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  1. 1. ITP 457 Network Security Computer Networks
  2. 2. Overview <ul><li>Brief Introduction to Computers and Computer Components </li></ul><ul><li>What is a network? </li></ul><ul><li>Introduction to Physical Networks </li></ul><ul><li>LANs, WANs, and MANs </li></ul><ul><li>Logical Network Topologies </li></ul>
  3. 3. Introduction to Computers <ul><li>Computers </li></ul><ul><ul><li>Made up of hardware and software </li></ul></ul><ul><ul><li>Software cannot run by itself, and without software, your computer is an expensive paperweight </li></ul></ul><ul><li>Main Components </li></ul><ul><ul><li>CPU (Central Processing Unit) – does the math that is necessary for computer use </li></ul></ul><ul><ul><li>Memory </li></ul></ul><ul><ul><ul><li>RAM (Random Access Memory) – temporary memory, very fast, not very big </li></ul></ul></ul><ul><ul><ul><li>Secondary Storage – Hard Disks, Optical Media; large and slow </li></ul></ul></ul><ul><ul><li>Network Interface Cards – allow computers to communicate with one another </li></ul></ul><ul><ul><li>Additional Add-In Cards include Sound, Video, SCSI, Firewire, etc. </li></ul></ul>
  4. 4. Operating Systems <ul><li>Manages hardware and software so the user does not have to micro-manage </li></ul><ul><li>Microsoft </li></ul><ul><ul><li>Windows 95/98/ME </li></ul></ul><ul><ul><ul><li>Very limited networking capabilities </li></ul></ul></ul><ul><ul><ul><li>Blue Screen of Death!!! </li></ul></ul></ul><ul><ul><ul><li>Microsoft has completely abandoned this Operating System. We will not cover these OSes in this class </li></ul></ul></ul><ul><ul><li>Windows NT/2000/XP/2003 </li></ul></ul><ul><ul><ul><li>Built on the NT kernel, which is a much more stable and network savvy kernel </li></ul></ul></ul><ul><ul><ul><li>Security is an issue, due to holes in the O.S. </li></ul></ul></ul><ul><ul><ul><li>We will cover these operating systems extensively </li></ul></ul></ul>
  5. 5. Unix <ul><li>Server-workstation operating system meant to be portable, multi-tasking, multi-user, & time sharing </li></ul><ul><li>Originally written in the 70s </li></ul><ul><ul><li>Extremely popular, even today as Solaris 10 </li></ul></ul><ul><ul><li>Was the primary reason that the programming language C grew to be the de-facto language </li></ul></ul><ul><li>We will not cover Unix in this class </li></ul>
  6. 6. Linux <ul><li>Uses the Linux kernel, with a bunch of other stuff </li></ul><ul><li>Its open-source, meaning its free to use and develop </li></ul><ul><li>Most people download a distribution, which is a package of the Linux kernel with a bunch of other useful modules </li></ul><ul><ul><li>You pay for documentation, proprietary modules, and support </li></ul></ul><ul><li>Is becoming very popular, due to the fact that it is free, reliable, and the linux community is very helpful in forums and IRC </li></ul><ul><li>We will spend a few weeks on Linux, due to its popularity as a workstation and server operating system </li></ul>
  7. 7. Mac OS <ul><li>One of the first graphical user interfaces </li></ul><ul><ul><li>Introduced in 1984 </li></ul></ul><ul><li>Original Mac OS (1984 – 2001) </li></ul><ul><ul><li>Versions 6 – 9 </li></ul></ul><ul><ul><li>No command line; single tasking or very limited multitasking </li></ul></ul><ul><ul><li>Horrible memory management – user had to manually allocate memory </li></ul></ul><ul><li>OS X </li></ul><ul><ul><li>Complete rewrite using the Mach Kernel and the Free BSD implementation of Unix </li></ul></ul><ul><ul><li>Has software emulation for older software </li></ul></ul><ul><ul><li>Now runs on Intel based processors </li></ul></ul><ul><li>We will not cover too much of Mac based security, but the same principles for Linux security can be applied to Macs. </li></ul>
