topic Re: process id's and portnumber in Operating System - HP-UX

process id's and portnumber

Amith_2 — Tue, 17 Oct 2006 03:51:45 GMT

Could anyone please tell me why port numbers are used in network programming instead of process id's

Re: process id's and portnumber

Hemmetter — Tue, 17 Oct 2006 04:48:28 GMT

Hi Amith,

A network connection is defined through a socket={src-ip,src-port,dest-ip,dest-port}.

If you open a connection, say http, you know that you have to adress dest-port=80/tcp (http) because that service is "well-known" (see /etc/services).
If not portnumbers but PIDs would be used for dest-ports, how do you know the PID of httpd who serves www.google.com?

Or

If you, for example, replace the src-port with your browser-PID and you visit a site with lots of gifs your multithreaded browser will open lots of connetions, all with the same PID, how would your browser determine what ip-packet belongs to which gif?

Now this work is done for every application by the tcp/ip stack. The applications only specify the target and will get a handle back for further work with that connection.

Now if you want to know to what process opened a certain connection use lsof(8)
$ lsof -i @yourhost:src-port

hns@AVALON:/home/hns> lsof -i @avalon:52545
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
ssh 829 hns 3u IPv4 0xc4a23910 0t0 TCP avalon:52545->snowdon:ssh (ESTABLISHED)

A good source for reading is
R. Stevens "UNIX Network programming Vol.I"

rgds
HGH

Re: process id's and portnumber

Steven E. Protter — Tue, 17 Oct 2006 05:27:48 GMT

Shalom,

http://www.faqs.org/faqs/unix-faq/socket/
http://www.google.com/url?sa=t&ct=res&cd=2&url=http%3A%2F%2Fwww.kohala.com%2Fstart%2F&ei=-a80RaGnMYe-2wLnk_20AQ&sig=__v746GYO1_ZHFw694VCXV27VnTY4=&sig2=nO-OpI9mIcHHiUZ3W59-dQ
http://www.google.com/url?sa=t&ct=res&cd=3&url=http%3A%2F%2Fwww.kegel.com%2Funpv1%2F&ei=-a80RaGnMYe-2wLnk_20AQ&sig=__Z8j9rt5Zb_jYe1Zp-aZUz-M8wT4=&sig2=SnqgRE1pvp-r0pN3YZYQyA
http://www.google.com/url?sa=t&ct=res&cd=5&url=http%3A%2F%2Fwww.scit.wlv.ac.uk%2F~jphb%2Fcomms%2Fsockets.html&ei=-a80RaGnMYe-2wLnk_20AQ&sig=__2ol3SoeAP-JHJijp3B9tE16w-hc=&sig2=cWGCPKkPv7F7w65G70Mlag

SEP

Re: process id's and portnumber

Calandrello — Tue, 17 Oct 2006 07:34:03 GMT

Friend
lsof |grep number-port
this goes to bring together numbers it of the process, that this leaving the door in Lock

Re: process id's and portnumber

Ivan Ferreira — Tue, 17 Oct 2006 08:25:13 GMT

Port numbers are not used instead of process id's. When you develop a network service, the program must start and listed in a network address/port to accept connections.

When the program starts, a PID is created for the process.

As many network services can be running in a server, you need a way to allow multiple services running on the same network address. There is where ports numbers plays. To avoid service conflicts, every network service listen on a different network port but in the same IP address.