General Network Connectivity Problems
MS-Windows Troubleshooting
General Network Connectivity Problems (e.g. cannot connect to remote computer)
Symptom:
Unable to connect to remote computer. General network connectivity problems.
Cause:
There are a number of things which can prevent two workstations from communicating with each other over the network. These include (and this is unlikely to be an exhaustive list):
- Poor or incorrect network protocol configuration
- Network hardware problems
- Software problems
The same can also cause problems even when superficially the network appears to be working.
Part of the problem in solving network connectivity problems is identifying what the underlying problem is or what the problems are.
Remedy:
The remedy to the problem depends on the root cause. The following should be regarded as a checklist of things to test:
- Check that the workstation be ‘pinged’, i.e.:
ping workstation
If this produces the message ‘Bad IP address workstation.’ then this indicates a name resolution failure, in other words NT has been unable to look up the IP address for the workstation. If the (target) workstation is on the same local network then ask the administrator to check that DSN is working correctly. If it is on a remote network then the IP address will probably need to be explicitly specified in the local TNSNAMES file. Alternately try pinging by specifying explicitly the IP address of the workstation, i.e.:ping workstation-ip-address
e.g.
ping 192.10.44.1(or whatever the ip address of the workstation is.)
If ping produces a message of the form:
Reply from ip-address: bytes=32 time<10ms TTL=128
Reply from ip-address: bytes=32 time<10ms TTL=128
Reply from ip-address: bytes=32 time<10ms TTL=128
Reply from ip-address: bytes=32 time<10ms TTL=128
Then this indicates that there is network connectivity between the two workstations. Packets are being sent to the workstation and replies received. The time may vary. However, if it produces the message:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Then this indicates that there is no network connectivity between the two workstations. Things to check:
- That the remote workstation is switched on.
- That both workstations are (physically) plugged into the network.
- That the hubs are switched on.
- That the ip address that is being pinged (which ping echoes) is correct for the workstation. If it is not then this indicates either a DNS failure or an incorrect TNSNAMES entry.
- That the remote workstation does not have a firewall that is preventing ping acknowledgements from being returned.
- If both workstations are on a local network that their TCP subnet is the same. This can be checked using:
ipconfigDo this on both workstations. For each network adapter this will show the following information:IP Address. . . . . . . . . : ip-addresss(may be blank)
Subnet Mask . . . . . . . . : subnet-mask
Default Gateway . . . . . . : gateway-ip
For a local network the subnets should be the same. The ip-address logically and-ed with the subnet-mask should give the same result. If it does not then the workstations are on different subnets. Check the ip-addresses.
ipconfigTo list all other possible gateways use the command:
route print
This lists other possible gateways that the workstation may use according to the ip address of the target. If the destination IP address does not match one of the network destinations listed then the default gateway will be used.If there is no default gateway the add the ip address of the gateway as the default. Otherwise check that the gateway is listed in the routing table. The ‘route’ command allows new entries to be added.
Repeat the process (at both ends) but by pinging the gateway. This will establish whether there is basic communications between the workstation and its local gateway. If both sides can communicate with their respective gateways then the problem must lie with the link between the gateways. Consult your network administrator.
- If the computers are on different networks try:
tracert workstation
This will show the route to the computer any may give a better indication of where on the route the problem lies.
