I was querying my router(Thomson TCW750-4) over the SNMP and stumbled upon some interesting information. I see that the router actually has five separate network configurations operational:
- Loopback(Router IP: 127.0.0.1)
- Local network(Router IP: 192.168.1.1, Subnet: 255.255.255.0)
- Local network 2(Router IP: 192.168.100.1, Subnet: 255.255.255.0)
- Broadband WAN network(Router IP: 109.X.X.X - dynamic, Subnet: 255.255.252.0)
- ISP internal network(Router IP: 172.21.X.X - static, Subnet: 255.255.248.0)
(I've hidden parts of the addresses for privacy reasons with X)
Now I'm interested in this number 5 network. I'm not actually sure if it is called 'ISP internal network' that is what I basically think it is. From my computer connected to the router I can not access other addresses on that network but I can access my router configuration page over that address the same way I do over 192.168.1.1!
However inside the router configuration there is a ping test page and through that ping I can ping other machines inside the 172.X.X.X network.
So my questions are: What is this network for? Is it essential for cable network to function properly? Is it just there so that my ISP can access my router configuration? Can other users on the network access my router configuration over this network? How?
I tried answering the last question by testing, but whatever I do(for example configure my PCs network to be in that network range) I can not access(ping) any other machine in that range. Pinging from the router test page however does work. So either the router is blocking traffic from local network to that network(which would be some sort of security measure) or I do not know how to configure things correctly. What I think would definitely work is, if someone managed to clone his cable modem on a more capable router machine running DD-WRT for example he could basically reach this network.
However I would be interested if it is possible to reach this network even through these primitive routers that the ISP is giving to its users(Mentioned Thomson router and the second option that users potentially get is a Scientific Atlanta DPC2203), by some sort of configuration.
Disclaimer: I'm primarily researching this to know if my personal network is vulnerable or not.