[CentOS] Modem network card conflict

Shawn Everett shawn at tandac.com
Wed Jul 30 14:06:40 UTC 2008

Hi All,

Here's a strange one for you...

I have a Linux box with a PCMCIA adapter PCI card in it.  Plugged into said 
card is a cellular modem card.

I can configure wvdial and dial the modem card perfectly.  My ppp0 
interface comes up and I can ping everything.

I also have a network card on the motherboard.  Once again, by itself the 
network card works correctly.  That is with the modem NOT dialed up.

Here's where things get interesting...

If I flush the firewall rules: iptables -F
Bring down the eth0 interface: ifconfig eth0 down
Connect with the modem: wvdial &
Bring up the interface: ifconfig eth0

At this point the ppp0 interface drops off and redials.  It is no longer 
able to maintain a stable connection.  ppp0 and eth0 do not use the same 
IP range.



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