Questions tagged [osi]

For questions about the Open Systems Interconnect (OSI) model defined by the International Organization for Standardization (ISO).

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38
votes
7answers
15k views

OSI Model and Networking Protocols Relationship

When most networking students first learn about the OSI model, they spend a great deal of time trying to figure out which layer of the model a particular protocol fits into. We get a lot of questions ...
17
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2answers
12k views

In which OSI/TCP-IP model layers do BGP, RIP protocols belong?

We know that in the OSI or TCP-IP model, the higher layer utilizes the services offered by the lower layer. For example, the data link layer uses services offered by the physical layer, network layer ...
16
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3answers
3k views

Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?

Why does one say fragmentation is bad and must be avoided due to performance issues when in reality fragmentation intrinsically occurs within the communication ? Example: User1 wants to send 100 000 ...
12
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3answers
23k views

How does a switch know where to route packet, when there is another switch in front of the destination?

I am just wondering how a switch does know how to route packets to destinations "hidden" behind another switch. In my understanding a switch has a table that maps each of its hardware ports to exactly ...
11
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8answers
2k views

Using sound waves in layer 1

Is it possible, in theory, to use sound waves as the physical medium to transmit data over a network? In other words, could you implement layer 1 of the OSI networking model using sound waves or am ...
10
votes
3answers
2k views

Why does PPP need an underlying protocol?

The Point-to-Point Protocol is (at least according to Wikipedia) a Datalink Layer Protocol. I know that different use cases exist for it but on examining the image below from Wikipedia one can see ...
10
votes
2answers
6k views

OSI model and physical location of the layers

Hi Cisco student/newbie here! I understand that data passes down through the OSI model and then at the physical layer is transported as bits across the networkcables. But I'm confused at exactly ...
10
votes
3answers
1k views

What is a "Layer 3 Switch"?

What is a "Layer 3 Switch"? I essentially understand the OSI model, well maybe I don't and maybe that is why I don't understand. Its just that I don't see how/when/if a "managed switch" becomes a "...
10
votes
3answers
21k views

Do Bluetooth Devices have MAC address with the same specification as the MAC addresses of the Ethernet and Wi-Fi Network cards?

I recently found out that ZigBee devices have MAC addresses. ZigBee is more related to Bluetooth from what I know rather than Ethernet or Wi-Fi. Do Bluetooth devices such as phones, headphones, ...
10
votes
2answers
3k views

Does session in "http session" mean the same as in "session layer" in OSI model?

Does session in "http session" mean the same as in "session layer" in OSI model? Is a http session a session in the context of "session layer" in OSI model? Is a http session only a pair of request ...
9
votes
5answers
72k views

What layer of the OSI model deals with ports?

I've read that the session layer is also called the ports layer, and a CBT nugget video implied ports were a layer 5 thing. I always thought they were layer 4, just because I guess. (well and tcp ...
9
votes
3answers
6k views

How are MAC/IP addresses used in routing

I have to teach my sixth form about MAC Addresses and IP Addresses in a few weeks time and there are some areas I am unclear on which I am hoping some of you will be able to clarify for me. I have ...
8
votes
5answers
3k views

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page?

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page (same layer as IP) when the ICMP protocol data is a payload of the IP packet? This is the article on Wikipedia that states ...
8
votes
3answers
6k views

Does a switch understand packets? If yes, what is the frame terminology for?

I was a little confused between packet and frame. The confusion was based on, if a switch is a layer 2 device, how does it reads a packet from a layer 3 device, and where is the 'frame' thing which is ...
7
votes
6answers
3k views

Why do we need FTP when there are layers to transmit data?

In OSI, there are layers for routing, encapsulating and transmitting the data. Then why do we need FTP? I read the following definition of FTP in books: FTP is used for transferring files on ...
7
votes
2answers
13k views

Why PPTP, L2TP, PPPOE are in OSI Layer2?

