How Mobile IP Works?
Presenter: Ajoy Singh
Agenda
Required background
What problems does Mobile IP solve?
Mobile IP: protocol overview
5/2/2002
Scope
Requirements
Design goals
Functional entities
How Mobile IP Works?
2
Agenda (continued)
The gory details
Agent discovery
Registration
Packet delivery
Case study: campus mobility
Q&A
5/2/2002
How Mobile IP Works?
3
Required Background
I am assuming you already know:
the different layers of the OSI model,
what IP and ICMP are,
what ARP, proxy ARP and gratuitous ARP
are,
IP:
how IP routing works.
IP:Internet
InternetProtocol
Protocol
ICMP:
ICMP:Internet
InternetControl
Control
Message
MessageProtocol
Protocol
ARP:
ARP:Address
Address
Resolution
ResolutionProtocol
Protocol
5/2/2002
How Mobile IP Works?
4
What Problems Does Mobile IP
Solve?
An IP address not only identifies a host
but also a point-of-attachment.
Host-specific routes approach suffers
from serious scalability, robustness and
security concerns if applied to the
global Internet.
Mobility
Mobilityisisthe
theability
abilityofofaanode
nodetoto
change
changeits
itspoint-of-attachment
point-of-attachmentwhile
while
maintaining
all
existing
communications
maintaining all existing communications
and
andusing
usingthe
thesame
sameIP
IPaddress.
address.
5/2/2002
How Mobile IP Works?
5
What Problems Does Mobile IP
Solve? (continued)
A host cannot change its IP address
without terminating on-going sessions
and restarting them after it acquires a
new address.
Other link layer mobility solutions exist
but are not sufficient enough for the
Nomadicity
Nomadicityallows
allowsaanode
nodetotomove
move
global Internet.
but
butititmust
mustterminate
terminateall
allexisting
existing
communications
communicationsand
andthen
thencan
caninitiate
initiate
new
connections
with
a
new
address.
new connections with a new address.
5/2/2002
How Mobile IP Works?
6
Mobile IP: Protocol Overview
5/2/2002
How Mobile IP Works?
7
Scope
Mobile IP is a network layer solution for
homogenous and heterogeneous
mobility on the global Internet which is
scalable, robust, secure and which
allows nodes to maintain all ongoing
communications while moving.
5/2/2002
How Mobile IP Works?
8
Requirements
MN must be able to communicate with
other nodes after changing its LL POA.
MN must be able to communicate using
only its home (permanent) IP address
regardless of its current LL POA.
MN:
MN:mobile
mobilenode
node
LL:
LL:link
linklayer
layer
POA:
POA:point-of-attachment
point-of-attachment
5/2/2002
How Mobile IP Works?
9
Requirements (continued)
MN must be able to communicate with
other nodes that do not implement
Mobile IP mobility functions.
MN must not be exposed to any new
security threats over and above those
which any fixed node on the Internet is
exposed to.
5/2/2002
How Mobile IP Works?
10
Design Goals
Mobile IP was designed to make the
size and the frequency of required
routing updates as small as possible.
It was designed to make it simple to
implement mobile node software.
It was designed to avoid solutions that
require mobile nodes to use multiple
addresses.
5/2/2002
How Mobile IP Works?
11
Functional Entities
Mobile Node (MN): a node which can
change its POA while maintaining any
ongoing communications and using only its
home (permanent) IP address.
Home Agent (HA): a router with at least
one interface on the MN’s home link which:
5/2/2002
MN keeps informed of its current location, i.e., its
care-of-address (COA),
intercepts packets destined to the MN’s home
address and tunnels them to the MN’s current
location (or COA).
How Mobile IP Works?
12
Functional Entities (continued)
Foreign Agent (FA): a router on a foreign
link which:
5/2/2002
assists the MN in informing its HA of its current
COA,
sometimes, provides a COA and de-tunnels
packets for the MN,
acts as the default router for packets generated by
the MN while connected to this foreign link.
How Mobile IP Works?
13
Correspondent Node
Home Agent
Router 3
Internet
Router 1
Foreign Agent
Router 2
Mobile
Node
5/2/2002
How Mobile IP Works?
14
Common Scenario (1)
HA
CN
4
Router 3
Router 1
3
FA
MN
Home Link
Internet
2
5
1
Router 2
Foreign Link
5/2/2002
How Mobile IP Works?
15
Common Scenario (2)
CN
HA
1
3
Router 3
2
Router 1
6
FA
MN
Home Link
Internet
4
5
Router 2
Foreign Link
5/2/2002
How Mobile IP Works?
16
Agenda Progress
Required background
What problems does Mobile IP solve?
Mobile IP: protocol overview
The gory details
Agent discovery
Registration
Packet delivery
Case study: campus mobility
Q&A
5/2/2002
How Mobile IP Works?
17
The Gory Details
5/2/2002
How Mobile IP Works?
18
Agent Discovery
Agent discovery allows the MN to:
Agent discovery consists of 2 messages:
determine whether it is @ home or not,
detect whether it has moved,
obtain a COA when away from home.
Agent Advertisement
Agent Solicitation
MN determines it has moved in 2 ways:
5/2/2002
move detection using advertisement lifetimes
move detection using network prefixes
How Mobile IP Works?
19
Registration
Mobile IP registration allows the MN to:
5/2/2002
request routing services from a FA,
inform its HA of its current COA,
renew a registration which is about to expire,
deregister when it returns home,
have multiple simultaneous COA’s registered with
its HA,
deregister a particular COA while retaining others,
dynamically discover the address of a potential
HA.
How Mobile IP Works?
20
Registration (continued)
Registration consists of 2 messages:
5/2/2002
registration request
registration reply
How Mobile IP Works?
21
Q&A
Any Questions?
5/2/2002
How Mobile IP Works?
22
Agent Solicitation Message
IP Header Fields
Type = 10
Code = 0
Checksum
reserved
5/2/2002
How Mobile IP Works?
IP header
ICMP
Router
Solicitation
23
Agent Advertisement Message
IP Header Fields
IP Header
Type = 9
Code
Checksum
Num Addrs
Addr Entry Size
Advertisement Lifetime
Router Address [1]
Preference Level [1]
ICMP Router
Advertisement
…
Type = 16
Length
Max Registration Lifetime
Sequence Number
R
B
H
F
M G
V
reserved
Care-of-address [1]
Mobility Agent
Advertisement
Extension
…
Type = 19
Length
…
…
5/2/2002
Prefix-Length[1] Prefix-Length[2]
How Mobile IP Works?
Prefix-Length
Extension
(Optional)
24
Registration Request Message
Type = 1
S
B
D
IP Header Fields
IP Header
UDP Header Fields
UDP Header
M G
V
rsv
Lifetime (requested)
MN’s Home Address
HA Address
COA Address
Fixed-Length
Portion of
Registration
Request
Identification (64 bits)
Optional Extensions
Type = 32
Length
Security Parameter …
… Index (SPI)
Authenticator (Default equals Keyed MD5)
Mobile-Home
Authentication
Extension
More Optional Extensions …
5/2/2002
How Mobile IP Works?
25
Registration Reply Message
(Fixed Portion Only)
Type = 3
Code
Lifetime (granted)
MN’s Home Address
HA Address
FixedLength
Portion of
Registrati
on Reply
Identification
5/2/2002
How Mobile IP Works?
26