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)


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:

Now the internal computers:
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.

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