Questions tagged [osi]

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

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31 views

What does it mean for a device to be layer n?

I've always read, the router is a layer 3 device, the switch is a layer 2 device, the hub and repeater are layer 1 devices and so on with other devices. But what does this mean? When I started ...
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1answer
20 views

OSI model: the session initializes the communication?

A simplified example of how the OSI model works, from this page: For example: Mr. Cooper wants to send Ms. Palmer an email. Mr. Cooper composes his message in an email application on his laptop and ...
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1answer
35 views

data link layer and encapsulation method used for specific types of media?

I was reading about the OSI model then found this question in the review questions : Which layer of the OSI model is responsible for specifying the encapsulation method used for specific types of ...
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2answers
38 views

In the ISO model how does the Network Layer and Application Layer knwo when frames and segments respectively are complete

I understand the general sense of the ISO model but it's my understanding that the Data from the Application layer which is usually large would get split into many TCP packets. The same thing would ...
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4answers
86 views

Do layer 2 protocols allow hosts to communicate without being on a network?

Please go easy on me as I'm just a noob in the networking space. As far as I have learnt, layer 2 protocols use MAC addresses for communication, which doesn't really depend on what network you're in ...
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18 views

Is OSI model merely used for troubleshooting purpose? [duplicate]

I'm a student and recently started understanding OSI model, from what I understand is that OSI model is just theoretical and not really used in real world. It's mainly for troubleshooting purpose. I'...
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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 ...
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1answer
42 views

Is NIC Layer 01 or Layer 2

Is NIC layer 01 or layer 02? I am asking this question because of I found both answers in different sources. Some-one says It is Layer 01. Someone says It is in layer 2. I am getting ready for ...
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3answers
65 views

Is it possible to have a local area network with only layer 1 and not layer 2 of the OSI model?

I know the OSI model has seven layers. Can you consider a LAN to exist without layer 2 and just layer 1? The answers that I saw on Quora were not clear. Some of the answers on Quora came close to ...
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0answers
12 views

OSI and TCP/IP models [duplicate]

my name is Alexander. I have problems with English, but I hope you will understand me anyway. I'm preparing for CCNA 200-301 and I have some problems with OSI model. Let me give you a little context. ...
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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 ...
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1answer
114 views

OSI model transition between layers (data chunking across layers)

There is something I don't understand regarding the OSI model. From what I learned, sometimes information will need to broken down into smaller pieces of information. My question is - let's say that ...
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1answer
442 views

What is “TIME_WAIT” connection in a TCP connection and what is it's purpose?

I am requesting a webpage running on local server port 8080 and was expecting one connection to be established between the server (port 8080) and client (random port). But one additional port is also ...
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2answers
80 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 ...
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0answers
19 views

Switch vs. Router and sequence of OSI Model [duplicate]

As I understand it: A switch (layer 2) seems to define a LAN and a router (layer 3) enables communication between distant LANs. A device on a LAN will give it's MAC address to the switch upon ...
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36 views

Configuration of a Dell managed switch clashes with my network understanding

I got the opportunity to play around with a Dell managed switch from the 2000 series with OS10. I tried to configure a management IP adress 10.10.12.141 (/24) according to the manual but somehow ...
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1answer
26 views

Propogation delay vs time required to send out a complete frame on channel

I was reading Data Communications and Networking by Behrouz A. Forouzan in which for simple Aloha protocol the vulnerable time given was T(fr) (time required to send out a complete frame on the ...
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1answer
50 views

Session layer role(with example) in OSI Model [duplicate]

Could someone provide some real world scenerios to understand the role played by session layer in OSI model. Example: Presentation Layer handles zip&unzip etc. Similarly what does session layer ...
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1answer
345 views

Network Protocol vs Framework?

I've been a network engineer for almost 4 years now. I thought I understand what a network protocol means. but now I'm having doubts. For me, Ethernet is a protocol used at layer 2. there would be ...
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1answer
136 views

Unicast and Multicast MAC address convention

I need help in understanding how Unicast and Multicast MAC address is differentiated as explained in wiki. According to what I understood, when the least significant bit is set as 0 in the first octet ...
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2answers
92 views

OSI Layer Model

I have been searching out for in depth knowledge of OSI layer model. I want to know that what information does a Application, Presentation and session layer header contains. Moreover where do these ...
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1answer
100 views

What steps must be accomplished in each layer of the TCP/IP model to connect a website?

What steps must be accomplished in each layer of the TCP/IP model to connect a website?
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1answer
214 views

How does a 802.11 (wifi) frame identify the payload's layer 3 protocol?

