12-30-2016
tcp ports are dictated by IANA So if you decide to "secure" port 25, nobody will be able to connect using ftp.
This link has 140 pages, just read a few.
Service Name and Transport Protocol Port Number Registry
My point is: you can break all kinds of services without knowing why. And if someone attacks a random port and there is no service behind it to respond, the attacks fails. So no need to block it. This is why attacks go for a lot of known ports. So known ports may require a minor tweak.
Are you trying to harden your box for a reason? A lot of linux boxes have special apps to help you. What OS and version of it do you have?
uname -a will show that, so please post it.
Edit: It is not uncommon to harden a UNIX and break some applications.
Last edited by jim mcnamara; 12-30-2016 at 09:02 PM..
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LEARN ABOUT CENTOS
portreserve
PORTRESERVE(1) TCP port reservation utility PORTRESERVE(1)
NAME
portreserve - reserve ports to prevent portmap mapping them
SYNOPSIS
portreserve
DESCRIPTION
The portreserve program aims to help services with well-known ports that lie in the bindresvport range. It prevents portmap (or other
programs using bindresvport) from occupying a real service's port by occupying it itself, until the real service tells it to release the
port (generally in its init script).
It is intended that portreserve runs from an initscript of its own, and services wishing to interact with it should use portrelease.
When the portreserve daemon is started, it examines the /etc/portreserve/ directory. Each file not containing "." or "~" in its name is
considered to be a service configuration file, and must contain a service name (as listed in /etc/services) or a port number. UDP services
may be specified by appending "/udp" to the service name, and TCP services by "/tcp". Several services may be specified, one per line.
For example, /etc/portreserve/cups might contain the string "ipp" or, equivalently, "ipp/tcp" and "ipp/udp" on separate lines.
For each service configuration file, a socket is created and bound to the appropriate port. A service wishing to bind to its port must
first run portrelease, which instructs portreserve to release the port associated with the service.
Once all the reserved ports have been released, the daemon exits.
FILES
/etc/portreserve/*
Service configuration files
/var/run/portreserve/socket
communication socket for portrelease
SEE ALSO
portrelease(1)
AUTHOR
Tim Waugh <twaugh@redhat.com>
Author.
portreserve 1 July 2008 PORTRESERVE(1)