Basic networking commands on Linux

ifconfig     
to see interfaces, IP address, MAC address, TX and RX packet/byte counts

route
shows routing table.  Add static routes

arp
shows arp cache (list of IP to MAC translations)

lspci
lists PCI devices, including NIC

ping
send ICMP Echo Request to a host

traceroute or tracepath
show path thru internet

nslookup
do a DNS resolution

whois
lookup domain information

netstat
networking activity, connections, listening services

nmap
port scanner

telnet
ssh
remote login


Files:
/proc/interrupts      device IRQs and interrupt count
/etc/resolv.conf       list of DNS servers to be used
/etc/hosts                   static hostname to IP translations
/etc/protocols           IP Protocol field values
/etc/services              TCP/UDP ports