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Mobile IP

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... stable for a longer time (HA responsible for a MN over a longer period of time) ... Centralised approaches don't work things change too quickly ... – PowerPoint PPT presentation

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Title: Mobile IP


1
Mobile IP
  • Why do we need it?
  • Data transfer and encapsulation
  • Security
  • IPv6
  • Micro mobility support
  • DHCP
  • Ad-hoc networks - routing

2
Revision IP addresses
Addressing example Internet Port
202.60.77.121 Router assigns private addresses
beginning with 192.168.x.x PC-A 192.168.0.2 PC-B
192.168.0.3 PC-C 192.168.0.4 PC-D
192.168.0.5 Mobile 192.168.0.7
202.60.77.0
3
What is the problem?
  • IP address net-id (used by routers) host-id
    When you move, how will routers know?
  • Easy assign a new IP address via DHCP
  • But who tells people if they want to contact
    you?
  • Easy DNS, change the name-address mapping
  • But DNS updates take time, not scaleable
  • Use explicit routing table entries for mobiles
  • But not scalable, RIP works in software, not
    very fast
  • Another problem what happens to TCP connections
    when you roam?

4
Requirements for Mobile IP
  • No changes to existing systems e.g. addresses,
    routing
  • Transparency to user e.g. TCP connections
  • Mobility awareness as necessary
  • Must be scalable increasing size of network
  • Efficient low overheads
  • Security IP spoofing is easy!

5
Components of Mobile IP
mobile end-system
MN, CN are the communicating nodes HA, FA, home
NW, foreign NWintermediaries COA may be IP
addr. of FA or a temp. (foreign) address for
the MN
6
Data transfer to the mobile system
HA
2
MN
Internet
home network
receiver
3
FA
foreign network
1. Sender sends to the IP address of MN, HA
intercepts packet (proxy ARP) 2. HA tunnels
packet to COA, here FA, by encapsulation 3.
FA forwards the packet to the MN
1
CN
sender
7
Overview
COA
foreign network
router FA
MN
router HA
home network
Internet
CN
router
foreign network
3.
router FA
MN
router HA
home network
2.
4.
Internet
1.
CN
router
8
Additional mechanisms
  • Agent discovery how to find a foreign agent?
  • Agent advertisements (ICMP) by HA and FA
  • Agent Solicitation MN seeks a router.
  • Frequency and number of such messages are
    strictly controlled.
  • The MN receives a COA perhaps via a FA
  • It can then register itself with the HA,
    authentication is needed.
  • UDP packets are used for registration

9
Moving to a new network
  • Agent Advertisement
  • HA and FA periodically send advertisement
    messages into their physical subnets
  • MN listens to these messages and knows if it is
    in the home or a foreign network
  • MN reads a COA from the FA advertisement messages
  • Registration (always with a limited lifetime)
  • MN signals COA to the HA via the FA, HA acks via
    FA to MN
  • these actions have to be secured by
    authentication
  • Route Advertisement
  • HA advertises the IP address of the MN (as for
    fixed systems), i.e. standard routing information
  • routers adjust their entries, these are stable
    for a longer time (HA responsible for a MN over a
    longer period of time)
  • packets to the MN are sent to the HA,
  • independent of changes in COA/FA

10
Registration
(a) COA in the FA and (b) COA colocated with
Mobile Node
11
Encapsulation
Standard IP in IP Minimum common fields
omitted Generic defined for use with non-IP
protocols
12
Encapsulation IPv4 in IPv4Standard
13
Minimum Encapsulation
  • Avoids repetition of identical fields
  • TTL, IHL, version, DS (RFC 2474, old TOS)
  • Only applicable for unfragmented packets, no
    space left for fragment identification

14
Optimization of packet forwarding
  • Triangular Routing
  • sender sends all packets via HA to MN
  • higher latency and network load
  • Solutions
  • sender learns the current location of MN
  • direct tunneling to this location
  • HA informs a sender about the location of MN
  • big security problems!

