LAN & Network Diagnostics

These notes cover a variety of LAN trouble situations. Hope they help.

Before you start

Before you do anything, before you touch anything else:

1. If you are tired or hungry you will not be at your best. If you are pulling your hair out in chunks you will not make smart decisions. Sometimes the best starting point for diagnosis is to take a break, have a rest or eat something - no matter what the short term pressures.
2. Write down a list of everything that has changed. Chances are high your problem lies with the change or a side-effect of the change.
3. Think it through first - running around doing things with no plan is a recipe for another disaster - once you find the original problem you've then got to go back and fix all the other problems you introduced when doing your imitation of a headless chicken.
4. Be methodical. Start at one place and work slowly out from there. Test each step and MAKE NO ASSUMPTIONS. Check everything.

<rant> If you have got network cables with broken tabs you deserve everything you get. Breathe on those guys and they come loose. Keep a pair of scissors handy and cut the connectors off. Period. </rant>

What you should have done!

Wise after the event advice is never very helpful - but:

1. Know what the NORMAL look of LEDs, flashing light and other indicators are. We typically look at these indicators only when something is NOT working and then assume they are telling us things that they probably are not.
2. Keep a 'gold standard' - something that you know works - could be a laptop, could be a long cable that will stretch everywhere and you KNOW WORKs. Use this to eliminate possible errors

RJ45 End Connectors

1. Make and test practice cables until you get it right every time - especially before you destroy cables you just spend 2 hours fitting.
2. When cutting the exterior cover of the cable be very careful not to cut the insulation cover of the conductors since this can cause shorts.
3. Expose a maximum of 1 inch of individual conductors when preparing the cable for connection.
4. Line up all the conductors according to the wiring standard you are using.
5. Measure the cable and trim the conductor ends so they are are all the same length and no individual conductor wire is visible outside the plastic cover of the RJ45 connector.
6. Carefully slide the prepared cable into the RJ45 connector making sure the end of the conductors reaches the end of the RJ45 connector.
7. Using the crimp tool make the connection using one firm squeeze operation.
8. Test the cable before fitting if possible.
9. The RJ45 connector is the critical connection always use the highest quality connectors you can afford. The most common cause of connection faults is bad connectors.

New Connections

1. Create and keep a 'gold standard' i.e. take a single PC/laptop connect it directly to the hub via a cable that is long enough to stretch from every room in the facility to the hub - confirm that the Hub/Switch LINK led works every time and preferably use a PC that has a LINK led on its LAN card.
2. Using this configuration move it to every location when you test the connection. At least you know something works. Plug this configuration into the wall connector under test and if you don't get LINK - its your cable.
3. Test every PC to wall LAN cable before you start by using them to connect to the Hub/Switch locally - you don't want to rip-up your installed cable until you are sure it's at fault.
4. Make no assumptions - test or check everything
5. Buy a cheap magnifying glass - its almost impossible to do a visual check of punch down connections without one
6. Use a 'continuity tester' or a volt-meter to check individual conductors in cables

Networks

Q1. What is Ping and what does it do?

'Ping' (actually its full name is 'ICMP Echo request') is a simple command that may be issued from the DOS Command Prompt (Start/Run/cmd/OK). Ping tells you if you can, or cannot, contact an IP address (another PC). Ping sends a small message to another computer which causes the receiver to echo back the same message (the message pings forward and backward). Ping is the simplest and most useful diagnostic tool to become familiar with and well worth a few minutes experimentation. To use Ping;

1. Run a command prompt (sometimes called a 'DOS box') (Start->Programs->Command Prompt (MSDOS) or Start->run enter command -> OK
2. Type:

3.  ping xxx.xxx.xxx.xxx

where xxx.xxx.xxx.xxx is the IP address that you want to check followed by ENTER. You can also use a URL with a ping:

ping www.sitename.com

For this format to work the DNS service must be contactable and working.

4. If ping works (you have successfully sent a message to the remote computer and received a response) you should get up to 4 replies of the form:

5.  Reply from xxx.xxx.xxx.xxx: bytes=32 time=yyms TTL=zz

Where xxx.xxx.xxx.xxx is the IP address that is responding, yyms is the time (yy) in milliseconds (ms) that the ping took and zz can be used to calculate the number of routers that it passed through on its journey.

6. If the Ping fails you will see a message like:

7.  Request timed out (connection or routing error)

8.  OR

9.  Host unreachable (routing error)

10.OR

11.Network unreachable (routing error)

Q2. Diagnosing Network Problems.

To diagnose a network problem you just start to verify the connections from a known starting point (your PC) moving progressively further into the network until you find the problem:

1. Always start with your own PC (it regularly fails). Issue a ping to your own PC (get it's address here). If this fails restart your PC and try the failing operation again.

