Thanks for all the good info. I've been reading lots of sites and have printed
out the posts here. I think I finally have a good handle of what is going
on.

But I don't understand one of the basics.

Let's say that you have DSL via router and DSL modem. AND you also have an old
US Robotics analog modem (which I'm using now!) connected to the serial port
(tty0?)

1. How does Kmail or Knode or a browser know whether to get/send the data....
through the ppp dial-up/serial port.... or through the ehternet card? How
does know what you are connected to? What file(s) "links" the email software
or browser to the hardware? Or is this done by some hardware on the mobo?

2. Is it possible to have DSL up and running and to also dial-out to an ISP
(Mindspring) on the analog modem? If so, how does Kmail know where to get
send data? (I doubt anyone would want to do this, but I'd like to know
anyway.... because SBC gives you a dial-up backup... but maybe it only works
if DSL is "down."?

I read "Howstuffworks.com" all morning but can't seem to find answer to this.
(Great site... thanks for the lead, Menno Duursma )



Al

A-B C. wrote :
>
> Let's say that you have DSL via router and DSL modem. AND you also have an old
> US Robotics analog modem (which I'm using now!) connected to the serial port
> (tty0?)
>
> 1. How does Kmail or Knode or a browser know whether to get/send the data....
> through the ppp dial-up/serial port.... or through the ehternet card?
>
They just don't care. All they care about is whether your computer
connected to the Internet or not

> 2. Is it possible to have DSL up and running and to also dial-out to an ISP
> (Mindspring) on the analog modem?

Yes. Just make sure that you don't setup something like a dial on demand.

> If so, how does Kmail know where to get send data?

If your KMail is setup to use servers at the Internet it just looks if
those servers are available. If they are data are being send or
received. If not you'll get an error message.
--
Thomas O.

This area is designed to become quite warm during normal operation.

On Sat, 17 Apr 2004 14:14:45 -0700, A-B C. wrote:

> Let's say that you have DSL via router and DSL modem. AND you also have an old
> US Robotics analog modem (which I'm using now!) connected to the serial port
> (tty0?)
>
> 1. How does Kmail or Knode or a browser know whether to get/send the data....
> through the ppp dial-up/serial port.... or through the ehternet card?

They don't know, and don't care. It's a basic abstraction. Only the kernel
cares about stuff like that, and it keeps tables for it.

> How does know what you are connected to?

You can list and manipulate that stuff, using utilities from the "tcpip"
and/or "iproute2" (and probably other) packages. If you want to know about
which utility/tool:

grep bin /var/log/packages/tcpip*

And read the manpages, which seem interesting ...

> What file(s) "links" the email software or browser to the hardware?

Applications just make calles to library routines, which either return
needed info directly, or in turn do a system call for it (to the kernel).
(Or the app might do the system call directly, "strace" knows about that.)

The call might return a file handle for a socket which might be connected
to some website, mail server, or whatever reqested. The app then just
sends commands and data over the socket.

> Or is this done by some hardware on the mobo?

Phisically, yes. But there is (the/another) abstraction layer in between.
The kernel makes the hardware look like some programmer-friendly platform.
Here is a list of available system calls:

cut -d' ' -f2 /proc/ksyms |less

> 2. Is it possible to have DSL up and running and to also dial-out to an
> ISP (Mindspring) on the analog modem?

Yes.

> If so, how does Kmail know where to get send data?

Again, Kmail doesn't know (if it does, i'd consider it broken).
The however kernel _does_ ofcource know, and it normally sends it to the
default gateway. But that can be manipulated (even on a per connection
basis) with "iptables", "ip" and others. Some programs _can_ source route
over some interface (such as "nc", "traceroute", "ping") but they're
specific tools for administation / testing.

> (I doubt anyone would want to do this,

I have done so before (that needs some tweaking though):
http://google.nl/groups?selm=pan.200...op.localdomain

> but I'd like to know anyway.... because SBC gives you a dial-up backup...

That's a good thing.

> but maybe it only works if DSL is "down."?

The above, yes. But you can run both connections at the same time. Even
round-robin between them (although that doesn't make any sence if you have
DSL - it would make sence to do between two DSL links ...)

> I read "Howstuffworks.com" all morning but can't seem to find answer to
> this.

For multiple PPP links (i know a working installation of this BTW):
http://www.cwareco.com/download/eqlplus.html

Fancy "iproute2" stuff (you can have lots of fun with that stuff):
http://qos.dyndns.org:3389/cgi-bin/f...file=1#file_44

And i just today came across thease (haven'd had a read through then yet):
http://www.ssi.bg/~ja/nano.txt
http://www.ssi.bg/~ja/dgd-usage.txt

> (Great site...

Yeah. Some articles are a /much/ better then others on that site though ...

> thanks for the lead, Menno Duursma )

s/\ Duursma/\./

--
-Menno.

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In alt.os.linux.slackware, A-B C. dared to utter,
> 1. How does Kmail or Knode or a browser know whether to get/send the data....
> through the ppp dial-up/serial port.... or through the ehternet card?

man route

The kernel keeps a routing table. Here's mine.

alan@carrier~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
localnet * 255.255.255.0 U 0 0 0 eth0
loopback * 255.0.0.0 U 0 0 0 lo
default 192.168.1.254 0.0.0.0 UG 1 0 0 eth0

This isn't quite as verbose as I'd like, but it will do. Basically
there are four things that are important here: Destination, Gateway,
Genmask, and Iface.

Destination: The network address you wish to connect to (default is a
catch-all that matches anything that no other rule matches. You can
only have one default).
Gateway: The first router (i.e. gateway) you have to pass through to
reach your destination (* if no router is needed).
Genmask: The network address mask of that network.
Iface: The interface through which packets to your destination should
travel.

So by combining these, we can see that if I want to talk to loopback, I
send those packets out through lo and don't send them to a router
first. If I want to send to localnet, I send those packets out through
eth0 and don't send them through a router. And if I want to send them
to any other network (let's say whatever network google is on), I just
send them to my gateway (192.168.1.254) and it will take care of the
rest.

This is getting REALLY in depth for alt.os.linux.slackware. You should
do a lot more reading up before asking here again, and preferably
should ask in a newsgroup or online forum dedicated to networking, as
this is not a slackware specific issue.

- --
It is better to hear the rebuke of the wise,
Than for a man to hear the song of fools.
Ecclesiastes 7:5
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In article <q1l8l1-ma4.ln1@news.inet.tele.dk>, Thomas Overgaard wrote:
> A-B C. wrote :
>> 2. Is it possible to have DSL up and running and to also dial-out to an ISP
>> (Mindspring) on the analog modem?
>
> Yes. Just make sure that you don't setup something like a dial on demand.
I don't see why one couldn't use dial on demand in addition to
their DSL. Just prioritize. try the DSL first, if the dsl is not
connecting then use regular ppp to dial your isp. You could
technically do both at the same time but thats redundant.


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