Questions tagged [ethernet]

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

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ISIS p2p on Ethernet media

I am looking for technical clarity on why someone should / shouldn’t use ISIS p2p topologies on Ethernet media. Ethernet is a broadcast medium , however if it’s configured as a p2p link with /31’s ...
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2answers
7k views

ARP Replies can they be Broadcast

I have been informed by certain networking professionals that ARP replies can and sometimes actually are broadcast packets instead of unicast. If and when would you use a broadcast ARP reply?
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1answer
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Run MACsec and VLAN in parallel?

MACsec (IEEE 802.1ae) adds a security tag to an Ethernet frame and encrypts the IEEE 802.1Q field, the EtherType and the payload field. If you want to use VLAN, you need the 802.1Q field to announce ...
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4answers
229 views

Is ethernet a term describing just the protocol or the interfaces also?

Is ethernet describing the protocol and therefore cat5 cables became labelled ethernet cables because they are used for this protocol?
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2answers
2k views

Load Balance NIC, Switch and Router (Redundancy)

I have two questions which I will separate to avoid confusion. I intend to build a network based on redundancy. There will be two pieces of every device, sometimes more than 2 such as NIC cards. I ...
7
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1answer
3k views

Position of source and destination IP in an IP packet

In an Ethernet frame header, the destination MAC (DMAC) is placed before the source MAC for obvious reasons (stations accept based on DMAC). But why is not the same thing maintained for destination IP ...
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5answers
2k views

Does a Layer 3 switch become a Layer 4 device when telnetting?

In order to Telnet to a switch (Layer 2) we create an SVI, thus a layer 3 point of contact is made. The switch inspects each packet sent from the remote client and responds to it so that it gets ...
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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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3answers
2k views

Ethernet Cable Orientation

I'm in an A+ course and was just working on wiring Ethernet cables. I was wondering, will an Ethernet cable function if the wires are reversed? Say instead of wiring 568B like striped orange, orange, ...
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2answers
30k views

What exactly is IPoE?

I am familiar with PPPoE but getting confused with the term IPoE. Is this same as usual ethernet with DHCP server? Does this have any auth built-in? How do I get authenticated? What can a client ...
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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 ...
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2answers
2k views

Ethernet padding value

When the data sent in an Ethernet frame is less than 46 bytes, extra padding needs to be added to the payload. The question is: Which is the value of that Ethernet padding? I'm asking since in real ...
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2answers
1k views

802.3x ethernet flow-control on user ports?

What is the best practice for putting 802.3x flowcontrol on a userport and does this inhibit performance if the application/system isn't designed for it? Eg) interface gig0/1 flowcontrol receive [...
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6answers
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SFP+ transceiver's ability to do 1GbE

I understand that most ports that support SFP+ transceivers can step down to allow an SFP to be plugged into it, but my question is around the transceivers/optics themselves. Can an SFP+ transceiver ...
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2answers
2k views

What is the reason for the different order of the Source and Destination in a L2 header?

A TCP/UDP header (Layer 4) lists the Source Port, then the Destination Port: An IP header (Layer 3) lists the Source IP, then the Destination IP: An Ethernet header (L2) and a WiFi Header (L2) lists ...
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3answers
9k views

Why do we have both MDI and MDI-X?

I understand which types of devices tend to use MDI or MDI-X, but why don't all devices just use one of them? It seems like Auto MDI-X was the solution to this but it still seems like all newly ...
6
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4answers
11k views

Toggle Switch for an Ethernet Cable

Is it possible to place a switch in one of the four/five wires of an Ethernet cable that will disable it? For my hardware project I would like the user to be able to disable the internet connection at ...
6
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1answer
380 views

Spanning tree question

I have the following setup: Distro Switch 1 <-> Distro Switch 2 || || Access Switch One cable is going from port 47 to Distro switch 1 and another ...
6
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2answers
418 views

How to connect a special device in a network

I have a question which is puzzling me. I have a couple of custom electronic devices (are identical, one is a master and the other is a slave) which implement only up to level 2 of the ISO/OSI layer, ...
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3answers
2k views

Posible to connect VLAN switch through dumb switch?

Is it possible to connect a VLAN switch into a dumb switch ? The router will know how to reach network connected by a VLAN through the dumb switch please ? No edge effect ? By example, a schema of ...
6
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3answers
9k views

Is Ethernet a protocol?

When I googled I found a lot statements about this. Like.. Ethernet is not an application protocol. But I'd still give it the description "protocol". A network protocol defines rules and ...
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2answers
1k views

Converting to extended STP system-id

We have some Cisco switches running PVST. I need to convert them to use extended system-id so I can use high numbered vlans. The Cisco stp docs say When you enable or disable the extended ...
6
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1answer
762 views

What should a device do with an Ethernet frame larger than its MTU?

When I test with Cisco 2960 series switches or with ISR routers, then if port receives an Ethernet frame larger than its MTU value seen in sh int output, then device drops this frame and increases the ...
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3answers
2k views

Monitoring best practice for thresholding errors on an interface?

