Lecture 11 Virtual Private Networks (Power Point)
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Lecture 11 Virtual Private Networks (Power Point)






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    Lecture 11 Virtual Private Networks (Power Point) Lecture 11 Virtual Private Networks (Power Point) Presentation Transcript

    • Virtual Private Networks and IPSec ECE 4112
    • What is a VPN?
      • VPN Stands for Virtual Private Network
      • A method of ensuring private, secure communication between hosts over an insecure medium using tunneling
      • Usually between geographically separate locations, but doesn’t have to be
      • Via tunneling and software drivers, computer is logically directly connected to a network that it is not physically a part of
    • Sidebar: What is tunneling?
      • Putting one type of packet inside another
      • Both parties must be aware of tunnel for it to work
      • Example in next slide - AppleTalk over IP Tunnel
    • Example: AppleTalk over IP Tunnel
    • What is a VPN? (cont…)
      • Uses some means of encryption to secure communications
        • IPSec
        • SSH
        • Software could be written to support any type of encryption scheme
      • Two main types of VPNs –
        • Remote-Access
        • Site-to-Site
    • What is a VPN? (cont…)
      • Remote-Access
        • The typical example of this is a dial-up connection from home or for a mobile worker, who needs to connect to secure materials remotely
      • Site-to-Site
        • The typical example of this is a company that has offices in two different geographical locations, and wants to have a secure network connection between the two
    • Remote-Access Example
    • Site-to-Site Example
    • Why Use a VPN?
      • Originally designed as inexpensive alternative WAN over leased lines
      • Now mostly used to securely connect computers over the internet
      • Convenient
      • Lot’s of cheap and convenient protocols are insecure (IP, 802.11, etc)
        • Can now communicate securely over these insecure protocols
    • Why Use a VPN? (cont…)
      • Example – it can simplify security
        • (what is about to be proposed is not the most secure thing in the world – so don’t raise your hands and tell how you would make it more secure… it’s just an example)
        • Assume simple security policy with IP based access management – for example, an FTP server with site-licensed software on it for employees
        • Before VPN, complicated to allow access to FTP site for telecommuters or traveling employees
          • Train all employees to use SSH tunnel, etc…
        • After VPN, employees offsite can still connect using an internal IP address
    • VPN Advantages
      • Improved Security
      • Consolidation of Scattered Resources
      • Transparency to Users
        • If set up properly
      • Reduced Cost (vs. Leased Lines)
    • VPN Disadvantages
      • Time Consuming Setup
      • Possibly Frustrating Troubleshooting
      • Interoperability with other Networks/VPNs
      • Small performance overhead
        • Should be negligible on today’s hardware
    • VPN Security
      • In academic terms, VPN can provide Confidentiality, Integrity, and Authenticity
      • Security against determined hacker (read: academic attacks) depends largely upon underlying protocols used
      • Assuming security of SSH, IPSec, or other protocol used, should be secure
    • How are VPNs set up?
      • Many different types of setup
      • Vary in:
        • Amount of hardware used vs. amount of software used
          • All hardware based
          • All software based
          • Mixed
        • Amount of transparency to end-user
          • Does the user even realize that they are using a VPN?
    • How are VPNs set up? (cont…)
      • The following is not an exhaustive list
        • Gateway to gateway
          • Using two VPN aware Gateways
        • End host to gateway
          • End host uses VPN Software
        • End host to end host
          • Both hosts use software
        • End host to concentrator
    • How are VPNs set up? (cont…)
      • SSH over PPP
      • SSL over PPP
      • Concentrator using IPSec
      • Others (PPTP, L2TP, etc)
    • VPN via SSH & PPP
      • Point-to-Point Protocol over a Secure Shell connection
      • Establishing a Network Connection
        • Establish an SSH connection
          • VPN Client  VPN Server
        • Each have PPP daemons that will communicate through the SSH connection
        • Viola! A VPN CONNECTION!
