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22 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 ...
Eddie's user avatar
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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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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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13 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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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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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 ...
Ricky'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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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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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

What do TCP/UDP add to "raw ip"?

IP can transmit data just fine, the problem is what happens when that data gets to the other end. The only identification information is the IP addresses of the hosts and a protocol number. Neither of ...
Peter Green's user avatar
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9 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 ...
Ron Maupin'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
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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 ...
Ron Maupin'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

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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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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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
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Accessing devices on different subnets using a switch

Now I can commonly deduce that both the devices are part of the 192.168.0.0/16 network. Is that a correct assumption. No, that's incorrect. You're using netmask 255.255.255.0, so that are two ...
Teun Vink'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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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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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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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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