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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. ...
Ron Maupin's user avatar
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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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
Ron Maupin's user avatar
  • 99.8k
13 votes

Using sound waves in layer 1

It's been done. I used to have a 300-baud acoustic layer 1 device.
Mark's user avatar
  • 230
12 votes

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

The original RFC for ICMP, RFC777 state that: ICMP, uses the basic support of IP as if it were a higher level protocol, however, ICMP is actually an integral part of IP, and must be implemented by ...
JFL's user avatar
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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 ...
Zac67's user avatar
  • 84.8k
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 ...
Zac67's user avatar
  • 84.8k
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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
fgrieu's user avatar
  • 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. ...
Jeff Learman's user avatar
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 ...
Austin Hemmelgarn's user avatar
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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
Bruno Rijsman's user avatar
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 ...
Ron Trunk's user avatar
  • 67.6k
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 ...
Richard Huxton's user avatar
8 votes
Accepted

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

There is much controversy about which protocols run at which layers in the models. Understand that the models, e.g. OSI Model, are just models, and the real world is often different. There are ...
Ron Maupin's user avatar
  • 99.8k
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? ...
freakish's user avatar
  • 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 ...
jonathanjo's user avatar
  • 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 ...
Zac67's user avatar
  • 84.8k
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 ...
jpa's user avatar
  • 356
7 votes
Accepted

Why is the network layer considered to be connectionless?

Because there is no "state " in the network layer nor signaling for connection setup. Packets are forwarded based on destination address and each packet is forwarded irrespective of previous traffic.
Ron Trunk's user avatar
  • 67.6k
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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
Ron Trunk's user avatar
  • 67.6k
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 ...
Martin Rosenau's user avatar
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 ...
Zac67's user avatar
  • 84.8k
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 ...
Barmar's user avatar
  • 426
6 votes
Accepted

What is persistent connection and session

First a word about: I understand word persistent as following : no one else can occupy wire at the time of persistent connection. So this connection is only one-to-one. But this is not right. ...
JFL's user avatar
  • 19.7k
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. ...
Peter Green's user avatar
  • 13.3k
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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
Ron Maupin's user avatar
  • 99.8k

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