Questions tagged [ethernet]

For questions relating to Ethernet networking, as defined by the IEEE 802.3 standards.

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Ethernet's frame format, length or EtherType?

Ethernet defines a 2 byte header for the payload's length in its frame format. This header has an ambiguous meaning: if smaller than or equal to 1500 it represents the payload length. if ...
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467 views

Odd Wired/Wireless Behavior Difference with Cisco Switch and Airplay (Bonjour) Device

Summary On a network (Cisco 2960E) with many Apple products, when I connect a computer via hard ethernet it cannot see Airplay devices (Airport Express) that it can see when connected via WiFi (WiFi ...
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586 views

How does an Ethernet hub work internally?

I have a Cisco WS-C412 Ethernet hub. Am I correct that internally all the Rx and Tx ports connect to a single wire/bus? Like here, where three NIC's are connected to first, fifth and ninth hub port:
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1answer
837 views

Can I aggregate multiple uplink ports between Ethernet switches?

Disclaimer: I'm not a network engineer; I just have to try to do a good-enough impression to solve this problem. We have two rooms in our office. In the first, I would like to put a large copper 10-...
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1answer
15k views

What is the voltage used in ethernet lines (UTP Cables)?

I am asking this because after doing some research I found some conflicting information. First, on Wikipedia page on Ethernet physical layer I found that the voltage on the lines is 2.5V. https://en....
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515 views

How does a NIC know where the start of a frame is?

A question popped into my head today and after a quick few searches on google, I have no idea. When a device is sent a frame there is a layer 1 header/preamble saying the length and layer 2 protocol (...
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2answers
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Ethernet SNAP frames - decision of type for upper layer still possible?

As stated in IEEE 802.3 section 3.2.6 the former Ethertype field can be used as a length field with a value <= 1500. Now I wonder how such packets are handled regarding the upper next layer. Can ...
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1answer
916 views

How does signal return loss affect network performance

Yesterday we measured a network with a Fluke network tester. Almost all cables failed the test, because of a too high return loss. Then we tested one of the failed cables using a 'real world' test. ...
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1answer
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Behavior of LLDP packets through tagged port

I have this simple topology - [S1][p1]----[p2][S2] Port p1 of switch S1 is connected to port p2 of S2. And port p2 on S2 is tagged. My doubt is if an LLDP packet is sent from p1 to p2, considering ...
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How does the switch analyse the EtherType field in Ethernet frame?

What exactly happens when switch receives the frame with given EtherType? Does it analyze it at all or only looks if the TPID is present?
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1answer
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Ensuring Network Stablity

I recently became the IT guy at a remote school with onsite staff. The network setup is a bit messy right now. I am curious about the best standards to use. Below is a map of the current network that ...
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2answers
396 views

VLANs isolating networks (VoIP/Wi-Fi)

I have to set up our network in our new office. I'm no networking expert (developer), but I need some input and advice here for some things I wonder about. I have purchased the following: 2 x Cisco ...
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2answers
7k views

Ethernet keystone jack color conventions?

In a similar vein as this question... Are there any conventions or standards that recommend a color scheme for the colors of Ethernet keystone jacks?
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1answer
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How to troubleshoot reason why ARP replies from ISP are not forwarded through our switch?

At one of our offices, a new ISP recently installed an Internet connection via Radwin microwave radios, going to an E1 line back to the capital where their routing equipment is. There is a very ...
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466 views

What is EtherType 9C9D?

