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Can a router send ARP requests to hosts?

ARP is used by a host on a LAN to resolve a layer-3 address to a layer-2 address so that a frame can be built for the LAN. A router is just another host on a LAN, and it will need to resolve layer-3 ...
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20 votes
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How LAN works in video games if only one station is permitted to transmit?

Only one device is allowed to transmit at any given time. At any other given time, another device is allowed to transmit. How can you have a conversation at a dinner table if only person can speak at ...
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18 votes

How LAN works in video games if only one station is permitted to transmit?

Some LAN protocols, on some media, are half duplex. That means that only one host on a LAN can send a frame at any given time. The classic example of this is the original ethernet, but the modern ...
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17 votes
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VXLAN vs VLAN over layer 3

Yes, from the packet switching point-of-view, VXLAN is just a matter of sticking some encapsulation on top of an L2 frame: something that other protocols do as well. The real difference it makes is ...
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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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16 votes

How Does A Layer 2 Switch Differentiate Between Different Networks?

A (layer-2) switch doesn't care at all about the IP networks you run through it. however, no normal traffic can occur between two nodes on two different networks. That is correct. Different IP ...
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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
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Difference between Giant Frame and Jumbo Frame

Generally, a giant frame is a frame that is too large for the receiving interface. As a malformed frame it is dropped. A jumbo frame is a frame that is larger than the standard allows (1518 bytes for ...
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12 votes
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Should I disable STP on my access ports?

You really, really do not want to disable STP where you connect switches to other switches. That is the entire purpose of STP. If you disable STP, and there is a problem, it will really be too late ...
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12 votes
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RIB vs FIB differences?

The forwarding information base (FIB) is the actual information that a routing/switching device uses to choose the interface that a given packet will use for egress. For example, the FIB might be ...
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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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How is the Groupwise Transient Key used in WiFi networks?

Why then does the client need to encrypt the broadcast using the GTK? It doesn't. Since the AP broadcasts, not the client, the client doesn't use the GTK to encrypt the frame. The AP does. Why can'...
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10 votes
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Cisco: Is it possible to see an EFP path within an EVC?

As soon as I offer a bounty I find the answer, typical! The magic commaned I needed is show mac-address-table bridge-domain 20 ME3600#show mac-address-table bridge-domain 20 Mac Address ...
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10 votes
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What does this "no switchport" command do?

This would have to be commands provided from an interface on a L3 capable switch. The no switchport command puts the interface in L3 mode (known as "routed port") and makes it operate more like a ...
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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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Why preamble is not considered a part of the Ethernet Header?

Adding to jonathanjo's answer: Ethernet has components in both layers 1 (because it can run over different media) and 2 (because the frames are the same on the different media). The Preamble, SoF ...
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10 votes
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What's use of Port Isolation vs traditional VLANs?

Port isolation -also called private VLAN (thanks @Stuggi)- is a very useful feature for switches that connect end users. In a typical network you will have many end-users computers grouped together ...
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10 votes
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Do layer 3 protocols use layer 2 protocols?

Layer 3 (mostly IP) generally relies on the underlying layer-2 network (mostly Ethernet or Wi-Fi) for delivery. Just like a layer-2 network uses layer-1 links to actually move the bits. The ...
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10 votes
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Collision domain question

not quite sure why the book (official Cisco) says that there are 5 collision domains in this example. Isn't it supposed to be 4? No, there are five collision domains. each bridge/switch interface ...
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9 votes

Why each and every single port on Layer 2 switches need to have it's own MAC address?

One key use for per port MAC addresses on switches is for Spanning-tree BPDU's. These are Layer-2 multicasts with source MAC address of the egress switch port. I would have to brush up on other ...
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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
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Do we send ack frames in ethernet? if not then how does a router know if its neighbors are down or not?

No, ethernet is connectionless, as is IP, and if you use UDP, the application would need to perform any connection-related handshaking (if needed). Typically, it is the responsibility of the transport ...
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9 votes

Does a router send frames or packets?

it seems that routers decapsulate the frame on arrival, and encapsulate the packet in a frame in order to send it. Yes. A router must strip off the layer-2 frame in order to get to the layer-3 ...
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9 votes
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What precisely is a link?

There is no single precise definition for a "link". A link can be a physical layer connection, two ports connected by a cable. A link can also be understood as general connectivity by data link ...
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9 votes
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How Does A Layer 2 Switch Differentiate Between Different Networks?

The switch doesn't even "see" what is going on above MAC layer. However, hosts are usually configured to send packets to another IP subnet via a default-gateway IP address. So the hosts ...
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8 votes
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In Cyclic Redundancy Check, how does the receiver knows what the generator polynomial is?

It's true that you have to know it in advance in order to calculate the CRC. The correct polynomial depends on the application of the CRC. For Ethernet, for example, the CRC-32 polynomial is part ...
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8 votes
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What is the difference between layer-2 and layer-3 broadcasts? Please explain with an example

You need to understand the difference between layer-2 and layer-3 for an answer to have any real meaning for you, and I suspect you don't. A layer-2 network is a LAN, and all hosts on it are peers. A ...
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8 votes

Posible to connect VLAN switch through dumb switch?

An unmanaged switch will only have one VLAN. Some unmanaged switches will drop tagged frames as damaged, others will strip the tag, and some will simply pass the frames unchanged. Unless you try it, ...
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8 votes
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What are neighboring ports?

Most basic example of neighbor ports would be as you mentioned: "ports on two different switches (or routers) that are connected by a cable" You won't find a defined definition for this phrase ...
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