Routing Essentials

Question

I'm a programmer trying to fill a big hole in my understanding of networking basics. I've been reading a good book (Networking Bible by Sosinki) but I have been finding that there is a lot of "assumed" information contained, where terms/concepts are thrown at the reader without a proper introduction to them.

I understand that a "route" is a path through a network. But I am struggling with visualizing some routing-based concepts. Namely:

1. How do routes actually manifest themselves in the hardware? Are they just a list of IP addresses that get computed at the network layer, and then executed by the transport?
2. What kind of data exists in a so-caleld routing table? Is a routing-table just the mechanism for holding these lists of IP address (read above)?
3. What are the performance pros/cons for having a static route, as opposed to a dynamic route?

Answer 1

A route isn't defined by any one piece of hardware. A router's job is to look at the IP and decide if the packet belongs on it's network, or another, and send it along its way depending on what it decides. A router is really only concerned with the next step and nothing past, no single device routes the entire path of a packet.

A routing table contains the information a router needs to know to decide whether a packet belongs on it's own network or not and the next hop to send it to if it needs to go elsewhere. From wikipedia:

The routing table consists of at least three information fields:

 -the network id: i.e. the destination network id
 -cost: i.e. the cost or metric of the path through which the packet is to be sent
 -next hop: The next hop, or gateway, is the address of the next station to which the packet is to be sent on the way to its final destination

 Depending on the application and implementation, it can also contain
 additional values that refine path selection:

 -quality of service associated with the route. For example, the U flag indicates that an IP route is up.
 -links to filtering criteria/access lists associated with the route
 -interface: such as eth0 for the first Ethernet card, eth1 for the second Ethernet card, etc.

Choosing a static route or dynamic route wholly depends on the application. Static routing is not very fault-tolerant, but may be easier to troubleshoot certain network issues as your route will never change.