Subj : Re: Default Route
To   : comp.os.linux
From : Minderbinder
Date : Fri Jul 09 2004 11:22 pm

On Thu, 08 Jul 2004 21:50:28 -0500, Shive wrote:

> However, the handshake goes ok and I connect with my ISP but it will
> never actually find a URL, nor will the email connect.
> 
> Lots of surfing (On my cast off Winders laptop, alas, and this broadband
> work PC) got me the answer of logging in as SU and then issuing a "route
> del default eth0".  After that, I can connect just fine till I power
> off.
> 
> Don't quite understand the default route thingie yet, but I will get
> there with enough reading.
> 
To cut a long story short: your system contains a routing table, which is
a list of rules that decide how traffic destined for particular networks
should be sent out of the system. So, one rule makes sure that traffic for
your LAN goes out through your Ethernet card (as opposed to sending it to
your ISP via MODEM). For destinations that are not directly connected to
your computer, there must be a rule that names an intermediate host to
which there is a direct connection (the intermediate host forwards your
traffic to the next hop, and so on until it gets to the final destination).

Making seperate rules for all destinations is too much work to be
practical. Instead, we define a default rule, which is applied whenever
there is not a special rule. For a normal client PC, the routing table
should be quite simple, with one or two rules for local directly-connected
hosts, and a default route that sends all other traffic (destined for
hosts not on your network, and therefore presumably on the Internet) on to
your ISP.

Your problem is, your default route is trying to send packets to your ISP
out through your Ethernet card - but it should be sending them to the
computer on the other end of your PPP (dail-up) connection.

> Where is the best/standard/accepted/etc) place to put the route command?
> Or is there a config file that I need to update? I made a script and
> then called it as a runlevel startup command. It worked but I have a
> feeling that my method is a kludge and there is a much better place to
> fix the problem.
> 
Yes, there should be a better way. Now, assuming that your system sets up
eth0 (your first ethernet card) on boot, but leaves your MODEM interface
unconfigured, it follows that the default route would be set to eth0
because there's no other option.

When you dial-in to your ISP, your MODEM should be configured as a network
interface, and the default route set to the address of the ISP's dial-up
access point, via the MODEM interface. However, for whatever reason, the
program you are using to manage your dial-up connection is not overwriting
the default route in the routing table. This should be done by your PPP
program each time you dial in, as the address of the host at the ISP side
may change each time. It would also be nice if, when you disconnect, the
software sets the routing table back to how it was before... There should
be no need manually to delete routing entries at any time.

Your PPP dial-up software is incorrectly configured.
Does your friend dial up with the same program? Try comparing the
configurations of the two systems... or using a different program to
manage your PPP connection.

Cheers,
Minderbinder.

.