Transcript Mobile IP - Department of Computer Science

Mobile IP
Outline
What is the problem at the routing
layer when Internet hosts move?!
Can the problem be solved?
What is the standard solution? –
mobile IP
What are the problems with the
solution?
Other approaches?
Internet hosts & Mobility
Wireless networking – allows Internet
users to become mobile
As users move, they have to be handed
over from one coverage area to another
(since the coverage areas of access
points are finite) …
Ongoing connections need to be
maintained as the user moves …
Problems?
What are the problems?
The IP address associated with a mobile
host is network dependent!
When user connects to another
network, IP address needs to change
Packets belonging to ongoing
connections somehow need to be
delivered to the mobile host
Problems (Contd.)?
What are the options?
Make IP address host specific instead of
network specific – obvious pitfalls?
Change IP address of host and start
using the new IP address in the
subsequent packets belonging to the
connections
Intuitive Solution
Take up the analogy of you moving
from one apartment to another
What do you do?
Leave a forwarding address with your
old post-office!
The old post-office forwards mails to
your new post-office, which then
forwards them to you
Mobile IP Basics
Same as the post-office analogy
Two other entities – home agent (old postoffice), foreign agent (new post-office)
Mobile host registers with home agent the
new location
Home agent captures packets meant for
mobile host, and forwards it to the foreign
agent, which then delivers it to the mobile
host
Reverse path?
Same as in the post-office analogy
Packets originating from the mobile
host go directly to the static
corresponding host …
HA
SH
• Hence the name
triangular routing
MH
MH
FA
Mobile IP Entities
Mobile host
Corresponding host
Home address
Care-of address
Home agent
Foreign agent
Mobile IP in detail …
Combination of 3 separable
mechanisms:



Discovering the care-of address
Registering the care-of address
Tunneling to the care-of address
Discovering the care-of
address
Discovery process built on top of an existing
standard protocol: router advertisement (RFC
1256)
Router advertisements extended to carry
available care-of addresses called: agent
advertisements
Foreign agents (and home agents) send
agent advertisements periodically
A mobile host can choose not to wait for an
advertisement, and issue a solicitation
message
Agent advertisements
Foreign agents send advertisements to
advertise available care-of addresses
Home agents send advertisements to make
themselves known
Mobile hosts can issue agent solicitations to
actively seek information
If mobile host has not heard from a foreign
agent its current care-of address belongs to,
it seeks for another care-of address
Registering the Care-of
Address
Once mobile host receives care-of address, it
registers it with the home agent
A registration request is first sent to the
home agent (through the foreign agent)
Home agent then approves the request and
sends a registration reply back to the mobile
host
Security?
Registration Authentication
Mobile IP requires the home agent and
mobile host to share a security association
MD5 with 128-bit keys to create digital
signatures for registration requests to be
used (registration message & header used for
creating signature)
Any problems? – replay attacks
Solved by using an unique message identifier
(timestamp or pseudorandom number)
Illustration
Foreign Agent Security?
No foreign agent authentication
required
Foreign agent can potentially discard
data once registration happens
However, the problem is same as in
unauthenticated route advertisements
(RFC 1256) in the wireline context
Home agent discovery
If the mobile host is unable to
communicate with the home agent, a
home agent discovery message is used
The message is sent as a broadcast to
the home agents in the home network
Tunneling to the Care-of
address
When home agent receives packets
addressed to mobile host, it forwards packets
to the care-of address
How does it forward it? - encapsulation
The default encapsulation mechanism that
must be supported by all mobility agents
using mobile IP is IP-within-IP (RFC 2003)
Using IP-within-IP, home agent inserts a new
IP header in front of the IP header of any
datagram
Tunneling (contd.)
Destination address set to the care-of
address
Source address set to the home agent’s
address
Tunnel header uses 4 for higher protocol id –
this ensures that IP after stripping out the
first header, processes the packet again
Tunnel header of 55 used if IP minimal
encapsulation used (RFC 2004)
Illustration
Recap
Host mobility and Internet addresses
Post-office analogy
Home agent, foreign agent, care-of
address, home address
Registration and Tunneling
IPv6 and Mobility support …
Mobile IP Basic Operation
Entities

Mobile host, home agent, foreign agent,
corresponding host
Discovering Care-of Addresses

Agent advertisements
Registering Care-of Address

Security
Tunneling to Care-of Address

IP-within-IP encapsulation
Mobile IP Problems?
Triangular routing overhead

What is the worst case scenario?
Registration latency and associated
problems
Ingress filtering and consequences
Infrastructure required for mobile IP
support?
Firewalls
Mobile IP Optimizations
Route optimization
Smooth hand-offs
Route Optimizations
Enable direct notification of the
corresponding host
Direct tunneling from the
corresponding host to the mobile host
Binding cache maintained at
corresponding host
Management of cache not stipulated
(e.g. least used entry replacement)
Route optimizations (contd.)
4 types of messages




