Reddit reviews Routing TCP/IP, Volume 1 (2nd Edition)

TL;DR

Books

TCP/IP by No Starch Press - Covers everything from layering (the OSI model), transmission media, error detection and correction, sliding windows to congestion control and much, much more.

Routing TCP/IP By Cisco Press - Long considered a bible of routing. Both an excellent reference (I still use it today as a programmer) and study material should in case you really want to crank up the masochism.

Optimal Routing -Another excellent book covering the mechanics of large internetwork installations.

Software

Nmap - you too can discover just how easy illegally breaking into networked computer systems can be.

Netcat - A classic tool for writing network IO to a classical descriptor

tcpdump - Does what it says on the tin

wireshark - a graphical version of tcpdump

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the tl; part

Oh Jeez, where do you even begin.

I was certified at the Cisco CCNP level prior to becoming a professional programmer. If you dive into Cisco, you'll start to get familiar with the "real deal" of how things work across the internet, especially as you move onto higher certifications. This is discussing things like core routing infrastructure like BGP, interior routing protocols like IS/IS & OSPF. Cisco is also famous for presenting a view of the world that... benefits Cisco exclusively. This means that Cisco-sanctioned protocols will be overemphasized, this means you'll be presented with a view of information security stuck firmly in 90s network centrist view, Cisco will play down application-level, memory-corruption and the more ordinary "leegit p0rn here" security (unless they are talking about IDS systems for catching script kiddies -- they can sell you that!).

You'll also, particularly as you move up the stack, become attached to the "Cisco way", which means your understanding of networking is less "protocols and packets" and more "press this key" (you'll know how to "type things in" to get the right results, but maybe not why they work).

This leads me to the most salient point - Frankly, there is simply no better way to really understand networking than be the person writing the tools rather than "getting the concepts" . The average programmer might not understand networking, but the average network oriented programmer is in a completely different league than a Cisco tech (this reminds me of an amusing anecdote wherein I leaned a little too heavy on the Cisco docs and managed to flap out totally invalid internal BGP routes and shut off the internet for a small corner of southwestern Colorado for a few minutes!)

If you've got a background in programming, things will also be a lot easier. Take STP (spanning tree protocol) for example - an extremely common feature of even small networks today. You'll be covering it extensively in CCNA material. Many network engineers struggle with understanding it's rules of resolution, the real meaning of it's various configuration options. As a programmer, you are already comfortable with thinking about systems like networks as graphs, you might also be familiar with the spanning or minimum spanning tree algorithms already. You'll have the principles down before you even sit down and the hardest part might be remembering what Cisco IOS chooses to call your parameters of choice.

On the other hand, even with very "low level" network programming, with sockets for example. You are dealing with a huge, layers of abstraction on top of things. The nomenclature doesn't quite match that of network engineers and the way it "really works" is totally hidden from you. You'll have to really dive in after the fact.

I think these two books will really help you fully understand IGPs, EGPs, and BGP.

Routing TCP/IP, Volume 1 (2nd Edition) by Jeff Doyle
http://www.amazon.com/Routing-TCP-IP-1-2nd/dp/1587052024/ref=sr_1_1?ie=UTF8&qid=1320531876&sr=8-1

Routing TCP/IP, Volume II by Jeff Doyle
http://www.amazon.com/Routing-TCP-CCIE-Professional-Development/dp/1578700892/ref=sr_1_2?ie=UTF8&qid=1320531876&sr=8-2

The books have a ton of information and are easy to read. I want to be Jeffy Doyle when I grow up. :P

Yes, you can have more than one ABR in both stub and totally stubby areas, as well as NSSA and totally NSSA. Like you said, it'll prefer the cost to the closer ABR, as long as its comparing the same LSA type (e.g. 3 vs. 3 or 5 vs. 5).

You can actually combine both stub and totally stub, or NSSA and totally NSSA, as only the ABR decides if the area is "totally" stubby or NSSA. One use case for this is OSPF traffic engineering based on route type, as opposed to route cost.

The OSPF path selection algorithm quickly starts to get complicated when you look into the deeper details of it. It's definitely beyond the scope of CCNA, but it's a key point if you're trying to fully understand how OSPF works.

I have a bunch of more detailed write-ups on OSPF path selection if you're more interested in its inner workings, such as: Understanding OSPF External Route Path Selection and OSPF Path Selection Challenge.

Also if you haven't already read it, you should definitely check out Routing TCP/IP Volume 1. It's the definitive text on how routing protocols work in Cisco IOS.

I consider Routing TCP/IP Volumes 1 and 2 to be my bible when it comes to layer 3:

http://www.amazon.com/Routing-TCP-Volume-2nd-Edition/dp/1587052024

I've read those two books cover to cover and I still use them as a reference guide. Network Warrior is another favorite of mine.