Voxen, I’ve seen now your post:
PCA -> SYN -> PCB
PCA <- SYN/ACK <- PCB
PCA <- SYN/ACK <- PCB
PCA -> RST -> PCB (ZeroWindow)
From what I understand, PCA does not respond to the SYN/ACK packet coming from PCB. I could help you better if you describe me exactly what you do, but I have a hint.
PCA generates a packet, you change the destination and PCB receives it.
PCB responds to the packet, sending the answer to PCA. But since PCA is not expeting an ACK from PCB (he thinks he’s talking with the original host you substituted) it will throw the packet away.
When you receive a packet from PCB, you must reverse what you’ve done before: substitute che source from PCB to the original destination.
I.e:
1) PCA sends a packet to PCX. You change the destination to PCB.
2) PCB answers to PCA, but PCA is expecting an answer from PCX, NOT PCB!
So you must reverse the changes you’ve done in step 1, reverting the sender from PCB to PCX.
I’m not sure it’s your problem, since you don’t describe exactly what you do. Btw, you are trying to NAT che packets, try reading some papers on this subject.