Virtual Private Networks

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Virtual Private Networks
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Why VPN

• Fast, secure and reliable communication between
  remote locations
• Use leased lines to maintain a WAN.
• Disadvantages
• High Cost
• No flexibility

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What is VPN

• Virtual Private Network is a private network that
  uses a public network (usually the Internet) to
  connect remote sites or users together. Instead
  of using a dedicated connection such as leased
  line, a VPN uses virtual connections routed
  though the internet.

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VPN Types

• Remote-access
• single remote network device to intranet
• Site-to-site
• connect multiple fixed sites over a public
  network
• Intranet -based
• Extranet-based

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VPN Technologies

• Tunneling
• Authentication
• Identity verification of network system.
• Access Control
• When an access request is presented, resource
  makes a decision to allow the access request to
  proceed or not.
• Performed at tunnel endpoints.

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Tunneling
 
                               

• Tunneling is the transmission of data intended
  for use only within a private, usually corporate
  network through a public network in such a way
  that the routing nodes in the public network are
  unaware that the transmission is part of a
  private network.

Tunnel
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Payload
Original IP Header
Payload
New IP Header
Original IP Header
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VPN Tunneling Protocols

• Layer 2 tunneling protocols
• A link layer frame is placed into the payload of
  a protocol data unit(PDU) from some other layer,
  including another layer 2 frame.
• Tunnel PPP frames through an IP network.
• Point-to-Point Tunneling Protocol (PPTP),Layer 2
  Forwarding protocol (L2F), Layer 2 Tunneling
  Protocol (L2TP).

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VPN Tunneling Protocols

• Layer 3 tunneling protocols
• A layer 3 frame is placed into the payload of a
  protocol data unit(PDU) from some other layer,or
  another layer 3 packet.
• VPNs within an IP network
• IPsec
• Label switching protocol
• Label is placed between layer 2 and layer 3
  header.
• MPLS

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Layer 2 tunneling protocol

• Tunnel PPP frames through the internet to the
  home network.
• Tunneling protocol
• Access concentrator(Client part)
• Network Server(server part)

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PPTP

• PPP access by remote computers to a private
  network through the Internet
• 1. Remote user dials in to the local ISP network
  access server using PPP.

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PPTP

• 2. The PAC establishes a control channel (TCP)
  across the PPP connection and through the
  internet to the PNS attached to the home network.

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PPTP

• 3. Parameters for the PPTP channel are
  negotiated over the control channel, and the PPTP
  tunnel is established.

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PPTP

• 4. A second PPP connection is made from the
  remote user, through the PPTP tunnel between the
  PAC and the PNS, and into the private networks
  NAS.

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PPTP

• 5. IP datagrams or any other protocols
  datagrams are sent inside the PPP frames

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L2F

• Tunnel is constructed from the service provider.
• Remote user dials in to the local ISP network
  access server using PPP/SLIP.

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L2F

• 2. L2F builds a tunnel from the NAS to the
  private network.
• Uses packet-oriented protocol that provides
  end-to-end connectivity, such as UDP, frame
  relay, etc. as the encapsulating protocol.

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L2F

• 3. L2F establishes PPP connection between NAS and
  home gateway.

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L2F

• 4. IP packets are sent over the PPP.

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L2TP
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Comparison

• Performance
• ISP dependence.
• End-to-end security

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IPsec
Payload
Original IP Header
Payload
New IP Header
Original IP Header
Security Header

• Protocol suite
• AH and ESP protocol
• Tunnel mode of operation
• Headers added to original packet.

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MPLS
Payload
IP Header
Payload
Link Layer Header
IP Header
MPLS Shim