Let's put into practice

Troubleshooting

TROUBLESHOOTING

There are some helpful tools that you can use for network troubleshooting purposes. Unfortunately, some of them are not available on Windows systems. Let's see them:

1) Arp (you provide an IP address and it gives the corresponding MAC address)
2) Dig (you provide an IP address and it gives corresponding DNS servers). Not available on Windows systems
3) Netstat (shows all opened ports)
4) Ping (the King tool)
5) Traceroute/Tracert (shows servers between you and a provided IP address or vice versa)
6) Ipconfig (shows your IP address). Available on Windows systems only
7) Winipcfg (shows your IP address). Available on Windows 95/98/ME systems only
8) http://www.whatismyip.com (shows your *external* IP address if you are using a router)

First of all, you have to double check IP addresses and netmasks. Remember that all computers in your LAN MUST USE THE SAME IP ADDRESSES RANGE. So if you have computer 1 using let's say 192.168.0.1 whereas computer 2 in your LAN is using 10.0.0.3, that simply doesn't work! So if you will use 192.168.1.x IP addresses, each computer in your LAN must use '192.168.1.something'. The same thing is true for netmasks. If you use 255.255.255.0, each computer in your LAN should use 255.255.255.0. Write down IP addresses and netmasks before starting. You should have:

1) your router IP address (the default gateway)
2) each computer's IP address
3) your access point's IP address
4) a netmask
5) each network interface card's MAC (optional, if you are setting up a wireless LAN)
6) your ISP's DNS server IP address

Before starting, disable any firewall (hardware and software), disable DHCP and use a root/administrator account. You can enable firewall and DHCP later. Now double check all cables and physical connections. Verify each network interface card's led. Green led is ok. If all physical connections seems ok, open a MS DOS prompt (if you are using Windows) or a Terminal window (if you are using Linux or Mac Os X) and type 'ping 127.0.0.1'. 127.0.0.1 is another special IP address: the loopback address. This IP address identifies YOURSELF. The ping command is used to discover if a specified host is up or down. It accepts some parameters and gives you some helpful information (such as TTL), but here will use it to find out whether the specified host is up and working or down. If you get an error here, the TCP/IP protocol is not installed or it is not working properly. Check if you installed network software and network devices drivers properly. If ping works well, you should get something like this:

PING 127.0.0.1: 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=255 time=2 ms

--- localhost ping statistics ---
10 packets transmitted, 10 packets received, 0% packet loss
round-trip min/avg/max = 2/2/2 ms

you could get more rows or an endless loop depending on your system configuration. If you get an endless loop, stop displaying rows by pressing Ctrl-C keys. If you pass this test, type 'ping 192.168.1.x' where 'x' is your computer IP address. If your computer's IP address is 192.168.1.3, type 'ping 192.168.1.3'. You should get an output similar to the output shown above. If you get errors here, check that all network card parameters have been correctly configured. If everything seems ok, go further and ping your local router and other computers in your LAN. If you can't ping your router, verify that:
1) your router is powered up :DD
2) all cables are connected correctly
3) your router IP is compatible with your LAN IP addresses range (AGAIN?!?) ;o)
If you can reach your router, try pinging each computer in your LAN. If you can't reach some of them, check the usual stuff (IP addresses range, netmasks, cables and so on). If you can reach everything inside of your LAN, try pinging the Internet. Type 'ping google.com'. If you don't get errors here, congratulation: you have a working network now! Furthermore, you can access the Internet. If you have not luck and you get errors such us 'network unreachable' or 'host unreachable' or 'host unknown' you must investigate further. If you get 'host unknown' maybe your ISP's DNS server is down or you set up a wrong DNS server. To find out if you configured the DNS server's IP address properly, type 'ping 64.233.187.99'. This is the Google's server IP address. If you can reach it now, chances are your ISP's DNS server is down or you misconfigured it. To find out if your ISP's DNS server is down, ping it. Besides, you can try some public DNS server. Some public DNS servers are:
4.2.2.1
4.2.2.2
you can get a list of public DNS servers here: http://80.247.230.136/dns.htm

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