No Internet suddenly

[krum_boy]

hello, 

We've got a checkpoint 1100 that is connect to the ISP with PPPoE. We now got a new ISP that unfortunately has to provide their own router so our checkpoint got to connect to the LAN port of the ISPs router, therefore we get on a 192.160 network. We applied the following but we get no Internet:

The ISP LAN is 192.168.1.0/24 so the checkpoint has got a statically assigned 192.168.1.99 on its WAN port. DNS is pointing to the ISP router as well as Google.

In this scenario none of the devices on the checkpoint gets Internet, although some devices get intermittent and very slow connection. The interesting thing is the ping go Google works fine. 

There is Internet for sure because when we remove the checkpoint and connect our switch to the ISP router, all devices are fine. 

Plugging back the checkpoint and configuring it with the old PPPoE also work fine. 

Firewall, and other protections are disabled on the checkpoint. 

I'm not sure what's happening but the checkpoint doesn't seem to like this setup. Can someone help please? 

Thanks