Transcript ECE/CS 4984: Lecture 10

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
Mobile Networks: IP Addressing and Mobile IP
2
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
● IPv4 addresses…
■ Uniquely identify an interface
■ 32 bits long
■ Consist of a network identifier and a host identifier
0
31
Network Identifier
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
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4
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
Class A
01234
0 netid
8
16
24
31
Class B
10
Class C
110
netid
Class D
1110
multicast address
Class E
1111
reserved for future use
hostid
netid
Mobile Networks: IP Addressing and Mobile IP
hostid
hostid
5
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
● 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
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IP Routing
● Router uses routing table to direct packets to the
appropriate interface
Target
2.0.0.0/24
3.0.0.0/24
4.0.0.0/24
Interface
a
b
c
3.0.0.2
3.0.0.3
4.0.0.5
4.0.0.6
3.0.0.4
b
a
Dest = 3.0.0.4
Router
Mobile Networks: IP Addressing and Mobile IP
c
8
Traditional Routing for a Mobile Host
● Host moving to another network is unreachable
Target
2.0.0.0/24
3.0.0.0/24
4.0.0.0/24
Interface
a
b
c
3.0.0.2
3.0.0.3
b
X
a
Dest = 3.0.0.4
Router
c
Mobile
Host
4.0.0.5
Mobile Networks: IP Addressing and Mobile IP
3.0.0.4
4.0.0.6
3.0.0.4
9
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
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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
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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
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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
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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
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Mobile IP Overview: Data Flow
Home
Agent
10.92.2.3
Correspondent
Node (Host)
10.0.8.5
10.0.8.5
10.92.2.3
10.4.5.43
10.4.5.0/24
Mobile Networks: IP Addressing and Mobile IP
10.0.8.0/24
Foreign
10.4.5.43
Agent
10.0.8.5
Mobile
10.0.8.5
Host
15
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
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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
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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
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Mobile IP Operation (3)
● Datagrams sent by the mobile node are delivered
directly to the destination
■ No need to pass through the home agent
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Mobile IP Details (1)
● Agent discovery 1
■ ICMP router discovery
■ Mobility agent discovery operation
■ Agent advertisement and solicitation messages
● Registration 2
■ Registration operation
■ Authentication
■ Registration request and reply messages
■ Security
■ Example
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Mobile IP Details (2)
● Datagram delivery 3
■ Encapsulation principles and schemes
■ ARP issues
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1
Agent Discovery
● 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
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1
Router Discovery Operation
● 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
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1
Router Discovery Message (1)
ICMP
Header
IP Header
ICMP
Message
ICMP Message
0
8
16
24
31
type
code
checksum
num addrs addr entr sz
lifetime
router address (1)
preference (1)
..
.
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1
Router Discovery Message (2)
● 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
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1
Router Discovery Message (3)
● 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)
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1
Router Solicitation Operation
● 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
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1
Router Solicitation Message
0
8
type
16
code
reserved
24
31
checksum
● Type: ICMP type (10)
● Code: code for this type (0)
● Checksum: checksum over full message
● Reserved: sent as 0; ignored by receiver
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1
Agent Advertisement
● 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)
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1
Advertising by Mobility Agents
● 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
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1
Agent Discovery by Mobile Hosts
● 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
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1
Advertisement Features (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)
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1
Advertisement Features (2)
● 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
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1
Agent Advertisement Extension (1)
(follows ICMP router discovery)
0
8
type
length
registration lifetime
16
24
31
sequence number
RBHFMGV
reserved
zero or more care-of addresses
● 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
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1
Agent Advertisement Extension (2)
● 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
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35
1
Agent Advertisement Extension (3)
● 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
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1
Agent Solicitation Message
● Same as ICMP router solicitation message
■ TTL = 1 required
● Used in a slightly different way
■ Frequency
■ Number of attempts
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2
Registration
● 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
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38
2
Registration Preliminaries (1)
● 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
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39
2
Registration Preliminaries (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
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40
2
Registration Via Foreign Agent
Mobile
Host
MH
(1)
(2)
FA
(5)
1.
2.
3.
4.
5.
Foreign
Agent
Home
Agent
(3)
HA
(4)
FA advertises service
MH requests service
FA relays request to HA
HA accepts (or denies) request and replies
FA relays reply to MH
