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

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1answer
36 views

Layer 3 switch model 3950 encapsulation

How to ensure trunk link in the switch are using dot1q encapsulation, when dtp (dynamic trunking protocol) is enable along with vtp. I know when manually setting trunk links, you can force the trunk ...
1
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1answer
15 views

Protocol Identification

At the data link layer, many protocols run simultaneously, or one after other, right? my question is how date link layer knows about which layer 2 protocol to run and at which sublayer?
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3answers
56 views

Why do clients request a MAC via ARP, if the router knows the local LAN's MAC addresses already?

If I have an infrastructure type network, why does a local PC send out an ARP request for a MAC? Doesn't the router know the MAC addresses already, since it is using at least Layer 2? Does it do ...
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3answers
52 views

Can Ethernet II frame's Type be Layer1's or Layer4's protocol?

The Ethernet II frame's Type field can be IPv4, ARP, so it can be Layer2 and Layer3's protocol. This is a snapshot of frame captured by WireShark. But I have a question, whether it can be other ...
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1answer
31 views

Connecting Layer 2 switchport to layer 3 port

I have a config that I am trying to bring up, and in my mind it should work, but perhaps I am missing something. The idea is that one end of the link is a layer 3 interface on a router. The other end ...
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2answers
33 views

Layer 2 Routing between subnets and VLANS [closed]

I am studying for my Networking exam and from what I have pieced together from other posts on here is this. Please correct me if I'm wrong: Layer 2 switches can only route packets between different ...
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0answers
22 views

What is the network address of this subnet? [duplicate]

I need help solving this question as i am not very good in networking lingo. Insert the Layer 2 and Layer 3 addresses used the following transfer from computer A to computer B. How many IP Addresses ...
0
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1answer
23 views

Separate network for test systems

I often read that you should put customer machines into a separate (testing) network like a DMZ. Is a layer 3 device (switch/router + firewall) a good option for this? Since some ports need to be ...
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0answers
23 views

Why is RTS/CTS optional for IEEE 802.11?

In wikipedia it is stated: Request to Send (RTS) frame: The RTS and CTS frames provide an optional collision reduction scheme for access points with hidden stations. A station sends a RTS frame as ...
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1answer
19 views

In Slotted Aloha Protocol divide up time into slots,each slot corresponding to one frame,is this same TDM?

In Slotted Aloha Protocol divide up time into slots,each slot corresponding to one frame,is this same Time Division Multiplexing?
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0answers
19 views

Fibre Channel Forwarding between devices behind single NPIV port

How does Fibre Channel switch with NPIV enabled port operates, when two devices behind the single NPIV port want to communicate with each other? e.g. Ethernet switch, would just drop frames, if ...
3
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5answers
375 views

Is there a Layer 2 address advertising protocol?

I needed help in understanding if LLDP/CDP is the Layer 2 equivalent to RIP or say any Layer 3 route advertising protocol. If not,is there a protocol that advertises the MAC Address Tables among ...
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1answer
36 views

Routing and Bridging on a Layer 2 or Layer 3 device

The thing that intrigues me is, say I have a router and I configure it’s interface as a Layer 2 and have 2 Vlans on the same router. So if I want to transfer the data from one Vlan(say VLAN-10) to ...
4
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1answer
526 views

Do we send ack frames in ethernet? if not then how does a router know if its neighbors are down or not?

So first off, do ethernet sends ack frames or not? if it doesn't : then how does a router know whether its neighbors are down or not? if it does : then is it cumulative ack with an ack timer or one ...
0
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1answer
37 views

Frame transfer from one switch to another configured with VLANS

Hi, My question is related to the Vlan. And this question would consist of 2 parts. 1)Would Switch 1 know all the devices present in Vlan 2 or Vlan 3, including the ones present in the Switch 2. ...
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1answer
21 views

How to show all data (bitstream with preamble, SFD) on Ubuntu with an Intel Ethernet Interface?

On my PC I have an Intel Ethernet Connection I217-LM with e1000e driver. If I receive packets in Wireshark or any libpcap based tool, the received ethernet frames start with Ethernet II frame and end ...
1
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1answer
59 views

Why are Frame Relay, ATM and MPLS called “Layer-2 VPN”?

