Virtual Private Network

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Virtual Private Network
Lecture-13

• BSIT-7th
• University of Okara

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Table of Content

• Why we need Virtual Private Networks.
• What a Virtual Private Network consists of.
• What a Virtual Private Network does.
• How a Virtual Private Network does what it does.
• Pros and Cons of VPNs

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Imagine the Following Scenario

• You are a network administrator hired by a
  company to create a network which is both private
  yet able to access the internet.
• How would you do it?

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You Could

• Create a network comprised of both an internal
  and external network. By internal we mean a
  network which is unavailable to those outside of
  the network. Conversely, by external we mean a
  network which is available to those outside of
  the network.

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Example

• As you can see, we have two networks. An internal
  network, on the right, which lacks access to the
  internet, i.e. is private, as well as an external
  network, on the left, which is allowed access to
  the internet, i.e. is public.

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Continuing With Our Previous Scenario

• Lets say the same company, which had previously
  hired you to build a network, decides to build
  another office building 100 miles away from their
  current office building. You are once again hired
  by the company to build a private network between
  the two office buildings.
• How would you do it?

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What Wont Work

• A LAN based private network would be out of the
  question due to the amount of money to both build
  and maintain such a network.

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Continuation of What Wont Work

• We could use a WAN based network to connect both
  office buildings. However, problems associated
  with the amount of money to build and maintain
  such a network would once again arise.
• What about Leased Lines?

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What Will Work

• What are Leased Lines?
• Leased Lines are connection based, rather than
  packet switch based, lines which a phone company
  or internet service provider will lease to an
  individual or corporation.
• Due to their connection based nature leased lines
  are guaranteed to remain private.
• Unfortunately, leased lines are expensive and for
  many companies out of their budget.

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Why We Need VPN

• VPN or Virtual Private Networks are a cheaper and
  effective alternative to leased lines which, as
  with leased lines, allow for networks to remain
  private.
• Unlike leased lines, VPNs do so using packet
  switched networks, i.e. virtual lines.

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What a VPN Consists of

• A Virtual Private Network basically consists of a
  router, with specialized software, which acts as
  a gateway between an external network, i.e. the
  internet, and an internal network, i.e. some
  private network.

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What a VPN Does

• When a host on an internal, i.e. private, network
  needs to send a packet to a host not on its own
  internal network it sends the packet to the
  specialized router.

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What a VPN Does (contt.)

• Once the specialized router receives the packet
  it examines the destination of the packet.
• The router than encrypts the packet, places it in
  a datagram, and sends it off to its destination.
  The destination in question belongs to another
  specialized router, similar to our previous
  specialized router. This second specialized
  router belongs to the destined hosts VPN and
  acts as its gateway.
• We are not initially sending the packet to the
  destined host.

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How a Virtual Private Network Does What it Does

• Virtual Private Networks use two basic techniques
  to allow them to remain both private, yet at the
  same time do so without the use of expensive
  connection based networks.
• The two techniques in question
• Encryption
• Tunneling

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NAT Continued

• Outgoing traffic replaces source IP address
• Incoming traffic replaces destination IP address

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References

• http//computer.howstuffworks.com/vpn.htm
• http//www.tcpipguide.com/free/t_IPNATPortBasedOve
  rloadedOperationNetworkAddressPor-2.htm
• IPSec vs. SSL VPNs for Secure Remote
  Accesshttp//www.ajoomal.com/descargas/aventail/I
  PSec_vs120_SSL_VPNs_For_Secure_Remote_Access_-_En
  glish_(A4).pdf
• http//penguin.dcs.bbk.ac.uk/academic/networks/tra
  nsport-layer/nat/
• Virtual private networks / Charlie Scott
• Internetworking with TCP/IP Principles,
  Protocols, and Architecture Volume 1 Fifth
  Edition. Author Douglas E. Comer. Publisher
  Pearson Prentice Hall

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Questions

• Define VPN, why its used?
• Design VPN into your campus.
• Define NAT.