NETWORKS – DIGITAL SILK

SOFTWARE DEVELOPMENT UNIT 4 – OUTCOME 2

NETWORKS• At its simplest, a network is two or more computers that are connected so they can

exchange information and share resources.Networks can be classified by:

• Their size (LAN, WAN, Internet)

• Their servers (Client-server, P2P)

• The rules they use to exchange data (Protocols – TCP/IP)

• How they are linked together (cable, wireless)

• Their logical shape (Bus, Star, Ring)

• How network messages travel (Ethernet, CSMA/CD)

NETWORKS• Efficiency – Better, faster communication – email, videoconferencing

• Cost savings (email vs phone calls, physical travel),

• Staff savings (e.g. networked helpdesk),

• Equipment savings: printers, internet connections, internet cache, CD drives

• Effectiveness – collaborative work is easier, access to resources is broader, group calendaring

NETWORKS• Management - control over internet & printing, staff monitoring

• Company image and “reach” – internet visibility makes any company international and accessible and “with it”

• Customer service – many more ways to help customers (e.g. FAQ, downloads, online advice, email contact)

NETWORKS

Types of Networks

• Local Area Network

• Wide Area Network

• Internet

• Personal Area Network

NETWORKS

Server Based Networks

• Client/Server model

• Automatically a pretty expensive choice compared to P2P

• File server at the heart of the network

• Server runs the Network Operating System (NOS)

• Controls access to data and equipment

• Runs ‘community’ programs

• Offers control, security, centralisation, automation

NETWORKSPeer to Peer Networks

• No server, cheap, simple, easy to run

• All users have equal authority and rights

• Little protection from each other

• Used at home or in small orgs with trusted users

• Share files, internet connection, printer

• Internet music sharing networks (e.g. Kazaa) are P2P - no central computer; data and software on users’ computers.

• P2P built into Win, Linux, Mac

NETWORKSNetwork Addressing

• Like telephones, every node on a network must have a unique identifier so the file server knows who is requesting information, and who is to be sent information.

• This unique network address is hardwired into the network card of each computer.

• Also, every active node of the internet needs a unique identifying address so TCP/IP knows where packets are to be sent.

• This is an Internet Protocol, or IP address.

NETWORKS• Humans like working with names (e.g. www.microsoft.com) but computers use IP

numbers (e.g. 10.77.91.19).

• IP address has four ‘octets’ separated by dots, each octet can be between 0 and 255.

• Remember - all internet communications use IP addresses, not URLs. Only humans use URLs.

• Domain name servers (DNS) – a distributed database on thousands of computers across the world - convert URLs into IP addresses.

• Like a phone book – look up a name (URL) to get a number (IP address).

NETWORKSNetwork Physical SecurityFile server failure can severely affect network users.

Server security:

• Locked in air-conditioned, alarmed room with barred windows, restricted keys

• No user access to server

• Uninterruptible power supply (UPS) protects against blackouts, brownouts and voltage spikes.

• Accessible fire fighting equipment.

• Locked floppy disk drives

NETWORKSNetwork Electronic Security

• Passwords are not strong protection – they can be guessed, forgotten or stolen.

• Daily backups are vital. Massive cost and effort to recover a single megabyte of lost data.

• Organisations need a data disaster recovery plan so they know what to do to recover from catastrophic data loss.

• A form of Electronic Security

• Makes data unreadable to unauthorised people even if a file is stolen.

• Web browsers use encryption to connect to a “Secure” SSL (Secure Socket Layers) site.

NETWORKSSecurity Threats

• TROJAN HORSES attempting to report ‘home’ or start a DOS/DDOS attack - can be blocked by a firewall.

• FIREWALLS in hardware (routers) or software (e.g. Zone Alarm) check for unauthorised incoming or outgoing network traffic, e.g. port scanning, being enslaved to help with a distributed denial-of-service (DDOS) or spam attacks.

• VIRUSES can disclose user passwords, steal information, destroy data, install “back doors” to let hackers in, clog print queues, disrupt Internet traffic, overload email servers etc. Keep scanners up to date.

NETWORKS – DIGITAL SILK

• Internet

• Intranet

• VPN

What is the difference?

Do all industries rely on the “net”?

INTERNET

• Worldwide network of WANs

• Uses TCP/IP protocol

• World Wide Web – only part of the internet – uses HTTP to send/receive web pages.

• Each device needs a unique IP address (e.g. 209.33.1.102)

INTERNETOther services are provided by the Internet:

• Usenet - a network of discussion groups

• File sharing networks – torrent sites, Kazaa, Limewire etc

• Email

• FTP

• Closed networks like Facebook, Twitter

• Blogs

• RSS feeds

DOMAINS

• Human readable URLs with domain names (e.g. microsoft.com) are not computer friendly

• Domain names are converted to an IP address to find the destination server.

• DNS (Domain Name System) does the conversion

• DNS = massive ‘phonebook’ with all domain names and matching IP addresses

WEB SERVER• Computer that stores web pages making up a site.

• Visitors use web browsers to make requests for web pages using HTTP.

• Web server uses HTTP to return requested page to visitor.

INTRANET

• Local, private version of the internet

• Uses the Internet Protocol to securely share information within an organisation’s Local Area Network.

• May involve local websites, email, collaboration tools, databases that are not available to those who are not within the LAN.

INTRANET• Can be as simple as webpages stored on a shared network drive.

• Uses page references to files on the file server rather than on a webserver.

• Simple to access with only a web browser.

INTRANET• Intranet is protected by a network gateway and firewall to keep outsiders out.

• Intranet can be made safe by using privatem, local IP addresses (e.g. 192.168.1.xx or 10.1.1.x) which cannot be used by outsiders to refer to computers within the LAN.

INTRANET• In some cases the intranet has a public face on the internet, but a password-protected login is needed

to gain access.

INTRANET USES• Collaboration – tools (e.g. Google docs, and shared documents)

• Communication (email, VoIP, messaging)

• Resource sharing

• Training

VPN• Virtual Private Network

• Used to provide access to a LAN or intranet to off-site people.

• A secure, private link using normal internet infrastructure.

• A VPN box creates the encrypted tunnel between the box and a same-keyed box elsewhere on the internet.

CORPORATE VPN• Corporate VPN box can support hundreds of simultaneous encrypted remote access connections.

• VPN can also be done with software (e.g. in MS Server) but is slower and less robust

• A 200-user VPN box can cost $7,000