After Bruno Magnani,  magnani.bruno AT alitalia.it 
tersely reported on resolving problems of coincident use of ethernet and ppp connections,
I asked him to please expand the report for inclusion in the Lucent DOCs/
He returned a very nice report, which with very little editing is that below.
The issue is much more generic than usage with the Lucent modem,
so it is appropriate to also provide it broadly to Discuss@Linmodems.org

Thanks again Bruno.

============================================================================================

Premise
-----------
These notes report about running a Lucent Microelectronics LT winmodem
driver on a Compaq Armada E500 that is mostly used to connect to a
Company's LAN through a network card.

Goals:
	- set up a handy configuration for dialup ISP accounts
	- avoid touching existing network configuration files
Technical context :
	- distribution Red Hat 7.2 (Enigma)
	- Kernel 2.4.7-10
Dialers:
	- wvdial 1.41
	- KDE kppp 2.0.8 (KDE 2.2-11, Qt 2.3.1)
Evidence of applicability to a different context: NONE
Please check the output of the following commands to verify your settings:
	# uname -a
	# wvdial --version
	# kppp --version

Startup Assumption
--------------------------
I installed the source package ltmodem-6.00b9, and assume the process 
of compiling, installing and autoloading the new drivers on your machine went ok. 

After that I now have: the new drivers installed at: 
   /lib/modules/2.4.7-10/kernel/drivers/char/lt_modem.o 
   /lib/modules/2.4.7-10/kernel/drivers/char/lt_serial.o ;
the device node /dev/ttyLT0 (as the port to be referred in dialup scripts);
the symbolic link /dev/modem --> /dev/ttyLT0 ; 
an updated /etc/modules.conf as well as 
an updated module configuration database.

Setting up name resolution with wvdial
----------------------------------------
The configuration file for this dialer is /etc/wvdial.conf, you can read through the wvdial man pages
and the documentation file ../DOCs/wvdial.txt for setting it up (remember to create the symbolic link 
"ln -sf /dev/ttyLT0 /dev/ttyS14" as suggested).

Here is what I get when attempting a connection:
-----------------------------------------------	
	/home/bruno> wvdial libero
	--> WvDial: Internet dialer version 1.41
	--> Initializing modem.
	--> Sending: ATZ
	ATZ
	OK
	--> Sending: ATM1L3
	ATM1L3
	OK
	--> Modem initialized.
	--> Sending: ATDT 00688531010
	--> Waiting for carrier.
	ATDT 00688531010
	CONNECT 48000 V42bis
	--> Carrier detected.  Waiting for prompt.
	Username:
	--> Looks like a login prompt.
	--> Sending: xxxxxxx@libero.it
	xxxxxxx@libero.it
	Password:
	--> Looks like a password prompt.
	--> Sending: (password)
	~Entering PPP mode.}-}*Async interface address is unnumbered (Loopback0)}-}*Your IP 
	address is 151.24.220.124. MTU is 1500 bytes}-}*}-}*jO~
	--> Looks like a welcome message.
	--> Starting pppd at Fri Feb 22 17:08:31 2002

And the corresponding output of "tail -f /var/log/messages"
------------------------------------------------------------
	kernel: CSLIP: code copyright 1989 Regents of the University of California
	kernel: PPP generic driver version 2.4.1
	pppd[1955]: pppd 2.4.1 started by root, uid 0
	pppd[1955]: Using interface ppp0
	pppd[1955]: Connect: ppp0 <--> /dev/ttyLT0
	kernel: PPP BSD Compression module registered
	kernel: PPP Deflate Compression module registered
	N4206624 pppd[1955]: local  IP address 151.24.220.124
	N4206624 pppd[1955]: remote IP address 151.5.160.151
	pppd[1955]: primary   DNS address 193.70.192.25
	pppd[1955]: secondary DNS address 193.70.152.25  (*)

(*) The last two lines are shown if you add the line "usepeerdns" in /etc/ppp/options
as suggested by Emin Liman when I raised a DNS issue in discuss@linmodem.org.

However when connected:
---------------------- 
I did not get name server resolution after this, that is 
I could ping using dotted quad notation IP addresses,
but domain name server (DNS) addressing failed. 

Even adding the two DNS addresses to /etc/ppp/resolv.conf was unsuccessfull. 
The only solution I found was to prepare a specific DNS configuration file for 
the ISP account (e.g. resolv.conf.libero) and write a simple script to substitute 
/etc/resolv.conf before the connection, then restoring the usual network configuration
upon exiting.  

//Comment from MarvS
If ethernet is not "ifdown eth0" before attempting ppp without the further configuration
work described below, there are frequently Netscape crashes and/or freezing of Xwindows
//

Setting up name server resolution with kppp
--------------------------------------------
Setting up kppp is easily done by starting the tool and clicking on setup, 
the various steps are well documented in the manual that is accessible through the ? button.
This process creates a configuration file in ~/.kde/share/config/kppprc 
listing all the accounts information.
If you provide your ISP's domain name, DNS addresses and set the option:
   "Disable Existing DNS Seervers during Connection" 
in the DNS section of kppp setup ~/.kde/share/config/kppprc 
will include lines such as

	DNS=212.17.192.216,212.17.192.56
	.....
	Domain=infinito.it
	ExDNSDisabled=1

Given this, DNS resolution (magically) works with out any need to touch /etc/resolv.conf.

However, when I use kppp I get a weird message:

	....modprobe: modprobe: Can't locate module ppp0
	... kernel: CSLIP: code copyright 1989 Regents of the University of California
	... 

in /var/log/messages. This can be (inelegantly) removed by inserting "alias ppp0 off" in
/etc/modules.conf. 

Endnote:
----------------------------------
Please consider that starting a serial connection on a public network 
while logged onto a LAN raises severe security issues and should be avoided.




