Questions tagged [ethernet]

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

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8answers
7k views

What do the positive and negative (+/-) transmit and receive pins mean on Ethernet cables?

So I'm trying to understand the pin layout of an Ethernet port, specifically for 8P8C which to my understanding is the most common. Of the eight pins, only four are apparently used for communication, ...
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2answers
283 views

RS_FEC OVERHEADS ON 25GBASE-R

I'd like to estimate the effective capacity of the 25 GbE link (25GBASE-R) to transfer an Ethernet payload of a particular size when Reed-Solomon RS(528,544) forward error correction (RS-FEC) is ...
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1answer
924 views

How to change network buffer of network interface to get NIC card errors? [closed]

I tried with sudo ethtool --set-ring eth0 rx 1020, but I'm getting this error: Cannot get device ring settings: Operation not supported` Is there any other way to change network buffer to simulate ...
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0answers
54 views

Why wifi and ethernet use the same frame format from tcpdump -d output?

If I execute tcpdump -i wlan0 tcp -d or tcpdump -i eth0 tcp -d I get the same output (000) ldh [12] (001) jeq #0x86dd jt 2 jf 7 (002) ldb [20] (003) jeq #0x6 ...
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1answer
120 views

Scaling fragment offset

I studied that fragment offset has 13 bits. At transport layer segmentation is done considering the the MTU at lower layers (network layer, data link layer). Ethernet format says the maximum data ...
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2answers
189 views

Can you stack Cisco 350 28P PoE switches with CAT5E or CAT6 ethernet cables?

I have four new Cisco SG 350 28P PoE switches, but no stacking cables. Can I use CAT5E or CAT6 ethernet cables to accomplish stacking them?
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2answers
49 views

Why do all leaf nodes in an E-Tree service belong in the same subnet?

I'm studying the CCNA R&S at the moment and I'm a bit confused about why E-Tree services require all leaf nodes to belong in the same subnet, despite the leaves only being able to send layer 2 ...
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2answers
84 views

Is Spanning Tree Protocol Needed?

If there are two switches connected directly together with two links is spanning tree protocol needed? please see below snippet
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2answers
125 views

Internet Entry Point

I am learning netwroking and would like to ask about how exactly we (as a casual user) get connected to internet and how a datacenter would do the same thing. i bet they dont use a regular modem which ...
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3answers
9k views

What is “industrial ethernet”?

When a teacher introduced it to us he gave the impression that it specifically covers some Siemens technology; that it's even a Siemens trademark. I believe the term covers something more general, ...
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1answer
206 views

Sending TCP packet to the other device without connection

I think the sending packet to other device works like the following. 1. The server device listens with port. for example 80 2. The client connects to the server devices. for example, the port of ...
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1answer
68 views

10 Gbit Network without Additional Switch

I've a question about my current setup: I don't want to buy additional 10G SFP+ switch. May I use R710's new Intel 10G Ethernet's second port to connect additional servers into my network? What is ...
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2answers
317 views

Which physical layers are part of PROFINET?

I understand that Profinet builds on Ethernet, but I am not quite sure how. Ethernet has a lot of different standards for the physical layer, eg 10Base2 (coaxial, 10 Mbit/s), 100Base-TX (twisted ...
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2answers
853 views

Confusions regarding byte and bit ordering of Ethernet Frame

I understand the concept of Endianess regarding numbers because there the bit significance is well defined. But when applied to things like Ethernet frame or Mac address, things are so clear to me, ...
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1answer
361 views

Weird Wireshark protocol list (eth:ethertype:ip:data where is the “udp”?)

I am capturing incoming and outgoing WAN to LAN data at a particular host on my LAN (i.e., the one actually receiving/sending the data). Sometimes I get anomalous captured frames that are missing the ...
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2answers
17k views

Why is the ethernet payload fixed between 46 and 1500 bytes?

Can anyone explain why the ethernet payload size is fixed between 46 and 1500 bytes ? I read so many articles never get the clarification?
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5answers
199 views

How do two computers with different speeds communicate

This is one extremely basic and probably equally dumb question that I just couldn't ever find a definite answer to. Suppose we have 2 computers one that can transmit data at say 10 bits per second (A)...
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2answers
91 views

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 ...
8
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1answer
5k views

Remote sniffing with ERSPAN to the desktop

I know how to use both SPAN and RSPAN. If I'm not wrong, ERSPAN leads us to the possibility of remotely monitoring a router through an IP network and a GRE tunnel. However a tunnel end-point is needed....
2
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1answer
320 views

Cisco nexus 9396PX TX output discard on 40G interface without link congestion

We have cisco nexus 9396PX with N9K-M12PQ module (12x40G Interface), We have 8x10G L3 LACP bonded connectivity with our ISP and so far so good no issue at all. but recently we migrated that LACP LAg ...
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2answers
13k views

RJ45 Cable only has 4 wires

The cable that connects to my rj45 only has 4 cables, blue, orange, blue stripe, orange stripe. When I connect them to their corresponding ports, there is no internet connection.(Blue = 4, Orange = 6, ...
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5answers
5k views

How exactly does an Ethernet collision happen in the cable, since nodes use different circuits for Tx and Rx?

I am trying to understand how a collision occurs in Ethernet, especially when a duplex mismatch exists or when on a legacy Ethernet network two nodes transmit simultaneously. Everyone explains the ...
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3answers
3k views

Why can a packet sniffer in an Ethernet LAN obtain all packets sent over the LAN?

