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