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Full Discussion: determining open ports
Top Forums UNIX for Advanced & Expert Users determining open ports Post 78160 by tom_xx_hu@yahoo on Friday 15th of July 2005 10:36:40 PM
Old 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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SOCKSTAT(1)						    BSD General Commands Manual 					       SOCKSTAT(1)

NAME
sockstat -- list open sockets SYNOPSIS
sockstat [-46clnu] [-f address_family] [-p ports] DESCRIPTION
The sockstat command lists open Internet or UNIX domain sockets. The following options are available: -4 Show AF_INET (IPv4) sockets. -6 Show AF_INET6 (IPv6) sockets. -c Show connected sockets. -f address_family Limit listed sockets to those of the specified address_family. The following address families are recognized: inet, for AF_INET; inet6, for AF_INET6; and local or unix, for AF_LOCAL. -l Show listening sockets. -n Numeric output only. No attempt will be made to look up symbolic names for addresses and ports. -p ports Only show Internet sockets if either the local or foreign port number is on the specified list. The ports argument is a comma- separated list of port numbers and ranges specified as first and last port separated by a dash. -u Show AF_LOCAL (UNIX) sockets. If neither -4, -6, nor -u are specified, sockstat will list sockets in all three domains. If neither -c nor -l are specified, sockstat will list both listening and connected sockets, as well as those sockets that are in neither state. The information listed for each socket is: USER The user who owns the socket. COMMAND The command which holds the socket. PID The process ID of the command which holds the socket. FD The file descriptor number of the socket. PROTO The transport protocol associated with the socket for Internet sockets, or the type of socket (stream, seqpacket or data- gram) for UNIX sockets. LOCAL ADDRESS For Internet sockets, this is the address to which the local end of the socket is bound (see getsockname(2)). For bound UNIX sockets, it is the socket's filename or ``-''. FOREIGN ADDRESS The address to which the foreign end of the socket is bound (see getpeername(2)) or ``-'' for unconnected UNIX sockets. SEE ALSO
fstat(1), netstat(1), inet(4), inet6(4), unix(4) HISTORY
The sockstat command appeared in FreeBSD 3.1. It was then rewritten for NetBSD 3.0. AUTHORS
This version of the sockstat command was written by Andrew Brown <atatat@NetBSD.org>. This manual page was written by Dag-Erling Smorgrav <des@FreeBSD.org> and was adapted to match the NetBSD implementation by Andrew Brown <atatat@NetBSD.org>. BSD
July 14, 2006 BSD
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