Linux Network troubleshooting step by step

Hi after working for 3 years in M3-consulting i have been looking for a job change. I am looking for a job

in Data Centers where i can gain knowledge and also get maximum exposure. I have got calls from IBM,TCS,Oracle and  Kanak, Hexagrid in Hyderabad  in one of the interview they asked me how can you  troubleshoot a network.

Here we go into the topic.

1- First check that your interface (Network adapter ) is enabled or not using:         ifconfig

2- To make sure there is no internal problem.

     ping to the loop back address  ping 127.0.0.1

   if there is no response  service network restart if same repeats check network settings again.

3- check cable problem from ethtool eth0 

         if everything is fine then last line will show

                Link detected: yes

     if link is not detected plug it or change the cable according to need and problem

 

4-check the gateway settings in 

/etc/network    and

 /etc/sysconfig/network-scripts/ifcfg-eth0
 

And check DNS settings in

 /etc/resolv.conf 

system-config-network 

netstat

route 

service iptables stop

( only disable the firewall for testing and dont forget to turn it on)

check boot messages if eth card is detected at boot time or not

cat /var/log/dmesg | grep -i eth0

or

dmesg | grep -i eth0

to check table of network interfaces

netstat -i


for more advanced troubleshooting

lspci | less
or
lspci | grep ethernet

to check all PCI buses and devices connected to them

These are enough to troubleshoot if still problem persist try installing drivers , check kernel related problems , check is there any need to recompile the kernel etc