Questions tagged [layer2]

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

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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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1 vote
1 answer
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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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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 ...
2 votes
1 answer
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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 ...
1 vote
1 answer
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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 ...
0 votes
0 answers
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OTN frames: How is partial filling and failed decoding dealt with?

I'm trying to understand some OTN concepts that are not immediately obvious from the G.709 standard documents. I'm curious about the case of Ethernet frames packaged into ODU frames. in case the ...
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2 answers
44 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) ...
8 votes
6 answers
2k 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 ...
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2 votes
1 answer
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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 answers
135 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 ...
1 vote
3 answers
132 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 ...
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1 answer
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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 ...
2 votes
1 answer
49 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-...
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1 answer
59 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?
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2 answers
152 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 ...
1 vote
1 answer
102 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 ...
1 vote
1 answer
83 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 ...
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1 answer
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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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1 answer
74 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....
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3 answers
144 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 ...
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2 answers
219 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 ...
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2 answers
212 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 ...
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1 answer
152 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, ...
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LLC layer: what's the multiplexing principle? [duplicate]

I wonder what is concretly the multiplexing principle done by the LLC layer. Can you please explain the principle with practicle example ? Many thanks for your help
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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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1 vote
2 answers
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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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1 answer
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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 ...
0 votes
1 answer
289 views

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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1 answer
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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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1 vote
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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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1 answer
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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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1 answer
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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 ...
3 votes
2 answers
494 views

Why the two connected routers via PPP doesn't use ARP but ethernet use ARP?

I have read from @Ron Maupin's answer of this question that your two routers are connected via PPP (this is not uncommon), ARP will not be used , but if the two routers are connected via ethernet, ...
1 vote
3 answers
657 views

Is there a ping equivalent on layer 2?

You can use ping to measure RTT between you and an IP host and thereby confirm connectivity. Is there an equivalent that can be used on L2/Ethernet with MAC addresses? i.e. l2ping AA:BB:CC:DD:EE:FF (I ...
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1 vote
2 answers
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How is P actually chosen in P-persistent CSMA?

I am struggling to understand how the probability value P is chosen for P-persistent CSMA for any particular station, what's the logic behind this.I have read from Wikipedia . P-persistent This ...
0 votes
1 answer
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Does creating frames done by device drivers?

If I got it right, TCP and IP packets are created normally by software running in the kernel. So when I as a user open up a socket of type TCP/IP and send a message, the kernel takes care of all those ...
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2 votes
1 answer
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Avoiding FPCs rebooting during RE switchover on Juniper EX8200 Switche

We have Juniper EX8208 chassis based switch running in a production environment. The switch has 2 REs running in active and standby role with RE0 being the primary routing engine. The device is ...
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1 vote
1 answer
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IGMP in multiple switches with multiple Senders and Receivers in same VLAN

I am trying to send multicast traffic from 3 Senders to corresponding Receivers in same VLAN (100) spread across 3 switches. I setup a Querier in one of the switch, but it doesn't seem to forward ...
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1 vote
2 answers
108 views

What layer 2 encryption can I run over a leased line with the underlay (MP-BGP with MPLS on top if it)?

My company has its branch sites connected to HQ using Ubiquiti airFiber24 HD. The company wants to acquire a leased line fiber connection to branch sites. We want to run our own encryption on top of ...
0 votes
1 answer
86 views

Does a router have multiple DLLs inside?

I came across a practice question of true/false answer type . The statement is: "A router has single network layer that will interact with 2 Data link layers" . Ans:True (no explanation ...
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3 answers
378 views

No internet access on VLAN

I'm trying to setup VLAN on my TL-SG3210 (3.0). I created simple VLAN: vlan 10 name "vlan10" Then, I assigned port 2 & 3 to VLAN. I also created interface: interface vlan 10 ip ...
1 vote
0 answers
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What are non-learning and learning VLANs?

I was going through some IEEE standards for switches (IEEE 802.1aq and IEEE 802.1Qca), and came upon a terminology of learning and non-learning VLANs. I read that learning VLANs are used in Shortest ...
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2 answers
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How do layer-2 devices (bridges/switches) join a multicast MAC address?

I was going through the IEEE 802.1Q (2018) standard on my own. The standard speaks about group addresses, and how these group addresses are learned by transit bridges, which is all fine. But how do ...
1 vote
4 answers
344 views

Do layer 2 protocols allow hosts to communicate without being on a network?

Please go easy on me as I'm just a noob in the networking space. As far as I have learnt, layer 2 protocols use MAC addresses for communication, which doesn't really depend on what network you're in ...
0 votes
0 answers
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How is it possible that CSMA/CA works in areas with a lot of users within a small radius (e.g. rallies, concerts, etc.)?

My understanding of CSMA/CA is that devices listen until a Wi-Fi channel is idle before sending packets. If a collision still happens, then the devices waits a random interval before attempting to ...
0 votes
2 answers
59 views

Is there a layer 2 protocol that can be used to send arbitrary data?

I would like to design several devices that receive simple commands from a single controller device all residing on the same layer 2 switch. Is there a protocol that allows me to do this without ...
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3 answers
98 views

Is it possible to have a local area network with only layer 1 and not layer 2 of the OSI model?

I know the OSI model has seven layers. Can you consider a LAN to exist without layer 2 and just layer 1? The answers that I saw on Quora were not clear. Some of the answers on Quora came close to ...
1 vote
1 answer
199 views

100BaseTX Ethernet Idle code ("/I/") 4B/5B origin

While searching how the PHY LINK status is determined, I stumbled across this answer : In 100BaseTX Ethernet, link pulses aren't used, but instead, link status is detected and maintained via the ...
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1 vote
2 answers
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Proxy-ARP when the destination device is connected to the same layer-2 switch, but belongs to a different subnet

I have recently learned about Proxy-ARP and am slightly confused about what would happen in the following scenario. Let's say I have two host devices A (IP: 10.0.0.10/24) and B (IP: 10.0.1.10/24) that ...
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