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