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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?

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

A Layer 2 switch learns most of its information about the location of other endpoints via "listening" to ingressing frames, and when it is not aware of the location, it uses floodingand will learn ...
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18 votes
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OSI model and physical location of the layers

tl;dr Many different devices can encounter multiple OSI levels. Whichever end point is requesting something from a layer 7 protocol (like HTTP), will use all 7 layers before putting it on the wire. ...
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17 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 ...
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15 votes
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In which OSI/TCP-IP model layers do BGP, RIP protocols belong?

You have to remember that models like OSI are just that, models. They are theoretical. The real world doesn't fall neatly into these models. For the most part, routing is a layer-3 function, but, as ...
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14 votes
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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 ...
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13 votes

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

Since firewalls essentially filter data, the answer depends on what kind of filtering you do. If you filter based on IP address (for example), you can say that your firewall is filtering at layer 3. ...
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13 votes

Using sound waves in layer 1

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

What is a "Layer 3 Switch"?

Managed switches are in simple terms switches that can be "managed." Managed means that they can provide information/statistics about their operation and usually that they can be configured. While the ...
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12 votes
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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 ...
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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 ...
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11 votes
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What layer of the OSI model deals with ports?

TCP or UDP ports are defined in either layer 4 of the OSI model or layer 3 of the TCP/IP model, both are defined as the 'transport' layer. OSI layer 5 'session layer' uses the ports defined in layer ...
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11 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 ...
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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 ...
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10 votes
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Difference between routing, forwarding, 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 ...
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10 votes
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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 ...
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9 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. ...
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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 ...
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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 ...
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8 votes

What layer of the OSI model deals with ports?

Layer 4 - Transport layer. This is the layer charged with handling end-to-end communication; be it reliable or unreliable. You'll frequently find that most networking concepts don't fit neatly into ...
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  • 126
8 votes

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

BGP is on top of TCP, so it would be Internet layer 4, OSI layer 7. Usually external BGP is done only between 2 directly connected peers, enforced by setting TTL flag on IP header, which is located at ...
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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? ...
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  • 211
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 ...
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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 ...
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7 votes
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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 ...
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7 votes
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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.
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7 votes
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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 ...
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7 votes
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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 ...
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7 votes
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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 ...
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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 ...
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