Thanks for the hint! It works now.

Maybe there should be a more sophisticated way to determine whether a servent can download from another servent. I.e., if two servents are on the same local network, this should be possible even if they are behind a firewall.

The next problem I have is that both servents also get connected to external servents, even though I have used my own hosts file.
Can it be that external servents have my servents in their caches and try to connect to my servents when they are online? This would mean that my servents to do not try to connect to external servents but external servents find them anyway.