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1141

The time to send a packet to a remote host is half the time reported by ping, which measures a round trip time. The display I was measuring was a Sony HMZ-T1 head mounted display connected to a PC. To measure display latency, I have a small program that sits in a spin loop polling a game controller, doing a clear to a different color and swapping buffers ...


177

Ports are a concept of UDP and TCP. Ping messages are technically referred to as ICMP Echo Request and ICMP Echo Reply which are part of ICMP. ICMP, TCP, and UDP are "siblings"; they are not based on each other, but are three separate protocols that run on top of IP. Therefore you can not ping a port. What you can do, is use a port scanner like nmap. nmap ...


177

The short answer is: some sort of interrupt system. Essentially, they use blocking I/O, meaning they sleep (block) while waiting for new data. The server creates a listening socket and then blocks while waiting for new connections. During this time, the kernel puts the process into an interruptible sleep state and runs other processes. This is an important ...


166

Basically, the telephony line is limited to 64 kbits/s for each channel (8 kHz channel with PCM modulation on 8 bits per Hz, making 8 kHz x 8 bits = 64 kbit/s). Unless you use another modulation(QAM for example) or more bandwidth(more than 8 kHz telephony channel, up to MHz for example), your transmission capacity will be ...


126

See below for an example of a scam that was sent to me, pretending to be from my friend, claiming she has been robbed and asking me for financial aid. I have changed the names — I am "Bill," and the scammer has sent an email to bill@domain.com, pretending to be alice@yahoo.com. Note that Bill forwards his email to bill@gmail.com. First, in Gmail, click show ...


116

Similar to mpez0's answer, but I like a good car analogy... I'm choosing the UK for this, since that's where I live. Imagine you live in a world where people follow road signs without question, and you happen to live right up in the north of Scotland, about as far from London as you can without crossing water. You live in a small town, and one day you ...


115

When retracting a RJ45 plug through narrow tubing or around corners, the clip tends to snap off, effectively making the network cable useless in most environments. The rubber dome (most commonly referred to as a cable boot) nearly always prevents that from happening. You wouldn't know how many network cables I've seen with broken off clips.


114

From experience, those retention clips break off a lot on the first sort of cables - those are fine for cables that are well protected and/or going to be plugged in and forgotten, but the moment those clips bend the wrong way, they break, and you end up with a cable that dosen't clip in place. They also snag each other sometimes and are just a PITA. Cable ...


108

There is nothing preventing you from attaching a box configured with someone else's IP address to the internet. However, this won't necessarily cause any issues for anyone else but yourself. If you steal someone else's IP address outside of the subnet that you are physically connected to, the only thing you will accomplish is not being able to receive any ...


98

What are MAC addresses used for? MAC addresses are the low level basics that make your ethernet based network work. Network cards each have a unique MAC address. Packets that are sent on the ethernet are always coming from a MAC address and sent to a MAC address. If a network adapter is receiving a packet, it is comparing the packet's destination MAC ...


91

If you don't want to replace the cable or install a new jack, you have a few of options: Glue it into a coupler or a short extension like one of the following (with the coupler you will need another short run of cable on the other side): Repair it with a zip tie. Use this guide for instructions: ...


88

Dial up connections use the voice circuit for data transfer so the bandwidth is limited to bandwidth of voice channel, whereas DSL uses a separate frequency range for data which is much broader than voice bandwidth (hence the term Broadband). DSL uses a splitter to separate the voice and data frequencies and therefore both can work simultaneously.


87

Sounds like you need autossh. This will monitor an ssh tunnel and restart it as needed. We've used it for a couple of years and it seems to work well.


84

It depends on the tool. For most purposes the two will be the same, but not always. For example, if you use a 3-digit number starting with a zero (or a two-digit one starting with zero, thanks @Dietrich-Epp), then ping will assume the numbers are octal. Microsoft Windows [Version 6.3.9600] (c) 2013 Microsoft Corporation. All rights reserved. ...


82

In the default setup, you should be able to reach your host through your default gateway, in my case 10.0.2.2. You can easily determine this IP address in Windows via ipconfig. It should dump out something like this: Windows IP Configuration Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : IP Address. . . . . . ...


74

Yes there is. Any electronics device will have capacitors that will store energy even after you unplug it. You may have noticed when you unplug, say a monitor or TV, the little diode will take another second or two to discharge remaining energy from the capacitors in form of electricity and stop glowing. This residue energy may not allow memory chips to ...