Binding
Binding
Binding
Binding
update
request
warning
acknowledge
Binding Update
When a home agent receives a packet to be
tunneled to a mobile host, it sends a binding
update message to the corresponding host
When a home agent receives a binding
request message, it replies with a binding
update message
Also used in the the smooth-handoffs
optimization
Binding Update (Contd.)
Corresponding host caches binding and uses
it for tunneling subsequent packets
Lifetime of binding?
Corresponding host that perceives a nearexpiry can choose to ask for a binding
confirmation using the binding request
message
Home agent can choose to ask for an
acknowledgement to which a corresponding
host has to reply with a binding ack message
Binding update (problem?)
What happens when a mobile host
moves?
Binding warning
When a foreign agent receives a tunneled
message, but sees no visitor entry for the
mobile host, it generates a binding warning
message to the appropriate home agent
When a home agent receives a warning, it
issues an update message to the
corresponding host
What if the foreign agent does not have the
home agent address (why?) ?
Illustration
Home Agent
BU
BW
BR
BA
Corresponding Host
Foreign Agent
BW
Mobile Host
Smooth Hand-offs
When a mobile host moves from one
foreign agent to another …
Packets in flight to the old FA are lost
and are expected to be recovered
through higher layer protocols (e.g.
TCP)
How can these packets be saved?
Smooth Hand-offs
Make previous FA forward packets to the
new FA
Send binding updates to the old FA through
the new FA
Such forwarding will be done for a prespecified amount of time (registration
lifetime)
Update can also help old FA free any
reserved resources immediately
Why better?
Mobile IP in IPv6
Route optimization and smooth hand-offs
used in IPv6 mobility
Binding updates easier since IPv6 supports
destination caches at sources
IPv6 security inherently stronger than in
IPv4. Hence, no explicit security mechanisms
needed for mobile IP
Source routing to be used instead of
encapsulation (why?)
Recap
Mobile IP problems
Mobile IP Optimizations
Mobility support in IPv6
Outline
Multicast-based architecture
Fast handoffs
MosquitoNet
End-to-end approach
Multicast-based Architecture
Very different from the mobile-IP
model
Based on the IP-multicast approach
Leverages the similarities in the two
problems (multicast and mobility)
Minor modifications to IP-multicast
required
Multicast
Multicast: group membership, packets sent
to a multicast address have to be delivered to
all members of the group
Members of a multicast group can be located
“anywhere”
IP-multicast infrastructure is overlayed on
the Internet (construction of infrastructure a
separate problem by itself – DVMRP, CBT,
etc.)
Forwarding of data happens on the
overlayed infrastructure, and routing is group
specific
Multicast (Illustration)
Tunnels
Multicast & Mobility
CH
Tunnels
Use IP-multicasting to support mobility!
MSM-IP Architecture
MSM-IP: Mobility support using Multicasting
in IP
Addressing: mobile host has multicast
address
Tunneling architecture: same as IP multicast
(sparse mode algorithm required)
Join and prune mechanisms: hand-offs made
more efficient
Resource reservation (RSVP) easier
Problems?
ARP replies
TCP support
IGMP registration
ICMP message delivery
Multicast address space
IP-multicast maturity
Fast Handoffs
Reduce the latency in resuming operations
when a hand-off occurs
Use hierarchical foreign agents
Example: domain foreign agents and subnet
foreign agents
Mobility within a domain kept transparent
from the home agent by appropriate
interactions between domain foreign agent
and subnet foreign agents
Fast Handoffs (Illustration)
Internetwork
Subnet A
FA
FA
Subnet B
FA
MosquitoNet
One of the first test-bed
implementations of Mobile IP
Introduced the notion of co-located
foreign agents
Improves deployability of the mobile-IP
approach to support host mobility
Trade-offs?
End-to-End Approach
Internet infrastructure does not change
(like in mobile IP)
Changes required at both the sender
and receiver
Does connection migration when
mobile-host moves
E2E Approach (Contd.)
Hostname used as the invariant to identify
mobile host
Mobile host uses DNS updates to change
hostname to IP address mapping
No consistency problem as DNS entries can
be made un-cacheable
If client is mobile, DNS-support not used
E2E Approach (Contd.)
When a mobile-host undergoes a handoff, it
re-issues a SYN (with a MIGRATE option
identifying the previous connection)
A unique token exchanged during initial
connection set-up used to identify connection
The receiver of the SYN changes its state to
represent the new address of the mobile-host
Connection proceeds as a regular TCP
connection from thereon
Trade-offs?
Puzzle
Power drill
Power drill that drills square holes?!
What would the cross-section of the
power drill look like?