Two routers connected to one modem - Need two isolated networks

Question

My setup is as follows.

+-------+
| Modem |
+-------+   
  |  |  |   
  |  |  +----> Internet
  |  |
  |  +-------> Router 1 [192.168.1.1] (Home & Private Network)
  |            |
  |            +---> Main PC & Own Mobile Devices
  |            +---> Lightning
  |            +---> Harmony Hub
  |            +---> Wi-Fi Repeater in Bridge Mode for Living Room Devices (No Repeating)
  |
  +----------> Router 2 [192.168.2.1] (Guest & Testing Network)
               |
               +---> Test & Webbrowsing PC
               +---> Mobile Devices of Friends and Guests

Is this setup correct so that the devices connected to router 2 are unable to see/connect to the devices connected to router 1 through my modem? I would like to keep my guest & testing network completely out of my private network.

I already checked and both routers have received different public IPs. Also, when I tried pinging my main pc from my test pc, it timed out as desired. However, when I did it the other way around, I got a message from my ISP "TTL expired in transit". What does that mean exactly? Shouldn't it time out like before?

PS: When I connected router 2 for the first time, its internal IP was also 192.168.1.1 but it worked just fine and there was no IP conflict with router 1. Does this mean they were already isolated from the get go? I changed it to 192.168.2.1 just to be sure.

Thanks for any help.

Answer 1

Although your setup is correct, I wonder what ip addresses your modem provides to both routers, because I think that's where your TTL expired in transit message comes from. I bet the modem also has a 192.168.1.x network.

Either put the modem in a different segment, or put router 1's network in a different segment. Given that you already are working with 2 routers, I would suggest 192.168.10.x and 192.168.11.x respectively, keeping the modem at 192.168.1.x, so things remain easy to recognize.

Answer 2

"Request Timed Out" means the computer that sent out the PING did not get any response back.

"TTL Expired in Transit" means a forwarding router along the path responded with an error.

Both, indicate that the Remote host was not reachable. The latter just means that a router along the way decided to tell you so.

It is a little strange to receive the TTL expired message. Likely one of two things are happening:

1. There is an anomaly or misconfiguration in the 192.168.2.1 router. Is it a different model than the other?
2. The modem side is not quite right. I wonder how you are getting 2 public IPs? Most service providers will offer only 1 dynamic public IP unless you are paying for multiple static IPs. If you did purchase static IPs you would normally program them in to each router manually, not use DHCP. So honestly, I think you are getting lucky on that one. This may cause you problems down the road. I wouldn't be surprised if one of your two public IPs is in conflict somewhere in the modem.