Mobile IPv6

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Mobile IPv6

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Overview

• Mobile IPv6 allows an IPv6 Mobile Node (MN)
• To be reachable and maintain ongoing connections
  while changing their location within the
  topology.
• Stateful and stateless address autoconfiguration
  allow for the change in addresses
• The existing connections are ungracefully
  terminated

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Key Benefit of Mobile IPv6

• Even though the mobile node changes locations and
  addresses
• the existing connections through which the MN is
  communicating are maintained.

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Components of Mobile IPv6

• Mobile Node (MN)
• A node that changes its location within the
  Internet topology.
• Correspond Node (CN)
• Any node that communicates within the mobile
  node.
• Home Address
• A stable address that belongs to the MN and is
  used by CNs to reach MNs.
• Home link
• A link to which the home address prefix is
  assigned.

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Components of Mobile IPv6 (Cont.)

• Home Agent (HA)
• A router located on the home link that acts on
  behalf of the MN while away from the home link.
• It redirects packets addressed to a MNs home
  address to its current location using IP in IP
  tunneling.
• Foreign link
• Any link visited by a MN.
• Care-of Address
• An address that is assigned to the MN when
  located in a foreign link.

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Mobile IPv6 Operation
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Mobile IPv6 Operation (Cont.)
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Mobile IPv6 Operation (Cont.)
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Mobile IPv6 Operation (Cont.)
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Mobile IPv6 Operation (Cont.)
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Mobile IPv6 Processes
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IPv6 Mobility

• Mobile nodes have one or more home address
• relatively stable associated with host name in
  DNS
• To hide the IP layer mobility from upper layers.
• A node will acquire a foreign address when it
  discovers it is in a foreign subnet (i.e., not
  its home subnet)
• uses auto-configuration to get the address
• registers the foreign address with a home
  agent,i.e, a router on its home subnet
• Packets sent to the mobiles home address(es)
• Packets are intercepted by home agent and
  forwarded to the foreign address, using
  encapsulation

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Moving From the Home Link to a Foreign Link

• When the mobile node (MN) attaches to the foreign
  link
• Receive a new care-of address.
• Based on stateless or stateful mechanisms.
• Discover a home agent on the home link (if
  needed).
• Register the primary care-of address with the
  selected home agent on the home link.
• By sending a Binding Update (BU) message.

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Moving From the Home Link to a Foreign Link
(Cont.)

• The binding update contains
• The MN s home address and its care-of address.
• To inform the HA of the MN s current address.
• The HA contains a binding cache
• Contains all bindings for the MNs it serves.
• Each entry in the binding cache stores a binding
  for one home address.
• The HA acts as proxy for the MN on the home
  link.
• The HA sends a proxy neighbor advertisement
  addressed to the all-nodes multicast address on
  the link.
• Ensures that any IP packet addressed to the MN is
  forwarded to the HA s link-layer address.

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Moving From the Home Link to a Foreign Link
(Cont.)
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A New CN Communicates with a MN

• Upon receiving a packet addressed to the MN s
  home address
• The packet is tunneled to the MN s care-of
  address.
• The tunnel entry point is the home agent and the
  tunnel exit point is the MN s care-of address.
• The tunnel is bidirectional.

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A New CN Communicates with a MN (Cont.)
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A New CN Communicates with a MN (Cont.)

• Data from the MN is sent from the care-of address
  to the CN's address
• Data from the CN is sent to the MN's care-of
  address

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A New CN Communicates with a MN (Cont.)
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Reverse Tunneling

• To maintain the transparency of mobility to upper
  layers.
• If the MN sends packet directly to the CN using
  the home address as a source address
• Ingress filtering causes the MN s packets to be
  dropped by the default router
• Since the source address is not derived from the
  foreign links prefix.

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Data Packet sent by a CN to the MN s Home Address
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Intercepted Packet Tunneled to MN by its HA

• Optionally, the HA can protect the packet by
  using IPSec ESP.

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Tunneled Packets to a HA
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Forwarded Packet from a HA to a CN
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Mobility Header

• is dedicated to carrying mobility messages
• the value of 135 identifies the Mobility
  extension header.

Reserved
Header Len
Payload Proto
MH Type
Checksum
Message Data
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Binding Update Format
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The HA

• When the HA receives the first binding update
  from a MN
• It performs DAD for the MN s home addresses
  included in the binding update.
• If the DAD fails, the MN is informed and is
  unable to use the home address.
• After a successful DAD operation
• The HA copies the contents of the message into an
  existing binding cache entry or
• Creates a new one if this was the first binding
  update.

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Binding Update Entries in the HA
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Binding Acknowledgment Format
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Retransmitting the BU

• MN continues to retransmit the binding update to
  the HA
• until an acknowledgment is received.
• Such retransmission is done based on an
  exponential back-off algorithm.
• The MN doubles the time between retransmissions
  every time a BU is sent.

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Binding Update List

• Is used by a MN to ensure that information is
  stored to be able to refresh the binding before
  it expires.
• Is equivalent to the binding cache maintained by
  the receivers of the BU.
• The lifetimes in the MN s binding update list
  and the HA s binding cache are synchronized.
• Through the binding update and acknowledgment.

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Refreshing Bindings

• MN should refresh bindings by sending another BU
  before they expire or when the MN s care-of
  address changes.
• Binding refresh request
• Requests that the MN update its current binding
  because its about to expire.
• Can be sent by the MN HA or a CN communication
  directly with the MN.

