Basic Network Troubleshooting - Submitted by UNSTABLE
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Possessing a simple understanding of networking and the tools used to troubleshoot networks will be incredibly helpful to everyone viewing your post. Under a microscope, networks are VERY complex, if you knew what was really happening when you open up Internet Explorer and type
http://forum.abit-usa.com and the page pops up, you'd be surprised it even worked! If you built your own computer, you can troubleshoot a network problem. Analytical skills are universal. When you flip the light switch to turn on your bedroom light, and it doesn't turn on, you don't replace the switch, or bust a hole in the wall to check the wiring, you replace the light bulb.
I'll do my best to keep this post to a bare minimum, but I have to assume that you know next to nothing about networking. Keep in mind as you look at the length of this, that I spent the time to type it up to HELP YOU.
TOOLS
80% of network troubleshooting happens at the command line. To access command line:
Win 9X: click start-->run type "Command¨ press return
NT/2000/XP: click start-->run type "CMD¨ press return
You now have a command window.
Type "IPCONFIG /ALL¨
quote:
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C:\Documents and Settings\unstable>ipconfig/all
Windows IP Configuration
Host Name . . . . . . . . . . . . : mycomputer
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Unknown
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : myISP.net
Description . . . . . . . . . . . : VIA Rhine II Fast Ethernet Adapter
Physical Address. . . . . . . . . : 00-50-8D-47-2D-33
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 10.10.255.200
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.10.255.1
DHCP Server . . . . . . . . . . . : 10.10.255.1
DNS Servers . . . . . . . . . . . : 158.237.164.107
158.237.164.108
Lease Obtained. . . . . . . . . . : Thursday, March 25, 2004 8:25:03 PM
Lease Expires . . . . . . . . . . : Friday, March 26, 2004 8:25:03 PM
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This is very useful information. It tells us the following:
IP ADDRESS
-Valid private IP address (10.10.255.200). Please note: if you are running a router and have left the DHCP settings as factory default, you will probably have a 192.168.x.x address, this is fine. A good rule of thumb is COMPARE your default gateway address and your IP address, all of the numbers except for the last octet should match (the last three digits). If you are connecting multiple machines and having problems communicating amongst them, check the IP addresses on all machines, ensure the only difference is in the LAST octet.
Default Gateway / DHCP Server
-This shows our router/default gateway which in this example is also our DHCP server. The Default Gateway is the first network device between YOU and the REST OF THE WORLD. If there ¡s something wrong with your default gateway, or the connection between you and the default gateway, you're not going anywhere!
DHCP is Dynamic Host Configuration Protocol, which basically means that we don't have to muck around with assigning IP addresses manually. If you don't have a router, there's a good chance the DHCP server and Default Gateway will be different, this is not a problem.
DNS Servers ¡V Domain Name Service
-DNS allows us humans to use names to find computers instead of IP addresses which are 12 numbers long! So when you open Internet Explorer and click that Forum.abit-usa.com link, your computer actually goes out to the DNS server (which in this example is 158.237.164.107) asks Where is forum.abit-usa.com? the DNS server replies: 65.123.7.5, then your computer heads over to 65.123.7.5.
l337 hax0rz note: 158.237.164.107 is not my dns server. It's a USMC.MIL address that I remember from my days in the Corps, I don't recommend messing with that net
So what good is this info?
This information alone tells us a bundle. If you're missing your default gateway, chances are there is a problem with communication between you and your router or ISP so check your physical connection to the router. If you're missing DNS addresses, you get no name resolution so typing forum.abit-usa.com in your address bar will leave you with a cannot find server error - check your router to ensure you're connecting to the ISP.
PING
Ping is an indispensable tool. Again, used from the command line. Used correctly, it shows whether you have connection to a website or network address.
quote:
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C:\Documents and Settings\unstable>ping forum.abit-usa.com
Pinging forum.abit-usa.com [65.123.7.5] with 32 bytes of data:
Reply from 65.123.7.5: bytes=32 time=99ms TTL=51
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Notice we got a reply from an IP address? This means name resolution is working. My computer went to my DNS server and said Where is forum.abit-usa.com? the DNS server responded 65.127.7.6 then my computer sent ping packets to that address and received a response. If your DNS server is down or you do not have connectivity to DNS you can also ping on IP address alone:
quote:
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ping 65.123.7.5
Pinging 65.123.7.5 with 32 bytes of data:
Reply from 65.123.7.5: bytes=32 time=97ms TTL=51
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If you're having problems connecting computers, PING is where you start. Get the IP addresses of both machines, and try pinging back and forth. If you are receiving responses your problem lies higher up (probably share permissions or NTFS permissions on the computers). You can check your network adapter by pinging the loopback address 127.0.0.1 (or hostname: localhost). This tells whether your adapter is working correctly or not. As you have probably already guessed, you can ping your gateway/router also to check connectivity.
Please note, some personal firewalls and the built-in XP firewall BLOCKS ICMP packets. In order to troubleshoot connections, it¡¦s best to turn these off.
It's helpful to post your IPCONFIG /ALL and also let everyone know what you can or can't ping.
Be sure to mask any host bits if you are NOT nat'ing (behind router). 192.168.1.100 is ok to post, 216.239.39.99 is not, change it to 216.239.39.XXX.
Contact the author of this guide >> UNSTABLE >>
http://testmy.net/forum/index.php?action=pm;sa=send;u=598
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