Questions tagged [layer2]
For questions about the OSI layer-2 (data-link layer).
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Encapsulation and decapsulation basics for OSI layer
I have read that encapsulation takes place down the layers while decapsulation takes place up the layers. In essence, the encapsulation starts at Application layer all the way upto Physical layer.
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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 ...
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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 ...
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Chained wireless links, low network bandwidth
I have a simple L2 network consisting of two chained wireless PtP links.
[LOC A] -------> [LOC B] -------> [LOC C]
.4ms .7ms
Here is a list of the PtP bandwidths:
A -> ...
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How does connection-oriented service at data link layer ensure each frame is sent and recieved 'once'?
I am reading Computer Networks by Tanenbaum. It says that there can be three types of services in data link layer.
Unacknowledged Connectionless
Acknowledged Connectionless
Acknowledged Connection-...
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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 ...
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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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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 ...
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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!
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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 ...
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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 ...
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How do I set up a VLAN between an ESXi VM and Physical Hardware? [closed]
First of all, I am a total noob. The extent of my VLAN experience is setting up a guest network on a wireless router.
I have recently gotten a request to set up a public network requiring filtering ...
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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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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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ISP L2vpn setup query
I am new in here and I hope to find my answer.
I'm working on sub ISP company which provide internet and ipvpn services to customers through infrastructure of main ISP.
We have a central data center ...
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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 ...
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MTU and Fragmentation
Consider the following: NAS with 10G interface connected to 10G interface on switch. Client computers connected to switch via gigabit Ethernet.
Will there be any gain in performance if MTU size is ...
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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 ...
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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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When are MAC addresses used instead of IP addresses in the OSI model?
Okay, so I'm studying for the Network+ exam, and I've gone over the OSI model about a million times, and I understand most of it fairly well, and my studies are coming along fine. However, there is ...
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VLAN Tags and QoS
I have a bunch of phones that are tagged as VLANID 20 with priority 7. I have the router setup with VLAN Tagging as well to mark VLANID 20.
My question in terms of switches. Do the switches need to ...
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Inter Vlan Packet Transfer
I am trying to establish communication between 2 devices within different vlan. But I require a router for that. Can I send packets within different VLAN without having a router or a Layer 3 device.
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Why are there checksums for different OSI layers?
Can anyone clarify the question "why we need checksum in both layer-2 and layer-3 of OSI layer", Layer-2 would encapsulate the rest of OSI layers into a single unit.
If Layer-2 has a checksum, ...
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Understanding VLAN tagging
Let's say we have 4 machines connected to a layer 2, managed switch which is connected to a layer 3 switch. Say that 1.2.3.0/24 is routed to the layer 3 switch. Our goal is to have 1.2.3.0-63 usable ...
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Why use 'switching' term for packet switching
On a packet switching network, a router is required to route packets to different networks.
Why does packet switching uses the term 'switching' when a packet is a term for a layer 3 PDU and ...
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Regarding MPLS L2 Vs L3
I'm studying about MPLS Network, i've doubt on that i.e.,
what is the difference between MPLS Layer-2 Vs Layer-3 Network ?
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Cisco ME3x00 - QoS for layer 2 trunks
I have some ME3800's running 15.3(3)S which aggregate layer 2 circuits from customers. They all have a similar configuration of an incoming trunk on Gi0/1 and then Gi0/23 & Gi0/24 are layer 3 p-t-...
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How does IS-IS carry IP routes?
IS-IS runs natively on layer 2 of the OSI reference model. How will the routing be done in that?
My doubt is that layer 3 has the ability to do the routing. But, ISIS does not run in layer 3 rather ...
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HP 1910 disable layer 3 mode
Is there a way i can make HP 1910 works in layer 2 mode.
I check the web interface but not seeing anything
Also i enable the cli and went to system view but not seeing any thing related no ip routing ...
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How do I use my SP Ethernet connection between HQ and Branch for Layer 2 and Layer 3
I am looking to use my provider Ethernet Connection between our HQ and Branch to do Layer 2 and Layer 3. The Ip addresses I hope to use for the remote are those being advertised to the ISP using BGP. ...
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Is Layer 3 web auth with Layer 2 PSK more secure?
I have configured a Cisco WLC to authenticate users using External Web Authentication at Layer 3. Are client wifi connections more resilient against eavesdroppers with a pre-shared key at Layer 2 ...
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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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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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Inter-switch IGMP on a VLAN with two switches, and a multicast source per switch
I have a network consisting of two HP 2810 switched. Attached to each switch is, on one port, a multicast video coder, and on a different port, a decoder.
There are two VLANs - a control VLAN (...
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What document or standard designated ffff.ffff.ffff as the Ethernet Broadcast MAC address?
Simple enough, question is in the title. Was trying to find an official document or RFC which designated (or reserved) ffff.ffff.ffff as the Ethernet Broadcast MAC address.
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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 ...
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Is STP used to prevent all traffic looping or just broadcast and multicast?
Let's say we have 3 switches in a logical triangle, each switch connected to the other two. This provides an opportunity for a loop when multicast or broadcast traffic is traveling here. STP is used ...
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Does a switch understand packets? If yes, what is the frame terminology for?
I was a little confused between packet and frame. The confusion was based on, if a switch is a layer 2 device, how does it reads a packet from a layer 3 device, and where is the 'frame' thing which is ...
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UDP Over Ethernet - Where exactly and in what order will the UDP information show up in the payload of my Ethernet frame?
I need to capture UDP information coming to me via an Ethernet frame. I have a point to point connection by fiber with 1000BASE-X Ethernet. The information coming to me is in GMII format; which is ...
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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 ...
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Why PPP cares about network layer?
Why PPP have protocol field? Isn't whole purpose of partitioning communication system to have simple isolated subsystems?
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How are layer 2 broadcast handled
I'm reading a text (possibly outdated) and it states that large amounts of Layer 2 broadcast can degrade the performance of the workstations on the network - due to CPU interrupts.
Is it possible ...
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Can a router send ARP requests to hosts?
I play with libpcap in C recently to create an arp sniffer program that captures arp requests on the air. I came up with a strange effect. I captured arp requests from my router. I don't know if this ...
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What is the difference between ff-ff-ff-ff-ff-ff (layer 2 broadcast) 255.255.255.255 (layer 3 limited broadcast)?
Please explain the flow of traffic in each case.
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Do packets take the same amount of time when they are within the MTU?
Without considering application processing or deep packet inspection, do packets that do not fragment all travel through the network at the same speed?
For example, if there is a network with an MTU ...
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Lowest Possible Failover Latency
Let’s say I have two networking devices (either L2 switches, L3 switches, or routers), and the two devices have two ethernet connections between them: port 1 to port 1, and port 2 to port 2. If one of ...
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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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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 ...
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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?
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Mikrotik CRS vlaning and accounting [closed]
i have mikrotik cloud router switch .
First of all i want to set vlanning for layer2 separating in all IPs (clients) qua all clients can't access to another. For the 2nd step i want to have an ...
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