15
Change of foreign agent
CN
HA
FAold
FAnew
MN
Data
Data
Data
Update
ACK
Data
Data
MN changeslocation
Registration
Update
ACK
Data
Data
Data
Warning
Request
Update
ACK
Data
Data
t
16
Mobile IP with reverse tunneling
  • Home IP address of MN may not be valid from the
    foreign network (topologically incorrect), may be
    rejected by firewalls.
  • The solution - a reverse tunnel from FA to HA
  • This has problems too
  • Security tunnel hijacking by MN the firewall
    no longer filters packets coming in on the tunnel
  • Triangular routing in reverse inefficient.

17
Reverse tunneling (RFC 3024, was 2344)
HA
2
MN
Internet
home network
sender
1
FA
foreignnetwork
1. MN sends to FA 2. FA tunnels packets to HA
by encapsulation 3. HA forwards the packet to
the receiver (standard case)
3
CN
receiver
18
Mobility with IPv6 is easier
  • No need for a separate FA, all routers perform
    router (agent) advertisement
  • COA addresses acquired via autoconfiguration are
    always co-located
  • MN can send its COA directly to the CN, HA not
    needed in this case (automatic path optimization)
  • Soft hand-over, (without packet loss), between
    two subnets is supported
  • MN sends the new COA to its old FA router
  • The old router encapsulates all incoming packets
    for the MN and forwards them to the new COA
  • Authentication is always granted

19
IP Micro-mobility support
  • Micro-mobility support
  • Efficient local handover inside a foreign
    domainwithout involving a home agent
  • Reduces control traffic on backbone
  • Especially needed in case of route optimization
  • Example approaches
  • Cellular IP
  • HAWAII
  • Hierarchical Mobile IP (HMIP)
  • Important criteria Security, Efficiency,
    Scalability, Transparency, Manageability

20
DHCP Dynamic Host Configuration Protocol
  • supplies systems with IP address, DNS server
    address, domain name, subnet mask, default router
    etc.
  • enables automatic integration of systems into an
    Intranet or the Internet, can be used to acquire
    a COA for Mobile IP
  • Client/Server-Model - the client sends a MAC
    broadcast
  • request to the DHCP server (might be via a DHCP
    relay)

21
DHCP - protocol mechanisms
client
server (not selected)
server (selected)
initialization
DHCPDISCOVER
DHCPDISCOVER
determine the configuration
determine the configuration
DHCPOFFER
DHCPOFFER
collection of replies
selection of configuration
time
DHCPREQUEST(reject)
DHCPREQUEST(options)
confirmation of configuration
DHCPACK
initialization completed
release
delete context
DHCPRELEASE
22
DHCP characteristics
  • Server - several servers can be configured for
    DHCP, coordination not yet standardized
  • Renewal of configurations
  • IP addresses have to be requested periodically,
    simplified protocol
  • Options to acquire other parameters addresses
  • Default routers, subnet mask, NTP (network time
    protocol) timeserver, SLP (service location
    protocol) directory, DNS (domain name system)
  • Big security problems!
  • RFC3118 specifies authentication of DHCP
    information.

23
Routing in wiress networks
  • Asymmetric links need to adapt algorithms
  • Redundant links all links are possible in
    theory!
  • Interference from other transmissions, varies
    with time.
  • Changing link quality (with time) - links are not
    defined by wires, not an on-off situation
  • Changing topology as nodes move, join and leave
  • Limited bandwidth now need to send routing info
    as well
  • Limited computing power of mobile nodes, sleep
    modes to save power.

24
Changes to routing algorithms
  • RIP, OSPF convergence too slow
  • Layer 3 knowledge not enough, layer 2 (link
    quality) needed.
  • Centralised approaches dont work things change
    too quickly
  • All nodes must participate not just routers
  • Connections may not be maintainable over any
    length of time quality may suffer.
  • Flooding is not such a bad way of routing but
    no. of hops must be controlled.

