63

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 thumb: no link light = layer 1 (cable/port) problem link light but no traffic = layer 2 problem (or higher) - VLANs, STP, port security, IP subnet mismatch, ... ...


29

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 turned on (and/or plugged in) when they complain about the screen being dark. A dumb question... but its amazing how many times they come back with a dumb answer. ...


24

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 whole box is sealed and buried or put in a cabinet.


17

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 enclosure will be stowed somewhere, e.g. in an underground chamber or an above-ground pedestal.


12

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, was) to replicate the behavior of a shared piece of coaxial cable, meaning that the individual hosts had to assure that only one member of the LAN was ...


10

Disclaimer: I work at Cumulus Networks To address a few of the high level points/concerns raised: 1.) Is ONIE getting traction? ONIE is the de facto method for getting software onto whitebox switches. It's been embraced by Dell, HP, Supermicro, Penguin, Facebook and a few others. It's run out of the Open Compute Project (http://www.opencompute.org/) an ...


9

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 lengthly cable" What is the purpose of the transformer? The primary purpose is isolation. Typically they are also used as part of the signal conditioning, turning a pair of ...


9

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 server room was across the hall from IT's offices. The server room had windows so we could see the racks, consoles, etc., and we could see the status LEDs of the ...


8

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 speeds because of the purpose-built hardware ASICs meant for network switching. A Xeon E5 can do it but will be slower since it is a general purpose chipset. Also ...


7

You're talking about 10GBASE-T - most other 10G flavors use straight 64b/66b. Two consecutive PAM-16 levels (on each lane) represent one two-dimensional symbol. Not all possible 256 symbols are used, but they are selected from 128 maximally spaced combinations (DSQ128). Of these 7 "raw" information bits, 3 are uncoded data, 4 are used for low-density parity ...


7

Hardware offloading feature 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 usually low to very low - there's little benefit gained from offloading but there's still a risk of buggy hardware/drivers. That probably drove the work sheet'...


7

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 meters. Due to this limitation they are mostly use in Direct Attach cables. (outside of networking, they are used in USB3 or Display Port cables for example).


6

Have you got a physical switch that is rated for Cat5 cabling? The answer to your question is the same as the answer to my question. More than likely you need to buy an electronic relay, and I know of some rated for Cat5.


6

Your thought process is based on faulty assumptions. By splicing 1 to 3 and 2 to 6 (which is what you have done), this does not put them in the same collision domain. Nor does this cause the devices to autonegotiate into half-duplex mode. Connect only one side of your main cable to one device and what you have now created is basically a "loopback." Look ...


6

is it reasonable to suggest that the relatively low mind share and vendor presence is a potential operational risk? There is the potential for both risks and rewards with choosing such a solution. Will the company disappear leaving the product abandoned? Possibly. Are there greater chances of bugs/problems with the code that aren't resolved in a timely ...


6

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 accessible via ifconfig For example it is my network system output: Time stamping parameters for eth0: Capabilities: hardware-transmit (...


6

The timestamping happens in hardware based on a clock in the NIC. Depending on your NIC there's either a NIC register where your timestamp will be written or some card (Intel 82580) can prepend the information to the packet buffer. For cards that write the timestamp to a register you have to read the register before it can timestamp the next packet, ...


6

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. Is that all? DPDK is a software library. As (@Zac67 mentioned) it has an EAL which allows an application to send and receive IP packets without having to know ...


5

VoIP runs over IP, so it is independent of layer-1. The only sort of restriction based on layer-1 would be the bandwidth required. Voice is not separate from data on the wire. You may be meaning a VoIP phone, which may be powered by PoE, but most have wall-warts, too. If the Category-3 cable has all four pairs, there is no real reason the it couldn't ...


5

First, packets are anything but physical ;) I assume you actually mean Ethernet frames (not packets) A simplified explanation: the ethernet hardware receives an entire frame in a queue structure, fetches one byte at a time, and clocks it out the interface one bit at a time. Then it fetches the next byte, and so on until the frame is complete. Because ...


5

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 your employer to have you certified as continuing education so BICSI can take their money, but if it's not applicable enough to your job, it's not. When I was ...


4

is it reasonable to suggest that the relatively low mind share and vendor presence is a potential operational risk? This is always an issue. Products from a small vendor could (and more often than not, do) end up abandoned. As long as they continue to function, there's little to worry about. But when they break, there's nowhere to go but somewhere else. ...


4

Mixing versions like this, depending on which version of CME and CUE you are using, will work in some instances. In your particular case however, it appears that the answer is no. CME 8.6 will only work with CUE versions 7.3, 7.4, 8.5, and 8.6. Since you're talking about a plain NM-CUE in a 2811, that module will only support up to CUE version 7.0. Your ...


4

Yes, the VPN module is a linecard that's plugged into the router and can be replaced. A 'DEAD' hardware state simply means the router has lost communication with the ISM. This does not actually mean the hardware is dead, as a variety of issues in the field have caused this for me: Cards that somehow get unseated, incompatibilities with IOS and the card's ...


4

I'm not sure why you are stuck on ARP (Address Resolution Protocol). It is not used in receiving bits on the wire. It resolves a layer-3 address into a layer-2 address in order to build a layer-2 frame, but when receiving, you are stripping off the layer-2 frame. Some things, like serial interfaces, may not use ARP or frames the way ethernet does. The ...


4

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 get a replacement flash SIMM. Cisco provide the procedure here: Cisco 2600 - Replacing the Internal Flash Memory SIMM Note: in some routers the NVRAM is ...


4

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 processes (juniper doc link). It's confusing this alarm is raised following installation of a new FPC. However, it's not anything to worry about. I suspect this ...


4

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 from your laptop will pass through a series of diverse networks, it will first pass through your ISPs access network, then into their core network. Depending ...


3

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 into Non Volatile RAM to keep settings after power outs.


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