Accessing cable modem SNMP?

[watusi]

I have a Motorola/Arris SB6183. My understanding is that it *probably* exposes SNMP to the CPE.

I did some research, and it looks like the cable modem does a trick to provide access to the modem's LAN-side web interface at 192.168.100.1 without needing the CPE to be on the 192.168.100.0 network.

So, there really isn't a route from the CPE (router) to that network. The router gets the WAN-side address assigned using DHCP, and the cable modem routes internally to 192.168.100.0. There's something fake-y going on here, at least from what I've read, though it does seem to support ping as well. But I get no response from SNMP.

(I haven't yet done the recommended test of hooking a PC directly to the modem and setting a static route to test. That's next.)

I'm assuming I need to use a script to add a static address to the WAN side of the router (AC87) to either the 192.168.100.0 network or just 192.168.100.1.

I have enough Linux background that I can stumble through that. (It's a lot easier on my Macbook or Mini - just set an additional address through GUI Settings...) I think I have to use ifconfig, right?

There doesn't seem to be any GUI way to add a static address to the WAN side, OTHER than for dual WAN purposes. I think it "would be nice" if this option were provided on the DUAL WAN pane (maybe with a rename of the pane, since then it would no longer be just dual WAN functionality.

This is such a common scenario that perhaps all that is needed (from the user standpoint) is a single check-box, since so many cable modems use the 192.169.100.1 standard.

Advice and thoughts?

BTW, i did enable SNMP on the router, and am able to access it. I do not understand the device assignments on the AC87, and from my experiments monitoring bandwidth, I am not really certain that I am monitoring the WAN side of the router. (I am even less certainly about the wireless interfaces... see separate post) So, I thought, "why not get it from the cable modem", and then I am sure of what I am getting!

 

[Ford Prefect]

...the modem being on 192.168.100.1 is a common pattern, if not even a standard.
Your router does not need a dedicated route, as it will use the default route to push the request via the WAN interface. This way the packets will reach the Modem and then will get "routed" internally, even if the network is not advertised.

I cannot comment on SNMP capabilities, but as for your idea to hook up a PC and set this to be part of the 192.168.100.xxx network I think this could do the trick.
I suggest that you remove all other networks, including default route from your PC interface when testing the 192.168..100.xxx net.
There is a chance that this network is configured with a non-standard netmask, affecting the
broadcast address but you will find out when you try and resolve an ARP request to that address, while being on that network.
If this is the case, I don't know how to find out the right settings though.