How is net connection selected?

[Greg Kedrovsky]

I have a question more out of curiosity than necessity. 

If I have 2 ways of connecting to the internet (primary: cable modem
with a static IP; secondary: dial-up), how does "Linux" know which to
use? Is it just a whichever-is-available scenario?

I have fetchmail and sendmail running on my machines to move mail around
internally, and in and out through the internet. fetchmail queries 4
different mail servers to get my mail and deliver it to sendmail here
locally. When I send mail, sendmail shoots all my mail out through a
mail server in... Alabama. 

My cable modem wigged out on me a couple weekends ago, and at that time
I hadn't fiddled with dial-up. I have a winmodumb and I was afraid it
would be like pulling teeth to get it going. But, the downed cable
connection motivated me to do it. I did. And now have a dial-up
connection just in case Mr. Cable Guy goes postal on me and I lose my
"broadband." 

I also wanted to get dial-up ready for when I move up into the mountains
(if anyone remembers the thread a month or so ago on broadband
alternatives for me, one of which was a high-gain antenna, etc.; neat
stuff). 

So, is there an easy explanation about how this works - how fetchmail
and sendmail "choose" how to connect to the net?

-Greg

-- 
Mutt 1.4.1i on Slackware 9.1 Linux
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