Ubuntu Server + NAT + PPPoE + port forwarding how to organize?

Question

iptables

Dear community, burning PPC.
I used to do it under Firestarter, but now I have to do it under pure iptables
Task:
there are 4 interfaces:

lo        Link encap:Локальная петля (Loopback)  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:16505 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16505 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:1141391 (1.1 MB)  TX bytes:1141391 (1.1 MB)

p1p1      Link encap:Ethernet  HWaddr 10:fe:ed:05:2c:1f  
          inet addr:192.168.0.2  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::12fe:edff:fe05:2c1f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8436443 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8401425 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:877453127 (877.4 MB)  TX bytes:723550148 (723.5 MB)

p2p1      Link encap:Ethernet  HWaddr bc:ee:7b:88:c6:5f  
          inet addr:10.10.2.1  Bcast:10.10.2.255  Mask:255.255.255.0
          inet6 addr: fe80::beee:7bff:fe88:c65f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8220307 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7593191 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:633156402 (633.1 MB)  TX bytes:692474991 (692.4 MB)

ppp0      Link encap:Протокол PPP (Point-to-Point Protocol)  
          inet addr:194.50.255.100  P-t-P:194.50.255.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1
          RX packets:14970 errors:0 dropped:0 overruns:0 frame:0
          TX packets:18925 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3 
          RX bytes:3504655 (3.5 MB)  TX bytes:7238200 (7.2 MB)

How to write iptables correctly?
Wrote:

sysctl -w net.ipv4.ip_forward="1"
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -t nat -A PREROUTING -p tcp -d 194.50.255.100 --dport 80 -j DNAT --to-destination 10.10.2.2:80
iptables -t nat -A POSTROUTING -p tcp --dst 10.10.2.2 --dport 80 -j SNAT --to-source 195.18.48.76

Pings go, but in the locale 10.10.2.0/24 TimViewer does not work, the feeling that the packets go in one direction from the outside.
The same situation with forwarding 10.10.2.2 if on port 80.

Answer 1

What do you have in other chains? obviously in the input and forward problem.