In most cases, the
Mobile Node and Correspondent Node communicate using Route Optimization.
Mobile IPv6 basic operation is used in initial communication, when
the Correspondent Node does not have information about the Mobile
Node’s Care-of Address, and in cases where the Correspondent
Node does not support Mobile IPv6 Route Optimization. In some topologies,
forcing Mobile Nodes to use basic operation also provides more security.
The following is the procedure for establishing Mobile IPv6
basic operation:
The Mobile Node detects
it is attached to a new network (movement detection).
The Mobile Node acquires a Care-of Address on the
foreign network.
The Mobile Node sends a Binding Update to its Home
Agent. The Binding Update contains the Mobile Node’s Care-of
Address and Home Address.
The Home Agent sends Neighbor Advertisements to
bind its link-level address with the Mobile Node’s home
address. This allows the Home Agent to capture IPv6 data-packets
addressed to the Mobile Node’s home address.
Movement
Detection |
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Mobile Nodes use IPv6
Router Advertisement and Neighbor Discovery methods to detect when
they have moved to or attached to a new network (also referred to
as movement detection). For example, if a
Mobile Node receives a Router Advertisement with a different network
prefix than its current prefix, the Mobile Node can assume it has
moved to a new network. A Mobile Node should also determine when
its current default router is still reachable, and can use IPv6
Neighbor Unreachability Detection. A Mobile Node might also actively
send Router Solicitation messages to solicit Router Advertisement
messages, to determine if the current default router is still reachable,
or to find a new default router.
The following is a list of events shown in Figure 1-5 “Movement Detection”, that a Mobile Node can use to determine
it has attached to a new network:
A Mobile Node travels into a foreign
network
The Mobile Node sends a Router Solicitation Message
A router on the foreign network responds with a
Router Advertisement that includes the network prefix of the foreign
network
The Mobile Node uses information in the Router Advertisement
message to determine it is away from its home link, and to generate
a Care-of Address
The Mobile Node sends a Binding Update message to
its Home Agent on its home link
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 | NOTE: After receiving the Binding Update, the Home Agent might
send a Binding Acknowledgement to the Mobile Node to acknowledge
the Binding Update and to indicate whether it was accepted or rejected.
The Home Agent will send a Binding Acknowledgement if the Mobile
Node sets the A-bit in its Binding Update. |
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Mobile
Node Acquires Care-of Address |
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When the Mobile Node
attaches to a new foreign network, it gets a new Care-of Address
using a stateless (IPv6 stateless autoconfiguration) or stateful
(such as DHCPv6) method. The Care-of Address has the network prefix
of the foreign network.
Mobile
Node Sends Binding Update to Home Agent |
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After the Mobile Node determines its Care-of Address, it sends
a Binding Update message to its
Home Agent. The Binding Update message
binds, or registers, the Mobile Node’s Care-of Address
with the Mobile Node’s Home Address. The Binding Update
message is encrypted and authenticated using IPSec.
When
the Home Agent receives the Binding Update message, the IPSec module
on the Home Agent authenticates the message. The Home Agent sends
a Binding Acknowledgement to
the Mobile Node. The Binding Acknowledgement is a message to the
Mobile Node, in response to it’s Binding Update, acknowledging
the Mobile Node’s Binding Update and indicating whether
it was accepted or rejected. The Binding Acknowledgement also includes
a fixed lifetime for the registration.
The Home Agent keeps
a record of Mobile Node’s home addresses and current Care-of
Addresses in a binding cache. The Home Agent
adds or updates the binding between the Mobile Node’s home
address with its current Care-of Address to this cache.
Home
Agent Sends Neighbor Advertisements for the Mobile Node |
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After the Mobile Node registers its Care-of Address with its
Home Agent, the Home Agent sends a Neighbor Advertisement message
on behalf of the Mobile Node to the all-nodes multicast address
for the local link. This Neighbor Advertisement binds the Home Agent’s
link-level address to the Mobile Node’s home (IP) address. The
other nodes and routers on the local network will update their Neighbor
Caches to link the Home Agent’s link-level address with
the Mobile Node’s home address. Data-packets addressed
to the Mobile Node’s home address will be sent to the Home
Agent’s link-level address, and processed by the Home Agent.
The Home Agent will also respond to any Neighbor Solicitation
requests for the Mobile Node’s home address by sending
Neighbor Advertisements with its link-level address and the Mobile
Node’s home IP address.
Basic Operation
Data Paths |
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Correspondent
Node to Mobile Node Data Path in Basic Operation
In basic mode,
the Correspondent Node sends data-packets back to the Mobile Node
through the Mobile Node’s home address using the following
procedure, and as shown in Figure 1-7 “Data Path: Correspondent Node to Mobile Node
in Basic Operation”:
The Correspondent Node addresses the
data-packet to the Mobile Node’s home address.
The Mobile Node’s Home Agent captures the
data-packet and encapsulates the data-packet in a new data-packet
with the Home Agent address as the source and the Mobile Node’s
Care-of Address as the destination. This process forms a tunnel
between the Home Agent and the Care-of Address on the Mobile Node.
The Mobile Node receives the encapsulated data-packet
at its Care-of Address, decapsulates it, and processes the original
data-packet.
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