Why can a packet sniffer in an Ethernet LAN obtain all packets sent over the LAN? In a limited broadcast environment, such as in many Ethernet LANs, a packet sniffer can obtain all packets sent ...
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1answer
76 views

Is there a MTBF related to port linking?

During a firmware upgrade, I've noticed one problem: An equipment keeps linking/unlinking on a specific port of a PowerConnect 3548(stp portfast, switchport access mode). I've contacted the local ...
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2answers
741 views

What all fields is the FCS/CRC in the trailer of the ethernet frame calculated over?

I am unable to find the correct answer to this question all over the web. Wikipedia states The FCS value is computed as a function of the protected MAC frame fields: source and destination address, ...
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1answer
266 views

Using an Ethernet cable and USB Ethernet adapter at the same time?

What would happen on using an Ethernet cable connected to one network and then plugging in another Ethernet cable but using an USB Ethernet adapter from a different network. Would it connect to both ...
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1answer
342 views

How does Kismet find WIRED devices when scanning Wi-Fi? [closed]

In an effort to better secure my Wi-Fi network by finding its weaknesses and mitigating them, I have employed the use of Kismet, a well known Wi-Fi security scanning tool. When I use Kismet to scan ...
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3answers
60k views

How does a switch learn a switch table?

Say the switch table is empty. If computer A sends a frame destined to computer B, the switch will broadcast asking who has the mac address of B. What if C suddenly sends a frame to A? What is the ...
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2answers
87 views

Circuitry for sending and receiving bit streams in networking

To my little knowledge , I know that digital signals are transferred over continuous EM signals . At the receiver end a bit 1 is detected when the amplitude crosses a certain threshold and a bit 0 is ...
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2answers
15k views

Role of SSAP and DSAP in Ethernet DIX frame format

I am well aware of Ethernet DIX format. But, the role of SSAP (Source Service Access Point) and DSAP (Destination Service Access Point) in IEEE802.3 Ethernet frame is confusing and always expressed ...
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3answers
2k views

Is there any reason to use a hub over a switch?

Given that hubs are essentially the same as switches, as far as I know, except they share bandwidth between all connected devices, while switches do not, resulting in faster connections. I am simply ...
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3answers
115k views

How does gratuitous ARP work?

Does gratuitous ARP work like a normal ARP request? Why is gratuitous ARP used for HSRP?
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2answers
187 views

what does the flag and mtu means in here

Reading some logs from my system it states eth0: flags 4163 < up, broadcast, running, multicast> mtu I am not sure what is the meaning of the flag here down below I see eth1,2,3 has the same flag ...
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3answers
520 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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1answer
486 views

What is the use of Phy and MAC chip?

Is it mandatory to have a MAC and PHY chip? Are these two chips within a NIC CARD? As I understand, these two chips are connected using RGMII or SGMII or xaui.
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2answers
6k views

Assign IP address using Router and Switch (DHCP)

I currently have a router and I was wondering if I could connect one of the LAN ports to a switch to connect more devices through Ethernet. I need each device to have a local IP address. I know that ...
4
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3answers
177 views

The recommended settings for giga ethernet connected to Ethernet port

What is the recommended duplex and speed configuration for giga ethernet port connected to legacy ethernet (10 mbps) port and there is no available duplex command available on the ethernet side? If ...
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1answer
55 views

MAc address or IP address? which one gets used from my pc to router? [duplicate]

Question 1) which one is used nowadays? NAT or PAT? Question 2) as I knew, when my pc requests some website, what happens is , the data(packets) from my pc go to router. then router makes the request ...
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0answers
234 views

How Cisco Line Protocol works

How do Cisco Line Protocol works ? I could read this: https://www.cisco.com/c/en/us/support/docs/content-networking/keepalives/118390-technote-keepalive-00.html, about Ethernet Interfaces keepalive ...
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2answers
5k views

Why maximum length of IP, TCP, UDP packet is not suit?

From many tutorials, I get follow knowledge(maybe I'm misunderstood) : maximum of an Ethernet packet is about 1500 bytes. maximum of an IP packet is about 65535 bytes. maximum of a UDP packet is ...
3
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1answer
487 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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1answer
5k views

What is the difference between RJ45 connection standards WE/SS and TE-AMP and when and where are they used?

I recently decided to run some CAT6 cabling and wanted to ensure that my Crimpmaster RJ45 die would work fine for the CAT6A shielded connectors. I noticed that several people had trouble using the ...
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2answers
1k views

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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1answer
228 views

Does the PHY signal interframe gap to the MAC?

I'm trying to decode an Ethernet II frame with type instead of length indication. Theoretically this should be done by receiving and storing the data between start of frame and interframe gap. However ...
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2answers
6k views

How do routers traverse packets to their destination?

Sorry in advance for such a noob set of questions. I understand that when set with the task of sending a packet to its destination, a computer first checks that the IP address of the destination is ...
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1answer
13k views

Ethernet frame IG/LG bit explanation - Wireshark

I have a screenshot of an ethernet packet frame from Wireshark. I need to explain what is the meaning of these marked lines (with dots and zeros). I searched in web, but still I don't have an answer. ...
4
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1answer
859 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
404 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 ...
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4answers
597 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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1answer
63 views

Which layer and protocol takes care of power-down and power-up of ethernet port

Which layer and protocol takes care of power-down and power-up of ethernet port (based on cable connected or disconnected) in a Linux machine. I think it (power-up and power-down) will be taken care ...

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