07-15-2005
As always I am a bit lost here.
Port starts from 0 (or 1 I don't remember) all the way up to 32555 (or sth similar). A port allocated by an active process (either serve or client) can be found by netstat. Everything else is not being used and so "available" for a process to allocate.
/etc/services is a differenet thing which may have implication for inetd or xinetd only. A port does not have to be "registered" in this file to be used by a process which has nothing to do with inetd.
There are more than one approaches to block a port. Conventional approach is via tcpwrapper. Now, people are more likely using (soft- or hardware based) firewall such as iptables in Linux.
I hope it answered all of your questions.
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LEARN ABOUT DEBIAN
netstat-nat
netstat-nat(1) General Commands Manual netstat-nat(1)
NAME
netstat-nat - Show the natted connections on a linux iptable firewall
SYNOPSIS
netstat-nat [options]
DESCRIPTION
netstat-nat Displays NAT connections managed by netfilter/iptables which comes with the > 2.4.x linux kernels.
The program reads its information from '/proc/net/ip_conntrack' or '/proc/net/nf_conntrack', which is the temporary conntrack-storage of
netfilter.
OPTIONS
-h displays help
-n don't resolve IPs/portnumbers to host/portnames
-p <protocol>
display NAT connections with protocol selection (see /etc/protocols)
-s <source host>
display connections by source IP/hostname
-d <destination host>
display connections by destination IP/hostname
-S display SNAT connections
-D display DNAT connections
-L display only connections to NAT box self (doesn't show SNAT & DNAT)
-R display only connections routed through the NAT box (doesn't show SNAT & DNAT)
-x extended view of hostnames
-r <src|dst|src-port|dst-port|state>
sort connections
-o no output header
-N display NAT box connection information (only valid with SNAT & DNAT)
-v prints version
FILES
/proc/net/ip_conntrack or /proc/net/nf_conntrack
SEE ALSO
http://www.tweegy.nl/projects/netstat-nat/
http://www.netfilter.org/
AUTHOR
netstat-nat has been written by D.Wijsman danny@tweegy.nl
The manual page has been written by marceln@xs4all.nl
July 2002 netstat-nat(1)