

…


MIPv4 main functions o Agent discovery

n  HA and FA advertize service availability n  MHs can send solicitations to discover if

an agent is present o Registration

n  MHs registers their COA at the HA either directly or through the FA

n  Registrations are stored in the tables o  Tunneling

n  Has tunnel datagrams to the COA through the IP-in-IP encapsulation


MIPv4 (RFC 3344)

o  Leaves Internet routing fabric unchanged

o Does not assume access points (“base stations”) exist everywhere

o Simple o CHs don’t need to know about

mobility o Works both for changing domains and

network interfaces


MIPv4 Operation (RFC 3344)

o  HAs and FAs advertise their availability using agent-advertisement messages

o  MHs receive advertisement messages and decide if it is a HA or a FA

o  If it is its HA and MH is returning to home network, it deregisters previous COA on the HA

o  If it a new FA, MH requests a COA (either FA COA, or a co-located COA)

o  MH registers the COA at the HA possibly via the FA


MIPv4 Operation (RFC 3344)

o  HA intercepts packets sent to the MH o  HA tunnels packets to the COA o  Packets from the MH are sent directly to

the CH


MIPv4 Operation


Agent Solicitation

Agent Advertisement

Registration Request


Registration Reply

Registration Reply

Data received

agent discovery

registration

tunneling

MH FA HA CH

Encapsulation Decapsulation

Home Agent Operation


MH

ARP reply ARP request

Gratuitous ARP reply

HA

HA

ARP reply

HA

ARP request

Proxy ARP

Home Agent location


Routing Optimization

o Suboptimal “triangle” routing n  Packets are sent to HA first and then

tunneled to the MH o  Possible Solution:

n  Home agent sends current care-of address to correspondent host

n  Correspondent host caches care-of address n  Future packets tunneled directly to care-of

address




Home Network

Foreign Network

MH 124.44.122.78/24



CH

HA

FIRST PACKET Binding cache

CH COA

124.44.122.78 131.175.21.34



Home Network

Foreign Network

MH 124.44.122.78/24



CH

HA

SUBSEQUENT PACKETS

Binding cache

CH COA

124.44.122.78 131.175.21.34

Problems with MIP

o  "Ingress" filtering n  Routers which see packets coming from a direction

from which they would not have routed the source address are dropped


Home Network

Foreign Network

MH 124.44.122.78/24



CH

HA

To: COA

ERROR: Topologically incorrect

Problems with MIP

o Security issues: n  Malicious host sends fake registration

messages to home agent "on behalf" of the mobile host

n  Packets could be forwarded to malicious host or to the bit bucket

n  Solution: use secure authentication for registration request/reply

n  Several other security issues …


Mobility in IPv6 o  Route Optimization is a fundamental

part of Mobile IPv6 n  Mobile IPv4 it is an optional set of

extensions that may not be supported by all nodes

o  Foreign Agents are not needed in Mobile IPv6 n  MNs can function in any location without the

services of any special router in that location o  Security

n  Nodes are expected to employ strong authentication and encryption


Hierarchy in MM

o  Registration needed every time MH moves o  Registration adds delay when HA is far away


Home Network

Foreign Network

A

MH

Internet

HA


Registration Reply

Foreign Network

B Registration Request

Registration Reply

Foreign Network

C

Hierarchy in MM o  Hierarchy of

FAs or Mobility Routers

o  Hierarchical MIP, Cellular IP, etc.


Home Network

Foreign Network

A

MH

Internet

HA


Registration Reply

Foreign Network

B

FA1

FA2

FA3

FA4 FA5

wi - 6 – ip mobility - politecnico di milanohome.deib.polimi.it/capone/wn/wi-en-5-ip...

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