Transcript home agent

Mobile IP
Overview and
Discussion
Mobility: Vocabulary
home network: permanent
“home” of mobile
(e.g., 128.119.40/24)
Permanent address:
address in home
network, can always be
used to reach mobile
e.g., 128.119.40.186
home agent: entity that will
perform mobility functions on
behalf of mobile device, when
mobile device is remote
wide area
network
correspondent
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Mobility: Vocabulary
Permanent address: remains
constant (e.g., 128.119.40.186)
visited network: network
in which mobile currently
resides (e.g., 79.129.13/24)
Care-of-address: address
in visited network.
(e.g., 79.129.13.2)
wide area
network
correspondent hosts:
wants to communicate
with mobile device
foreign agent: entity in
visited network that
performs mobility
functions on behalf of
mobile agent.
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Mobility: approaches


Let routing handle it: routers advertise permanent
address of mobile-nodes-in-residence via usual
routing table exchange.
– routing tables indicate where each mobile node is
located
– no changes to end-systems
Let end-systems handle it:
– indirect routing: communication from
correspondent to mobile device goes through
home agent, then forwarded to remote
– direct routing: correspondent gets foreign
address of mobile device, sends directly to
mobile device
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Mobility: approaches


Let routing handle it: routers advertise permanent
address of mobile-nodes-in-residence
via usual
not
routing table exchange.
scalable
– routing tablestoindicate
where each mobile
millions of
located
mobiles
– no changes to end-systems
Let end-systems handle it:
– indirect routing: communication from
correspondent to mobile device goes through
home agent, then forwarded to remote
– direct routing: correspondent gets foreign
address of mobile device, sends directly to
mobile device
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Mobility: registration
visited network
home network
2
1
wide area
network
foreign agent contacts home
agent: “this mobile is resident in
my network”
mobile host
contacts foreign
agent on entering
visited network
End result:
 Foreign agent knows about mobile device
 Home agent knows location of mobile device
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Mobility via Indirect Routing
foreign agent
receives packets,
forwards to mobile
home agent intercepts
packets, forwards to
foreign agent
home
network
visited
network
3
wide area
network
correspondent
addresses packets
using home
(“permanent”)
address of mobile
1
2
4
mobile unit
replies directly
to correspondent
8
Indirect Routing: comments



Mobile uses two addresses:
– permanent address: used by correspondent
(hence mobile location is transparent to
correspondent hosts)
– care-of-address: used by home agent to forward
datagrams to mobile device
foreign agent functions may be done by mobile
device itself
triangle routing: correspondent-home-networkmobile
– inefficient when
correspondent, mobile
are in same network
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Forwarding datagrams to remote
mobile via Tunneling
foreign-agent-to-mobile packet
packet sent by home agent to foreign
agent: a packet within a packet
dest: 79.129.13.2
dest: 128.119.40.186
dest: 128.119.40.186
Permanent address:
128.119.40.186
dest: 128.119.40.186
Care-of address:
79.129.13.2
packet sent by
correspondent
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Indirect Routing: moving between
networks

suppose mobile user moves to another
network
–
–
–
–

registers with new foreign agent
new foreign agent registers with home agent
home agent update care-of-address for mobile
packets continue to be forwarded to mobile (but
with new care-of-address)
Mobility, changing foreign networks is
transparent: on going connections can be
maintained!
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Mobility via Direct Routing
correspondent forwards
to foreign agent
foreign agent
receives packets,
forwards to mobile
home
network
4
wide area
network
2
correspondent
requests, receives
foreign address of
mobile device
visited
network
1
3
4
mobile device
replies directly
to correspondent
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Mobility via Direct Routing:
comments
overcomes triangle routing problem
 non-transparent to correspondent:
correspondent must get care-ofaddress from home agent

– What happens if mobile node changes
networks?
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Mobile IP

RFC 3344 (August 2002) - three
main components of standard:
– agent discovery
– registration with home agent
– routing considerations
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Mobile IP: agent discovery

agent advertisement: foreign/home agents
advertise service by broadcasting ICMP
messages (typefield = 9)
0
type = 9
24
checksum
code = 0
H,F bits: home
and/or foreign agent
R bit: registration
required
16
8
router address
type = 16
length
registration lifetime
standard
ICMP fields
sequence #
RBHFMGrT
reserved
bits
0 or more care-ofaddresses
mobility agent
advertisement
extension
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Mobile IP: registration
example
home agent
HA: 128.119.40.7
foreign agent
COA: 79.129.13.2
visited network: 79.129.13/24
ICMP agent adv.
COA: 79.129.13.2
….
registration req.
COA: 79.129.13.2
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 9999
identification: 714
encapsulation format
….
Mobile agent
MA: 128.119.40.186
registration req.
COA: 79.129.13.2
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 9999
identification:714
….
Message is sent
via UDP to port
434.
registration reply
time
HA: 128.119.40.7
MA: 128.119.40.186
Lifetime: 4999
Identification: 714
encapsulation format
….
registration reply
HA: 128.119.40.7
MA: 128.119.40.18 6
Lifetime: 4999
Identification: 714
….
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