Internet Mobility

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Internet Mobility

• Presented by Nitin Bahadur

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References

• Mary Baker, Xinhua Zhao, Stuart Cheshire,
  Jonathan Stone, Supporting mobility in
  Mosquitonet, Proceedings of USENIX, Technical
  Conference, 1996.
• Stuart Cheshire and Mary Baker, Internet Mobility
  4x4, SIGCOMM 96.
• Kevin Lai, Mema R., Diane Tang, Xinhua Zhao, Mary
  Baker, Experiences with a Mobile Testbed,
  Proceedings of WWCA 98.

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References

• C. Perkins, IP Mobility Support for IPv4,
  Internet Draft, draft-ietf-mobileip-rfc2002-bis-01
  .txt, Jan 2000.
• C. Perkins, Route optimization in Mobile IP,
  Internet Draft, deaft-ietf-mobileip-opim-09.txt,
  Feb 2000.
• David Maltz, Pravin Bhagwat, MSOCKS An
  Architecture for transport layer mobility, IEEE
  INFOCOM 98.

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Outline

• Motivation and Challenges
• Some proposed solutions
• IP Mobility
• Routing Optimizations
• Security Issues
• Recent Extensions
• Conclusions

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Motivation

• Ubiquitous connectivity, continuous connectivity.
• Ability to maintain current conversations/connecti
  ons during movement.
• Move from one kind of network to another.
• Move to networks that do NOT provide support for
  mobility.

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Challenges

• Movement causes change in IP address
• Problems with TCP connections
• Maintaining transparency
• Efficient routing to new location of mobile host
• Security issues

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Some Solutions

• Use Host specific routes - possible with IPv6.
• Link Layer solutions
• Limited to a single medium
• A new solution for every medium
• Compatibility issues with other mediums
• Use extended DNS to register COA with DNS
• Information propagation time
• Global change in DNS

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Basic Terminology

• Mobile Host (MH)
• Correspondent Host (CH)
• Home Agent (HA)
• Foreign Agent (FA)
• Care of Address (COA)

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Split TCP

• Two TCP connections, CHltgtHAltgtMH
• Transport Layer mechanism

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Split TCP
Drawbacks

• Two TCP connections instead of one
• Changed end points
• HA acks. packets to CH even before MH has
• received them.
• Home agent is responsible for final packet
  delivery
• Multiple traversal through the TCP protocol
  stack
• HA needs to maintain a TCP connection for every
  TCP
• connection of all its mobile hosts

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TCP Splicing

• Two TCP connections, CHltgtHAltgtMH
• Transport Layer mechanism
• Acks are sent on TCP-I to CH only when MH sends
  them on TCP-II

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TCP Splicing
The scheme works like 1 TCP connection
Location transparency is maintained - Multiple
traversal through the TCP protocol stack - HA
still needs to maintain a TCP connection for
every TCP connection of all its mobile hosts
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Mobility using Foreign Agent

• MH obtains COA from FA
• FA discovery using Agent Advertisement or Agent
  Solicitation messages
• MH host registers COA with HA through FA

• HA intercepts packets for MH
• HA encapsulates and sends packets to FA
• FA decapsulates packets and sends it to MH
• Everything done at IP levelno TCP
• Same mechanism in the reverse direction
• This is called Bidirectional tunneling

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Mobility using Foreign Agent
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Encapsulation IP in IP
HA
FA

• Encapsulation maintains consistency in Source and
  Destination address fields.
• Allows MH to receive packets as it moves from
  network to network.

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Encapsulation Issues

• IP encapsulation and automatic decapsulation is
  dangerous
• How can one verify if the inner packet has a
  source address if claims to be !
• Encapsulation can cause packet fragmentation
• TCP breaks data in chunks of 1460 bytes and gives
  it to IP
• Encapsulation will automatically lead to packet
  fragmentation in such cases. So extra overhead.

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Mobility without Foreign Agent

• MH obtains a COA using DHCP
• MH registers COA with HA directly
• MH performs encapsulation and decapsulation

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Implementation in MosquitoNet

• Altered the route lookup function ip_rt_route
• Mobile Policy Table helps in combination with
  ip_rt_route is used for making routing decisions

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Home Agent Functionality

• Maintaining information about MHs current
  location
• Acting as an ARP proxy for MH
• ARP. to get link-layer address for an IP address
• Proxy ARP..done to answer a new ARP request on
  behalf on MH
• Gratuitous ARP.done to update ARP information of
  MH in all nodes
• Forwarding packets to CH and MH

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Movement of MH away from home network

• Detection by MH
• received a different agent advertisement message
• stopped receiving agent advertisement messages

• Disable ARP
• Register with FA or HA
• HA performs Gratuitous ARP on behalf of MH

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Movement of MH to home network

