| Command | Description |
| ifconfig | Display the link and address status of active interfaces. |
| ip addr show | Display the link and address status of active interfaces. |
| route -n | Display all the routing table in numerical addresses. |
| ip route show | Display all the routing table in numerical addresses. |
| arp | Display the current content of the ARP cache tables. |
| ip neigh | Display the current content of the ARP cache tables. |
| plog | Display ppp daemon log. |
| ping google.com | Check the Internet connection to “google.com”. |
| whois google.com | Check who registered “google.com” in the domains database. |
| traceroute google.com | Trace the Internet connection to “google.com”. |
| tracepath google.com | Trace the Internet connection to “google.com”. |
| mtr google.com | Trace the Internet connection to “google.com” (repeatedly). |
| dig [@dns-server.com] example.com [{a|mx|any}] | Check DNS records of “example.com” by “dns-server.com” for a “a”, “mx”, or “any” record. |
| iptables -L -n | Check packet filter |
| netstat -a | Find all open ports |
| netstat -l –inet | Find listening ports. |
| netstat -ln –tcp | Find listening TCP ports (numeric). |
| dlint example.com | Check DNS zone information of “example.com”. |