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Simplified Networking and Troubleshooting for K-12 Teachers AREN Topology Multiple Star Network Stars originate at the hub sites and hubs are connected by a North-South backbone DS3/Partial OC-3 backbone DS1 (T1) or Multiple T1 to clients Multiple Internet access points (DS3+)

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Slide1 l.jpg

Simplified Networking

and Troubleshooting

for K-12 Teachers

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AREN Topology

  • Multiple Star Network

    • Stars originate at the hub sites and hubs are connected by a North-South backbone

  • DS3/Partial OC-3 backbone

  • DS1 (T1) or Multiple T1 to clients

  • Multiple Internet access points (DS3+)

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Network Related Services

The following services are currently offered by AREN to all clients at low or no cost

- High speed Internet access

- DNS hosting and management

- Web hosting and server management

- Email hosting and server management

- Expert network consulting (LAN and WAN)

- Content filtering

-CIPA “Technology Protection Measure”

- Router management and site monitoring

- In state Quality of Service (QoS) configuration

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What is a Computer Network?

  • Group of computers that are connected together and can communicate with each other in some way

  • Connections can be serial, parallel, bus, radio, satellite, phone, etc.

  • Can use Copper, Fiber-optics, Airwaves

  • Can speak many different “protocols”

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Component Review

What are they and what are their uses?

  • Computer

  • NIC

  • Printer

  • Hub/Switch

  • Router/CSU

  • Proxy Server

  • Email/Web Server

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Simplified K12 Network Troubleshooting

  • Day 1 (Theory and equipment)

    • Introduction to Computer Networking (OSI)

    • Review of Common Components (show and tell)

    • Ethernet ins and outs (theory and hands-on)

    • Intro to TCP/IP addressing (don’t worry!)

    • DNS explained

  • Day 2 (It’s broken, what do I do?)

    • Quick review of Day 1 with any questions

    • The Internet is down!

    • My email doesn’t work!

    • I can’t print!

    • Where’s my network drive!?!?

    • I can’t join this domain!

    • Anything else y’all can throw at me  

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OSI Reference Model

  • Layer 1 – Physical

    • Hardware interface, electrical signaling, transmission of raw bit stream.

  • Layer 2 – Data Link

    • MAC (hardware) addressing, frame type, topology, switching

  • Layer 3 – Network

    • Logical addressing, IP is here, host to host communication

  • Layer 4 - Transport

    • End to end delivery guarantees, port addressing, stream delineation

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Physical Layer (Ethernet)

  • The “Big Phone Plug”



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Crimping Ethernet Cables

  • Show and tell time

  • No clip art available 

  • Practice checking cables by sight

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Ethernet Types (Flavors)

  • Ethernet

    • 10Base-2 (~200m, Coax)

    • 10Base-5 (500m, Coax)

    • 10Base-T (100m, Unshielded Twisted Pair = UTP)

    • 10Base-FL (2000m=2km, Multimode Fiber)

  • Fast Ethernet

    • 100Base-TX (100m over CAT5 UTP)

    • 100Base-FX (2000m=2km over MM Fiber)

  • Gigabit Ethernet

    • 1000Base-SX (300m over MM Fiber)

    • 1000Base-LX (550m over MM Fiber, 3000m over SM Fiber)

  • 10Gig

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Ethernet: Classical (Data Link)

  • 10 Mbps


    • Carrier Sense Multiple Access with Collision Detection

    • Think CB radio (shared media, only used by one at a time)

  • Can be configured with cable, hubs, or switches

  • 1500 Byte Frames

  • MAC addresses

    • 08-00-46-4C-9C-B5

    • 08:00:46:4C:9C:B5

    • 0800:464C:9CB5

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Limitations of Classical Ethernet

  • Distance limitations of UTP or Fiber

  • Network size limited by the 5-4-3 rule

    • just remember hosts cannot talk to each other if they are connected through more than 4 hubs or repeaters

  • One Broadcast Domain, One Collision Domain

    • collisions likely as number of hosts increases

  • Users generally don’t know about the 5-4-3 rule and just keep on adding hubs at random points

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Ethernet: Current Baseline

  • Layer 2 switches (Ethernet, FastE, GigE)

    • Switching decisions are made based on MAC address

    • Segments network into separate collision domains

    • No more 5-4-3 rule

    • Broadcasts are still heard by all hosts (1 bcast domain)

    • Does not affect IP subnetting

    • 802.1p provides QoS and is essential in Voice/IP or VTC implementations

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TCP/IP Protocol Suite(don’t worry about remembering this now)

  • IP = Internet Protocol

    • Responsible for core rules: addressing, routing, packet size etc

  • TCP = Transmission Control Protocol

    • Responsible for creating point to point communication over the connectionless Internet

  • UDP = User/Datagram Protocol

    • Provides port address resolution

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IP Addresses

  • Each computer also must have an IP address.

