[ale] default devices or routes

[jknapka at earthlink.net (Joseph A Knapka)]

John Wells wrote:
> 
> I have two NICs (eth0 as external to internet, eth1 as
> internal to internal net).  I have the default route
> set up as going out through eth0 (external).
> 
> How do networked applications determine which device
> to use?  I can ping my external DNS server but mozilla
> won't resolve hosts, and in order to ping a host by
> hostname I have to specify "ping -I eth0
> www.yahoo.com".  Do mozilla and the like use the
> routing table, or am I mistaken in my thinking?

The proper interface is determined by IP address.
Your routing tables must enable the machine to
decide the proper interface for any IP. If you
have a default route specified, any packet whose
destination cannot be determined by looking at
the routing table is sent to the default
destination for further routing. The default
route must indicate a host that will be able
to route packets to their destination, not
just an interface; and the default host
must be reachable on a physical network
segment to which your machine is connected.

Cheers,

-- Joe
# "You know how many remote castles there are along the
#  gorges? You can't MOVE for remote castles!" - Lu Tze re. Uberwald
# (Obsolete) Linux MM docs:
http://home.earthlink.net/~jknapka/linux-mm/vmoutline.html

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