When monitoring interface errors, what percentage of traffic should you set your 'critical' threshold to according to best practices and does it depend on the interface type (T1, Ethernet etc)? It ...
6
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1answer
511 views

Spoofing Ethernet with Source as Broadcast

I was wondering the following: Assume I am attached to a switch with an Ethernet Cable and I try to spoof the source/origin MAC address of an Ethernet frame with FF:FF:FF:FF:FF:FF. How would it behave?...
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1answer
2k views

ARP Questions (Packet Types, Ethernet, Cache, Gratuitous)

Lately I have been doing some research on the Address Resolution Protocol, and even though I know the idea behind it I still have some questions. Q1: Are there more types of ARP messages that I am ...
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3answers
1k views

Media Access Control for WAN protocols (equivalent to IEEE 802.3 Ethernet sublayer)

Ethernet can be divided into 2 sublayers; MAC and LLC. For WAN protocols like PPP, HDLC and frame relay, it is not discussed in regards to protocol sublayer for media access control. On serial ...
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1answer
519 views

Responsibility of the physical sublayers of Ethernet

I'm learning about Ethernet and the sources I've found seem to be controversial regarding the role of the physical sublayers of Ethernet displayed on the following image. Just to mention an example ...
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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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3answers
1k views

Unknown EtherType

I am parsing an ethernet dataframe. It has the form : (destination_mac_6_bytes) + (source_mac_6_bytes) + (ether_type_2_bytes). Usually, I see ethertype like Ox86dd (IPv6). But I came across this ...
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5answers
1k views

Why do we need repeaters since there are bridges (or switches)?

I was reading the HowStuffWorks article on ethernet. From the article, I understand that bridges are just like repeaters, but with the added benefit of not cluttering up other collision domains. So I ...
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3answers
2k views

How to debug L1 Auto negotiation issues?

One of our Linux hosts has started switching its gears recently. While checking the interface speed, I could see that the interface has switched down to 10Mbps. The NIC and Switch are capable of 1G ...
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2answers
231 views

What is the springing mechanism for on the top of this transceiver module?

Some Ethernet SFP modules have them, some do not. What is the yellow springing mechanism and the attached metal wire meant for?
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5answers
2k views

Why can't two hosts (in two different logical networks) connected to each other through cross-over cable communicate?

Let us say, i have two computers (hosts) A and B. Where A has been assigned an IP address of 192.168.1.10/24 and host B has been assigned an IP address of 192.168.2.11/24. And both of them has been ...
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3answers
1k views

Cables on a closed rack

I've just spent the last few days building my first server rack. It will be a significant upgrade to our current mess. I was asked to buy and install one and so I did. I was not completely aware of ...
5
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4answers
29k views

CAT7 Ethernet cable: order of wires in the clamp

On a CAT 7 Ethernet cable each twisted pair is individually shielded, and all pairs together are inside a shielded jacket: Colors of the wires may change, for instance I recently got my hands on a ...
5
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2answers
32k views

Enabling flow control on my ethernet NIC

When running "ethtool eth0", I get a line in the output that states -> Supported pause frame use: No Does this mean my Ethernet card does not support flow control at all? I try to enable the flow ...
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3answers
4k views

Can normal CAT6 be buried? [closed]

I have the leftover from a long spool of CAT6. I'd like to run a line to my garage, which is separate from the house. Can "typical" CAT6 be directly buried, or should I buy one of the "waterproof" ...
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2answers
1k views

Building a 3 port network tap (100mbps half-duplex)

I've tried building a network tap with only three ports: the two communicating parties and a tap side. I knew this would force the communicating sides to use at most half-duplex 100mbps, but detection ...
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3answers
25k views

Avoiding ARP broadcast storms

We ran into a problem the other day when a member of our staff inadvertently doubly connected in a cheap switch (no STP) into another switch that had STP disabled. (The second switch was connected to ...
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2answers
5k views

How does auto-negotiate determine link speeds?

I have two Linux hosts connected via category 6 wire. How do the LAN cards negotiate a link speed? Essentially, I am trying to solidify if I am actually hammering a 1GbE NIC with traffic from a 10Gbe ...
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1answer
4k views

Do LACP MTUs (or other link-level MTUs) need to match?

Does setting a custom MTU on the host side of a LACP bond require also customizing the MTU on the switch side?
5
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1answer
242 views

malloc failures and ARP packed on a Cisco 2901

I have a 2901 between a network and the internet. It shipped with the routing defined as follows. ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1 Using the interface like this instead of an IP struck ...
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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
7k views

End-to-End delay

I’m working through questions from computer networking top down approach and was hoping to get some clarity on the end-to-end delay calculation. At this stage we are not considering processing, ...
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3answers
242 views

Where are UTP cable speeds defined for Ethernet?

I have consulted several Network+ exam preparation books, Network+ practice exam questions, the IEEE 802.3-2015 standard, and several older TIA-568 standards. However, I'm having trouble finding a ...
5
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1answer
2k views

Why does 10Gbps ethernet claim PAM16 encoding then use a squared DSQ128 constellation?

I've been looking into the way that 10 Gbps Ethernet encodes its data and I'm a little confused by the nomenclature. I have gathered, e.g. from here http://www.ikn.no/download/Whitepaper-10G-...
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2answers
4k views

Ethernet Neighbor Discovery?

I am trying to familiarize myself at the moment with the Ethernet network protocol. However, when looking at the standard a Ethernet frame needs a destination MAC address, and the source address MAC ...
5
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2answers
1k views

Did the LSB-first method of transmitting the canonical MAC address in Standard Ethernet have any specific advantages?

When MAC addresses are sent out they are sent such that the Group Address Indicator is the first bit of the Ethernet frame but when stored in memory this forms the LSB of the leftmost byte of the MAC ...
5
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1answer
599 views

Long Reach Ethernet

In our corporate headquarters we are looking at replacing a 20+ year old phone system and making the switch to VoIP. This is a high rise where we have some limits around options for cabling. ...

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