Open ports in Debian

[Rutger Wessels <rutger@dds.nl>]

Hello,

I administer a debian installation that is connected to the Internet. 
When I run nmap, I found the following:
Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2005-11-23 00:29 CET
Interesting ports on xxxxxxxxxx
(The 1657 ports scanned but not shown below are in state: closed)
PORT    STATE SERVICE
22/tcp  open  ssh
25/tcp  open  smtp
80/tcp  open  http
111/tcp open  rpcbind
113/tcp open  auth
903/tcp open  iss-console-mgr

22,25,80 that are the ones I understand. But what are the other ones? Is 
it harmful to have them open?

I run Debian Stable and apt-get upgrade tells me I am up-to-date.

regards,
Rutger