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22 votes
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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 ...
Ron Maupin's user avatar
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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 ...
mere3ortal's user avatar
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17 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 ...
Zac67's user avatar
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14 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 ...
rnxrx's user avatar
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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 ...
Ron Maupin's user avatar
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11 votes
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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
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11 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 ...
Zac67's user avatar
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10 votes
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At which layer does router operate?

Network address translation (NAT) is a feature of Router which is required for routing traffic. That is completely incorrect. NAT is a kludge (a clumsy, inefficient solution) designed to extend the ...
Ron Maupin's user avatar
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10 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 ...
Ron Maupin's user avatar
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10 votes

How does Deep Packet Inspection work with encrypted packets?

As you point out, traditional DPI methods have limited ability to deal with encrypted traffic completely. They can still address encrypted traffic at a surface level at the very least, but it does ...
YLearn's user avatar
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9 votes

When is 'Timestamp' and 'Timestamp Reply' are used in ICMP protocol?

The usual ping command uses ECHO REQUEST and ECHO REPLY, as you've seen. It does indeed locally keep track of sent time and matches with the incoming reply to determine the round trip time. ...
jonathanjo's user avatar
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9 votes

Is static routing used in large networks?

I work at a large ISP and before at a different large ISP and both networks extensively use static routing. Mostly on the firewalls as they don’t want to run an IGP or BGP on the firewalls, but you ...
Tommiie's user avatar
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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 ...
manish ma's user avatar
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8 votes

What layer of the OSI model does NAT work?

Nat is a cross-layer process. It involves at least layers 3 (IP) and 4 (TCP, UDP, etc). In some cases it can also involve layer 7 (application). A one to one NAT needs at minimum to modify the IP ...
Peter Green's user avatar
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8 votes
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Is it possible to perform a Layer 2 (MAC address) traceroute?

But is there any way to do a traceroute that will show Layer 2 information? Short answer: no. Longer answer: traceroute exploits IP's TTL feature. There is no such concept in Ethernet, hence no ...
Zac67's user avatar
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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 ...
DRP's user avatar
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8 votes
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Why do transport layer do data chunking. If there is fragmentation in Network Layer

The transport-layer protocol needs to make sure that data can be properly packetized. If it lacks support for that (like UDP), the application layer needs to take care of it. IP fragmentation in the ...
Zac67's user avatar
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8 votes
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Is a datagram from an upper network layer converted 1:1 to one of the lower layer?

A single TCP segment is always converted to a single IP packet by adding IP header, which is in turn converted to a single Ethernet frame by adding Ethernet header (and footer). In other word, a ...
Ron Maupin's user avatar
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7 votes

Need of routers and IP addresses

Imagine you are connected to a bridge with 3 ports. One port is connected to your host; one connects to networks to the west of you, and the last one connects to networks to the east of you. Now ...
Ron Trunk's user avatar
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7 votes

VXLAN vs VLAN over layer 3

As you've already stated, VXLAN is L2 tunneling over IP. It's a solution to use any L3 network for creating a L2 segment. While this is also possible with other protcols, VXLAN doesn't require ...
Zac67's user avatar
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7 votes
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What are the reasons for seeing an incomplete ARP?

For a layer-3 switch, the layer-3 module in the switch is a router, and it works just like a router, which works like any other host for ARP. A layer-3 switch is still primarily a layer-2 switch, and ...
Ron Maupin's user avatar
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7 votes
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Is there a Layer 2 address advertising protocol?

LLDP is not a layer 2 equivalent of RIP. RIP is a routing protocol, advertising routes between routers. LLDP is a device discovery protocol, so neighboring devices can learn about each other. ...
Ron Trunk's user avatar
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7 votes
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Leaf-Spine network without routing

do I need a router (or l3) since everything is on the same network and the network is flat Technically, no - if all nodes reside in that flat network. However, such a large subnet is not good ...
Zac67's user avatar
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7 votes
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Why is default gateway in routers configuration usually set as an IP address?

why not just ... a MAC address? A router might not use a MAC address on an interface - not all L2 protocols use MACs even though many do (mainly the IEEE ones like Ethernet or 802.11). Also, routers ...
Zac67's user avatar
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7 votes

How do I know the switch is layer 2 or layer 3?

In addition to @Zac67 answer, in the Catalyst product line, layer 3 capabilities are often unlocked by licenses. So a given switch can be layer 3 capable but, depending on the installed license, may ...
JFL's user avatar
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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
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6 votes

What's the difference between port number and protocol number?

The protocol number is used by the the layer-3 protocol (IPv4 or IPv6) to determine to which layer-4 protocol in the network stack it should send the payload of the packet. A port number is an ...
Ron Maupin's user avatar
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6 votes
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Router vs VLAN in networking?

There are a couple of problems with your idea. You cannot get traffic from one VLAN to another VLAN without routing. Either you have a dedicated router, or a layer-3 switch, which is really a router, ...
Ron Maupin's user avatar
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6 votes

Why can't two hosts (in two different logical networks) connected to each other through cross-over cable communicate?

A host knows if the destination address is on a different network (the same way that you do, by masking the host and destination addresses with the host mask). If the destination is on the same ...
Ron Maupin's user avatar
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6 votes
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Connecting Layer 2 switchport to layer 3 port

With your switch configuration, you are adding VLAN tags to the frames, but the router is not, so the switch assumes the traffic belongs to VLAN 1. Since this is layer-3 switch, you should simply ...
Ron Maupin's user avatar
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