- Ping demonstrates that there is network connectivity between the two workstations. To check network reliability trying pinging with larger packets and for longer. Try each of the following:
ping workstation -l 1024 -t
ping workstation -l 4096 -t
ping workstation -l 8192 -t
The ‘-l’ parameter specifies the size of the message to send (the default is 32bytes, real applications will send much larger blocks of data). The ‘-t’ parameter specifies that it should continue pinging until you ‘control-C’ it. I would recommend trying each in turn and only breaking it after a complete screen full of responses. As the packet size increases the time will also increase. However even with 8192 byte packets there should be no ‘Request timed out’ messages. If any are seen then this indicates a hardware problem, either with the network hardware or with one of the adapters in either of the workstations.Typical response times I would expect for a set of sample packet sizes are as follows:
Packet Size 100mbps LAN 10mbps LAN 100mbps to 10mbps LAN via single gateway -l 4096 time<10ms <10ms 10ms -l 8192 time<10ms 10ms 10ms -l 16000 time<10ms 30ms 30ms -l 30000 time<10ms 50ms 50ms -l 60000 time=10ms 100ms 110ms Network topology will vary between sites (for instance the number of routers and switches that the network traffic request must navigate), so please regard these as ballpark/guideline figures. Any small variation between these figures and the figures are your site are probably not significant. The first ping message may show a higher time or even timeout, this is not significant provided it is only the first message.To check whether it is a network adapter on either of the workstations look in the NT (system) event log. This may indicate if the adapter is giving problems. It could also be the network cable, hub or particular hub port. If the problem affects one particular workstation then this is indicative of either a network card failure, bad network cable or network hub port failure. For example if there are problems between workstations ‘A’ and ‘B’, also between ‘A’ and ‘C’ but not between ‘B’ and ‘C’ then this clearly indicates that the problem is related to workstation ‘A’. Try a different port on the network hub, then a different network cable and then try a different network card.
- If ping attempts fail the network appears to be totally unresponsive at one workstation (i.e. it cannot see anything on the network, even other workstations on the local network for which there are no network connectivity issues) then it is worth reinstalling the latest service pack. Some old dlls on the system can produce network related problems. It’s worth a try.
- Enable ‘Black Hole Router detection’. Part of the underlying network protocol involves the network cards in both computers negotiating agreeing on the largest packet size that they can mutually manage. (For Ethernet this is typically 1550 bytes.) When communicating over a WAN it is possible that some of the routers or bridges along the route will not be able to handle packets as large as the network cards can manage. These should return a message indicating when a packet is too large and at the same time specify the maximum packet size they in turn can manage. Normal TCP-IP communication is self tuning in this way. However some (older?) routers or bridges fail to respond correctly and quietly drop the packet if it is too large. These are known as ‘black hole routers’. In NT black hole router detection is disabled by default. To turn it on requires adding (or modifying the following registry key):
HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters\ EnabledPMTUBHDetect=1
If adding this registry entry then add it as aREG_DWORD.
Other than event log, registry and service pack references these notes are also applicable to Windows
LAN & Network Diagnostics
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.
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
'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)
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.
2. 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.
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.
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.
Convert Any File Online
To day i got a image in .bmp format and i wanted to convert it to jpg format. I searched over internet and found many softwares. But i found an online site that easily convert any file to any format. Convert any file using the free online Zamzar service. This service allows you to convert any image, document, music, video, e-book, or compressed file format into another. Below are some different common examples of how this service could be used.
- Convert a .jpg image into a .png, .gif, or .bmp, etc.
- Convert a YouTube video into a .avi, .mov, .3gp, .flac, .m4a, .wmv, etc.
- Convert a .docx to a .doc, .pdf, .html, etc.
- Convert a .pdf into an e-book format your e-reader supports.
- Convert a .rar into a .zip
CAT-5 CABLE AND RJ45 CONNECTORS
The CAT-5 is a standard cable which has four twisted pairs of colours. It is easy to crimp a RJ45 connector to CAT-5 cable and make it into a straight cable or cross the cable as required. To make a straight cable, the ends must be crimped in the same way at each end. When making a crossover cable, some wires of certain colours have to be reversed.CAT-5 cable is usually divided into 4 twisted pairs of colours:
Green / green-white
Blue / white and blue
Brown / brown-whiteStraight Cable Colour Code
To make a straight cable, the tips must be crimped typically the same way ateach end by respecting the twisted pair size.