An ISP came and set up their radios the other day. After connecting my router to the radio and configuring it with the IP address, netmask, and gateway which they specified, I can't ping their gateway ...
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1answer
512 views

Link pulse when autonegotiation is off on FE, GE Ethernet

According to Wikipedia about link pulse, link pulse is used to detect link failure/L1 status. Autonegotiation on FE and GE use link pulse mechanism. When speed and duplex are forced and ...
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1answer
834 views

Creating multiple trunk ports on a Cisco ME3400

I have a cisco ME 3400 switch . And I have configured fa0/23 as trunk port and connected this to a router for carrying multiple vlan traffic. And i have created some vlans eg: 1500, 1501 etc and added ...
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0answers
236 views

IOS XE minimum frame size

I recently encountered an issue upgrading from an IOS device to an IOS XE ASR 1000 router concerning Ethernet Over SONET (EOS). VLAN tags are used to map traffic from the hub router to SONET ...
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5answers
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What is the main purposes of ARP CACHE in the Switch?

I know that when a PC send a packets to any remoter router then first of all it checks out the Router MAC address which is connected with it, but it gets this MAC Address of Router from ARP Cache, ...
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4answers
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How does DHCP assign an IP address?

I understand that IP address is a unique address to identify a machine in a network. But for the first time when i Plug in say ethernet cable of a network to my PC's Ethernet Port, how the IP address ...
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24k views

Is it possible to access more than one VLAN?

If I have a layer 2 switch, is it possible to access two VLANs from one computer? VLAN1: 192.168.1.x with netmask 255.255.255.0 VLAN2: 192.168.2.x with netmask 255.255.255.0 If my computer has only ...
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417 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 ...
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4answers
596 views

What is the difference between Ethernet types, considering bandwidth?

Different types of Ethernet (standard Ethernet, Fast Ethernet, Gigabit Ethernet) have different speed of data transfer (10 Mbit, 100 Mbit, 1 Gbit). Why is that? On the physical layer, the speed of ...
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Trying to understand crossover cables

I'm trying to understand how crossover cables work, and am looking at this image: I can understand from the image that the transmission wires are swapping with the receive wires, and I know why that ...
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1answer
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Is Ethernet considered a reliable protocol?

Ethernet uses a sliding window to resend lost frames (error correction). It uses a sequence number to account for unordered frames (error correction). It has a frame check sequence to discard ...
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How does ethernet understand what is the upper layer? What are the values in Ethernet II field?

How does ethernet understand what is the upper layer of a frame? What are the values in Ethernet II field? Ethernet is in data link layer, so the upper layer is network layer. When processing at ...
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360 views

What is likely to occur with the frames addressed to x, if x is disconnected from the switch. then reconnected on another link?

I don't see how this could be a problem, as the switch table would remember the destination MAC address. My teacher says this is a problem and that the switch would need to reconfigure. could you ...
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Cisco IOS CLI — Difference between global configuration and console line configuration mode (using line console 0 command)?

Student here. Could someone please explain to me the difference between these two? I'm using a serial connection for this. Does the latter refer to one individual serial terminal session? Why would ...
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Since we ran out of IPv4 now, what does it mean for consumers?

I'm trying to understand what it means for users... Does it mean that some content will not load on websites, increasingly so in the upcoming year or so? Does it mean that certain CDNs or hostings ...
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1answer
503 views

What is meant by Jumbo frame ? what happen when a frame size is greater than the MTU size?

I know that the frames having size greater than the MTU size should be dropped . i.e, The Ethernet frame having size more than 1522 should be dropped . But my doubt here is what is Jumbo Frame ?
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936 views

Are normal packets ever combined into jumbo packets?

Do routers ever combine multiple small frames into a jumbo frame then split them up again on the other end? I know that most of the time it wouldn't make sense to do because you would add latency by ...
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rj45 - simulate interface “link up” state

My colleague told me today he saw some sort of RJ45 dongle that intended to simulate a "link up" state for the connected interface (for testing purposes). Can this be achieved by doing a specific ...
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Why the network switch drop the frame acording to ethertype/length?