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Movement Detection
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Movement Detection (Cont.)

• To minimize packet losses, both detect movement
  and form a new care-of address need to be
  executed as quickly as possible.
• A MN can only be certain about movement when two
  events have taken place
• A new prefix has appeared on link, and
• The current default router has disappeared.

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A new prefix has appeared on link

• Is achieved when the MN receives a RA containing
  a new prefix option.
• The amount of time that passes before the
  reception of the RA clearly depends on the
  frequency of the advertisements.
• Mobile IPv6 relaxes the minimum interval between
  RAs to 0.05 seconds.
• A new advertisement interval is defined for
  inclusion in RAs.

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Returning Home

• When the MN attaches to its home link after being
  away from home
• Send a binding update to the HA with a lifetime
  of zero and a care-of address equal to the MN s
  home address.
• Inform home link nodes that the correct
  link-layer address for the home address is now
  the mobile node's link-layer address.
• Send binding updates to all CNs to delete the
  binding for the MN.

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Returning Home (Cont.)
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Returning Home (Cont.)

• The MN sends a multicast Router Solicitation
  message on the home link.
• Either because the link layer indicated a media
  change or
• because the MN received a Router Advertisement
  that contains a new prefix.

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Returning Home (Cont.)

• All routers on the home link reply with a RA
  message.
• The reply is
• Either unicast (because the RS was sent from a
  link-local address)
• Or multicast (because the RS was sent from the
  unspecified address)
• The MN determines that it is attached to its home
  link.
• Because the RA contains the address prefix that
  matches its home address prefix.

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Returning Home (Cont.)

• To remove the binding cache entry for the HA
• The MN sends the HA a BU with the care-of address
  set to the MN s home address and
• With the home registration (H) and Acknowledge
  (A) flags set.
• The MN determines the HA s link-layer address
• Either from the Link-Layer Address filed in the
  Source Link-layer Address option in the RA sent
  by the HA.
• Or using address resolution because the global
  address of the HA is known.

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Returning Home (Cont.)

• Upon receipt of the BU, the HA
• Removes the entry for the MN from its binding
  cache,
• Stops defending the use of the MN s home address
  on the home link, and
• Responds with a BA.

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Returning Home (Cont.)

• After receiving the BA from the HA
• The MN must inform nodes on the home link that
  the link-layer address for the home address has
  changed to the link-layer of the MN.

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Route Optimization

• Routing packets through the HA adds additional
  delays.
• Such routing uses more network bandwidth than
  direct communication.
• If all MN s traffic is forwarded through the HA,
  operators would need to be careful about
• The location of the HA
• The capacity of the links attached to it.
• Worst case
• If the MN and the CN share the same link.
• Best case
• If the CN were on the MN s home link.

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Route Optimization (Cont.)
Worse Case
Best case
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Route Optimization (Cont.)

• Routing packets between a MN and a CN, using the
  shortest possible path.
• The MN can decide whether it should attempt to
  optimize the route between itself and the CN.
• How does a MN know whether the communication with
  a CN will last for a short or a long time ?

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Route Optimization (Cont.)

• A smart MN may make the following assumptions to
  decide whether the route optimization is needed.
• the type of applications used between the MN and
  CN
• The duration of a connection
• The RTT
• The amount of data being sent between the two
  nodes

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Sending Route Optimized Packets to CNs

• When a MN receives a packet tunneled from the HA,
  it must decide whether route optimization is
  needed. If so .

(MN s home address)
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Sending Route Optimized Packets to CNs (Cont.)

• The MN uses the same binding update message.
• The CN maintains a binding cache similar to the
  one maintained by the HA.
• When the MN sends a binding update to a CN, it
  needs to indicate the home address for which the
  binding is sent.
• The home address is included in the home address
  option, which is included in the destination
  options extension header.

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Sending Route Optimized Packets to CNs (Cont.)

• When a CN receives a packet containing a home
  address option
• it replaces the source address in the packet s
  header with the address included in the home
  address option before passing the packet to upper
  layers.
• Which effectively makes the packet appear to be
  received from the MN s home address when viewed
  by upper layers.
• Mobility is kept transparent to upper layer.

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Sending Route Optimized Packets to CNs (Cont.)
IPv6 Header Src HoA Dst CNA
IPv6 Header Src CoA Dst CNA
IPv6 Header Src HoA Dst CNA
Dst opt header CoA
Dst opt header HoA
Application Data
Application Data
Application Data
(a) Original Packet
(b) Home address option added
(c) Final packet to be sent
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Receiving Route Optimized Packets from CN

• The CN can communicate directly with the MN by
  sending packets to the MN s CoA

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Receiving Route Optimized Packets from CN (Cont.)

• When CN sends packets to a MN for which it has a
  binding cache entry
• It must include a new routing header (with a type
  field set to 2)
• When receiving the packet, the MN processes the
  routing header.
• This results in replacing the destination address
  in the packet (CoA) with the address in the
  routing header (the home address).
• The packet is passed to upper layers with the MN
  s home address in the destination address field.
• Hiding the address change from upper layers.

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Related Links

• Introduction to Mobile IPv6 at http//www.microsof
  t.com/technet/community/columns/cableguy/cg0904.ms
  px