[ILUG] Question about networks and interfaces on a laptop

[Anthony Staines]

Hi,

I run Red Hat 7.2 on a laptop, which moves between work, where it gets a 
fixed IP address on eth0 (network card) and home, where it picks up an 
IP address courtesy of Eircom on ppp0 (a modem). So far so fine.

Both of these work nicely, except that when at home I can't access my 
work websites, or the servers here. I get '-Site- could not be found' 
messages in Mozilla. I can't ping them, and I can't traceroute them by 
name. In fact I can't see any of the ucd.ie domain. By IP address there 
are no problems. (In other words 'ping XXX.ucd.ie' gets nowhere; 'ping 
137.43.XX.XX' works normallly).

If I bring down eth0 at home everything is hunky-dory, and it all just 
works. I assume that the problem is connected with the DNS setup linked 
to eth0, and when I kill this interface everything defaults to the ppp0 
interface on the modem.

Now for the question - I'm very lazy, and resent typing 'ipconfig eth0 
down' regularly. Can I set things up either not to bring up eth0 if it 
isn't plugged in, or so that this won't interfere with name resolution.

As is obvious I don't really understand how all of this hangs together - 
  a pointer to a nice simple tutorial would be welcome also.

Anthony Staines
-- 
Anthony Staines, Lecturer in Epidemiology, Department of Public Health,
   UCD, Earlsfort Terrace, Dublin2, Ireland. http://phm.ucd.ie/
   E-mail :- Anthony.Staines at ucd.ie Web :- http://astaines.ucd.ie/
     Work :- + 353 1 716 7345       Fax :- +353 1 716 7407
     Home :- + 353 1 849 1089    Mobile :- +353 1 86 606 9713