25
The following slides are not required for exam
purposes
26
Cellular IP Security (for info only)
  • Advantages
  • Initial registration involves authentication of
    MNsand is processed centrally by CIP Gateway
  • All control messages by MNs are authenticated
  • Replay-protection (using timestamps)
  • Potential problems
  • MNs can directly influence routing entries
  • Network key known to many entities(increases
    risk of compromise)
  • No re-keying mechanisms for network key
  • No choice of algorithm (always MD5, prefixsuffix
    mode)
  • Proprietary mechanisms (not, e.g., IPSec AH)

27
Cellular IP (for info only)
  • Operation
  • CIP Nodes maintain routing entries (soft state)
    for MNs
  • Multiple entries possible
  • Routing entries updated based on packets sent by
    MN
  • CIP Gateway
  • Mobile IP tunnel endpoint
  • Initial registration processing
  • Security provisions
  • all CIP Nodes sharenetwork key
  • MN key MD5(net key, IP addr)
  • MN gets key upon registration

28
Cellular IP Other issues (for info only)
  • Advantages
  • Simple and elegant architecture
  • Mostly self-configuring (little management
    needed)
  • Integration with firewalls / private address
    support possible
  • Potential problems
  • Not transparent to MNs (additional control
    messages)
  • Public-key encryption of MN keys may be a
    problemfor resource-constrained MNs
  • Multiple-path forwarding may cause inefficient
    use of available bandwidth

29
Mobile ad hoc networks (for info only)
  • Standard Mobile IP needs an infrastructure
  • Home Agent/Foreign Agent in the fixed network
  • DNS, routing etc. are not designed for mobility
  • Sometimes there is no infrastructure!
  • remote areas, ad-hoc meetings, disaster areas
  • cost can also be an argument against an
    infrastructure!
  • Routing - no default router available every node
    should be able to forward

30
Manet Mobile Ad-hoc Networking (for info only)
31
Routing examples for an ad-hoc network
Routing Table at N5 Time T1 N1-N4 N2-N4 N3-N3
N4-N4 Time T2 N1-N3 N2-N4 N3-N3 N4-N4
32
DSDV (Destination Sequenced Distance Vector)
  • Two additions to distance vector routing
  • Sequence numbers for all routing updates
  • assures in-order execution of all updates
  • avoids loops and inconsistencies
  • Decrease of update frequency
  • store time between first and best announcement of
    a path
  • inhibit update if it seems to be unstable (stored
    time values are too short)

33
Dynamic source routing I
  • Similar to token rings.
  • Two stages route discovery maintenance
  • No periodic updates needed
  • Route Discovery
  • only if no path is currently available
  • Source node broadcasts request (destination id)
  • Non-destination nodes add their addresses and
    broadcast
  • Destination node responds with the best path.
    It may have to do a route discovery back to the
    source
  • Optimisation are possible limit hops, caching

34
Path Maintenance
  • Maintaining paths
  • after sending a packet
  • wait for a layer 2 acknowledgement (if
    applicable)
  • listen into the medium to detect if the next
    station(s) forward the packet (if possible)
  • request an explicit acknowledgement
  • Any intermediate node detecting connectivity
    problems either informs the sender or tries to
    find a local route itself

35
Alternative Routing Metrics
  • Traditional no. of hops
  • Interference choose a path which minimises
    interference from other nearby nodes potential
    interference at a node is proportional to number
    of neighbours audible at that node.
  • Reliability how good has the link been over
    time?
  • Error rate can be measured and averaged

36
Categories of routing protocols(research area)
  • Flat ad hoc routing all nodes are equal
    examples AODV, DSDV, DSR. May be proactive or
    reactive AI techniques may be used.
  • Hierarchical similar to autonomous systems
    scalable. Divide the nodes into clusters, with
    one node within a cluster having responsibility
  • Geographical position based using GPSbut
    geographical closeness may not ensure a good
    link!

37
Finding routes min. hop, LIR
38
Dynamic Source Routing Example
good link weak link
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