Check with someone else in the office - if you are the only person having the problem you have already isolated it to your PC or its wiring. Now you only have to find it - in all cases it is not a remote network problem.

1. Restart your PC - 90% of all problems disappear with this one act.
2. Check the link LEDs on your PC LAN card (if it has any).
3. Check your cabling .
1. Now check your local network.

Your local PC is OK - someone else has same problem.

Ping the local router (its address is the Default Gateway IP that you get here). If this fails we may have a problem with the local LAN or the router.

Now you have to move from your desk.

Find your router and Hub/Switch check the LED displays. If they are not normal remove and immediately replace the power connection or switch the unit OFF then ON.

Go back to your PC and retry to ping your local router and then repeat the failing operation.

3. Check the remote network.

Your local router is OK - we can reach it and its LEDs are normal.

Issue a tracert command to 64.58.76.176 (www.yahoo.com) NOTE: always use the -d option with this command and you can abandon it using CTRL+C when you see two three consecutive rows of '*'.

Note the hop number of the first failure and contact your service provider.

Q3. What is a trace route (or tracert) command?

A tracert (or trace route) command tells you all the routers between your PC and the place you want to trace to (can be either an IP address or a URL e.g. www.smokeyjoe.com )

To run a tracert command:

1. Click start->programs->Command Prompt (or Start->run enter cmd then OK)
2. Enter:

3.  tracert www.xxx.xxx.xxx -d' (or www.smokeyjoe.com -d)

Replace the IP address with the one you want or use the URL of the site if you know it. NOTE: The -d in the command line stops a DNS lookup and speeds up the command considerably.

4. tracert outputs the following display:

5.  a bbbb cccc dddd ee.ee.ee.ee

Where:

a is the hop number starting from 1

bbbb is the time is milliseconds that the first attempt took to reach the site. Asterisk means it timed out.

cccc is the time is milliseconds that the second attempt took to reach the site. Asterisk means it timed out.

dddd is the time is milliseconds that the third attempt took to reach the site. Asterisk means it timed out.

ee.ee.ee.ee is the IP address of the router at this hop number.

NOTES:

1. If you do NOT add the -d then after the dddd entry you will see a router name first then an IP address in square brackets.
2. You can abandon the command at any time by typing CTRL + C.

Q4. How do I find my TCP/IP configuration?

There are two methods of doing this - the quick and the long method depending on how much information you want:

The quick method (limited configuration):

1. Load a Command Prompt (a DOS box) (Start->programs->Command Prompt or Start->run enter command then OK)
2. If using windows '95 enter:

3.  winipcfg

This will display your IP address, subnet mask and default gateway (local router)

4. If using Windows NT, windows '98, Win2K, XP enter

5.  ipconfig /all

this will display your IP address, subnet mask, default gateway (local router) and MAC address

The long method (full configuration)

Windows '95, '98 and NT 4.x, Windows 2K:

1. Click start\settings\control panel.
2. Double click 'Network'
3. Select 'Protocols' tab
4. Select TCP/IP then click 'Properties'
5. Navigate to the relevant tab to find the required information.

Basic LAN scenario

basic lan configuration of 2 computers 

lan configuration between 2 networks

lan configuration between 2 networks

Kiwi International Limited (KIL) is a telecommunications equipment manufacturing company based in Wellington. The company has leased space in Auckland city consisting of one level of an office block and a warehouse in a separate location, some 1000 meters away. KIL wishes to purchase and install some network equipment in Auckland to provide a network for their Windows XP workstations and for three servers: two NetWare servers (NET1) and (NET2) and one Windows 2003 server (WINS).

Auckland Office
All machines have Combo cards installed. The network must comply with the following criteria:

• Two departments: Equipment and Services are in the warehouse
• Two departments: Sales and Marketing are in the office block
• Each warehouse department has five users and one network-connected printer
  (Total = 10 users; 2 printers).
• Each office block department has six users and one network-connected printer
  (Total = 12 users; 2 printers).
• The two sites (warehouse and office block) should be connected to one another using Ethernet switches.
• NET1 (a NetWare server) should be located at the Warehouse.
• NET2 (a NetWare server) and WINS (Windows 2003 server) should be located in the office block.

Question: Draw a diagram detailing how KIL's new Auckland network will be set up.

eMART, an international company (with a head office in Wellington), has recently established three regional branches located in Auckland, Christchurch, and Japan. Based on the following description, draw up a detailed diagram to illustrate the company’s networking infrastructure. Include in the diagram the whole internal network (all LANs) with the connecting devices, the Internet connections, and all telecommunication links. Clearly label the elements of the diagram.

