I am also not able to ping my gateway.
Probably your device and host is not routed properly. This question (post) should have included what returns to query: ---# route -n
but since it is not there let me only assume many important things and recommend the basic remedy as follows, to wit:
Set all interface down:
~# ifconfig lo down
~# ifconfig eth0 down
Set your host to the loop device:
/sbin/route add -net 127.0.0.0 netmask 255.0.0.0 lo
Set your loop (host) and the IP of your device:
/sbin/ifconfig lo 127.0.0.1
/sbin/ifconfig eth0 192.168.1.18 broadcast 192.168.1.255 netmask 255.255.255.0
Then set device to route to your your network (I am not sure whither comes your IP but I only assume that your ethernet router acting as DHCP served it to you ) so do this:
/sbin/route add -net 192.168.1.0 netmask 255.255.255.0 eth0
You can also fix this from the configuration file to be served by a DHCP=yes.
And route your network to the gateway:
/sbin/route add -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.1.1 eth0
Then set the gateway to be your default:
/sbin/route add default gw 192.168.1.1 eth0
Ask (call) your internet provider what is your DNServer IP, if they don't give you there is another way to uncover it but that should not apply since they (ISP) are bound by contract to set it or to declare it to you.
Then add that DNS server IP number to your configuration, for example:
~# echo "xxx.xxx.xxx.xxx. myinternet.provider.com" >> /etc/resolv.conf
That's it. Launch Firefox and you should be surfing over the internet.
Hope that helps.