  8. 8. Computer Networks <ul><li>Minimum: Two or more connected computers </li></ul><ul><li>A good computer network consists of the following </li></ul><ul><ul><li>All hosts must use the same standard method for sending and receiving data </li></ul></ul><ul><ul><li>Information must be delivered without any corruption </li></ul></ul><ul><ul><li>There must be a way of acknowledging that the data has reached it’s destination </li></ul></ul><ul><ul><li>Nodes must be able to determine the source of the communication </li></ul></ul><ul><ul><li>The network should be scalable </li></ul></ul><ul><ul><li>Nodes must be able to identify other nodes </li></ul></ul><ul><ul><li>The network should run without the need for user micro-management </li></ul></ul>
  9. 9. Computer Network Components <ul><li>Two main parts to the network </li></ul><ul><ul><li>Physical Network </li></ul></ul><ul><ul><ul><li>Physical connection between devices or nodes </li></ul></ul></ul><ul><ul><ul><li>Hardware </li></ul></ul></ul><ul><ul><ul><li>Wiring </li></ul></ul></ul><ul><ul><ul><li>Wireless devices as well, but they are a little bit more complicated to understand </li></ul></ul></ul><ul><ul><li>Logical Network </li></ul></ul><ul><ul><ul><li>Lays out the roles and routes for data transmission </li></ul></ul></ul><ul><ul><ul><li>Dependent on the Protocol used for networking </li></ul></ul></ul><ul><ul><ul><li>Software </li></ul></ul></ul>
  10. 10. Physical Network <ul><li>Wires, cables, printers, hubs, switches, computers, servers, etc. </li></ul><ul><li>Computers use Network Interface Cards (NICs) to interact with the network </li></ul><ul><li>Network Topology </li></ul><ul><ul><li>Physical layout of components on the network </li></ul></ul><ul><ul><li>Star, Ring, and Bus are the most common topologies </li></ul></ul><ul><ul><ul><li>Mesh is becoming more prevalent, especially with wireless </li></ul></ul></ul>
  11. 11. Bus Topology <ul><li>A long line with computers connected </li></ul><ul><ul><li>Called “taps” in the line </li></ul></ul><ul><li>Components on the computer motherboard are connected using a bus </li></ul><ul><li>10Base2, 10Base5 use bus topologies </li></ul><ul><li>Advantages: </li></ul><ul><ul><li>Simple </li></ul></ul><ul><ul><li>Cheap </li></ul></ul><ul><ul><li>Quick Set-up </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Difficult to troubleshoot </li></ul></ul><ul><ul><li>One break in the line causes the whole network to go down!!! </li></ul></ul><ul><ul><li>Performance is directly proportional to the number of nodes on the line </li></ul></ul><ul><ul><li>Very low security – all computers on the line can see the data </li></ul></ul><ul><ul><li>Collision!!! </li></ul></ul><ul><ul><ul><li>Two computers trying to send information at the same time </li></ul></ul></ul><ul><ul><ul><li>Carrier Sense Multiple Access fixes this somewhat </li></ul></ul></ul>
  12. 12. Ring Topology <ul><li>Every node has two connections, to create a closed network </li></ul><ul><li>Token Ring and FDDI (Fiber Distributed Data Interface) use Ring Topologies </li></ul><ul><li>Advantages: </li></ul><ul><ul><li>Additional nodes do not directly impact performance (with a good protocol) </li></ul></ul><ul><ul><li>No packet collision </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Slow – data must pass through multiple nodes to reach destination </li></ul></ul><ul><ul><li>Any node failure causes the ring to die </li></ul></ul><ul><ul><li>To add a node, you must shut down the network </li></ul></ul><ul><ul><li>All systems must be on for the ring to work properly </li></ul></ul><ul><ul><li>Complete dependence on one cable – no redunancy </li></ul></ul>
  13. 13. Star Topology <ul><li>The most common topology for home and business networks </li></ul><ul><li>Nodes have a connection to a central hub </li></ul><ul><li>The hub can be connected to other hubs to create intricate diagrams </li></ul><ul><li>10BaseT, 100BaseT </li></ul><ul><li>Advantages: </li></ul><ul><ul><li>Good performance – limits the number of nodes to travel through </li></ul></ul><ul><ul><li>Easy to set-up and expand </li></ul></ul><ul><ul><li>A non-centralized failure will not bring down the network </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Most expensive topology – requires the most cabling and most hardware </li></ul></ul>
