HELP! Mysterious socket 843/tcp listening on CURRENT system

[O. Hartmann]

Hopefully, I'm right on this list. if not, please forward.

Running CURRENT as of  FreeBSD 11.0-CURRENT #3 r287780: Mon Sep 14 13:34:16
CEST 2015 amd64, I check via nmap for open sockets since I had trouble
protecting a server with IPFW and NAT.

I see a service (nmap)

Host is up (0.041s latency).
Not shown: 998 filtered ports
PORT     STATE SERVICE
843/tcp  open  unknown

and via sockstat -l -p 843, I get this:
?        ?          ?     ?  tcp4   *:843                *:*

I double checked all services on the server and i can not figure out what
daemon or service is using this port. The port is exposed throught NAT (I use
in-kernel NAT on that system).
This service is accessible via telnet host-ip 843:

Trying 85.179.165.184...
Connected to xxx.xxx.xxx.xxx.
Escape character is '^]'.


Well, I feel pants-down right now since it seems very hard to find out what
service is keeping this socket open for communications to the outside world.

Anyone any suggestions?

Thanks in advance,
Oliver