• The company’s eCommerce site (B-to-C) is hosted by the company itself and is physically located in the head office in Wellington. The company’s databases are physically located in Auckland.
• The head office (Wellington) has one Novell Netware server, one Web server, four PCs and one printer networked together in a LAN using STAR physical topology.
• The Japan branch has one Novell Netware server, four PCs and one printer networked together in a LAN using STAR physical topology.
• The Christchurch branch has one Novell Netware server, four PCs and one printer networked together in a LAN using BUS physical topology.
• The Auckland branch has one Novell Netware server, one Database server, four PCs and one printer networked together in a LAN using RING physical topology.
• The Wellington and Japan branches use a high-speed digital link (1.54 Mbps) to access the Internet.
• Both the Christchurch and the Auckland branches have an ADSL (740 kbps) for fast Internet access.
• Each branch has a dedicated router for linking to the outside world over the Internet. All the branches use a local ISP for their Internet connection.

Answer:

Scenario 3
Designing a network on multiple floors in two buildings
Kiwi Computer Company (KCC) Limited is a manufacturer of computer supplies (who design, manufacture and wholesale a range of computer hardware components). KCC Ltd has recently leased two adjacent buildings in Central Auckland and will set up new departmental networks. The diagram below shows the basic structure of the company’s operation that spans seven floors in two buildings (viz, Reception & Conference rooms, Human resources, Administration, Management & Personnel, Design, Manufacture & Assembly, Stores & inventory, Sales & Marketing). 

he following is a schedule of the number of PCs, printers, file servers, database servers, web server, and some additional equipment required by each department.

	PCs	Printers	File servers	Database servers	Web servers	CAD/CAM workstations
Reception & Conference room	3	-	-	-	-	-
Human Resources	15	1	-	1	-	-
Administration	20	1	1	1	-	-
Management & Personnel	20	1	-	1	-	-
Design, Manufacture, Assembly	40	2	1	1	1	2
Stores, Inventory	10	1	1	1	-	-
Salea & Marketing	10	1	-	1	-	-

Question: Draw a detailed diagram of the proposed network.
Answer: 

Scenario 4 University Network Design Two of the departments of the University are about to be rehoused, and jointly need to install a new computer laboratory. This laboratory will occupy two adjacent rooms, with each room containing 40 PCs. The departments require: Each laboratory must be capable of operating independently. It should be possible to disable the network in each room separately, and at a single point. The two laboratories should be capable of being combined for use with large classes. Each laboratory requires access to its own Windows 2003 server. Both laboratories require access to the same Linux server. Question: Draw up a LAN diagram for the situation described above. Answer:

Creating a LAN(local area network)

Why set up a local area network?

When you have several computers, it can be convenient to connect them to each other to create a local area network (LAN). Setting up such a network costs very little, contrary to what people may think.

Here are a few advantages you could enjoy by setting up a local area network:

·         File transfers;

·         Sharing of resources (internet connection sharing, printer sharing, shared disks, etc.);

·         Mobility (in the case of a wireless network);

·         Discussion (mainly when the computers are remote);

·         Network games.

The two types of local area networks

There are two main types of local network architecture:

·         Wired networks, based on the Ethernet technology, which represent almost all local area networks. Given that Ethernet networks generally use RJ45cables, people often talk of RJ45 networks;

·         Wireless networks, which generally use the WiFi technology.

Necessary hardware

To create an RJ45 local area network in Windows, you will need:

·     Several computers running Windows (computers running two different versions of Windows can be part of the same network);

·    Ethernet cards on a PCI or ISA port (with an RJ45 plug) or built into themotherboard. When applicable, make sure the diodes on the back of the network card light up when the computer is on and that a cable is plugged in! There are also network adapters for USB ports, particularly in the case ofwireless network adapters;

·     RJ45 cables in the case of wired networks;

·     A hub, a device you can connect the RJ45 cables from the network's various computers to, which are fairly inexpensive (expect to pay around €50), or a switch, or, as an alternative option, a crossover cable if you want to connect just two computers.

Network architecture

To create an RJ45 local area network, it is recommended that you adopt a so-called "star" structure, where the computers are each connected to the hub via an RJ45 cable. A hub is a device that transfers data from one computer to another. The choice of hub will be made in function of the number of connected computers in order to have enough plugs (called "ports") on the hub.

In the event of a large network or a network with substantial bandwidth requirements, a switch will favorably replace the hub, as it makes it possible to distribute packets only to the computers concerned, whereas a hub systematically sends packets to all connected computers.

The structure of such a network looks like this:

If you want to connect two computers only, it is possible to avoid using a hub, by directly connecting the two computers with a crossover RJ45 cable.

Architectures to avoid

The following network structures will not work, even if they appear to be correct at first, unless the computers have several network interfaces (several cards) and the cables used between two computers are crossover cables:

Configure IP address on both the computer ,note that they must be in a same range and subnetmask 

here i had shown C class IP address and corresponding subnetmask