A VPN results, when two physically separate networks become virtually one bigger network. But Frame Relay, ATM and MPLS don't do that, they just connect two network, but they don't unify them. So ...
3
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2answers
806 views

Does it make sense to map a VLAN to each LAN?

I saw a picture of a network-structure with VLANs in it: Why would somebody structure their network like this? Does this even make sense? I mean, they are in a different LAN, why then mapping a VLAN ...
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1answer
92 views

Bridging networks without NAT: how it's done?

I have quite limited networking experience, so probably i'm asking about very simple things. I'm reading about linux bridge interfaces, and documentation states that there is no NAT by default and ...
0
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0answers
21 views

Bit Stuffing Complication (Data Link Layer)

In Bit Stuffing technique, where we add an extra bit in our frame, so that a particular sequence of bits in our actual data doesn't match the EFD (End of Frame Delimeter); Consider: Data = 110001001, ...
5
votes
1answer
72 views

ETH II vs 802.2 LLC/SNAP

I have a project where there is a custom implemented layer 2 protocol. An engineer before me decided to use what I'm used to as the Ethertype field as a size field. For awhile this looked right ...
1
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2answers
56 views

1 Layer 3 Switch, 2 Vlans, 2 Subnets, and an Unmanaged Switch

Is it possible to for a device with the ip address 192.168.0.1 and Vlan 100 to communicate with an other device with the ip address 192.168.1.1 and Vlan 200 with the following architectures Senario 1:...
3
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2answers
370 views

Is there 64k range VLAN support?

All i have learnt and understood so far about VLAN is - we can create a max of 4k VLANs (subjected to platform capability). However, as per the protocol 802.1Q there is only 12 bits kept for ...
2
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2answers
106 views

Routing steps on a serial port

"Because the exit interface is not an Ethernet network, R2 does not have to resolve the next-hop IPv4 address with a destination MAC address." - this is routing from serial port , can anyone explain ...
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1answer
83 views

How would you map a network at layer 2 without CDP or LLDP?

I'm on an ASA right now and can path my directly connected next hop devices via IP address, but I want to make sure there isn't a switch in between. Another related question, when I "show arp" it ...
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1answer
55 views

Advertise routes in simple switched network

I'm trying to build a fairly simple network. I've got a few devices acting as the network core, which are basically all connected to each other by a simple Ethernet switch. Each of these devices (I ...
4
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2answers
155 views

High availability LAN segment with Cisco ISR4451X and 2 x Netgear GS724 - Port-channel vs. BDI vs. BVI?

I have a customer that is getting a new 1Gbps ISP connection and wants his servers connected across two switches for redundancy and protection from: failure of a router port failure of a network ...
1
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2answers
91 views

CSMA/CD - CSMA/CA switch mix

Suppose I have 2 switches; one CSMA/CA (gigabit) and the other CSMA/CD (gigabit), would they work together when connected and if so would there be any dip in network performance? Thanks in advance!
0
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1answer
64 views

How might I test layer2 latency over ethernet without a target IP address? [closed]

Is there a way, via standard ethernet layer2 protocols, to test latency to a device without using it's IP address? Background: I have a fibre "box" provided by my ISP physically connected to my ...
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7answers
3k views

How LAN works in video games if only one station is permitted to transmit?

I've read the in a LAN the data is transmitted in packets so as to allow only one station to transmit at a given time, so how could this be applied in video games LAN parties if only one device is ...
2
votes
2answers
167 views

What is the difference between CAM and FIB table?

As far I know, CAM table is Content Addressable Memory table where MAC address is stored FIB table is Forward Information Base table which is a dynamic table that maps MAC addresses to ports. Both ...
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3answers
163 views

Cannot Ping Linux PC through L2 Switch

I’m a little embarrassed to be asking this but here goes. In a training video for CCENT, I see a switch connected to 2 PCs that are pinging each other on the same subnet. I try to replicate the ...
3
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1answer
67 views

Does an ethernet checksum include padding bits?

