[libtorrent] port 6881 blacklisted

[Alexander D. <ale...@gm...>]

Hello,

I've found, that this port (default in LT) is blocked on some torrent 
trackers for some reason.

E.g. this is discussed in this topic:
https://forum.utorrent.com/topic/4299-port-6881-blacklisted/

1. Why is it blocked? Why "In either cases, dont use any ports between 
6881-6889. It's just asking for trouble ;]" ?

2. Why is it a default port in LT if it can cause troubles?

3. What is the best resolution of this issue?