IPv6 Multihoming Support in
the Mobile Internet
Presented by Paul Swenson
CMSC 681, Fall 2007
Article by M. Bagnulo et. al. and published in the
October 2007 issue of IEEE Wireless Communications
Mobile Device Networking Support
• Modern “fourth-generation” (or 4G) mobile
devices support multiple network interfaces
– Today, in the US, can buy advanced PDA phones that
can speak both 802.11g (Wi-fi) and 1xRTT/EV-DO for
data service.
– Carriers will soon be rolling out 802.16 WiMAX
networks in the 2.5GHz and 700MHz bands (pending
FCC auctioning of the new wireless spectrum).
– Mobile phones of tomorrow will support these
technologies and more for accessing Internet
resources.
Benefits of Multiple Physical
Interfaces
• By providing multiple redundant data interfaces,
•
roaming capabilities are greatly enhanced
Multiple path technology would allow for fault
tolerance in data connections
– Preservation of established communications through
outages of service or requisite roaming from one
service to another
• Ability to route flow of data based on predefined
quantifiers such as cost of access or quality of
the connection
Problems with Current
Implementations
• None of the currently-available mobility protocols
•
•
support those advanced features
Current mobile devices support different
interfaces, but switching is far from seamless,
mostly a manual process right now
In order to fully realize the possibilities of
modern mobile networks, a mechanism to
provide mobile host multihoming support is
required
Mobile IPv6 and SHIM6
• The paper’s proposed solution to this
problem is a combined Mobile IPv6
(MIPv6) and SHIM6-based approach
– Backwards-compatible with existing transport
protocols/applications
– Any existing TCP or UDP-based protocols will
benefit from the enhanced fault tolerance
provided
– Works around limitations inherent to MIPv6
Mobile IPv6 Multihoming Support
• Mobile IPv6 supports multihoming natively
•
•
without any extra help
Requires the client to send a special “Binding
Update” MIPv6 message that it is going to be
changing its active interface from the home
address
Packets then are redirected to the “Mobile Node”
until another “Binding Update” redirects them
back to the home address
Disadvantages to this Approach
• If the connection between the handset and the
•
•
home network is broken, there is no automatic
failover to the mobile node
Connections established while connected to the
home network or one of the mobile nodes must
be re-established, no automatic failover
Requires the home agent (a server running on
the home network) to be available even when
roaming as a mobile node for traffic to get
through
Why IPv6?
• IPv6 provides any-to-any route
optimization support allowing packets to
flow across whichever route is best suited
(or available) to carry the flow of
information
• Allow direct communication between the
mobile node and the remote server w/out
depending on the home agent
SHIM6 and Multihoming
• SHIM6 handles the case where you have a
host A with n distinct addresses wanting
to communicate with a host B with m
distinct addresses.
– A and B should be able to communicate
across any of the addresses to any of the
other addresses and all packets should make
it to their destination w/out any input from
the protocol layer
SHIM6 and Multihoming (2)
• Within the SHIM6 scheme, host A will do a DNS
•
•
lookup, obtaining a subset of the addresses for
host B.
SHIM6 will then use the RFC 3484 address
selection process for IPv6 to choose one of the
addresses of B to contact it on.
Now, as part of the SHIM6 negotiation, the two
peers exchange alternate locators so that in the
event that one of the links fails, each end of the
communication will know all possible ways to
reach the other host.
SHIM6 and Multihoming (3)
• IPv6 Reachability Protocol (REAP) is then
used to verify that the currently used path
is functioning.
• Special keepalive packets are sent when
data has not been transmitted after a
certain amount of time in order to allow
REAP to detect an outage based on time
since last packet received
SHIM6 and Failures
• When a failure is detected by one of the hosts, that host
•
•
enters an “exploratory phase” in which special probe
packets are sent to each of the known addresses on the
other end of the link (and using multiple interfaces on
that host’s side)
Based upon the received responses the communications
channel is redirected over links that were successful in
reaching the other host, thus preserving the information
flow (be it connection-oriented or connection-less).
Thanks to SHIM6 and MIPv6, packets end up going to
the target system, not a specific IP address on that
system.
Security in SHIM6
• SHIM6 protects against redirection attacks
using Cryptographically Generated
Addresses (CGA)
– CGAs are regular unicast IPv6 addresses that
are signed with the interface identifier, a
public key and the prefix of the address
• This allows a host to claim ownership over
a specific CGA since it owns the private
key
Architecture (MIPv6 and SHIM6)
• The SHIM6 layer is considered to be on
top (it is what applications interact with)
• The Mobile IPv6 layer is then situated
below that in a block diagram
• The IP forwarding sublayer is then below
the MIPv6 layer
Conclusions
• Article provides an architecture for providing
•
•
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multihoming + failover support to 4G wireless nodes that
will be capable of multiple simultaneous network links
Makes use of standard Mobile IPv6 and overlays SHIM6
on top to provide advanced failure detection using REAP
and recovery support thanks to SHIM6
Works without any modifications to the Mobile IPv6
protocol, making use of a standards-compliant
multihoming mechanism layered on top of it.
Minimizes changes required to existing protocols (they
should be able to function with little or no change and
without being aware of the SHIM6 layer at all).