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Questions tagged [layer2]

For questions about the OSI layer-2 (data-link layer).

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Enhancing 802.11ac MU-MIMO Efficiency: Simultaneous STA-AP and AP-STA Transmission Impact on Goodput Prediction

In 802.11ac' MU-MIMO two things (it's a XOR) can happen since wireless is half duplex: 1)at the same time more STAs transmit to AP 2)at the same time AP transmits to more STAs. Is this true? If so, if ...
allexj's user avatar
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1 vote
2 answers
48 views

Does Internet access using computers, PCs always require the support of a MAC protocol?

In my opinion, if the link is point-to-point then MAC protocol should not be required. But I am still confused because the question contains 'Internet access'.
Uthred Ragnarson's user avatar
4 votes
4 answers
1k views

TCP/IP and data cut

I would like to clarify my understand about TCP/IP model and packet cutting. I think it's done by layer 3 (Transport, eg. TCP) but I'm note sure about layer 2 (Network, eg. IP) or even layer 1 (...
PanCho's user avatar
  • 53
1 vote
1 answer
47 views

Does PPP do broadcasting? [duplicate]

Let's consider the scenario below: Router 1 <---> Router 2 <---> Router 3 Routers 1 and 3 establish a link with router 2, then will Router 2 broadcast to the interface connected to routers ...
Darevil294's user avatar
3 votes
1 answer
106 views

Address Field In PPP Protocol

What is the actual use of the Address Field on PPP As I know, it is always set to 11111111 and this doesn't seem to have any purpose because we use ppp we dealing with the direct link communication
Darevil294's user avatar
0 votes
1 answer
84 views

Mac-address identification through traceroute

i would like to know the command syntax to trace a mac address in a lan. I'm experiencing some issue in quick localization of a device by using only that information, I remember the use of 'traceroute ...
Matteo's user avatar
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0 votes
1 answer
131 views

What are different encoding schemes used in gigabit ethernet?

I was reading about digital transmission, there are many steps namely: Analog to Digital conversion Source coding Channel coding Line coding Pulse shaping Modulation Multiple access techniques ...
SUNITA GUPTA's user avatar
-1 votes
1 answer
40 views

ISP ARP tables and routing [closed]

So I'm Network+ certified and have a beginners understanding of how network communication works, my head starts to split a bit though when I think about how the information is actually communicated ...
user1047228's user avatar
0 votes
1 answer
305 views

In HDLC, how to recognize bit stuffing?

In framing for the HDLC protocol, assume the receiver receives the following string of bits: […] 011111010 […] How can it realize whether the sequence “011111010” is real data, or the result of a bit ...
mgiordi's user avatar
  • 101
1 vote
2 answers
170 views

Understanding VLAN Tagging for Network Segmentation

I've been reading up on network segmentation and the use of VLANs to enhance security and network management. However, I'm still a bit unclear about the concept of VLAN tagging. Can someone please ...
Mahesh's user avatar
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2 answers
83 views

RSTP convergence of p2p links

Ramping up on RSTP here. One thing that is unclear to me is how RSTP links converge initially on P2P links. Consider the classic 3 switch topo as below: For RSTP, won't all the links move to ...
host_unreachable's user avatar
0 votes
1 answer
165 views

How do layer 2 switches route based on MAC when daisy-chained?

Trying to think about this from a hardware design perspective, if I had to design an FPGA or a uC or something to manage a single port being the gateway port and one or more switched ports for routing,...
Qix - MONICA WAS MISTREATED's user avatar
2 votes
2 answers
119 views

How can a router not recognize a gratuitous ARP MITM attack?

I'm reading the chapter for DHCP Snooping/DAI in the OCG for the CCNA and I have a question regarding how gratuitous ARP message attacks work. I'm sure there is a piece I am missing, but I've searched ...
Alex's user avatar
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1 vote
2 answers
405 views

How does L2 switch forward tagged VLAN?

I am a student of networking and have a question. I am currently doing an internship / project at a school where they have 3 buildings. I will name them for now A (subnet 172.16.x.x) --> Each with ...
Bartballon's user avatar
1 vote
1 answer
222 views

Understanding IPv4 model of operation

I'm new to networking and reading RFC791 about IP protocol specification and got some question regarding the paragraph 2.2 Model of Operation. Here is what is discribed: The internet module prepares a ...
Some Name's user avatar
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3 answers
154 views

If all subnets are a part of same vlan, then the network segregation using subnets does not make sense

This is what we know about subnetting. By dividing a network into subnets, you can separate different departments, locations, or security zones, creating distinct broadcast domains. This segmentation ...
RRHS's user avatar
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1 answer
68 views

how can a STP switch time out MAC addresses from the table in Listening state?

