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
aconnect(1)						      General Commands Manual						       aconnect(1)

NAME
aconnect - ALSA sequencer connection manager SYNOPSIS
aconnect [-d] [-options] sender receiver aconnect -i|-o [-options] aconnect -x DESCRIPTION
aconnect is a utility to connect and disconnect two existing ports on ALSA sequencer system. The ports with the arbitrary subscription permission, such as created by aseqview(1), can be connected to any (MIDI) device ports using aconnect. For example, to connect from port 64:0 to 65:0, run as follows: % aconnect 64:0 65:0 The connection is one-way, and the whole data to the sender port (64:0) is redirected to the receiver port (65:0). When another port (e.g. 65:1) is attached to the same sender port, the data is sent to both receiver ports. For disconnection, use -d option. % aconnect -d 64:0 65:0 The address can be given using the client's name. % aconnect External:0 Emu8000:1 Then the port 0 of the client matching with the string "External" is connected to the port 1 of the client matching with the "Emu8000". Another function of aconnect is to list the present ports on the given condition. The input ports, which may become sender ports, can be listed with -i option. % aconnect -i client 0: 'System' [type=kernel] 0 'Timer ' 1 'Announce ' client 64: 'External MIDI-0' [type=kernel] 0 'MIDI 0-0 ' Similarly, to see the output ports, use -o flag. You can remove all existing exported connections using -x option. This function is useful for terminating the ALSA drivers, because the modules with sequencer connections cannot be unloaded unless their connections are removed. OPTIONS
CONNECTION MANAGEMENT -d, --disconnect Disconnect the given subscription. -e, --exclusive Connect ports with exclusive mode. Both sender and receiver ports can be no longer connected by any other ports. -r, --real queue Convert time-stamps of event packets to the current value of the given real-time queue. This is option is, however, not so useful, since the receiver port must use (not necessarily own) the specified queue. -t, --tick queue Like -r option, but time-stamps are converted to the current value of the given tick queue. LIST PORTS -i, --input List existing input (readable) ports. This option is exclusive to -o. -o, --output List existing output (writable) ports. This option is exclusive to -i. -l, --list List the current connection status. The connected and connecting ports from/to each port are listed together. The suffix flag [ex] means the connection is exclusive. The suffix flag [real:#] and [tick:#] mean the connection includes real-time and tick conversion on the listed queue, respectively. REMOVE ALL CONNECTIONS -x, --removeall Remove all exported connections. SEE ALSO
aseqnet(1), aseqview(1) AUTHOR
Takashi Iwai <tiwai@suse.de> August 31, 2000 aconnect(1)
All times are GMT -4. The time now is 10:26 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy