29
votes
Accepted
Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?
Fragmentation is resource intensive in a router, and it slows packet forwarding. Today, we use PMTUD to determine the smallest MTU in the path so that packets are properly sized prior to sending. ...
- 100k
18
votes
Why does PPP need an underlying protocol?
Why does PPP need a wrapping protocol?
PPP is not a layer-1 protocol, so it needs a layer-1 protocol to carry it. Protocols like ethernet are both layer-1 and layer-2 protocols, so PPP can use ...
- 100k
14
votes
Accepted
Does a switch understand packets? If yes, what is the frame terminology for?
You need to understand the concept of layers.
An application will send data to the Transport Layer. The Transport Layer protocol will encapsulate the data inside headers for the Transport Layer ...
- 100k
13
votes
12
votes
Accepted
Why do we need FTP when there are layers to transmit data?
The network layers provide a framework to structure the complex functions for sending data over a network - as byte stream, in dialogue, telegram style datagrams, ...
On the very top, the application ...
- 86.4k
12
votes
Why does PPP need an underlying protocol?
PPP is designed to ride on top of a byte-oriented, point-to-point physical-layer protocol like a simple modem-style serial link.
Ethernet is no simple serial protocol but it requires frame-level ...
- 86.4k
11
votes
Accepted
Difference between routing, forwarding, and switching
In general, forwarding refers to a device sending a datagram to the next device in the path to the destination, switching refers to moving a datagram from one interface to another within a device, and ...
- 100k
11
votes
Do Bluetooth Devices have MAC address with the same specification as the MAC addresses of the Ethernet and Wi-Fi Network cards?
Bluetooth devices are required to have a unique device
address, assigned from the same registry as Ethernet and Wifi MAC addresses. Quoting the Bluetooth specification version 5.0 volume 1:
Each ...
- 243
10
votes
Why PPTP, L2TP, PPPOE are in OSI Layer2?
PPTP, PPPoE, and L2TP all provide OSI Layer 2 services. That is, the user of these protocols (usually, a network layer protocol suite) thinks it's running over a "normal" link layer. ...
- 330
10
votes
Accepted
Using sound waves in layer 1
It's very much possible. Even excluding the old acoustically coupled modems that eventually evolved into a direct connection to a phone line, there are also programs that will let you use a sound ...
10
votes
session layer in OSI model
The OSI model is just a model, and OSes do not implement the OSI model. Modern OSes are much closer to the IP Services model, but it, too, is just a model, and things in the real world do not always ...
- 100k
10
votes
session layer in OSI model
The session layer sits on top of the transport layer. In the case of a connection-oriented services, the transport service is responsible for providing reliable flow-controlled end-to-end data ...
- 339
9
votes
Does session in "http session" mean the same as in "session layer" in OSI model?
I have to disagree with @ronroyston here. The OSI model is an idealized abstract model, and there are no protocols in use today that follow it. HTTP was created without regard to the OSI model, so ...
- 67.9k
9
votes
Why do we need FTP when there are layers to transmit data?
The OSI Model is seven layer model of how you can build a networking system. The TCP/IP networks that we all use does not follow this model and roughly ends at the transport layer with higher-level ...
- 191
8
votes
Why do we need FTP when there are layers to transmit data?
Here's a simple answer. Consider a file of 5 bytes abcde. You can send that data over the network, sure. But how would you tell the other side hey, I've done sending my file in order to send next one? ...
- 211
8
votes
Accepted
Where does DNS resolution fit within the TCP/IP stack?
DNS resolution sits at the application layer: a host communicates over DNS to a server, which is encapsulated in (usually) UDP (the transport layer), which is encapsulated in an IP packet (the ...
- 16.3k
8
votes
Using sound waves in layer 1
Anything that can transport information can be used as physical layer - sound waves as well as pigeons.
Some air-gap attacks use (ultra)sound to communicate across the air gap.
However, since the ...
- 86.4k
8
votes
Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?
IP packet level fragmentation occurs when the transmitting side is not properly aware of the MTU of the path. This results in worse performance than if the packets are sized correctly already at the ...
- 366
7
votes
Accepted
Is UDP used in every TCP/IP connection?
UDP and TCP are completely separate Transport Layer (Layer 4 in the OSI model) protocols. There are also other layer-4 protocols, but TCP and UDP are the most commonly used. UDP was first, and it is a ...
- 100k
7
votes
OSI layer of Neighbor Discovery Protocol
The OSI model is a conceptual idea -- it doesn't relate to anything that people actually built. Moreover, IPv4 and IPv6 were developed without the OSI model in mind, so there is no direct correlation ...
- 67.9k
7
votes
Accepted
OSI layer of Neighbor Discovery Protocol
First of all: In every "model" you will find some aspects that do not describe the reality correctly. This is true for "models" in computer science, financial theory, politics or ...
- 2,356
7
votes
At which OSI layer a user-generated data resides?
Data isn't stored in a network, it is transported.
User data is transported as payload by the application-layer protocol (L7) - HTTP, FTP, SMTP, ...
For instance, if you write some text and send ...
- 86.4k
7
votes
Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?
IP fragmentation can cause excessive retransmission at the TCP level.
TCP transmits information as a series of segments, and these are the units of acknowledgement and retransmission as well. If a TCP ...
- 426
6
votes
In the TCP/IP model, how does the application layer inform the Internet layer of the destination IP address?
In addition to the data some metadata must be communicated betwen the application, transport and internet layers.
Technically how metadata is communicated between layers is an implementation detail. ...
- 13.6k
6
votes
Does the OSI model support connectionless communication in the transport layer?
First, the OSI model is just a model, and things in the real world do not necessarily match. In particular, OSes, do not implement the Session and Presentation layers separately from the Application ...
- 100k
6
votes
Accepted
Error Detection across OSI layers confusion
I know that in the data link layer that is responsible ensuring that
frames has been transmitted successfully by sending acknowledgement
That is incorrect. There are very few data-link protocols ...
- 100k
6
votes
Accepted
Do the concepts of IP address and network interface not belong to the same layer?
Tim, you are trying very hard to map abstract concepts to real life hardware and software. They don't map exactly, so you always will have things that don't fit. Software is modularized for ease of ...
- 67.9k
6
votes
Accepted
At which OSI layer a user-generated data resides?
The OSI seven layer model is an abstraction whose purpose is to clarify concepts and make it easier to compare different networking approaches: such as the differences between internet protocol and X....
- 16.3k
6
votes
Accepted
Why does PPP need an underlying protocol?
( As others have already said, PPPoE is literally PPP over Ethernet. And similarly PPPoA is PPP over ATM. )
Ethernet and ATM are oddities in the networking world as they define both a layer-1 and ...
- 32.4k
6
votes
Accepted
Is there a term for application layer protocols that are responsibilities of network engineers?
Sometimes I wish they would stop teaching the OSI model. It causes more confusion than any other part of networking.
There is no commonly accepted name for these protocols, and as @zac67 mentions, ...
- 67.9k
Only top scored, non community-wiki answers of a minimum length are eligible