What is the required setting of the firewall if both the sender and the receiver are behind NAT?

[mimi3421]

Excellent work. I have been looking for the file transfer application from home to the office without the expensive relay server. Although there are techniques like UDT, QUIC, STUN or something else, the qft seems as the only takeaway and nearly workable one. I have recompiled the binaries for linux and raspberry-pi here . The linux version is compiled in static way and is hoped to solved the missing glibc6 problem.

There are still two problems I met:

The first is that the qft is workable when at least one of the sender or receiver have global Internet IP. If both the machines are behind the NAT router, the process would stop after sending the first package like this:

# the receiver
 ./qft receiver tudbut.de:4277 KEYS hi.txt.gz 
Holepunching IP:PORT (partner) and :38116 (you).
Connecting...
Holepunch and connection successful. # [Freeze here, do not receive anything]

# the sender
./qft sender   tudbut.de:4277 KEYS hi.txt.gz
Holepunching IP:PORT (partner) and :53757 (you).
Connecting...
Holepunch and connection successful.
Length: 20003073
Sent 983040 bytes; Speed: 512 kb/s
10s passed since last packet ==> Contact broke. Trying to resend packet...
10s passed since last packet ==> Contact broke. Trying to resend packet... # [Repeat this line]

In my opinions, the UPnP setting or something else is needed for any one of the mchine, but I'm not sure what exactly is.

The other one is that when the packages size is larger than 256, it's more likely that the process will fail or packages will be dropped. I think this should be solved with paralelling transfering of ~1MB blocks with small package size.

[TudbuT]

Normally, it should be possible to work behind two NATs. Can you check if the partner port and the port displayed on the partner are identical?

[TudbuT]

I think one of your NATs has full port randomization, meaning the port changes when the destination changes, not just when the sender changes. That is really difficult to work around, sadly. Packets are already sent in bursts and later start synchronizing themselves to find the perfect balance, the packet size shouldn't matter too much, and packet drops are entirely fine, because qft corrects them.

[TudbuT]

Closing this due to no response, feel free to respond and ask for a reopen.