    • VPN via SSL & PPP
      • Point-to-Point Protocol over a Secure Socket Layer connection
      • Secure Socket Layer
        • Built-in support for Host Authentication
        • Certificates
    • VPN via SSL & PPP (cont…)
      • Establishing a Network Connection
        • Initial Handshake for secure communication
        • “Hello” messages establish:
          • SSL Version, support for Cipher suites, and some random data
        • Key is determined separately from handshake
        • SSL Connection Complete!
        • Data transferred over the link
    • VPN via Concentrator
      • What is a Concentrator?
        • Concentrator is NOT a gateway or firewall
        • Specialized device that accepts connections from VPN peers
        • Authenticates clients
        • Enforces VPN security policies
        • Takes overhead of VPN management and encryption off of gateways and local hosts
    • VPN via Concentrator (cont…)
      • Steps to Establish VPN
        • Set up Concentrator (add users, specify authentication mechanisms, set IP address ranges, etc)
        • Install client software
        • Client runs software when wants to be on VPN
    • Other Methods
      • Point-to-Point Tunneling Protocol
        • Microsoft’s Implementation of VPN
        • Data is first encapsulated inside PPP packets
        • PPP packets are then encapsulated in GRE packets and sent over the link
      • PPTP uses two connections
        • One for the data being sent
        • Another for a control channel
    • Other Methods (cont…)
      • Any technology can be used
        • Must have hardware or software to support it
      • Another example: L2TP on Gateways
        • Layer 2 Tunneling Protocol
        • Supported by routers
        • If two routers support L2TP, and are properly configured, then VPN is set up between routers
        • Transparent to end user
    • Intro to IPSec
      • Created to add Authentication, Confidentiality, and Integrity to IP traffic
      • Designed to combat specific shortcomings in IP
      • IPSec is large and implementation is complicated
      • What follows is a high-level overview
      • As will see in lab, need not be used only as VPN technology – can be stand alone
    • Intro to IPSec (cont…)
      • IP Sec ≠ VPN
        • IP Sec is a protocol used in many VPNs
      • Two main modes
        • Transport
        • Tunnel
      • Two main services
        • AH (Authentication Header protocol)
        • ESP (Encapsulating Security Protocol)
    • Intro to IPSec (cont…)
      • Authentication Header protocol
        • Offers Authenticity and Integrity
        • Uses cryptographic hash
          • Covers entire packet, including static header fields
        • If any part of original message changes, it will be detected
        • Does not encrypt message
        • Can be used to authenticate –
          • Prevents IP Spoofing
    • Intro to IPSec (cont…)
      • Encapsulating Security Protocol
        • Provides Integrity and Confidentiality
        • Encrypts payload
        • If used in tunnel mode, encrypts original IP header
    • Intro to IPSec (cont…)
      • Transport Mode
      Or Real IP Header IP Options IPSec Header Payload (For example, TCP and Payload) ESP Header Could be either AH Header Authenticates Over Encrypts Over
    • Intro to IPSec (cont…)
      • Tunnel Mode
      Or GW IP Header IPSec Header Real IP Header Payload (For example, TCP and Payload) ESP Header Could be either AH Header Authenticates Over Encrypts Over
    • Intro to IPSec (cont…)
      • AH and ESP can be used together
        • Tunnel ESP through AH transport packets
      • Want to protect cryptographic keys
      • Internet Key Exchange protocol (IKE)
        • Secure way to exchange session keys based on shared secret
        • Can also use certificates (public key cryptography)
    • Resources
      • Books:
        • Building Linux Virtual Private Networks
          • Oleg Kolesnikov, Brian Hatch
        • Linux Server Hacks
          • Rob Flickenger
        • Network Security
          • Charlie Kaufman, Radia Perlman, Mike Speciner
    • Resources (cont…)
      • Lecture Slides by Wenke Lee (see below)
      • Websites:
        • http://vpn.shmoo.com/
        • http://www.tldp.org/HOWTO/VPN-HOWTO/
        • http://www.onlamp.com/lpt/a/3009
        • http://www.cisco.com/warp/public/471/how_vpn_works.shtml
        • http://www.cc.gatech.edu/classes/AY2004/cs4803_fall/ipsec_1.ppt
        • http://www.cc.gatech.edu/classes/AY2004/cs4803_fall/ipsec_2.ppt