Checking cable modem signal levels through router

[jptech]

I have an RT-N66U. It's currently running 380.70. I recently bought a Motorola MB8600 cable modem. I cannot seem to load the diagnostic page at 192.168.100.1. My internal network is .0.0 and I can ping the IP fine, but cannot load the web page. If I plug directly into port 2 on the modem and assign a 192.168.100.x IP, I can reach the page. I spoke with motorola directly and their answer made my blood boil. I was told, "it doesn't work on some routers". This is complete nonsense since I was able to load the page at the same IP from my previous arris modem just fine through the router with this and previous builds. Is there any sort of diagnostic I can use to determine where the point of failure is? I was thinking of attempting a tcpdump on the router, but it's not installed and I'm not going to load entware just for this. This should work with no extra configuration, but it doesn't. I've got a suspicion the cable modem starts dropping connections to port 80 as soon as a public IP has been established. These are the steps I've taken so far:

• assigned a subif to eth0. eth0.2 with the ip 192.168.100.2
• assigned a static route to the .100.0 network through eth0
• temporarily disabled the firewall
• tried to wget the modem page directly from the router
• changed the internal network to .1.0 and .100.0

 

[RMerlin]

I've got a suspicion the cable modem starts dropping connections to port 80 as soon as a public IP has been established. These are the steps I've taken so far:

Some ISPs (like Vidéotron) will disable the webui at boot time/connection time on some modems.

 

[jptech]

Some ISPs (like Vidéotron) will disable the webui at boot time/connection time on some modems.

I have comcast. They weren't blocking it before, and I can still reach it if I plug directly into the modem on port 2. It's definitely the router that doesn't allow the page to be loaded. I'm wondering if it has to do with the public IP. The modem is a bridge. The public IP is assigned to the router. The cable modem has the .100.1 IP.

 

[RMerlin]

I have comcast. They weren't blocking it before, and I can still reach it if I plug directly into the modem on port 2. It's definitely the router that doesn't allow the page to be loaded. I'm wondering if it has to do with the public IP. The modem is a bridge. The public IP is assigned to the router. The cable modem has the .100.1 IP.

No idea. All I can say is that I don't have any problem here reaching my modem's webui from the LAN (it also uses 192.168.100.1).

 

[jptech]

No idea. All I can say is that I don't have any problem here reaching my modem's webui from the LAN (it also uses 192.168.100.1).

Yeah, I think the modem is blocking it somehow. I could reach the arris fine.

 

[RMerlin]

Might be a security measure, where the modem blocks connection from IPs outside of its own subnet. You would need a special iptables configuration then to DNAT/MASQUERADE your IP.

 

[Protik]

Sometimes the IP of the modem can conflict with the IP of the router. That's what happened with my AT&T modem. Change the IP of the router to something like 192.168.2.1 and see if that resolves the issue.

Sent from my Moto G (5) Plus using Tapatalk

 

[consorts]

reading this thread...

i'm about to change from fios which hosts my wan on it's ont - so my router is 192.168.1.1

to charter which bridges the wan thru it's modem to a lan port i plug into at 192.168.100.1

will i need to make changes to my ac3100 router in order to accommodate this wan scheme?

or will a simply power cycle suffice.

 

[azdeltawye]

I have comcast. They weren't blocking it before, and I can still reach it if I plug directly into the modem on port 2. It's definitely the router that doesn't allow the page to be loaded. I'm wondering if it has to do with the public IP. The modem is a bridge. The public IP is assigned to the router. The cable modem has the .100.1 IP.

I have the same setup (Comcast ISP & MB8600 modem in bridge mode) except with the RT AC86U router and I don't have any problem reaching the modem UI on 192.168.100.1 from devices on the router LAN.
However, I have noticed that during an outage (which seems to happen frequently) where the modem has lost sync with the CMTS because of T3 & T4 timeouts, I cannot access the modem UI from the LAN and have to plug my PC directly in the modem WAN port..

 

[jptech]

Might be a security measure, where the modem blocks connection from IPs outside of its own subnet. You would need a special iptables configuration then to DNAT/MASQUERADE your IP.

what about when I create the subif on the same subnet though? It should work perfectly fine then. I even changed my WAN IP to that subnet. As expected, I lost Internet, but the IP was .100.200. It should then have allowed the connection. Especially wget. But no luck at all. It's definitely related to the webserver running on the MB8600. I can ping the IP perfectly fine even through the router.