  14. 14. Mesh Topology <ul><li>Think of a combination of a star and ring topology </li></ul><ul><li>Multiple ways for data to travel from source to destination </li></ul><ul><li>Wireless Ad-Hoc networks are mesh networks </li></ul><ul><ul><li>Wireless infrastructure (wireless access points and routers), are more of a star topology </li></ul></ul><ul><li>Advantages: </li></ul><ul><ul><li>Extremely reliable & self healing </li></ul></ul><ul><ul><li>Easily scalable </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>You never know exactly how the data is going to travel </li></ul></ul><ul><ul><li>The data may not flow in the most optimized manner </li></ul></ul><ul><ul><ul><li>In order to find the most optimal route, all routes must be tested </li></ul></ul></ul><ul><ul><li>Virus propagation is a HUGE issue </li></ul></ul>
  15. 15. Network Sizes <ul><li>Completely arbitrary – no set definition of each </li></ul><ul><li>LAN – Local Area Network </li></ul><ul><ul><li>All computers are networked together </li></ul></ul><ul><ul><li>Only occupies one “site” </li></ul></ul><ul><ul><li>Typically high speed (100 Mbits/sec or 1 Gbit/sec) </li></ul></ul><ul><li>WAN – Wide Area Network </li></ul><ul><ul><li>Geographically separated LANs connected with routers and high-speed interconnections </li></ul></ul><ul><ul><li>Typically connected with telephone, T1 or T3 lines, or Cable/DSL lines </li></ul></ul><ul><li>MAN – Metropolitan Area Network </li></ul><ul><ul><li>Larger number of WAN or LANs connected typically using wireless or fiber lines </li></ul></ul><ul><li>Internet </li></ul><ul><ul><li>Either a WAN or a MAN, depending on how you define it  </li></ul></ul>
  16. 16. Logical Topology <ul><li>While the physical topology defines how the nodes are connected, the logical topology defines how the data is to be sent and how the network behaves from a software standpoint </li></ul><ul><li>Ethernet </li></ul><ul><li>Token Ring </li></ul><ul><li>FDDI </li></ul>
  17. 17. Ethernet <ul><li>Most common logical topology </li></ul><ul><li>Logical common bus topology </li></ul><ul><li>Single bus to which all communication occurs </li></ul><ul><li>Uses CSMA/CD – Carrier Sense Multiple Access/Collision Detection </li></ul><ul><ul><li>All computers share a single network segment </li></ul></ul><ul><ul><li>Every computer listens on the network segment </li></ul></ul><ul><ul><li>If no other computer is transmitting at that time, then the computer can transmit data </li></ul></ul><ul><ul><li>If two computers send data at the same time, then a collision occurs. Both computers sense the conflict, and stop sending. They wait a “random” amount of time (in nanoseconds), then retransmits the data. </li></ul></ul>
  18. 18. Ethernet Continued <ul><li>Is classified as IEEE 802.3 & 802.3u </li></ul><ul><ul><li>10BASE-2: coaxial networking – dead </li></ul></ul><ul><ul><li>10BASE-5: thicknet – dead </li></ul></ul><ul><ul><li>10BASE-T: 2 of 4 pairs of unshielded twisted pair wire called CAT5 cabling; speed of up to 10 Mbits/sec; dead </li></ul></ul><ul><ul><li>100BASE-TX: fast ethernet; 2 of 4 pairs of unshielded twisted pair wire; speed of up to 100 Mbits/sec; seen everywhere </li></ul></ul><ul><ul><li>100BASE-FX and 100BASE-FL – fast ethernet on optical fibers; speed of up to 100 Mbits/sec; more expensive than 100BASE-T; not used a whole lot anymore </li></ul></ul><ul><ul><li>1000BASE-T: uses all 4 pairs of CAT5e or CAT6 cabling; speed of up to 1000 Mbits/sec </li></ul></ul>
  19. 19. Token Ring <ul><li>Problem with CSMA/CD: Lots of computers on a network segment can cause starvation – computer may never get to transmit data </li></ul><ul><li>IEEE 802.5 – Token Ring </li></ul><ul><ul><li>A special packet called a Token packet is passed around the ring </li></ul></ul><ul><ul><li>A computer can only transmit data when the computer has the token </li></ul></ul><ul><ul><li>When the computer is done transmitting, it releases the token </li></ul></ul><ul><li>FDDI – Fiber-Distributed Data Interface </li></ul><ul><ul><li>Uses fiber optic lines instead of a copper wire </li></ul></ul><ul><ul><li>Can support thousands of users </li></ul></ul><ul><ul><li>Speed of up to 100 Mbits/sec </li></ul></ul><ul><ul><li>Has backup-ring in case of primary ring failure </li></ul></ul><ul><ul><li>Gigabit ethernet has made FDDI obsolete </li></ul></ul>