I am looking over some materials describing STP's port states (the original version from 802.1d) and they say that a port in Listening state can not modify the MAC address table (it doesn't learn new ...
Marcus's user avatar
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0 answers
27 views

Why are connected switches not a good substitute for the network layer? [duplicate]

Unless I am missing something, because switches can be chained together, I am not sure why the network layer is needed. Theoretically, one can dedicate a frame to any MAC address, and assuming there ...
Aviv Aviv's user avatar
  • 109
0 votes
3 answers
168 views

One layer 2 switch in the middle of router network

In general, The connection should be like PC---SW---ROUTER---Many ISP router---Router---SW---PC so the packet will be from layer 2 ---layer 3---layer 2 What if I put one layer 2 switch in the network ...
jacky chong's user avatar
0 votes
0 answers
16 views

Are ARP messages always used for the process of "Flooding" even when layer-3 is not involved? [duplicate]

I'm new to learning networking so please bear with me. I've learned that ARP messages and flooding are used to find mac addresses when IP addresses are involved. I've learned that when the mac address ...
William's user avatar
  • 101
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1 answer
66 views

What datalink protocol is used in aircraft to ground station communication? [closed]

Laptops, mobile devices, and smart TVs communicate to access point via WiFi. Wireless peripherals (mouse / keyboard) communicate to workstations via Bluetooth. Mobile phones communicate to base ...
Noob_Guy's user avatar
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0 votes
1 answer
86 views

I am trying to wrap my head around NDP

I know before PC10 can ping PC11 it will use IPv6 Neighbor Discovery to resolve the Destination MAC address for layer 2 header. But what would the DEST MAC ADDR be and what topics can I learn this
s3lectstar's user avatar
0 votes
4 answers
2k views

Communication between different VLANs

In my previous understanding, there is no way to communicate between two VLANs using only layer 2. After all, this is the purpose of having VLAN. I found a forum that claims the following. 1.VLANs can ...
jacky chong's user avatar
1 vote
2 answers
342 views

Differences between TCP congestion and TCP flow control

From my understanding, flow control essentially how much the receiver can process. Suppose I can send packets at 100mb/s but the receiver can only process information at 10mb/s, flow control would ...
Randy's user avatar
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1 vote
1 answer
221 views

What happens if the layer 2 destination MAC address mismatches?

I was wondering, what happens if I send a packet with layer 2 destination (say 1ebf) different that what will receive it, lets say a router (mac 22ff) recieves it. Will it drop the packet? Or ...
AlazOz's user avatar
  • 13
1 vote
1 answer
779 views

Can a switch fragment a jumbo frame?

In all resources seen that tackle the term of "jumbo frame", I understand that it is applied in a LAN, because: It's a Jumbo frame, and a frame is for Layer 2 These resources talk a lot ...
Lee's user avatar
  • 63
3 votes
1 answer
586 views

Length of Ethernet Preamble on 10Gb network

I know (see https://en.wikipedia.org/wiki/Ethernet_frame) that an Ethernet frame includes a 7 byte preamble of 0x55s and a one byte start frame delimiter (SFD) 0xD5, for a total of 8 bytes before the ...
Erik Parkinson's user avatar
2 votes
1 answer
609 views

What's the difference between MTU and MRU ? How come people talk so often about MTU and little consideration is given to MRU?

I don't understand why MRU isn't mentioned as frequently as its counterpart MTU. Are they always arranged to have the same value on a device ? A few days ago I noticed that my Windows machine accepted ...
Kode1000's user avatar
2 votes
1 answer
1k views

MTU mismatch scenario, two hosts handle in a different way ingoing packets bigger than local interface MTU. How does MTU really work?

I’ve been struggling with the MTU topic for a while and I still can’t get how it really works. The majority of books that I read and the courses that I attended all seem to treat this subject in a ...
Kode1000's user avatar
0 votes
2 answers
134 views

Where is priority for a particular frame set?

The Medium Access Control sublayer appends 3 bits for the priority of the frame. The possible choices for the priority are Traffic Type Priority Background 0 (lowest) Best effort 1 (default) ...
user84425's user avatar
8 votes
6 answers
5k views

How Does A Layer 2 Switch Differentiate Between Different Networks?

I know that different IP-based networks can be connected to the same layer-2 switch. and I know each network's nodes can communicate just fine, however, no normal traffic can occur between two nodes ...
Shadi's user avatar
  • 285
2 votes
1 answer
812 views

Ethernet: How does receiver know end of frame? [duplicate]

I need to implement an 'ethernet-wannabe protocol' with a sender and a receiver.(only layers 1,2). Assuming a sender\receiver model for an Ethernet frame with varying payload length. As for the sender-...
Danny Blozrov's user avatar
1 vote
3 answers
260 views

Do telephone calls work at Layer2?

We know that Wi-Fi works in both layer1 and layer2 and travel through air in layer1. My question is when we create mobile phone call during connection establishment phase sender Mac address and ...
S. M.'s user avatar
  • 398
1 vote
3 answers
627 views

Why switch uses Mac address during implementation of spanning tree protocol (STP)?