72

127 is the last network number in a class A network with a subnet mask of 255.0.0.0. 127.0.0.1 is the first assignable address in the subnet. 127.0.0.0 cannot be used because that would be the wire number. But using any other numbers for the host portion should work fine and revert to using 127.0.0.1. You can try it yourself by pinging 127.1.1.1 if you'd ...


69

This serverfault answer has good guidance on what to do, but since you (I mean, me) asked for tools and measurement.. Below are some good tools, first for understanding connectivity health within the local wifi network, and then to an internet endpoint. Wifi Tools NetSpot (for mac) It tracks the local WiFI APs and provides basic data like SNR, Channel, ...


68

This is because ping on Windows Vista and newer Windows uses IPv6 by default when available. ::1 is a shortened notation of IPv6 loopback address - equivalent of IPv4 loopback 127.0.0.1. The full notation of the abbreviated ::1 IPv6 address is 0000:0000:0000:0000:0000:0000:0000:0001. If you want to force ping to use IPv4 instead you can specify the IPv4 ...


67

Check out the arp-scan command - you will probably have to install it eg: sudo apt-get install arp-scan http://manpages.ubuntu.com/manpages/hardy/man1/arp-scan.1.html And to give further detail: sudo arp-scan --interface=eth0 --localnet Where eth0 is your device. You can find your device with: ifconfig


65

I found a fix by changing "internet options" -- so I guess Windows is detecting the "internet" as my own network.. sigh. Click Start / Control Panel / Internet Options Click Security tab. Click Local Intranet Click Sites button. Click Advanced button. Enter the IP Address of the other machine or server (wildcards are allowed) and click Add Click Close, ...


64

You can turn off taking over your entire connection by going to the properties of the VPN, Networking tab, "Internet Protocol (TCP/IP)" properties, Advanced, untick "Use default gateway on remote network". This may or may not leave a route to 192.168.123.0/24 depending on the VPN server's setup. If it doesn't, you'll have to manually add the route each time, ...


63

Due to the way TCP/IP works, connections can not be closed immediately. Packets may arrive out of order or be retransmitted after the connection has been closed. CLOSE_WAIT indicates that the remote endpoint (other side of the connection) has closed the connection. TIME_WAIT indicates that local endpoint (this side) has closed the connection. The ...


62

There's specifically a blackhole prefix in IPV6, as described in RFC 6666, it's 100::/64. IP4 does not have an explicit black hole like that, but a non-existent host on one of the reserved blocks would have that effect. (e.g., 240.0.0.0/4 is "reserved for future use" and will not be routed by anything.)


61

Enable ONE network adapter. Set it to NAT and start your machine. Don't need to configure anything. On guest machine's browser type http://10.0.2.2 which will show you the same content as "localhost" in the host OS. 10.0.2.2 is the "default gateway" for NAT connections and your guest OS' IP is 10.0.2.15 Of course you can set a "HOST-ONLY" or an "Internal ...


61

RDP is semantic. The RDP is aware of controls, fonts, and other similar graphical primitives. This means that when rendering a screen across a network, this information is used to compress the data stream significantly. For instance, if you know that this region of the screen if occupied by a button, with the color grey, then you don't need to send an image ...


61

It's on Windows 7, but it's pretty well hidden. Go to Control Panel -> Network and Sharing Center -> Change adapter settings -> The hit Alt to get the menu and choose Advanced -> Advanced Settings. Then you can re-order your connections in that list. Although Windows should already automatically prefer your wired over your wireless connection. It chooses ...


60

Imagine one of those pneumatic tube message systems. Ethernet is the tube used to send the message, IP is an envelope in the tube, and TCP/UDP is a letter in the envelope. Someone (an application) writes a letter and stuffs it in an envelope. Another person (a NIC) looks at the address on the envelope, puts it in a tube, caps it off, stuffs it in the right ...


56

Assuming all software you are using is using dot-decimal and subnetting correctly, yes they are the same. 192.168.0.1 for example is only the friendly dot-decimal notation of the dot-binary value 11000000.10101000.00000000.00000001. Whether you type it as 192.168.0.1 or 192.168.000.001 they are both equal to 11000000.10101000.00000000.00000001



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