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61 votes
Accepted

Is Ethernet port blinking really useful?

Yes, blinkenlights are your friends! The lights can be very helpful when diagnosing problems - especially when dealing with non-managed switches or remote diagnosis with unexperienced users. Rule of ...
Zac67's user avatar
  • 85.2k
29 votes

Is Ethernet port blinking really useful?

My very first step in troubleshooting network issues is this: "Are there winky-blinky lights?" It's the network port equivalent of asking someone if their computer and/or monitor is actually ...
Dustin Kreidler's user avatar
25 votes
Accepted

What is this device used by a networking technology company?

Connecting two fiber trunks is a tedious process. Those are splice cassettes for optical fiber - each single fiber is fusion spliced and looped into one of the cassettes for protection. Afterwards the ...
Zac67's user avatar
  • 85.2k
17 votes

What is this device used by a networking technology company?

They're a fiber splicing crew. The white plastic trays are used to organize fiber connections. A waterproof enclosure will protect the whole assembly from debris when their job is finished, and the ...
Jeff Wheeler's user avatar
  • 5,503
13 votes

What is the purpose of an Ethernet magnetic transformer, and how are they used?

I have been told that Ethernet magnetic transformers are used for base-t Ethernet when transmission is sent over a lengthy cable. They are always used, not just when "sent over a lengthy cable&...
Peter Green's user avatar
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13 votes
Accepted

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

For the most part, no. Hubs are also known as repeaters - meaning that they basically echo whatever is coming in to a given port out all other ports in the domain. The idea is (or, more properly, ...
rnxrx's user avatar
  • 6,124
11 votes
Accepted

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

You're talking about 10GBASE-T - most other 10G flavors use straight 64b/66b (10GBASE-R), but that doesn't work on 500 MHz Cat 6A. With 10GBASE-T, two consecutive PAM-16 levels (on each lane) ...
Zac67's user avatar
  • 85.2k
10 votes

Does it make sense to generally "Disable TCP Checksum Offload"?

Hardware offloading features may have bugs but they are generally beneficial. I only deactivate them on certain NICs or vendors which do have problems. However, on a workstation/PC the network load is ...
Zac67's user avatar
  • 85.2k
9 votes

Is Ethernet port blinking really useful?

The patterns of blinking lights on a switch can give you a quick overview of network health. I used to work at a medium-sized company of about 100 staff, 250 PCs, a dozen servers, and the main ...
Ward - Trying Codidact's user avatar
8 votes

Software Switches vs Hardware Switches

It comes down to what is accelerated through purpose-built hardware/ASICs versus what traffic flows can be punted to software/CPU for processing. Physical switches have extremely fast switching ...
cmschmidt15's user avatar
7 votes
Accepted

How to check if a NIC supports hardware timestamps

I guess you could run the command below, it will depict every capability your software and hardware networking has, sudo ethtool -T <interface> interface information such as names are ...
Alireza Sanaee's user avatar
7 votes
Accepted

Are LC-UPC connectors compatible with LC-PC?

Yes. PC, SPC and UPC are just different polish grades of perpendicular, physical contact connectors. Their end-faces match, so they work nicely together. In contrast, APC uses an angled surface (...
Zac67's user avatar
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6 votes
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What advances in hardware allowed DPDK to increase performance on packet processing?

I've tried to do a little research, and the most of what I've been able to undestand is that: DPDK allows application to bypass Linux kernel, reducing some copying and an amount of IRQ requests. ...
Baldrick's user avatar
  • 5,300
6 votes

How can twinaxial cables be faster than CAT cables

Simply put, twinaxial cables allow only very short distances, under 10 meters. And they are used in networking, for example both 40Gb and 100Gb standards support twinaxial cables... ...up to 7 ...
JFL's user avatar
  • 19.7k
5 votes
Accepted

What certifications are there for Fiber Optic termination and splicing?

It's not terribly difficult to train yourself, if you care about the doing. If you care about selling yourself more, BICSI will happily take your money as a certifier. Probably better if you can get ...
Ecnerwal's user avatar
  • 2,746
4 votes

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

Hubs are bad news, from both a network performance as well as a security point of view. As a network admin you may find it handy to have a hub or two sitting in the store for the day when you want to ...
mere3ortal's user avatar
  • 2,416
4 votes

Cisco router boot error

The problem is exactly what is stated in the message you see: the nvram (non volatile ram) of your router is corrupted. You need to change it. It seems it is something quite easy to do, provide you ...
JFL's user avatar
  • 19.7k
4 votes

Does it make sense to generally "Disable TCP Checksum Offload"?

I've just spent about 2 days debugging and figuring how to workaround a problem that seems to have come down to buggy TCP offloading with linux and Intel ethernet drivers/chipsets in Intel NUCs. ...
JosephH's user avatar
  • 141
4 votes
Accepted

CB fabric links require upgrade/training after adding New FPC in Juniper MX480

When upgrading a fabric e.g. from SCB to SCBE, there is a process to train the fabric links so they operate at higher speed. The require upgrade/training alarm is documented in the related upgrade ...
Jeff Wheeler's user avatar
  • 5,503
4 votes
Accepted

How do internet backbones (and their terminations) work?

Details will obviously vary and i'm not an expert but i'll try to answer the question from what I understand. web browser in an Australian household laptop, and a web server in a US data centre Data ...
Peter Green's user avatar
  • 13.4k
3 votes

Is it possible to create a collaborative network?

There are a lot of solutions on market. I would check if any of your local ISPs support line bonding. That would be ideal option.
Datagram.Network's user avatar
3 votes

Software Switches vs Hardware Switches

The basic architecture of general purpose compute is just that - general purpose. It's great at applying significant amounts of processing power to a huge variety of workloads but it doesn't truly ...
rnxrx's user avatar
  • 6,124
3 votes

What advances in hardware allowed DPDK to increase performance on packet processing?

It's not just an optimization library. DPDK is about controlling hardware functions through a framework with an Environment Abstraction Layer (EAL) that provides a general API for various device ...
Zac67's user avatar
  • 85.2k
3 votes

What is the purpose of an Ethernet magnetic transformer, and how are they used?

The ethernet magnetic transformer is required by the ethernet standard. You will find this question, "Why Are Ethernet/RJ45 Sockets Magnetically Coupled?" answered on the Electrical Engineering SE. ...
Ron Maupin's user avatar
  • 99.9k
3 votes

DLink switch loses configuration on power off!

This has just happened to me with my Dlink DGS 3120-24SI. Apparently you need to go to the web gui then select Save ... Save Configuration / Log. Change Type to All, then Apply. This saves everything ...
Patch67's user avatar
  • 31
3 votes

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

In general, no, there's no reason to use a hub over a switch, but they do still have a purpose in some special cases. One case is if you need to capture traffic to a host but the host can't run a ...
Jesse P.'s user avatar
  • 4,690
3 votes
Accepted

Is temperature sensor on zero enough to prove PoE Control Module is failed?

(converted from comments) The "Total Power" figure should show what the PSU can deliver, regardless of what's currently in use. The "0 W" pretty clearly shows there's something wrong. Possibly, the ...
Zac67's user avatar
  • 85.2k
3 votes
Accepted

Does it make sense to generally "Disable TCP Checksum Offload"?

Checksum offload is generally quite reliable. The last NIC I knew of that had a bug around this was a 100 Mbps Sun hme interface, which had a problem with UDP checksum offloads for IPv6 only. That ...
Garrett D'Amore's user avatar

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