• Re-enable ARP
• De-register itself with HA
• HA performs Gratuitous ARP on behalf of MH

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Advantages of using Foreign Agent

• No need for a temporary COA for every MH
• If MH leaves foreign network, then Inflight
  packets can de directed by FA to new location of
  MH
• Less packet loss
• Less complexity in MH

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Advantages of NOT using Foreign Agent

• MH can visit networks without a foreign agent
• FA is not a bottleneck or single point of failure
• No need for a FA on each network

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Triangular Routing

• Proposed by Mobile IP working group
• CH sends packets to HA which forwards it to MH
• MH sends directly packets to CH

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Problems with Routing Techniques

• Bidirectional tunneling and Triangular routing
• Inefficient, increase in RTT, increase in path
  length
• HA is a bottleneck and a single point of failure
• Source address filtering problem with triangular
  routing

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Source Address Filtering Problem

• Foreign network might not allow transit traffic

Source MH ! foreign network Destination CH
! foreign network gt TRANSIT TRAFFIC gt DROP IT !
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Source Address Filtering Problem

• Filtering at CH network

Source MH CH network But packet has come
from a different network ..hmmm.drop it !
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Routing Optimizations - I

• Similar to triangular routing
• MH encapsulates packet to avoid source-address
  filtering problem
• Better than triangular routing and bidirectional
  tunneling !

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Routing Optimizations - I
CH
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Routing Optimizations - I
Advantages

• Direct delivery to CH
• Valid source address, so no source address
  problem
• Location transparency is maintained
• Will work in all situations

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Routing Optimizations - II

• Direct delivery mechanism
• Both MH and CH encapsulate packets and send
  directly to each other

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Routing Optimizations - II
CH
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Routing Optimizations - II
CH
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Routing Optimizations - II
Advantages

• Direct delivery between CH and MH
• Valid source address, so no source address problem

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Routing Optimizations - III

• Direct delivery mechanism
• Both MH and CH DO NOT encapsulate packets and
  send directly to each other using MH and not COA

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Routing Optimizations - III
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Routing Optimizations - III
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Routing Optimizations - III
Applicability When MH and CH are on same link
layer segment
Advantages

• Direct delivery between CH and MH

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Routing Optimizations - IV

• Direct delivery mechanism
• Both MH and CH DO NOT encapsulate packets and
  send directly to each other using COA and not MH

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Routing Optimizations - IV
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Routing Optimizations - IV
COA
CH
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Routing Optimizations - IV
Advantages

• Direct delivery between CH and MH
• No encapsulation overhead

Drawbacks

• CH needs to be aware of current location of MH
• No Location transparency
• Packets will be lost if MH changes location

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Routing Optimizations - IV
Applicability
Short lived connections such as HTTP
browsing Situations where location transparency
is not an issue
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Making CH intelligent

• Introducing mobile awareness in CH
• Why - for efficient routing
• How ?
• Binding Warning messages are sent by MH to HA so
  that HA sends binding update message to CH
• Binding update messages are sent by HA to CH
  whenever HA receives a tunneled packet
• MH can also directly send binding update messages
  to CH

MH can specify to HA which CH should be informed
of its current location
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Gains using optimizations
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Practical implementation of optimizations

• Optimizations must not cause break in connection
  or packet loss
• Start with the most pessimistic routing method
• do
• Send ICMP echo messages in background using a
  better method
• If that succeeds switch to the better method
• while (no more methods)

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Security Issues

• For registrations and communication between HA
  and MH an authenticator is used
• Authenticator is optional for communications
  among HA - CH, FA and MH - CH,FA
• Authenticator default algorithm is 128-bit keyed
  MD5
• Since key distribution may be a problem, messages
  with FA and CH may not be authenticated
• Replay protection done using timestamps and/or
  nonces

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Mobile Policy Table Performance
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Mobile Policy Table and Flexibility

• Supports multiple packet delivery methods
  simultaneously
• Adaptively selects the most appropriate method
  according to characteristics of each traffic flow
• Makes use of multiple network interfaces
  simultaneously
• Controls interface selection of both outgoing and
  incoming packets for different packet flows
• MH can register with HA flow specification and
  corresponding interface binding for that flow

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Why support multiple pkt delivery methods

• MH pays for extra cost of mobility support only
  when
• actually required

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Why support multiple network intefaces

• Smoother handoffs
• QoS
• Link asymmetry
• Cost and billing
• Privacy and Security

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Conclusion

• A schema for supporting ubiquitous and continuous
  connectivity
• Support for multiple packet delivery methods
• Use of multiple packet interfaces simultaneously
• Dynamic adaptation of routing optimizations
• MH can specify which CHs should be informed of
  current COA

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Issues to think about

• IP encapsulation overhead problem
• IPSec and IP-in-IP interactions
• Multicast for Mobile hosts.check out Alex