How to set up an Ubuntu gateway?

Question

ubuntu

I have a pc with ubuntu 14.04 server. 2 network cards. One (eth0) looks to the provider's network, the second (eth1) to the local network. The Internet rises on pppoe. The problem is this: the Internet disappears every 2-3 minutes.
From the gateway I ping the provider's network. Pings go around 500 - 1000 requests and disappear at 30-50 requests. After the appearance of a ping, the first one starts with a time of 1000 ms. The provider says that at this time the network card that looks into my local network is trying to register with them. And they show me the poppy address eth1 with an attempt to register ip 192.168.24.1.