MikeL's ActionTec C 1900 modem HowTo

MikeL's ActionTec C 1900 modem HowTo

[20210415] Been running a Zyxel C3000Z dual DSL modem now for several years, too lazy to make a new page for it.
I've had to do some firewall changes. Set to "All Public" and "Low". Add the following:
drvwymon tcp 23256 tcp (my drvwymon program)
RTC-Discord chat 50000-65536 udp (Ellis' online chat app)
Cumulus/CWOP tcp 14580 tcp (Cumulus software)
named zone xfr tcp 53 tcp (named zone transfer)

16-Nov-2018

I have QWest/CenturyLink Dual DSL, using an ActionTec C 1900 modem. I've had a heck of a time getting it set up for a fairly simple configuration. I'll jot a few notes here about what I had to settle for.

The goal was to have DHCP turned on for the inside LAN; any computer plugged into it, or any computer using wireless would simply be allocated a protected internal IP address.

The exception is that there are several servers that need to be available to the outside world.

I have a block of static IP addresses from CenturyLink. When you get this, you are actually allocated a block of 8 (hence the .248 subnet mask), however only 5 are available to you for use.

Here's what got it working:

Browser into modem http://192.168.0.1/
First time after factory reset or new install, straight to Advanced Setup->Adminstrative password, configure reasonable pswd.
Advanced Setup->Wan Settings
ISP Protocol: "auto" (selected is PPPoE)
PPP username, pswds filled in, "Auto Connect" is checked, "No credentials" is NOT checked. user/pswd provided by Centurylink.
IP addressing type: "Block of Static IPs"
Your gateway address is provided by Centurylink, it's 1 higher than the last usable IP address in your block. (e.g. I have .177-.181, gateway is .182.
subnet mask: 255.255.255.248
Here's the important one -- DO NOT select "Public Static Subnet". This would make every internal address available externally - you only want specific ones available! What this checkbox does (I talked with a real human at Centurylink that actually knows what he's talking about!) is basically just tell DHCP to use INTERNAL ADDRESSES (e.g. 192.168.0.x) for any connections requesting DHCP. Static addresses (of course within the proper range) will simply work.
Static DNS, phone co should have provided this along with your IP block.

Now the internal computers:

On each server (in other words every machine that will be externally visible), you will hardcode the IP address. Connect these each to a port on the modem.
Plug any PRIVATE machines, e.g. in-house wireless, routers or desktops into other modem ports, but configure them to connect via DHCP. These will get an internal (192.168.0.*) address and not be visible externally.

One last word of caution. The builtin firewall in the modem may get in the way of your servers activity. If you suspect this is the problem (data not making it into your server), try moving the server into a DMZ (advenced setting). If this fixes it, you've got a modem firewall issue.

I have a tricky system that uses one of these servers to do SMS messages with cellphones. This is implemented via HTTP (normal looking web requests via port 80). The factory default setting of this modem is for FIREWALL ENABLED, at LOW security. Note that this setting allows web requests (port 80), outgoing, BUT NOT INCOMING. I had to go into the firewall configuration screen and select port 80 incoming - this is true for you if you're running a web server.