Questions tagged [layer2]
For questions about the OSI layer-2 (data-link layer).
394
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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 ...
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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
...
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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 ...
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1
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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 ...
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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 ...
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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 ...
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1
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91
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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,...
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2
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101
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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 ...
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101
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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 ...
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1
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219
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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 ...
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3
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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 ...
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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 ...
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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 ...
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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
...
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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 ...
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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 ...
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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
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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 ...
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2
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225
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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 ...
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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 ...
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542
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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 ...
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1
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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 ...
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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 ...
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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 ...
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108
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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)
...
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6
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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 ...
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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-...
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3
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194
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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 ...
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527
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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 ...
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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 ...
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1
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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-...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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....
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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 ...
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540
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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 ...
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540
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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359
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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 ...
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959
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Why or when do we need Layer 2 NAT? [closed]
What is the point of public addresses in Layer 2? Why or when do we need it? When is it healthy to use? Or is it even a common thing?
Sorry I am kinda new at networking and I just googled it but ...
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Does the length of a frame influence the likelihood of a collision?
Considering two separate analog signals on the same frequency transmitting digital data that represents a frame, from my understanding if any portion of the two signals overlap, this is a collision.
...
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Logs on my Cisco ASA show the public gateway (ISP router) is pinging the internal network, how? [closed]
Im (remotely) working with an issue where the network has intermittent drops. i suspect possible routing loop, but havent confirmed that yet.
In the logs of our Cisco ASA 5506, i see that the public ...
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Does a router work both on Layer 2 and Layer 3? [duplicate]
According to TCP/IP model router works at Layer 3. But when data has to be transmitted to different network it is based on IP address but hop-to-hop transmission is based on MAC address.
That means ...
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Passing Modbus TCP/IP nodes (connected in multiple VLANS, same network) via Toffino firewall
I have been assigned to check the security aspect of the below network shown in image.
When i asked question on security of individual modbus device, I was told to create individual vlans for each ...
