[clue-tech] Qwest Choice Internet Basic (DSL) Gotcha - bridge mode not supported?

[David L. Anselmi]

Jeff Cann wrote:
> In follow-up to my post a few weeks ago about DSL.  The good news is that I'm 
> learning a lot more about networking...
> 
> I have the DSL installed and selected Qwest Choice Internet Basic as my ISP.  
> I purchased a static IP.  I tested in PPPoA for a week on a single laptop, 
> connected directly to the modem.  This weekend, I decided to plug the modem 
> into my LAN switch.  The LAN hosts all received a DHCP lease from the modem, 
> but none of them can connect to the WAN.  Doh!

You do not want bridge mode.  You want PPPoA with the modem doing NAT 
between your internal (RFC1918) subnet and your external, static IP. 
This is exactly what I'm using, though I have a Cisco modem.

I don't have an Actiontec handy to look at the screen but I didn't think 
it was hard last I set one up.  They *do* support NAT and so they will 
share one public IP with many devices on your LAN.

I can stop by after work most any day and take a look, if you want ;-)

[...]
> I assumed the bridge because this is how my comcast account works accept it's 
> assigned dynamic IP on the unit.  Since the comcast unit is a DHCP server and 
> is configured as a bridge, it's easy to set up a LAN - get a switch, plug 
> everything in, and set all LAN hosts as DHCP clients.  You're done in 30 
> minutes.

No, if the Comcast unit is a DHCP server then it isn't bridging.  Back 
in the day (remember all the "cable isn't as secure as DSL" hype?) a 
cable modem was a bridge and you needed a "cable router" between the LAN 
and the modem.  Now cable modems are like DSL modems--a WAN port where 
the coax goes (versus phone line) and 4 LAN ports, built in DHCP, NAT, 
filtering, etc.

FWIW, a bridge is a little like a switch.  At the IP layer it's 
invisible and thus you'd be on a QWest subnet and all your IPs would be 
assigned by them (and possibly public).  Thus no IP on the modem, no 
DHCP server on the modem, no NAT on the modem.  That's not what you have 
on your QWest connection, nor what you want.

You want PPPoA with the modem doing DCHP on the LAN and NAT between the 
LAN addresses and your static address.

HTH,
Dave
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