PPTP, L2TP, PPPOE - these are tunneling protocols. And they are Data link Layer protocols. Why? As I understood, Layer2 protocols work only in same subnet. They don't use IP addresses and cannot be ...
6
votes
4answers
1k views

OSI layer of Neighbor Discovery Protocol

NDP operates using ICMPv6 and, even though ICMPv6 messages are encapsulated in payload field of IPv6 datagram, ICMPv6 and ICMP are usually considered as network layer protocols. At least, on Wikipedia ...
6
votes
6answers
29k views

Difference between routing, forwarding, switching

I feel like the three terms are often used as synonyms but actually all mean something different. I did look at Wikipedia sites but I'm still unsure about the definitions of the three. From my ...
6
votes
4answers
4k views

In the TCP/IP model, how does the application layer inform the Internet layer of the destination IP address?

New to networking. How does the application layer inform the Internet layer of the destination IP address? Let's say I make a Http request to www.google.com, which the application layer resolves to 8....
6
votes
1answer
655 views

Responsibility of the physical sublayers of Ethernet

I'm learning about Ethernet and the sources I've found seem to be controversial regarding the role of the physical sublayers of Ethernet displayed on the following image. Just to mention an example ...
5
votes
3answers
65k views

How to know at what OSI Layer(s) does a firewall operate

I understand that Firewalls may operate on different OSI layers depends on the firewall itself. but how can I know if I install specific firewall at what OSI Layer(s) it does operate ?
5
votes
5answers
1k views

How we can assume which network protocol is working in which OSI Layer?

For a long time, I have this kind of silly question: How we can say some network protocols are working in X layer of the OSI model? For example, HTTP working in L7 of OSI, OSPF is L3, ICMP is L4, TCP ...
5
votes
3answers
1k views

When are MAC addresses used instead of IP addresses in the OSI model?

Okay, so I'm studying for the Network+ exam, and I've gone over the OSI model about a million times, and I understand most of it fairly well, and my studies are coming along fine. However, there is ...
5
votes
2answers
11k views

Which layer does modem operate and are they still used?

I was searching this for quite long time but I haven't found any satisfying result so my question is basically that, if I understand correctly how modems work and when they are used. I have some more ...
4
votes
3answers
2k views

Error Detection across OSI layers confusion

Confusion: How does the transmitter know that his information( bits in physical layer, frames in data link layer, packet in network layer ) was transmitted correctly to the receiver? I know that in ...
4
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3answers
3k views

Session layer vs Transport layer

It seems both do the same thing (or establishing a session between two hosts differs from establishing a connection between two?) So what exactly is the difference here that make us consider them as ...
4
votes
1answer
7k views

Why are there checksums for different OSI layers?

Can anyone clarify the question "why we need checksum in both layer-2 and layer-3 of OSI layer", Layer-2 would encapsulate the rest of OSI layers into a single unit. If Layer-2 has a checksum, ...
4
votes
1answer
123 views

Why is the network layer considered to be connectionless?

Why is the network layer in the OSI model considered to be connectionless when you have Virtual Circuits that are a part of the layer and is connection oriented?
4
votes
1answer
1k views

How are duplicate packets handled at the Data Link Layer?

Reading up about the data link layer I found that the logical link control sublayer uses sequence numbers to find duplicate packet frame transmissions. I understood the sequence number game with ...
4
votes
1answer
707 views

How does a NIC know where the start of a frame is?

A question popped into my head today and after a quick few searches on google, I have no idea. When a device is sent a frame there is a layer 1 header/preamble saying the length and layer 2 protocol (...
4
votes
2answers
205 views

Understanding Internet Protocol Suite; The Internet Layer

I am trying to understand the Internet Protocol Suite as described by Wikipedia. What is confusing me is the Internet Layer. So, to see if I understood it, this layer is simply the IP header and ...
3
votes
2answers
359 views

Do the concepts of IP address and network interface not belong to the same layer?

https://unix.stackexchange.com/a/508065/674 You are confusing the device driver layers and the IP layers of the stack. At the IP layer, 127.0.0.1 is just another IP address and treated the ...
3
votes
2answers
5k views

How does IS-IS carry IP routes?