  • This address is similar to the street address of a house in that each address is unique.

  • Schools are assigned a group of IP addresses. This similar to a zip code for a street address.

  • Example : -

    • IP addresses are written in dotted-decimal notation with the last number designating a particular computer***

Points to machine with

“street address” number 78

Points to the School’s “Zip Code”

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IP Subnet Masking

Network = 207.157.55

Host = 78

Network = 207.157

Host= 55.78

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Default Gateway

The “Default Gateway” refers to the device that provides connectivity to (or towards) the rest of the world

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Static vs. DHCP

  • Static addressing

    • Each computer is “hard coded” with IP configuration.

    • IP address never changes (Static)

  • DHCP addressing

    • Dynamic Host Configuration Protocol

    • Computer automatically obtains IP address by sending broadcast query to the network

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Private Addressing (RFC1918)

  • Addresses that have no meaning to Internet routers

  • These addresses are often used by school systems instead of public routable addresses

  • Computer’s with these types of addresses must access the Internet through either proxy servers or translation devices

From RFC1918:

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets: - (10/8 prefix) - (172.16/12 prefix) - (192.168/16 prefix)

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Network Address Translation (NAT)

  • RFC1918 addresses can be translated into routable public addresses

  • PAT=Port address translation

    • A single “real” address can be used to provide Internet access to thousands of computers using private addresses

  • Exercise for the student: What is our “Real” address?

  • (

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Proxy Server Instead of NAT

  • Unlike NAT no address translation is used

  • Client computer requests web page

  • Proxy server retrieves web page and then passes page to client

  • Protocols supported can be limited

    • Some proxy servers only allow web access

      • No telnet, ftp, chat, email, etc….

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DNS: Making English out of Numbers(DNS = Domain Name Service)

  • IP addresses are hard to remember for humans, so IP names are much more useful.

  • A computers IP address can be associated with an IP name.

  • IP Names use a dotted notation, for example

  • Using the same address analogy, the Linden k12 network has been assigned a domain name (“zip code”) of All computers are also given a host names that are the “street addresses”.

Host name (“Street Address”)

Domain Name (“Zip Code”)

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Troubleshooting at last!

Commands you must know and love:

ping (the daddy of them all)

traceroute (tracert in Microsoft land)

ipconfig (ipconfig /all for details)

ipconfig /release (ipconfig /renew)

winipcfg (for Win95)

nslookup (not available in Win9x)

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The Internet is Down !

This is a very generic statement and generally means that folks can’t get to web sites with their browser (Internet Explorer and/or Netscape).

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The Internet is Down !

Step 1: Check link light and Ethernet cable

- if no link check cable

- check hub/switch lights and power

Step 2: Confirm IP is configured on host and address is valid

- check with ipconfig (or winipcfg)

Step 3: Ping Default Gateway

- find Gateway using ipconfig (or winipcfg)

Step 4: Ping school proxy server and/or NAT device

Step 5: if all of the above is fine ping and trace to

Step 6: if all of the above is fine ping and trace to

Step 7: if all of the above is fine ping and trace to

Step 8: if all of the above is fine ping and trace to

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My Email Doesn’t work !

Step 1: Confirm that you have access to other Network resources (web, ftp, telnet, etc.)

Step 2: Check email server configuration in email client (method varies by client)

Step 3: Can you receive email from outside school system?

Step 4: Can you receive email from inside school system?

Step 5: Can you send email to addresses outside system?

Step 6: Can you send email to addresses inside system?

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I Can’t print! (Network Printer)

  • Is the printer “online”?

  • Confirm that you have access to other Network resources (web, ftp, telnet, etc.)

  • If IP address of printer or print server is known, try to ping it.

  • If printer attached to a computer, can you print from that computer?

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I Can’t print! (Local Printer)

  • Is the printer “online”?

  • Is the printer out of paper? Ink?

  • What message(s) are you getting from the driver?

  • Is the local driver software still installed?

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Can’t “see” anything in Network Neighborhood (no access to network shares)

Step 1: Confirm that you have access to other Network resources (web, ftp, telnet, etc.)

Step 2: Did you authenticate into the local domain (hitting cancel at login is not a good idea)

Step 3:Is the share reached via Network Neighborhood or a pre-mapped drive letter?

Step 4: Can you ping the share name?

Step 5: Can you ping the IP address of the file server?

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I can’t get this “&*#ing” computer to join the domain!

New Computer:

1) You must be an administrator to add a computer to a domain.

Existing Computer that worked previously:

1) Confirm that you have access to other Network Resources (web, ftp, telnet, etc.)

2) Do you have a valid domain username/password?