Can't access cable modem page from LAN, on a Arris CM8200A

Installing and Using OpenWrt
1

OK, this should be simple... though I admit I'm kind of a Idiot/Savant when it comes to networking.

I have the classic cable modem (Arris CM8200a) with the common 192.168.100.1 address for the web admin interface. I have a mini x86 box as the router and etc, on OpenWRT, running the common 192.168.1.1 as it's address and gateway to the common NAT/DHCP service to a switch, and then either eth or the wifi AP, to everything in the house.

The modem's webpage used to transparently be accessible by local LAN locations. Somewhere a ways back, that stopped. Browser reacts now like no destination, no ping response, etc. Disconnect the router and plug directly into the modem, you get the page.

Found a few articles, spent some time trying to set up a static route, didn't get anywhere. Have been trying to do it thru Luci. Found something in the OpenWRT documentation, but it mentioned Barrier Breaker, and the web interface was hardly recognizable, and it dealt with features that don't exist now.

Hopefully someone can show me how simple this is, or what setting I changed long ago, to get this back.
Also, would be good to determine if it's something I set at some point, vs did something default change in OpenWRT settings over version changes.

2

Create a new interface, say "modem". Assign it a static address on 192.168.100.0/24 network. Add this interface to the WAN zone. Specify the same physical interface as your WAN interface.

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3

Ok, looks like I may have not read all the fine print (or followed the fine links)
Took a look at the link on the page, lead to a 2014 dated method, with another link to an updated version, dated 2020. Seems to create a whole 'nother network interface, just to let the modem in.

What do you all think? A reasonable way to go, or is there better/simpler ways?

https://ciphermenial.github.io/access-your-modem-through-openwrt-router/

4

That's what I just told you to do. It just creates an IP alias on the WAN interface

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5

Sorry, I was typing.

6

Is the linked method a good description of what's needed? And why do you think I never had to do that before, just worked with vanilla out of the upgrade OpenWRT?

7

Yeah, it's a good description. There's not really much to it actually - I summarized it in two lines.

8

What do you think about me never having to do that before? There never would have been a custom device in the default setup. It feels like there was some other routing rule that was removed that used to be in there to allow such traffic.

I'll go off and set that up, but its bugging me that it never needed it before.

9

OK, set that up, there were a few minor Luci field differences... and... I get the OpenWRT sign in. I seem to be getting sent to 192.168.1.1, not 192.168.100.254.

10 
config interface 'modem'
        option proto 'static'
        option ifname '@wan'
        option ipaddr '192.168.100.X'
        option netmask '255.255.255.0'
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11

And for your /etc/config/firewall you need an entry thus

config zone
        option name 'wan'
        ...[other entries]...
        option network 'wan wan6 modem'
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12

OK, am copying the existing stuff and files, so I can see what's what, if I need to go back. Might also check against what Luci puts there... maybe somethings buggy. I'm kind of Luci handicapped, sadly haven't been learning command line stuff, and forgetting a lot from the 1.4-2.0 kernel days...

13

Blockquote ```
config interface 'modem'
option proto 'static'
option ifname '@wan'
option ipaddr '192.168.100.X'
option netmask '255.255.255.0'

Well, have been poking at it with the Luci interface, and looking at it thru the command line/uci, and I seem to get the results matching what you gave me, except I have the ipaddr as the full address, not the 192.168.100.X. OTOH, you probably mean that to be whatever address I might map it to, and whether it's 1 or 2 or 254, I still get the same result. I can ping it, OK, but when I hit it with the browser, I get the OpenWRT signup page, which seems to mean I actually go to 192.168.1.1.

Very confused now...

14

Collect the diagnostics and post it to pastebin.com redacting the private parts:

uci show network; uci show firewall; \
ip address show; ip route show table all; ip rule show; iptables-save
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15
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16

Is your modem running bridge mode?

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17

Ha, Trendy!! Neat trick, that. Opened the page and was all "wow, a modernized page very similar to that extremely dated one I was looking at last night...." and then I realize it's the SAME page, and Thomas had majorly overhauled it just a few hours ago.... :wink: Will read it over and see what's new in there...

Vgatera.. I'll get to that, probably later tonight...

Krazeh.. I don't think it it is, or even could, be. Brand new CM8200a, pretty sure it's a bare cable modem.

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18

Kudos and thanks to @vgaetera who modernized the instructions and uses uci instructions to make it a lot faster and easier.

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19

OK did the pastebin signup tango, and a load of pasting... I hope I haven't sanitized stuff you needed to see, probably cleaned a few things I didn't need to...
Pastebin Link

And following the updated page... sadly, it seems it's pretty much the same instructions I'd tried earlier, more or less. And, it still doesn't work, I type the assigned modem address, (192.168.100.2) and the router box's OpenWRT page promptly pops up. (192.168.1.1)

I have only tried the Luci page set of instructions, will look at the uci based stuff, to see how it compares with what I tried last night.

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20

So following the Luci info, the only thing I see somewhat different, is when I go to the Firewall Settings tab I see "LAN" and "WAN, WAN6, Modem" as the choices and picked the latter.

Looking further, I see in the entirely different section of Network - Firewall - General Settings... I see firewall zones. Does something need to be created here?

And I assume that you all assume and expect that this is the standard, vanilla router setup where WAN - LAN thru NAT and DHCP server, right?