IS-IS runs natively on layer 2 of the OSI reference model. How will the routing be done in that? My doubt is that layer 3 has the ability to do the routing. But, ISIS does not run in layer 3 rather ...
3
votes
3answers
266 views

TCP/IP protocol suite

I read that "TCP/IP protocol suite contains relatively independent protocols which can be mixed and matched which is not possible in OSI". What is the meaning of mix and match over here ? Can we mix ...
3
votes
3answers
4k views

Where do the layers of the OSI Model operate in the operating system?

The OSI model describes them as layers. But where do these layers actually operate in the operating system? For example, where and what actually does TCP? All these layers are described as using ...
3
votes
1answer
494 views

Where does DNS resolution fit within the TCP/IP stack?

I know that it's possible to whitelist/blacklist IP addresses (for example, only allowing a few external IP addresses to be contacted from within a VPN). But since IP address destinations are the ...
3
votes
3answers
9k views

When does the three way handshake take place in relation to data flowing down the OSI stack?

I am very new to networking and I am currently trying to get my head around the order things happen in relation to the OSI stack. I know that the Transport layer takes the data stream and converts it ...
3
votes
2answers
2k views

Encapsulation and decapsulation basics for OSI layer

I have read that encapsulation takes place down the layers while decapsulation takes place up the layers. In essence, the encapsulation starts at Application layer all the way upto Physical layer. ...
3
votes
1answer
1k views

What is persistent connection and session

There is one thing I still cannot understand is persistent connection and sessions. I will explain how I understand all network stuff. Physical layer . This is just voltage levels going through ...
3
votes
1answer
2k views

What is the need for transport Layer?

In 5-layer model. Why we need additional transport layer? I read these two points Users who interact with software have no control over the sub-net; Transport Service can provide a more reliable ...
3
votes
2answers
84 views

Networks theory: Layers, Services and Interfaces

I want to learn about computer networks from the bottom up. I don't really understand the nuances of networking layers, with books mentioning that layers provide services to layers above them, but the ...
3
votes
2answers
121 views

In IP, to what extent are the network addresses coordinates?

Routing of data relies on being able to reach the destination address. There are network addressing systems proposed where the addresses are coordinates, Vivaldi from MIT, for example. The routing in ...
3
votes
1answer
163 views

Do I need to read standards to understand how networks work?

I am Computer and Communication Engineer, and I read many books about data communication and networking, all discussing basic concepts like OSI Model, topology in general, multiplexing, etc., but I ...
3
votes
2answers
126 views

What protocols apart from TCP support cumulative acknowledgements?

I know about cumulative and selective acknowledgements TCP protocol offers. Do you know any other protocols (apart from TCP), that support cumulative acknowledgements?
3
votes
3answers
1k views

what is the OSI session layer (5) used for? [closed]

I have been reading about the OSI model and understand all the other layers but this layer seems to have many websites describing it differently Are the sessions to keep track on connections, such as ...
3
votes
1answer
1k views

Why is the OSI model used to describe real-world networks?

OSI is a theoretical model, so why are its concepts used to describe real-world networks?
3
votes
2answers
162 views

Do protocols ever have standards that affect multiple layers of networking?

I'm reading about higher-level protocols such as HTTP and SOAP (concerning the application layer at the highest level) in addition to lower-level ones such as TCP. So far these protocols concern only ...
3
votes
1answer
2k views

Data link layer acknowledgement

I'm confused with some concepts please help me out, Data link layer manage flow control hop to hop. Flow control requires acknowledgement receiving but If we observe data link layer header, it does ...
3
votes
1answer
254 views

Application Layer Protocols [closed]

I'd like to know, What the Application Layer Protocols have in common? client-server model could be one? How to know if the protocol belongs to application layer just observing their features?
2
votes
2answers
882 views

At which OSI layer a user-generated data resides?

I am getting a bit confused about which OSI layer is being used to store user-generated data. As far as I understand the process of encapsulation, the higher layers (starting with layer 7 - ...