03-27-2018 10:00 AM - edited 03-08-2019 02:25 PM
Hi everyone,
I am in a confusion of some network concept that speaks of port number.
my question is on which layer of the model OSI and TCP / IP is the port number?
cf. https://twitter.com/LearningatCisco/status/972562741910278144
Identifying the Applications
To pass data streams to the proper applications, the transport layer must identify the target application (Figure 3). To accomplish this, the transport layer assigns each application an identifier called a port number. Each software process that needs to access the network is assigned a port number unique to that host. cf. CCNA 1 Chapter 9 section 9.1 topics 9.1.2
Kind Regards,
03-27-2018 10:35 AM
03-28-2018 02:11 AM
thanks for your quick answer, but when you say 4. I presume 4th layer of the OSI model or TCP / IP?
03-28-2018 03:11 AM - edited 03-28-2018 03:14 AM
Yes, its the 4th layer (transport) of the 7 layers for the OSI model.
Reading your last post/question, if you're also asking about the TCP/IP model, it's the 3rd layer (transport) of the 4 layers for that model.
Port numbers, in IP, are used by both TCP and UDP. Port numbers all quick "sorting" of received packets, to processes that want them. Some applications have been "assigned" specific port numbers. For example, HTTP has assigned to it port 80. So, when a client wants to contact a HTTP server, its uses destination port of 80 and a source port unique to the process making the request. This allows the receiving host to send any received packets with a destination of port 80 to the processes "listening" for those packets, which if there is one, would normally be a HTTP server process.
When the HTTP server responds, it uses the client's source port as the reply's destination port and it might use port 80 for the reply packet's source port. This allows the original client to forward the port quickly to the process that made the request.
Although many applications have "assigned" ports, applications might use other port numbers. I.e. the port number doesn't control an application, it's just a convenience. For example, you could configure a HTTP server to "listen" on port 8080. Now, either the client needs to know that too, or it would need to send its HTTP request to all possible 65K port numbers.
03-30-2018 05:27 AM
03-30-2018 09:23 AM
04-02-2018 06:07 AM
the image comes from CISCO. So logical port at the level of the SESSION layer of the OSI model is equal to the port number (ex: 80 for HTTP)?
04-02-2018 06:41 AM
04-04-2018 01:47 PM
please can you have the example of logical port?
04-04-2018 04:49 PM
04-05-2018 04:30 AM
thanks
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