This happens in the embedded very often when you are desingning your target file system fom scratch or modifing the exsisting one. I came accross same situation. and thinking why and finally figured out root for problem.
#ifconfig eth0 192.168.1.5 netmask 255.255.255.0 up
Now my interface is up. So to check it I do a ping to some system ( my network gateway )
# ping 192.168.1.1
Ping is sucessful. Now ping my own IP 192.168.1.5
Now it fails…. what could be the problem for this. ? I was looking around the kernel configs, driver etc,. but no solution.
And finaly I did type just ifconfig alone in the prompt and found there is no loopback interface up. I brought up the interface up and now I am able to ping by own IP.