Unable to get port forwarding to work on R7800

[hux2000]

I can't get port forwarding to work at all on my R7800. Here's what I'm doing:

- 'Advanced' tab -> 'Advanced Setup' -> 'Port Forwarding/Port Triggering'

- From the 'Service Name' drop-down, select 'HTTP'

- Enter the IP of the destination server

- Click '+ Add' button and the service appears successfully in the port forwarding list

- Start web service on destination server (for testing, the firewall on this server is disabled)

- Confirm web service is reachable by connecting to its default web page from another system on the LAN

- Attempt to connect from a system on the WAN side by doing 'telnet [public IP] 80': no response

- Attempt to do the same from a system on the LAN: no response

I've tried this with several different port, using TCP, UDP and both, but nothing gets forwarded.

My network is pretty simple:

Comcast modem -> R7800 -> wired and wireless clients

Any ideas? Something to do with the modem, maybe?

[antinode]

> Comcast modem -> [...]

   Not a very detailed description of that device.  Has it a maker and
model number?  Is it actually a (simple) modem (good), or is it a
modem+router (bad)?

> - Attempt to connect from a system on the WAN side by doing 'telnet
> [public IP] 80': no response

   What is "[public IP]"?  If you're worried about revealing secrets,

then the top half of the address, "a.b" out of "a.b.c.d", would satisfy
most of my curiosity.  Or, plug that address into the form at:
https://whois.arin.net/ , and see if it is a public or private address.

   What's the IP address of the WAN/Internet interface on the R7800
(ADVANCED > ADVANCED Home : Internet Port : Internet IP Address)?  Same
or different?

   For the usual problems with port forwarding, see:

      https://community.netgear.com/t5/x/x/m-p/1859106

   I'd worry about "1".  You seem to have covered the others.

[hux2000]

Thanks for the reply! Answers to your questions below...

"Has it a maker and model number?"

Arris TG862

"Is it actually a (simple) modem (good), or is it a modem+router (bad)?"

It's a modem + router. I thought I'd disabled the router part but now when I try to login to check, it doesn't let me. (I'm waiting on Comcast to do a password reset on it.)

The WAN-side IP associated with my Comcast account, i.e. 24.21.x.x (the output of https://icanhazip.com, for example).

"What's the IP address of the WAN/Internet interface on the R7800?"

10.0.0.6 - it's getting that from the modem.

"I'd worry about "1"."

Yeah, I think you're right: looks like 24.21.x.x is the modem's WAN address and the R7800 doesn't know about that. (Because why would it?) So I guess I really need to get into that modem and set port forwarding there. Or else (hopefully) find a setting that'll just make it pass everything through unchanged.

[antinode]

> 10.0.0.6 - it's getting that from the modem.

   There's your problem.  (That's why it's "1" in the list.)

> [...] So I guess I really need to get into that modem[+router] and set
> port forwarding there. Or else (hopefully) find a setting that'll just
> make it pass everything through unchanged.

   Yup.  If the TG862 has a modem-only ("bridge") mode, then you could
use it with the R7800 acting as your (only) router.  Otherwise, with the
TG862 in modem+router mode, _it_ could do the port forwarding, and the
R7800 could be configured as a wireless access point.  (It's in the
R7800 User Manual.)

   You might have a chance with the TG862 in modem+router mode, and the
R7800 acting as its DMZ server, but no bets.

[hux2000]

"If the TG862 has a modem-only ("bridge") mode, then you could use it with the R7800 acting as your (only) router."

I resolved this a slightly different way: the TG862 is an old modem and my connection almost maxes it out. So I took a look at my Comcast account and it seems I can get a free upgrade, so I put in an order for one. It arrived the following day (impressive!) and it has a bridged mode option.

So the upshot is: now the R7800 sees the correct public WAN address and port forwarding is working as it's supposed to. Yay!

Thanks for the assist. 🙂