For ethernet II (aka ethernet DIX) frames that are padded to contain 64 bytes total, is the checksum in the last 4 bytes computed with the padding bits as input?
1
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1answer
227 views

SD-WAN vs MPLS VPN

Citing wikipedia on MPLS VPN There are three types of MPLS VPNs deployed in networks today: 1. Point-to-point (Pseudowire) 2. Layer 2 (VPLS) 3. Layer 3 (VPRN) I am confused about the difference ...
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0answers
60 views

type of architecture leaf spine

Please I would like to know, what is the difference between the two types of leaf spine architecture (layer 2 and layer 3) and, is it possible to have a topology with both types? So the difference ...
0
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1answer
96 views

Layer 2 ARQ protocols

Some authors (i.e. Tanenbaum, Stallings) reference ARQ protocols as layer 2 mechanisms for handling errors. Even this page from Wikipedia says that these protocols reside in the Data Link or ...
4
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3answers
628 views

Error Detection across OSI layers confusion

Confusion: How does the transmitter know that his information( bits in physical layer, frames in data link layer, packet in network layer ) was transmitted correctly to the receiver? I know that in ...
3
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1answer
62 views

Example VLAN without any Router — Security Problems?

I was reading a VLAN setup walkthrough, and the author had an interesting idea for setting up VLANs without a router (which you don't normally see). At first glance, this doesn't seem like it actually ...
3
votes
1answer
58 views

VLAN Isolate Setup

How can I set up a switch so that devices on one switch port are isolated from devices on other switch ports? I'm guessing this should be done with VLANs, but I'm open to other options as well. ...
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1answer
26 views

Package Delay (Theory) [closed]

I have a question to the following excercise that I have from school. How big is the delay of a package if it gets send via satelite (~35km above earth)? I assume I need to calculate this one. ...
1
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1answer
114 views

What is the correct CSMA p-persistent algorithm?

After reading some books and sources I understand that the CSMA p-persistent protocol works like this: if the channel is idle, it transmits with probability p, and with probability 1 - p it defers to ...
0
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1answer
561 views

Router vs VLAN in networking?

Why do we need Routers at all when we have VLAN ? Vlan breaks the broadcast domain. Vlan along with the use of SVI can be used for routing. So why do we need routers for in networking ?
0
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1answer
230 views

Does a switch generate TCN BPDU when it elects a new root bridge?

what are the scenarios in which a switch generates a TCN BPDU other than when a port goes down or come back up? switch-1---------------switch-2----------------switch-3 (root bridge) (Non Root)...
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2answers
80 views

Is it possible to have a single port serve a layer 2 and 3 link simultaneously?

We are moving to a new L2 fiber network and i'm having trouble figuring out how to connect the DR. We are using a spoke and hub topology, with HQ as the hub. The branch locations all have unique ...
11
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2answers
5k views

VXLAN vs VLAN over layer 3

I read that one of the benefits of VXLAN over VLAN is that it can spawn across WAN and multiple layer 3 networks by creating overlay layer 2 networks. However AFAIN VLAN can also do the same using ...
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2answers
159 views

Does a router divide a LAN into two seperate LANs, or a single LAN with two subnets?

The figure below is part of a networking homework question. The question asks about the source/destination IP and MAC addresses of frames sent throughout the system. My question doesn't touch on that ...
4
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1answer
1k views

What's use of Port Isolation vs traditional VLANs?

I've seen several switch products advertising port isolation feature as "way to limit ports communication without configuring VLANs" and it sounds quite... sketchy? If i understand it correctly port ...
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2answers
140 views

Why Ethernet was chosen to be the primary protocol + why carrier ethernet was created?

I'm currently trying to investigate the extra benefit that Ethernet has to offer for the internet today. As far as i investigated & know, Ethernet gives us a new hardware, cables and functionality ...
6
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4answers
2k views

Why preamble is not considered a part of the Ethernet Header?

If I search where does my data start in an Ethernet frame, I get a common answer which says TCP header( 20 bytes) + IP header ( 20 bytes) + Ethernet header( SA + DA + Type) i.e 14 bytes. So, in short ...
1
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1answer
46 views

L3 routing between switches with some VLAN's trunked

During a migration various L2 equipment will be replaced with all Cisco L3 switches and over time traffic migrated to routed subnets instead of trunked. There are two straightforward approaches that ...