There are a number of online resources - as nutty as it sounds setup a secondary PC - or use a vps and then browse a large number of the hacking websites on the web.
BlackHat conferences while a bit expensive, will teach you a large amount about TCP/IP...
Architecturally here are few things I can tell you regarding TCP/IP
Since TCP/IP identifies parties by
addresses hacker's attempt to spoof
Address resolution within TCP/IP, DNS
and ARP are not authenticated
You can easily masquerade as some
other person or node
ARP spoofing circumvents switches....
Some TCP/IP Explolits include:
- MAC Layer (ethernet) TCP/IP exploits
- TCP Session hijacking
- TCP Session application peeking/viewing
- TCP Password Monitoring
- Various Back channels
- Packet Generation Attacks & Relays
These few things should help you get started in google searches ...
I can post more on each - however truth to be told... I would rather not Teach Hacking in a public community