My understanding is that the 802.11 frame header is an equivalent of ether header. In the ether header, there is an EtherType field that identifies the payload protocol, such as IPv4/IPv6/ARP etc. ...
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1answer
319 views

Confusion about TCP/IP data flow in layers

I'm confused about how the data flows through the layers of the TCP/IP model, so I'll just tell what I think it happens (using an email example) and I'd appreciate if you can point my mistakes. ...
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0answers
25 views

What Invariants/guarantees do various layers of the OSI model provide? [duplicate]

I saw it stated in an answer to this other question What transmission service gurantees does Ethernet give? that every layer of the OSI model provides both "hard" and "soft" guarantees to the layer ...
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1answer
209 views

Transport layer segmentation and Ip layer fragmentation [duplicate]

From the OSI Model's point of view: If we already have Ip fragmentation which happen due to the network limitation, why the transport layer provides the segmentation mechanism via TCP protocol? why ...
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1answer
3k views

Logical Link Control (LLC) vs Medium Access Control (MAC)

What differs the LLC sublayer from the MAC sublayer? From what I've understood - The MAC sublayer does what the PHY layer should be doing: detection (error, collision), channel listening, analog-to-...
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1answer
601 views

Understanding EUI-64

I was reading Forouzan's book. It says following: In IPv4 addressing, there is not a specific relation between the hostid (at the IP level) and link-layer address (at the data-link layer) because ...
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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 ...
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0answers
21 views

how OSI and TCP/IP layers work? [duplicate]

I am really confused by how the layers these model work. I'm not asking about what are their functions. I read that transport layer provides end-to-end of all packet delivery, and networking also ...
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3answers
1k views

Do routers understand transport protocol?

We are taught about the difference between hubs, switches, and routers. A hub is a layer 1 device, it only knows layer 1 and doesn't care about layer 2 and above. Similarly, a switch is a layer 2 ...
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2answers
551 views

Which physical layers are part of PROFINET?

I understand that Profinet builds on Ethernet, but I am not quite sure how. Ethernet has a lot of different standards for the physical layer, eg 10Base2 (coaxial, 10 Mbit/s), 100Base-TX (twisted ...
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2answers
10k views

VPNs are working in which layer of the OSI model? [closed]

As the following picture shows, it is possible to categorize VPNs in two general categories: Client-based VPNs Network-based VPNs When it is required to choose a VPN for implementation in a network, ...
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1answer
38 views

Whats the security difference between Policy Based IPSec VPN tunnel vs HTTPS + Basic auth

We have several customers with the same service installed within their DMZ. This service is a HTTPS server. The server does not have authentication, this is solved by configuring the NetScaler ...
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1answer
299 views

What's the meaning of `circuit level gateway`?

The proxy server is an important security function provided by the Internet "circuit level gateway". Its work is mainly at the session layer of the Open Systems Interconnection (OSI) model, which acts ...
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2answers
44 views

LLC connections

TCP establishes a logical connection before sending data,where LLC connections are physical and are being held just between two computers,not more. Is this correct? If so,why LLC=LOGICAL LINK ...
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1answer
70 views

why can't we use the sequence number to distinguish them since every packet has a different sequence number? [closed]

It is a question from Networking stanford course. A server typically listens for TCP connections on a particular port (e.g. 80 for HTTP or 22 for SSH). Which fields can the server use to ...
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2answers
877 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 - ...
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3answers
2k views

How to explain the data flow of OSI model layers in a single picture [duplicate]

Take an example of searching www.example.com in a web browser. I have some confusions at each layer and they are We have opened a web browser and searched for www.example.com. Now, As far as I know, ...
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2answers
356 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 ...
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1answer
193 views

Message formatting and encapsulation

I've gotten confused when reading about encapsulation and the OSI and TCP/IP models. I first read about message formatting and encapsulation and the diagram I read showed: Destination | Source and ...
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1answer
193 views

OSI Model vs Network Model: Does It Matter Which One You Use?

The OSI (Open Systems Interconnection) model is comprised of the following layers: 7. Application Layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link ...
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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 ...
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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 ...
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1answer
104 views

Abstract service primitive

In SNMP RFC documents, often the concept of abstract service primitive (ASP) is used. What is ASP in fact ? I think it is also used in ISO OSI.
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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 ...
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2answers
156 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 ...
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1answer
461 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 ...
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1answer
1k views

Dependency between IEEE 802 and OSI model [duplicate]

My question is focussed on IEEE 802.11x for (WLAN) and 802.15.1 (Bluetooth) Wikipedia and other sources underline, that the mentioned IEEE standards just define the PHY and MAC layer from the OSI ...
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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 ...