Port question

[(V)URD0K]

I was watching The Screen Savers on TechTV today and they were doing a Call-athon on hacking the entire show. One question was what was ports, and leo (host) said they are metaphoric holes(not like for hacking) where software talks into and out of, like quake is on 666... MY question is: Since ports are metaphoric, is it possible to make a program that talks to another computer on port 888888888(for example) or is there a set limit to the amount of ports on a computer. I was just wondering because the explanation kind of confused me. Thanx in advance! -(V)

[cyrus2778]

now im not completely sure but i think there are no set number of ports on a computer.

[slarty]

Firstly, ports only exist in some protocols. There are two commonly used protocols on the internet which have "ports". These are TCP and UDP. TCP and UDP are independent, an two applications wishing to communicate must use the same one (however many use both, often for different functions).

In TCP and UDP, valid port numbers are 1-65535, hence there are 65,535 port numbers in total.

Port zero is a bit of a tricky one - I read the RFCs on TCP, and I haven't found anything that explicitly prohibits using port zero, but most (i.e. All popular operating systems) implementations do not allow applications to usefully use it because it's used as a placeholder for "I don't care" in the bind() call.

So no, there are not an infinite number of them.

Some other protocols don't use ports (for example ICMP). Some people incorrectly refer to ICMP ports. There is no such thing.

Lesser-used protocols also have ports. IPX is the protocol used by Novell networks (particularly older ones), common on LANs and smaller WANs. As far as I know, it also has 65,535 port numbers (someone correct me if I'm wrong).

I have no idea about ipv6. Someone help out here

[Dark Phoen1x]

I believe there's exactly 65,000 ports. But i could be very wrong

[THE RADICAL]

Heh, heh nah, Slarty is exactly right, there are excactly 65,535 in those protocol suites.

(\/)URD0CK, it's good that you show an intrest in ports. Sense they are a very important part of understanding how the internet actualy works and how to remain secure on the internet. Also it's important to know that each port that is assigned has a very specific function, here's a good list that will help you on that.

http://www.opendoor.com/doorstop/ports.html

There are also TONS of other links and tutorials that will give you more info on the subject. It's important to take it step by step though, so your not overwhelmed. Just search this site to find what your looking for or google if anything else...

On a sidenote, The Screen Savers is a great show, I really wish I could have won that $100,000 tech makeover!

--Peace

[IKnowNot]

I believe slarty is correct ( I think he usually is )

port numbers are made up of 16 bits

1111111111111111 in binary is 65535 in dec.

In addition to the RFCs you can read up on it in IBM's RedBook

TCP/IP Tutorial and Technical Overview

not for the faint of heart

[(V)URD0K]

Thanx slarty, radical, and iknownot for the answer... helped me out a lot! So it is impossible to "create" a port i guess then. Thanx again or the help i understand them now!

[journy101]

>>So it is impossible to "create" a port i guess then.

You use an existing port, if two programs are to comunicate with one another, ports are used, this is implemented useing sockets. One end point may be the server, while the other is the client. Assumeing we are designing a server:

You create the socket,
You bind the socket to a port,
You listen to the socket
And you acept any incomeing conections

The client, has less work to do

Create the socket
Then conect your socket to a remote host, useing Conect.

EDIT: the port must not already be in use. And in Windows, Winsock must be initiated first using WSAStarup