D'oh!

[Lennart Sorensen]

On Tue, Dec 11, 2007 at 06:06:41PM -0500, Chris Aitken wrote:
> James Knott wrote:
> 
> >chris-n/jUll39koHNgV/OU4+dkA at public.gmane.org wrote:
> >
> >>James Knott writes:
> >><snip>
> >>
> >>>I assume you're using DHCP.  Is there any reason you can't assign a 
> >>>dedicated IP address to that computer's MAC address?
> >>
> >>
> >>Wouldn't that mean I can't have a LAN address as well? We have on 
> >>eprinter attached to one computer and the other three computers need 
> >>to print to it.
> >
> >
> >Judging from the other messages, it's hard to see what it is you want. 
> >I assume you want both a local lan address as well as one assigned by 
> >an ISP.  Is that correct? 
> 
> Exactly.
> 
> If so, you need 2 addresses, the 2nd being an "alias". 
> 
> Okay.
> 
> IIRC, if you want both a static and DHCP address on a NIC, only the 
> alias can have a DHCP address. 
> 
> Okay.
> 
> As someone else mentioned, you cannot have two addresses on the same 
> subnet assigned to the NIC.  A little more detail about what precisely 
> you're trying to do would help, instead of trying to guess what you're 
> doing.
> 
> Okay. I gave a verbal diagram in another email. Here it is so you have 
> it handy:
> 
> I have four computers:
> cpc (connected by usb to a printer which is shared) runs ubuntu 7.10,
> ppc (fedora core 4),
> dpc (ubuntu 7.10), and
> bpc (fedora  7)
> 
> All four computers are attached to a router. The router is attached to 
> the cable modem. The cable modem is attached to, well, the Internet. 
> That's it. ppc, ppc, and bpc all print (vian cups) to cpc's printer.
> 
> Just so we're clear, I'm okay now - I mean I am printing to the remote 
> printer and all computers are on the Internet. Lennart is still 
> concerned as my /etc/network/interfaces is "working" it is a bit funky. 
> Maybe, the next cable modem reboot, or computer reboot I'll have trouble 
> because of this crazy /etc/network/interfaces file (on cpc by the way). 
> dpc is the next computer I want to configure with a local address so it 
> can print to cpc's printer. Interestingly, it has no entry whatsoever in 
> /etc/network/interfaces for dhcp-assigned connection though it is 
> happily on the Internet as we write. It seems to truly be getting it's 
> address from the cable modem (and through the router) with no help from 
> any configuration file.

The router gets an address from the cable modem.  Everyone else gets an
address from the router (which masquarades the outbound traffic).  You
can't pass a dhcp request through the router to the cable modem since
they are seperate networks (well dhcprelay could, but that gets very
complicated and a cable modem wouldn't support that).

--
Len Sorensen
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