We know that layer2 switch doesn't use Mac address ,uses only certain port number to accept the frame. But I have been read on book as well as internet that uses Mac address to find spanning tree for ...
S. M.'s user avatar
  • 398
1 vote
1 answer
419 views

How FDB (Filtering Database) is filled out

I would like to understand what is used as a VLAN column in the FDB. For ACCESS port it is PVID if frame untagged or frame VID if frame is tagged, for TRUNK it is allowed VLANs? We can represent the ...
Manticore's user avatar
  • 141
2 votes
1 answer
193 views

Fragments taking different routes?

I have trouble understanding why sometimes it occurs that during IP fragmentation certain fragments take different routes. I was following this the second example: https://www.gatevidyalay.com/ip-...
mato_kan's user avatar
1 vote
1 answer
409 views

Why need Ack flag if we already have ack number in TCP

If we have ack number so from there we can trace that how many bytes are received and which byte is need next so then what is the use of Ack flag there?
user83095's user avatar
0 votes
2 answers
922 views

How PPPoE uses addressing to know destination Mac address?

Case.1 We know that when router connected via point to point(PPP) protocol then ARP isn't used to know the destination Mac address. Case.2 When two router connected via PPP as well as Ethernet which ...
S. M.'s user avatar
  • 398
1 vote
1 answer
114 views

How n level come to know the n+1 level contents?

Suppose in application layer is running some application. And application has respective source port number and destination port number. And know that n layer has no authentication to know about n+1 ...
S. M.'s user avatar
  • 398
1 vote
1 answer
262 views

Router could get packet of size more than 1500 bytes?

Suppose transport layer get the segment 4000 bytes from application layer at sender site. But we know maximum MTU in layer2(Ethernet) is 1500 bytes. My question is so fragmentation is happening at ...
S. M.'s user avatar
  • 398
0 votes
1 answer
558 views

What is the differences between flow control and access control?

We first apply access control methods to get access to the channel link followed by the flow control methods to stop the receiver from overflowing. Suppose we are using CSMA/CD in access control ...
S. M.'s user avatar
  • 398
0 votes
1 answer
146 views

Understand router Ip address and Mac address, Switch Mac address

Scenario:1 Suppose external Router R1 has interface a connected with interface b of the site Router R2. And Router R1 using IP address 80.0.0.0/8 for a. Router R2 has 4 subnets 80.0.0.0/10, 80.64.0....
S. M.'s user avatar
  • 398
0 votes
3 answers
413 views

How NAT router use layer4 contents in layer3?

I followed from this question and @PeterGreen's Answer , and come to know that NAT router working in layer3, but using layer4 contents(layer4 port number,layer4 checksum). My question is when layer3 ...
S. M.'s user avatar
  • 398
0 votes
2 answers
663 views

Acknowledgement, retransmission of layer2 is actually belongs to layer4?

I followed from this question understand that only transport layer responsible for acknowledgement. But I have read on book stop and wait, GBN, SR protocols uses acknowledgement, retransmission in ...
S. M.'s user avatar
  • 398
0 votes
2 answers
715 views

What is responsibility of different layers of OSI model and intermediate devices between sender and receiver when data packets are lost/corrupted?

Suppose sender sending some data to receiver and there are 3 routers between them. R1, R2, R3 are routers. Now sender starts sending data packet D through it's AL, TL, N/W L, DLL,PL to router R1 ...
S. M.'s user avatar
  • 398
1 vote
1 answer
432 views

EtherType multiplexing used by LLC layer

What's the type of multiplexing used by Ethernet (LLC layer)? It says in Wikipedia "The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (e.g. IP, ...
ragnar's user avatar
  • 17
0 votes
2 answers
267 views

Ethernet compatibility

I am improving my knowledge about the Ethernet protocol. During my study, I noticed that they are multiple versions of the protocol. Example: 2.5GBASE-T and 5GBASE-T and 100BASE-TX. I wonder depending ...
ragnar's user avatar
  • 17
0 votes
0 answers
29 views

Why collision domain occurs in hubs but not switches [duplicate]

if anyone knows the actual point and in depth answer to my question please help. the links in the comments didn't helped at all Most of the websites which i saw are just vaguely saying that collision ...
vinter's user avatar
  • 101
1 vote
2 answers
516 views

Best way to configure layer 2 daisy chain with 2 layer 3 switches/gateways at either end?

I would like to implement a linear daisy chain for the purpose of transmitting internet over a considerable distance. One motivation behind the use of a linear daisy chain for this problem is that ...
Doug's user avatar
  • 13
0 votes
1 answer
443 views

Total delay of virtual circuit switching? [closed]

We know that virtual circuit switching(VCS) has both features of circuit switching and datagram switching. It uses connection oriented path but may or may not dedicated that means resources may or may ...
S. M.'s user avatar
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