Gecko/20110303 Thunderbird/3.1.9   
   UTC)   
   .os2.networking.tcp-ip:202   
   From: Jonathan de Boyne Pollard    
      
   >> Perhaps you misconfigured your DHCP server. Did you erroneously tell    
   >> it to map two clients to a single static IP address?   
   >>   
   > I did not configure anything, I just unplugged the Mac laptop, which    
   > had worked fine for years, and plugged in the Linux machine, then    
   > rebooted everything (including the router, eventually.)   
   >   
      
   You probably *did* configure things, back when you bought your router    
   and first used it.   
      
   >> If your router is your DHCP server, its WWW configuration interface    
   >> (which you should be able to access from the machine whose network   
   >> connectivity is working, after all) will tell you what MAC addresses    
   >> each of its DHCP clients has.   
   >>   
   > I don't see anything like that in the configuration pages.   
   >   
      
   You don't tell us what router it is, but if it's anything like what I    
   think it is, you didn't look far enough for the DHCP settings.  They're    
   under "LAN Setup" on that very menu.  On an "IP and Mac Address Binding"    
   page of that, you'll see what static DHCP leases you've configured but    
   now don't remember; and on a "DHCP client" page you'll see all of the    
   currently assigned leases.   
      
      
      
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