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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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AREN

CISCOSYSTEMS

CISCOSYSTEMS

ComputerComputer Computer

Server

CSU/DSU

Example Client Site

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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”• http://www.rabcomputers.com/resources/cablepinout.htm

• http://www.aptcommunications.com/ncode.htm

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Crimping Ethernet Cables

• Show and tell time

• No clip art available

• Practice checking cables by sight

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More Ethernet Hardware

Workstation WorkstationWorkstation

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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

• CSMA/CD – 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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Common Ethernet Topologies

Ethernet

IBM Compatible IBM Compatible Server

Mac IIWorkstation

ComputerComputer ComputerComputer

Hub Hub

Hub

ComputerComputer

Computer

Computer

Computer

Computer

Stackable Hubs

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Limitations of Classical Ethernet

Distance limitations of UTP or FiberNetwork 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

129.66.32.4

129.66.32.1129.66.32.2

Ethernet Switch

Ethernet Hub

129.66.32.3

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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 : 207.157.55.1 - 207.157.55.254

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

207.157.55.78

Points to the School’s “Zip Code” Points to machine with “street address” number 78

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IP Subnet Masking

207.157.55.78

255.255.255.0

207.157.55.78

255.255.0.0

Network = 207.157.55

Host = 78

Network = 207.157

Host= 55.78

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Default Gateway

AREN

CISCOSYSTEMS

CISCOSYSTEMS

ComputerComputer Computer

Server

CSU/DSU

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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Internet Settings

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Static/DHCP Demonstration

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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:

10.0.0.0 - 10.255.255.255 (10/8 prefix)

172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

192.168.0.0 - 192.168.255.255 (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?

• (http://www.avl.lib.al.us/whatweknow.phtml)

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Network Address Translation (NAT)

Internet

Private NetworkWith RFC1918 addresses

10.10.10.2

10.10.10.3

10.10.10.4

10.10.10.1and

207.157.78.50

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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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Proxy Server

Internet

Private NetworkWith RFC1918 addresses

10.10.10.2

10.10.10.3

10.10.10.4

Outside address: 207.157.87.3Inside address 10.10.10.1

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Proxy Settings

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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 www.foxnews.com

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

www.linden.k12.al.us

Host name (“Street Address”) Domain Name (“Zip Code”)

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DNS Tree

Local DNS server

Workstation

us root

al.us server

k12.al.us server

linden.k12.al.us server

1)

Lin

den

.k1

2.a

l.u

s ?

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Routing 101

The Internet

Router Router

LAN

LAN

RouterRouter

LANLAN

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Traceroute – Tool of the Gods

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Traceroute – no DNS (fast)

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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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Interactive Command Review

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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 deviceStep 5: if all of the above is fine ping and trace to 129.66.12.151Step 6: if all of the above is fine ping and trace to www.asc.eduStep 7: if all of the above is fine ping and trace to 149.149.11.7Step 8: if all of the above is fine ping and trace to www.tntech.edu

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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)

1) Is the printer “online”?

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

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

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

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I Can’t print! (Local Printer)

1) Is the printer “online”?

2) Is the printer out of paper? Ink?

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

4) 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?