OT: Using my (new) cable based ISP with their modem in bridge mode and my existing router

[rhkramer@gmail.com]

Some key phrases / sub topics:
   * Astound (cable based) ISP in eastern Pa. area
   * Arris DG2470A modem / router in bridge mode with Ubiquiti Edge Router X
   * Ubiquiti Edge Router X in DMZ 

Aside: I'm in a catch 22 -- my new, cable-based ISP (Astound / RCN) says my 
questions are out of scope and I should talk to the manufacturer.  The 
manufacturer says that the Arris DG2470A modem / router is not something they 
sell to the end user (only to ISPs or such), and thus I should get support 
from the ISP, so:

For the the last 10 years or so I've used a DSL modem (in bridge mode) and a 
Ubiquiti Edge Router X.  With the modem in bridge mode the router was 
responsible for connection to the ISP (and using, afaict, pppoe).

I've now signed up to a new ISP (Astound / RCN) that provides access via cable 
(and, of course, a cable modem, an Arris DG2470A -- it does include a router 
but without all the features I'd like to have).  So far, I have not been able 
to connect to Astound with the modem in bridge mode (and using DHCP in the 
router).

(The new modem / router does work fine in non-bridge mode, so my connection and 
such works.)

I'm not 100% sure whether Astound (in my area, around Allentown, Pa.) uses 
PPPoE or DHCP to make the connection.  So far, I've tried only DHCP. 

Astound does need to do something on their end to register the modem in order 
to make it work.  They have told me that the thing they need to register the 
modem is the MAC address (and, of course, they have that for the Arris).

I am thinking of doing something like cloning the modem's MAC address in the 
router (and also maybe putting a different MAC address in the Arris) so that 
maybe Astound will accept a logon from the Ubiquiti router (of course, I don't 
know if the problem is that Astound doesn't like that the Ubiquiti is trying 
to make the connection).

I've also seen a suggestion that I put the Ubiquiti in the DMZ zone of the 
Arris, but I haven't fully assimilated that suggestion, for example, I'm not 
sure what IP address to assign to the (WAN) port of the Ubiquiti in that case 
-- a private address on my LAN or something else.  

(Right now I've got a bunch of web pages open, some of which I've started to 
read -- when I find / get back to the page that suggests putting the Ubiquiti 
in the DMZ, my questions might be answered (on the subject of putting the 
Ubiquiti in the DMZ).  

I'm also not sure what problems having the Ubiquiti in the DMZ might cause -- 
in general, I'd prefer to have the Ubiquiti connected to the Arris in bridge 
mode (because of my past experience).

I did think about using both the Ubiquiti (and DHCP, if that's what Astound 
uses in this area) and the Arris sort of in series (the Ubiquiti ("downstream" 
of the Arris) then doing the DHCP (and other features, e.g. QOS) for the LAN, 
but I'm leery of doing that because I've seen (somewhat vague) warnings on the 
Internet about doing double NAT.  (Maybe that is only an issue of speed, which 
I don't think would bother me -- the Astound connection could be 30 (or  more 
(or less)) times as fast as the DSL connection.)

I suppose I could do the two in series (as mentioned above), leave DHCP turned 
on in both, but the firewall turned off in the upstream modem / router.

I'm getting too old -- trial and error (as I've done a few times) is nerve 
wracking for me.  Even getting the Ubiquiti back to the configuration to use on 
my DSL ISP drove me crazy, I had to try a few times to do that (I haven't 
cancelled my DSL ISP yet), and I'm not sure that I know the exact steps to get 
that setup working again if I have to (i.e., if I try the Astound connection 
and don't get it working), but I feel, since I accomplished it once, I can do 
it again (i.e., I'm seeking comments on the problems of connecting to 
Astound rather than those of reconnecting to my DSL ISP).

Thanks!