why is port 111 open?

Maybe this is no big deal, but I'm wondering why port 111 is open by
default...

  [email protected]:~> netstat -an | more
  Active Internet connections (servers and established)
  Proto Recv-Q Send-Q Local Address  Foreign Address  State      
  tcp        0      0 0.0.0.0:111    0.0.0.0:*        LISTEN
  tcp        0      0 0.0.0.0:22     0.0.0.0:*        LISTEN
  tcp        0      0 0.0.0.0:631    0.0.0.0:*        LISTEN
  udp        0      0 0.0.0.0:111    0.0.0.0:*            
  udp        0      0 0.0.0.0:631    0.0.0.0:*

I do understand that port 22 is for ssh, and port 631 is for cupsys -
both of these I want to keep open.

According to the information I've been able to find, port 111/tcp is
sunrpc (SUN Remote Procedure Call). I haven't seen this particular port
open on my other two currently installed OSs (Slackware and FreeBSD).
There may be a valid reason for keeping it open, but if not, I'd like to
close it. I'm actually not sure how to close port 111, so any advice on
that would be appreciated.

Knoppix is actually pretty lean on the number of ports it opens by
default - Slackware in particular seems to keep a lot of ports open. So
I'm not complaining, but merely curious.

best regards,
Robert