Router Primer Recommendation

[Thorgear]

I need a primer on routing, iptables, bridging, etc. Everything I find is either too simple or too complex. Can anyone recommend some mid-level documentation?

Thanks.

 

[RMerlin]

This isn't up-to-date, but for routing it still contains a lot of valuable information:

http://lartc.org/

 

[Thorgear]

This is good stuff, especially the Rusty stuff. Thanks Merlin.