First:
Try pinging some server on the internet. Something like this. (The used ip address is of one of google's name servers)
Code:
Orion:~$ ping -c 4 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_req=1 ttl=54 time=21.1 ms
64 bytes from 8.8.8.8: icmp_req=2 ttl=54 time=21.4 ms
64 bytes from 8.8.8.8: icmp_req=3 ttl=54 time=20.6 ms
64 bytes from 8.8.8.8: icmp_req=4 ttl=54 time=21.1 ms
--- 8.8.8.8 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 20.674/21.089/21.414/0.285 ms
This will tell you if there is a connection to the internet.
Second:
Check your default gateway:
Code:
Orion:~$ netstat -rn
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 192.168.10.254 0.0.0.0 UG 0 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
The bold value should point to the address of your firewall's green address.
Third:
Try to do a name lookup
Code:
Orion:~$ nslookup google.com
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
Name: google.com
Address: 209.85.147.105
Name: google.com
Address: 209.85.147.99
Name: google.com
Address: 209.85.147.103
Name: google.com
Address: 209.85.147.147
Name: google.com
Address: 209.85.147.106
Name: google.com
Address: 209.85.147.104
This will tell you if your nameserver is configured correctly.