Mobile Networks: IP Addressing and Mobile IP
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2
Authentication (1)
● 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)
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42
2
Authentication (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
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2
Registration Message Format
● Carried in UDP datagrams
IP Header
UDP Header
Mobile IP
Message Header
Extensions …
● 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
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44
2
Registration Request Message (1)
0
8
type
16
24
31
SBDMGVrsv
lifetime
home address
home agent
care-of address
identification
extensions ...
Mobile Networks: IP Addressing and Mobile IP
45
2
Registration Request Message (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)
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46
2
Registration Request Message (3)
● 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
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2
Registration Request Message (4)
● 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
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2
Registration Request Message (5)
● 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
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49
2
IP for Registration Requests
● 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
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2
UDP for Registration Requests
● Source port: Variable (dynamically assigned by
operating system, for example)
● Destination port: 434 (well-known port number)
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2
Registration Reply Message (1)
0
8
type
16
code
home address
home agent
24
31
lifetime
identification
extensions ...
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52
2
Registration Reply Message (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
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2
Registration Reply Message (3)
● 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
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54
2
IP for Registration Replies
● 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
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2
UDP for Registration Replies
● Source port: Variable
● Destination port: Copied from the source port of the
associated registration request
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56
2
Security Parameter Index
● 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
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57
2
Authentication Extension
0
8
type
code
SPI (second two bytes)
16
24
31
SPI (first two bytes)
authenticator …
● 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)
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58
2
Order of Extensions
● Example -- registration request from mobile host to
home agent via foreign agent
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
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59
2
Registration Information (1)
● 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
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60
2
Registration Information (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
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2
Registration Information (3)
● 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
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62
2
FA Care-of Address Example
● Example values
■ Mobile host’s home address
■ Mobile host’s home agent
■ Foreign agent’s link address
■ Foreign agent’s care-of address
■ Mobile node’s source port
■ Foreign agent’s source port
■ Care-of registration lifetime
■ Home agent-granted lifetime
■ SPI (mobile node/home agent)
129.34.78.5
129.34.78.254
137.0.0.11
9.2.20.11
1094
1105
60,000 s
35,000 s
302/303
From C. E. Perkins, Mobile IP: Design Principles and
Practices, Addison-Wesley, Reading, MA, 1998.
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63
2
Example: 1) Agent Advertisement
● Foreign agent discovery
Type=9
Code=16
IP Header
ICMP Header Router Adv
S=137.0.0.11
D=255.255.255.255
F=1
Mobile Networks: IP Addressing and Mobile IP
Mobile Ext
Life=60,000
COA=9.2.20.11
64
2
Example: 2) Mobile to Foreign
● Registration using the foreign agent
S=1094
D=434
IP Header
UDP Header
S=129.34.78.5
D=137.0.0.11
TTL=64
Mobile Networks: IP Addressing and Mobile IP
SPI=302
Mobile IP
Auth Ext
Type=1
Life=60,000
COA=9.2.20.11
HA=129.34.78.254
MH=129.34.78.5
65
2
Example: 3) Foreign to Home
S=1105
D=434
IP Header
UDP Header
S=9.2.20.11
D=129.34.78.254
TTL=64
Mobile Networks: IP Addressing and Mobile IP
SPI=302
Mobile IP
Auth Ext
Type=1
Life=60,000
COA=9.2.20.11
HA=129.34.78.254
MH=129.34.78.5
66
2
Example: 4) Home to Foreign
S=434
D=1105
IP Header
UDP Header
S=129.34.78.254
D=9.2.20.11
TTL=64
Mobile Networks: IP Addressing and Mobile IP
SPI=303
Mobile IP
Auth Ext
Type=3
Code=0
Life=35,000
HA=129.34.78.254
MH=129.34.78.5
67
2
Example: 5) Foreign to Mobile
S=434
D=1094
IP Header
UDP Header
S=137.0.0.11
D=129.34.78.5
TTL=1
SPI=303
Mobile IP
Auth Ext
Type=3
Code=0
Life=35,000
HA=129.34.78.254
MH=129.34.78.5
● Successful registration is complete
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3
Datagram Delivery
● 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)
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3
Tunneling Basics
Source
Destination
Tunnel
Encapsulation
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Decapsulation
70
3
IP-in-IP Encapsulation (1)
Original
Endpoints
Tunnel
Endpoints
Outer
IP Header
Original
IP Header
Original IP
Payload
Original
IP Header
Original IP
Payload
Other
Optional
Headers
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3
IP-in-IP Encapsulation (2)
● 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
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3
Special Forms of ARP
● 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
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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
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Route Optimization (2)

Binding
Cache

Corresponding  Datagram 1
Host
Datagram 2

Binding update
Home
Agent

Tunnel
Foreign
Agent
ACK
Mobile
Host
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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
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