Questions tagged [osi]

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

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What is the difference between a private IP and a MAC address? [duplicate]

I am taking a course preparing me for the Network+ certification. I wanted to know what the purpose of a private IP is when a MAC address exists. From what I understand, the MAC address is used to ...
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How to benchmark time a packet spend in each OSI layer?

I'm benchmarking latency of sending a TCP packet from a client to a server. The payload of the packet is the nanosecond timestamp (using clock_gettime() on Linux) right before the send() socket ...
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Can refer a detailed low level explaination of the OSI model at operating system level? [duplicate]

I understand the function of each layer in OSI model but I can not comprehend the inner working at the operating system level. I can't mentally picture the life cycle of data from application layer to ...
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HTTP and TCP relationship

I always wondered how HTTP knows when it has enough TCP segments in order to process a request or response. Can someone give me more information about the process? Thanks.
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Why need Ack flag if we already have ack number in TCP

If we have ack number so from there we can trace that how many bytes are received and which byte is need next so then what is the use of Ack flag there?
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How n level come to know the n+1 level contents?

Suppose in application layer is running some application. And application has respective source port number and destination port number. And know that n layer has no authentication to know about n+1 ...
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Why is cable classfied in layer 1 in OSI model

I am learning about the OSI model and TCP/IP Protocol. In my understanding, they classify cables to layer 1 (Physical Layer). But, when you connect two different devices you have to use cables no ...
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What is responsibility of different layers of OSI model and intermediate devices between sender and receiver when data packets are lost/corrupted?

Suppose sender sending some data to receiver and there are 3 routers between them. R1, R2, R3 are routers. Now sender starts sending data packet D through it's AL, TL, N/W L, DLL,PL to router R1 ...
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EtherType multiplexing used by LLC layer

What's the type of multiplexing used by Ethernet (LLC layer)? It says in Wikipedia "The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (e.g. IP, ...
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LLC layer: what's the multiplexing principle? [duplicate]

I wonder what is concretly the multiplexing principle done by the LLC layer. Can you please explain the principle with practicle example ? Many thanks for your help
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Ethernet compatibility

I am improving my knowledge about the Ethernet protocol. During my study, I noticed that they are multiple versions of the protocol. Example: 2.5GBASE-T and 5GBASE-T and 100BASE-TX. I wonder depending ...
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Why in the TCP/IP model the link & physical are one?

I'm currently learning about the OSI model and the TCP/IP models, and I was wondering: Why in the TCP/IP model the physical layer and the data link layer are combined? I'll state how I understand the ...
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Understanding the definition of layer 2

The Wikipedia (and other sources) page about the OSI model explains layer 2 as such: The data link layer provides node-to-node data transfer—a link between two directly connected nodes. ... Let's ...
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Why router can't be used for converting different model of network but gateway can do this?

We know that Router can't be used for converting different model (e.g OSI model to TCP/IP or TCP/IP model to OSI) of network. It isn't a multiprotocol converter. But gateway is a highly sophisticated ...
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Does the OSI model apply anywhere else other than computer networking? [duplicate]

I try to understand the OSI model, more about why it was created and what exactly it tries to achieve. The Wikipedia page says: The Open Systems Interconnection model (OSI model) is a conceptual ...
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What is the goal of the OSI model? [duplicate]

I'm currently learning about the OSI model, trying to understand exactly what it is and what is the purpose behind it. The Wikipedia page says: The Open Systems Interconnection model (OSI model) is a ...
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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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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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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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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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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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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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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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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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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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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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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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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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2 answers
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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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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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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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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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1 answer
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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