Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: ports???
Special Forums IP Networking ports??? Post 34414 by Perderabo on Thursday 20th of February 2003 06:27:54 PM
Old 02-20-2003
That's pretty close, but you are are ignoring the protocols. The IP address gets the packet to the box. The next thing that happens is the IP layer looks at the protocol. The protocol might be TCP, UDP, ICMP, and a few others. So the IP layer hands the packet to the proper protocol layer. This will usually be TCP or UDP. Both TCP and UDP will then look at the port number. If a program has that port open it will get the packet.

The program could be client or server.

Try this:
grep telnet /etc/services

You should see:
telnet 23/tcp

So a telnet daemon might be running and if it is, it would be using port 23 but under the tcp protocol. A packet coming in to port 23 with the udp protocol would be an error of some kind. It is even possible that some other program is using 23/udp but that would be rare.

I don't want to write a complete book here, but one more point... tcp is connection oriented. That means that your average tcp packet has a second port and a second ip address that tell where it came from. So there 4 things to look at:
destination ip address
destination port
source ip address
source ip port

All 4 have to match. That is how you can have 20 telnetd's running. They all have the same local ip address and they use port 23. But it takes all 4 numbers to define a socket.

There is more to this and you really should read a book. I suggest TCP/IP Illustrated Volume 1 by Rich Stevens.
 

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

ports

how can i check to see if my mail ports are open (port 110 for incoming and 25 for outgoing)? I want to do this because i am having a problem sending email out. If one of the ports has a problem, how can i open it? Thanks in advance! (9 Replies)
Discussion started by: djatwork
9 Replies

2. UNIX for Dummies Questions & Answers

Ports

How To Close ports,for example finger port 79?? :confused: :confused: :confused: 10x (6 Replies)
Discussion started by: Yaki
6 Replies

3. UNIX for Dummies Questions & Answers

Ports

I know i can look in the /etc/services file to look at referenced port numbers, but is there a command that will list the current ports being used? (i.e. what is the application does not have an entry in the services files :confused: ) (2 Replies)
Discussion started by: Ralf
2 Replies

4. IP Networking

Ports

What are some good sites that list all TPC/UDP ports? ~thanks (3 Replies)
Discussion started by: ireeneek
3 Replies

5. UNIX for Dummies Questions & Answers

Ports...

Hello UNIX people... This is my first foray into the UNIX world so go easy on me... I have a client who has hired me to do some work on his windows stuff, BUT it just so happens his UNIX server started giving him problems... He is running SCO Open Server 5.0.6 The TTY ports won't... (5 Replies)
Discussion started by: TechKnow
5 Replies

6. HP-UX

Ports

Can any one tell the command for which process are running on a perticular port (1 Reply)
Discussion started by: zsujith
1 Replies

7. Solaris

regarding ports

Hi , I need one help... Is there any command on solaris 10 to free the ports. For e.g I used netstat -na| grep 8080 it displays either it is listening or established.. i want to free the ports... Anyone please help me on this... Thanks, Shanmuga (2 Replies)
Discussion started by: shanshine
2 Replies

8. Solaris

ports

Hi, If for example i try to start tomcat in a solaris server and get errors related to address already in use, how can I know if this port is really used for another process? If someone can point any documentation it will be very helpfull. Thanks! :rolleyes: (9 Replies)
Discussion started by: ffpradella
9 Replies

9. UNIX for Dummies Questions & Answers

ports

When the netstat -an command is run on current unix machine, it seems that there's an excessive amount of ports established (roughly 600). How can I tell what each of these ports are being used for? (1 Reply)
Discussion started by: lastchance551
1 Replies

10. UNIX for Advanced & Expert Users

Ports

** forum admins: Before you come down on my like a wrath of something, I can get no decent answers so I have to come to these Gurus' court *** I am by no means Unix expert. However, none of our unix admin (aix & hpux) can give me an answer that makes sense. My Issue: Assigned ports in 8601,... (7 Replies)
Discussion started by: rsheikh
7 Replies

LEARN ABOUT OSF1

iscc

iscc(7) 						 Miscellaneous Information Manual						   iscc(7)

NAME

       iscc - serial communications interface

SYNOPSIS

       controller  iscc0  at  isa0

DESCRIPTION

       An  onboard  Zilog  8530  DUART	provides  AXPvme-based Single Board Computers with console (CON) and auxiliary (AUX) serial communications
       ports.  Both serial communications ports can operate at baud rates from B50 to B38400,  excluding B134 (see tty(7)).

       On AXPvme Single Board Computers configured with a graphics head as the system console, the CON serial communications port (/dev/tty01)	is
       available for use by application programs as an additional communications port.

       In  the	absence  of a graphics head, the CON serial communications port (/dev/console) becomes the system console. When used as the serial
       system console, the CON serial communications port always operates at 9600 BPS, 8-bits, and no parity.

       Regardless of system console, the AUX serial communications port (/dev/tty00) is always available for use by application programs.

RESTRICTIONS

       Data communications equipment attached to the CON serial communications port must be set to 9600 BPS, 8-bits, no parity when configured	as
       the serial system console. The iscc terminal driver enforces this restriction.

       No modem control is supported for either the CON or AUX serial communications ports.

FILES

       console terminal local terminal local terminal

RELATED INFORMATION

       console(7), devio(7), tty(7), MAKEDEV(8) delim off

																	   iscc(7)
All times are GMT -4. The time now is 12:22 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy