Modem loses internet connection when connecting another modem

[Bees ZA]

Hi.

When my brother has his friends over for a lan, they take one of the older modems and connect it to our fibre modem using a lan cable in order to get internet in another room. When he does this, everything on the fibre modem at random intervals loses internet connection. They do not drop connection once. Everything works fine if it is just the fibre modem. It is really frustrating and google just gives me answers to things I am not searching for.

Hopefully someone here can help me out.

 

[Bees ZA]

Fixed it by doing the following for those interested.

1. Set the second modem to bridge mode [Internet].
2. Turn off UPnP on the second router.
3. Turn off DHCP Server settings on the second modem.
4. Make sure IP Subnet Mask is the same on both modems.
5. Change the IP on the second modem to 1 more than on the original modem. [So if it is 10.0.02, make it 10.0.0.3]

 

[Grouter]

It was #3 what did it...