In general, the colour code used is:
1) orange-white
2) orange
3) green-white
4) Blue
5) blue-white
6) Green
7) brown-white
8) brownCrossover Cable Colour Code
For a crossover cable, swap 1 with 3, and 2 with 6, in the list above. This gives:
1) green-white
2) green
3) orange and white
4) Blue
5) blue-white
6) orange
7) brown-white
8) brownStandard EIA / TIA 568 (A &B) Colour CodeStraight cable
1) white-green / white-green
2) green / green
3) white-orange / white-orange
4) Blue / blue
5) white-blue / white-blue
6)
7) white-brown / white-brown
8) brown / brownCrossover cable 10/100baseT Colour Code
1) white-green / white-orange
2) Green / orange
3) white-orange / white-green
4) Blue / blue
5) white-blue / white-blue
6) Orange / green
7) white-brown / white-brown
8) brown / brownComplete crossover cable or crossgigabit Colour CodeOn Gbic 1000BaseT eg
1) white-green / white-orange
2) Green / orange
3) white-orange / white-green
4) Blue / white-brown
5) white-blue / brown
6) Orange / green
7) white-brown / blue
8) Brown / white-blue
Note:
Many Gigabits (10/100/1000 multi speed) are auto MDI / MDIX and automatically adapt to the type of cable connected.Courtesy : Foreign Post Office Mumbai
Batch file to Switch Between WAN and Broad Band in WAN Offices
In WAN Offices often we are using Broad Band in so many circumstances. For Swinth between WAN and Broad band we have to change Default gateway, and DNS server's ip each time.Here is the simple solution to switch between WAN and Broad band.
Steps:
1.Before creating batch file.IP and Subnetmask of Broad band Modem must be in WAN IP Series. For this task please refer mannual.Click here to download mannual
2.Create a new notepad(.txt document)
3.Copy and paste the following script
@ECHO OFF
color 2
Echo * Now System IP Changes to WAN Settings*
Echo ** If ready to switch to WAN ** PRESS ENTER *** or else Ctrl+ C
pause
set vargw=10.102.154.193
set vardns1=164.100.3.1
set vardns2=164.100.17.3
ECHO Setting Gateway
netsh int ip set address name = "Local Area Connection" gateway = %vargw% gwmetric = 1
ECHO Setting Primary DNS
netsh int ip set dns name = "Local Area Connection" source = static addr = %vardns1%
ECHO Setting Secondary DNS
netsh int ip add dns name = "Local Area Connection" addr = %vardns2%
Echo **** Now You are in Wide Area Network ****
pause
4.Change set vargw=Router IP of WAN or Modem IP of Broadband
set vardns1=Primary DNS of WAN or Broadband
set vardns2=Secondary DNS of WAN or Broadband
5.Save the file.
6.Rename it as WAN.bat or Broadband.bat
7.Just double click to Switch between WAN and Broadband
Note:This batch file works in Computers which are having Single Network Adapter only.Configuration of Broadband and leased line in Switch
FOLLOW THE FOLLOWING STEPS FOR CONFIGURATION OF BROAD BAND MODEM.
01. PING 192.168.1.1(DEFAULT IP ADDRESS OF BROAD BAND MODEM)
02. OPERN YOUR WEB BROWSER TYPE http://192.168.1.1
03. type user name: admin, password: admin.
04. goto advanced setup>WAN
05. click on edit on line containg vpi/vci 0/35.
06. click on next > change the connection type to pppoe
07. click on next > enter username and password and service name.
08. click on next>next> save
09. again advanced setup screen will appears
10. click on save/reboot.
after two minutes.
01. again open the web browser and type 192.168.1.1
02. enter username : admin and password: admin
03. click on device info.
04. note down the primary dns server and secondary dns server.
05. configure the system in which you want broad band as follows
ip address 192.168.1.x
subnet mask 255.255.255.0
default gateway 192.168.1.1
preferred dns server: <enter the value from step 4>
alternate dns server:<enter the value from step 4>
or
ip address 192.168.1.x
subnet mask 255.255.255.0
default gateway 192.168.1.1
preferred dns server: 192.168.1.1
if you dont want borad band in a system then dont configure the default gateway, preferred dns server and alternate dns server in that system.
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