MikeL's ActionTec C 1900 modem HowTo
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)
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
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:
Now the internal computers:
- Browser into modem http://192.168.0.1/
- First time after factory reset or new install, straight to
Advanced Setup->Adminstrative password, configure reasonable
- 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
- 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
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
- 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
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.
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