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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
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
A. Capone: Wireless Internet 4
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
A. Capone: Wireless Internet 5
MM @ Application Layer
o Dynamic DNS
A. Capone: Wireless Internet 6
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
MM @ Application Layer
A. Capone: Wireless Internet 7
Foreign domain
Home domain
sip.polimi.it
sip.ucla.edu
3 - INVITE
4 - SIP/2.0 302 Moved Temp.
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. Capone: Wireless Internet 8
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
A. Capone: Wireless Internet 9
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
A. Capone: Wireless Internet 10
MM @ routing layer: IP Layer
o How to manage mobility at IP layer?
Home Network
Foreign Network
Mobile Host (MH) 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24
Mobile Host (MH) 124.44.122.78/24
Internet
Corresponding Host (CH)
?
A. Capone: Wireless Internet 11
MM @ routing layer: IP Layer
o How to manage mobility at IP layer? n Can we use the same approach for link
layer mobility è per host routes ?
Network
Network address 131.175.21.0/24
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
A. Capone: Wireless Internet 12
MM @ routing layer: IP Layer
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
A. Capone: Wireless Internet 13
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
A. Capone: Wireless Internet 15
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
A. Capone: Wireless Internet 16
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
A. Capone: Wireless Internet 17
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
A. Capone: Wireless Internet 18
Basics
Home Network
Foreign Network
Mobile Host (MH) 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24 Internet
Corresponding Host (CH)
A. Capone: Wireless Internet 19
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
A. Capone: Wireless Internet 20
Foreign agent care-of address
Home Network
Foreign Network
Mobile Host (MH) 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24 Internet
Corresponding Host (CH)
A. Capone: Wireless Internet 21
Home Agent
To: COA
Foreign Agent
Co-located care-of address
Home Network
Foreign Network
Mobile Host (MH) 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24 Internet
Corresponding Host (CH)
A. Capone: Wireless Internet 22
Home Agent
To: COA
Tunneling
o Packet is encapsulated in another IP packet
A. Capone: Wireless Internet 23
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
…
A. Capone: Wireless Internet 24
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
A. Capone: Wireless Internet 25
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
A. Capone: Wireless Internet 26
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
A. Capone: Wireless Internet 27
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
A. Capone: Wireless Internet 28
MIPv4 Operation
A. Capone: Wireless Internet 29
Agent Solicitation
Agent Advertisement
Registration Request
Registration Request
Registration Reply
Registration Reply
Data received
agent discovery
registration
tunneling
MH FA HA CH
Encapsulation Decapsulation
Home Agent Operation
A. Capone: Wireless Internet 30
MH
ARP reply ARP request
Gratuitous ARP reply
HA
HA
ARP reply
HA
ARP request
Proxy ARP
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
A. Capone: Wireless Internet 32
Routing Optimization
A. Capone: Wireless Internet 33
Home Network
Foreign Network
MH 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24 Internet
CH
HA
FIRST PACKET Binding cache
CH COA
124.44.122.78 131.175.21.34
Routing Optimization
A. Capone: Wireless Internet 34
Home Network
Foreign Network
MH 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24 Internet
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
A. Capone: Wireless Internet 35
Home Network
Foreign Network
MH 124.44.122.78/24
Network address 131.175.21.0/24
Network address 124.44.122.0/24 Internet
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 …
A. Capone: Wireless Internet 36
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
A. Capone: Wireless Internet 37
Hierarchy in MM
o Registration needed every time MH moves o Registration adds delay when HA is far away
A. Capone: Wireless Internet 38
Home Network
Foreign Network
A
MH
Internet
HA
Registration Request
Registration Reply
Foreign Network
B Registration Request
Registration Reply