Wikipedia pages to read if you want to become a network expert

http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol

http://en.wikipedia.org/wiki/Nmap

http://en.wikipedia.org/wiki/Media_Access_Control

http://en.wikipedia.org/wiki/Tracert

http://en.wikipedia.org/wiki/Ping_%28networking_utility%29

http://en.wikipedia.org/wiki/Ifconfig

http://en.wikipedia.org/wiki/Nslookup

http://en.wikipedia.org/wiki/Netstat

http://en.wikipedia.org/wiki/Lsof

http://en.wikipedia.org/wiki/Subnet_mask

http://en.wikipedia.org/wiki/Default_gateway

http://en.wikipedia.org/wiki/Routing_table

http://en.wikipedia.org/wiki/DHCP


interesting Linux Networking Manual http://www.faqs.org/docs/linux_network/index.html
Basic intro to several commands