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36 votes

What is the difference between MSS and MTU?

The MTU is the Maximum IP packet size for a given link. Packets bigger than the MTU is fragmented at the point where the lower MTU is found and reassembled further down the chain. If no ...
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25 votes
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What is the difference between MSS and MTU?

In addition, MSS value is derived from the MTU. Consider that you have data of 2260 bytes to be sent to a remote device. If MTU is 1500, and we consider IP header + TCP header to be 40 bytes, then ...
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23 votes
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What do TCP/UDP add to "raw ip"?

IP is a Layer 3 protocol. TCP/UDP are Layer 4 protocols. They each serve different purposes. Layer 3 is in charge of end to end delivery. Its sole function is adding whatever is necessary to a packet ...
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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 ...
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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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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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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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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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11 votes
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Advantage of layer 3 switch over Router

In general, layer-3 switches move packets faster (near line rate) because everything they do is in hardware. They tend to be cheaper and cheaper to operate (power, personnel, etc.) vs. a comparable ...
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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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10 votes

Why is the IP layer aware of higher layers in the network stack?

Every "header" has some sort of "Next Protocol" identification field. This is necessary because on the wire, the data is nothing but a string of 1's and 0's. The receiving endpoint must have a way ...
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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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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 ...
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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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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

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 ...
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9 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 ...
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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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  • 1,449
8 votes

Access Multiple VLANs from One Computer

Add multiple aliases to my laptop NIC and do VLAN trunking on the port the NIC is connected to Your keywords here are "tagged VLAN". You might set up a switch port as a tagged member of all ...
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8 votes
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How to assign a static IP to a Cisco Layer 3 switch in order to connect using SSH?

interface FastEthernet0 switchport switchport mode access switchport access vlan 1 ! interface GigabitEthernet0/1 switchport switchport mode access switchport access vlan 1 ! interface ...
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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

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. ...
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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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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 ...
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7 votes

Difference between router leg and static routes

By "router leg" they mean a (directly) connected route (and use a strange way of putting it). What is a connected route compared to a static route? Connected route (router leg) A connected route is ...
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7 votes
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Layer 3 Switching in Packet Tracer not working

On the switch, your IP for interface vlan 20 is wrong. # interface vlan 20 # ip address 10.1.2.1 255.255.255.0 # no shutdown Then make sure you have ip routing on. Also the gateway for PC A should ...
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7 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 ...
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7 votes

Why use 'switching' term for packet switching

A very good question coming at it from a networking viewpoint. Your question is based on the networking models that were developed long after packet switching was proposed as a concept. However ...
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7 votes
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Should my layer 3 switch rewrite this MAC address?

A layer 3 switch will do both routing and switching. In this case: The packet arrives on some layer 3 interface. The destination IP is 10.5.89.34, and the MAC address on the incoming frame is the MAC ...
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