 

[CaptainSTX]

I have an RT-N66U. It's currently running 380.70. I recently bought a Motorola MB8600 cable modem. I cannot seem to load the diagnostic page at 192.168.100.1. My internal network is .0.0 and I can ping the IP fine, but cannot load the web page. If I plug directly into port 2 on the modem and assign a 192.168.100.x IP, I can reach the page. I spoke with motorola directly and their answer made my blood boil. I was told, "it doesn't work on some routers". This is complete nonsense since I was able to load the page at the same IP from my previous arris modem just fine through the router with this and previous builds. Is there any sort of diagnostic I can use to determine where the point of failure is? I was thinking of attempting a tcpdump on the router, but it's not installed and I'm not going to load entware just for this. This should work with no extra configuration, but it doesn't. I've got a suspicion the cable modem starts dropping connections to port 80 as soon as a public IP has been established. These are the steps I've taken so far:

• assigned a subif to eth0. eth0.2 with the ip 192.168.100.2
• assigned a static route to the .100.0 network through eth0
• temporarily disabled the firewall
• tried to wget the modem page directly from the router
• changed the internal network to .1.0 and .100.0

I have Comcast, MB8600 and when I was using my N66 I had no problems connecting to modems Admin page. My router uses subnet 192.168.xxx.xxx. Just for grins change the subnet you are using on your LAN and see what happens.

 

[jptech]

I have Comcast, MB8600 and when I was using my N66 I had no problems connecting to modems Admin page. My router uses subnet 192.168.xxx.xxx. Just for grins change the subnet you are using on your LAN and see what happens.

My normal subnet is 192.168.0.0/24 I've changed it to .1.0 and .100.0

I'm going to try 10.0.0.0/24 next

 

[CaptainSTX]

My normal subnet is 192.168.0.0/24 I've changed it to .1.0 and .100.0

I'm going to try 10.0.0.0/24 next

From your OP it appeared to me that you might have been using some very out of the ordinary subnet on your LAN. I doubt my original suggestion is going to solve your problem.

 

[dlandiss]

No idea. All I can say is that I don't have any problem here reaching my modem's webui from the LAN (it also uses 192.168.100.1).

Nor do I. ASUS RT-AC68U w/Merlin's 384.6, Cisco modem.

 

[jptech]

Nor do I. ASUS RT-AC68U w/Merlin's 384.6, Cisco modem.
View attachment 14727

It's not a cisco modem which is at issue. I could reach the webui for my arris just fine. It's the Motorola MB8600 which isn't letting me through.

 

[dlandiss]

Good! That suggests that the problem is Motorola, not ASUS.

 

[jptech]

Good! That suggests that the problem is Motorola, not ASUS.

The problem is definitely with Motorola. I already tried an internal lan of 10.0.0.0. It had no effect. But I do have an RT-AC88U as an AP that I will swap with the N66 and we'll see the results.

 

[sfx2000]

Might be a security measure, where the modem blocks connection from IPs outside of its own subnet. You would need a special iptables configuration then to DNAT/MASQUERADE your IP.

It usually is - many of the Moto Surfboards had an URL where one could reboot/reset the modem without LAN side auth, and it was open to CSRF attacks, so some cable operators disable the WebGUI, and some just disable the WebGUI options to reset/restart the modem.

Probably should put some props to the Gam3r community there where it was a popular Denial of Service attack to bounce someone out of the game at hand...

 

[RMerlin]

It usually is - many of the Moto Surfboards had an URL where one could reboot/reset the modem without LAN side auth, and it was open to CSRF attacks, so some cable operators disable the WebGUI, and some just disable the WebGUI options to reset/restart the modem.

Probably should put some props to the Gam3r community there where it was a popular Denial of Service attack to bounce someone out of the game at hand...

The real culprit there is whoever thought it would be a good idea to provide an interface to reboot a device without any authentication.

 

[Jack Yaz]

You mentioned earlier it works when connected to LAN port 2, which port is the router connecting through? On my Openreach DSL modem I had to change a setting to remove the binding to port 2 and allow the WebUI to be accessed from both ports.