I have a network switch IC , and I am using to the send BPDU packet. I can send packet with 2 byte ethertype/length field like this : 81 00, 80 00, 91 00 and some special hex number. But if I try to ...
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What are the reasons for ADSL to use ATM instead of Ethernet

I'm a newbie to networking and I wonder what are the reasons for ADSL to use ATM instead of Ethernet ?
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1answer
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Two computers connected by straight through Ethernet cable, communicating with APIPA addresses

Good day, I connected two computers together with an Ethernet straight-through cable. I did not configure any ip address, and after a while they both got APIPA addresses. Now they can ping each other ...
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644 views

100BASE-TX, PoE and PSTN over a single UTP Category 5 cable?

Is it possible to use a UTP cable for: 12V DC (~30W), 100BASE-TX Ethernet, and A single phone line, at the same time? 100BASE-TX should give me two spare pairs, can I use one pair for the phone line ...
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1answer
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Why bb:bb:bb:bb:bb:bb is non-unicast mac address?

For testing purposes decided to add static IP addresses to my router for some mac addresses. For simplifity I started with aa:aa:aa:aa:aa:aa and assigned ip 192.168.1.100. These combination has been ...
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2answers
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What does an Ethernet collision look like?

I have spent the last two hours trying to capture an Ethernet collision using wireshark and a few other tools in vain. I have hooked up 7 computers to a hub and Am transferring a large video file ...
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3answers
297 views

Are modems needed to connect routers?

I apologize for the stupid question; I'm trying to wrap my head around the basics of networking. Also, please feel free to direct me to the right SE forum, if this is not the right place. My question ...
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3answers
829 views

How fragmentation works in real world

I have one example scenario, let consider i am sending 1500 bytes of frame over the internet. which is passing through 576 bytes MTU capable router. My question is, Is that router will do the ...
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1answer
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standard results for gigabit ethernet iperf

I can't achieve good transfer rate through scp and I wonder if the network configuration isn't tuned up correctly. I've noticed some differences when running iperf through tcp vs udp. Are these ...
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1answer
972 views

Any ideas why Cisco 3560G switch isn't passing broadcasted Ethernet packets?

I have a 24 port Cisco 3560G switch that I'm using to try and pass broadcasted Ethernet packets. I have a computer plugged into one port, and a IEC-61850 GOOSE publisher plugged into another port. ...
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4answers
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Ethernet device works on certain ports on Ethernet switch but not on others

I have a small and inexpensive ethernet switch which is giving me some headache. For some reason some devices only work when I plug them into specific ports. The ports are not broken, as other devices ...
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1answer
486 views

What does MTU depend on?

I'm trying to understand what factors determine the MTU. For instance, why 802.11 has MTU of 2304 while Ethernet MTU of 1500? Are there restrictions of the physical medium or arbitrary design ...
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501 views

Does MACsec (IEEE 802.1AE) support multicast / broadcast?

In general, Ethernet supports both multicast and broadcast. However, once you start encrypting the payload, you need a key management. I am wondering if IEEE 802.1AE supports multicast and broadcast? ...
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Why is the 100base-TX maximum distance unchanged from the original specification on better cable?

I understand that the 100base-TX Ethernet standard is from 1995, and was originally designed for older and poorer grade CAT-5 cabling than what is now commonly available. With the introduction of the ...
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Autonegotiation disabled, different speed, hub

I am beginner in networking and I have two questions, because I can't understand it well. I know how auto-negotiation works, but what happens if two connected devices have different speeds and auto-...
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515 views

Chip to Chip communication over Ethernet MDI

Does anyone have any experience with the inter-processor communication over Ethernet MDI interface. Normally, I would connect two devices with the RJ45 connectors(with RJ45 ethernet cable) and then ...
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2answers
190 views

Are IP source and destination fields necessary on LAN?

When sending a packet from one computer to another over LAN, you send both an ethernet header and an IP header. The ethernet header has a source and designation MAC address, and the IP header has ...
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Get MAC address of directly connected network neghbor

I have a PC (in the successive diagrams pc1) equipped with a network interface that can be directly connected to another PC or to a managed switch. I want to be able to get the MAC address of the ...

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