UNIX for Dummies Questions & Answers

I'm trying to learn the basic in's and out's of networking on my own through the use of a book. When it comes to routing tables I'm completely lost. I apologize for the alignment of the table below. The book vaguely explains routing tables, then has the following example:

Code:

E15.3) Consider the following netstat –rn output from a Linux system. Describe the routes and figure out the network setup. 
Which network 10.0.0.0 or 10.1.1.0, is closer to the Internet? Which process added each route? 

Destination	Gateway	    Genmask	   	Flags	  MMS	  Iface
10.0.0.0     	0.0.0.0	   255.255.255.0	U	  40 	           eth1
10.1.1.0     	0.0.0.0	   255.255.255.0	U	  40	           eth0
0.0.0.0	        10.0.0.1	     0.0.0.0			UG	  40             eth1

From my understanding, there are two networks - 10.0.0.0 & 10.1.1.0. Neither required a gateway, and are both listed as up (u) with a maximum segment size of 40. For packet(s) to leave the network and reach the internet they are passed to 0.0.0.0 to reach the 10.0.0.1 gateway. In terms of which is closer to the internet, I'd say that 10.0.0.0 is closer since it is also located on eth1, but I'm honestly not sure. In terms of which process is added to each route, that doesn't even make sense to me.

If anyone has any insight into routing tables and this example it would be greatly appreciated. Thank you!

The designation of how the "default gateway" is represented varies by OS.

Here, in this case look for the flag UG.

You may want to look at "ip" and "ip route". That tool replaces netstart -rn. With "ip" could can create more complex routing scenarios.

Consider the commands:

Code:

ip route list
ip rule show
ip route show table main

Implication... you can add (for example) your own route tables.
See more (an example) at: NTLUG | Calendar / Calendar February 25, 2012 browse

Thank you cjcox. I appreciate the help. For now I'm trying to understand this example before moving on to more complex scenarios.

What the example says is this:

If you want to send to a system in the 10.0.0.0 network, you don't have to use a gateway (router). Just send the packet out of the eth1 interface and the destination system will receive your message directly.

If you want to send to a system in the 10.1.1.0 network, you also don't have to use a gateway. Just send the packet out of the eth0 interface and the destination system will receive your message directly.

In every other case, send the message to the gateway system (10.0.0.1) and hope that this machine will know how to deliver your message. Use the eth1 interface to reach the gateway.

Did that help?

Thank you, Hergp, that does help!

In terms of which is closer to the actually internet - would it be 10.0.0.0 or 10.1.1.0, or neither? I still don't understand that part of the question, or "which processes were added to each route." Thank you.

Doesn't really make much sense to say which is closer, however you could at least say that the default gateway of 10.0.0.1 is out through eth1 on the 10.0.0.0/24 network.

Your host knows where the default gateway is and how to get there.... so closeness isn't an issue.

Your host knows about the 10.0.0.0/24 network on eth1 and knows about the 10.1.1.0/24 network on eth0.

All internet traffic will go out eth1 because it doesn't know about those networks and that's where the default gateway can be found.

(assumes that the default gateway knows how to get to those Internet addresses)

Thank you, Cjcox! That's a huge help. Do you understand what they mean by which processes were added to each route? That makes no sense to me.