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1179

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 ...


367

As you can see from the output, you aren’t actually pinging some server in Arizona or even the United States. Apparently, they decided to protect their website with Cloudflare, which employs a content distribution network to even the load. A CDN works with many nodes, each servicing a (geographic) region. That means the node you’re pinging is very close to ...


220

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 ...


180

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 ...


167

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 ...


146

This answer is about pretty much an guest OS setup in VirtualBox; you just need to use the network gateway address on the guest OS to connect to the host OS from a guest OS. In the default Vagrant setup, you should be able to reach your host through the default gateway. On Windows based guests, you can easily determine this IP address by running the ...


133

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 ...


131

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. autossh -M 20000 -f -N your_public_server -R 1234:localhost:22 -C More details on the -M parameter here


120

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 ...


117

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 ...


114

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.


113

What's the difference between 127.0.0.1 and 0.0.0.0? 127.0.0.1 is the loopback address (also known as localhost). 0.0.0.0 is a non-routable meta-address used to designate an invalid, unknown or non applicable target (a no particular address placeholder). In the context of a route entry, it usually means the default route. In the context of ...


110

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 ...


106

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 ...


102

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


98

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 ...


97

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 ...


94

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: ...


94

They are not the same. 127.0.0.1 is part of the 127/8 network which is reserved and points to the same computer. 0.0.0.0 is a special IP address that means different things depending on context. In the Internet Protocol Version 4, the address 0.0.0.0 is a non-routable meta-address used to designate an invalid, unknown or non-applicable target. To ...


89

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. ...


89

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.


89

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, ...


83

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 ...


82

The auto proxy detection system works by downloading a file called wpad.dat from the host wpad. First confirm this host exists from a command prompt: ping wpad If it doesn't exist, you may have to put the correct DNS suffix. In the same command prompt, type ipconfig /all You should see a Primary DNS Suffix and a DNS Suffix Search List Try appending ...


82

The Internet is a system of interconnected smaller networks that can reach each other through routing. You could essentially "follow the path" to any server you're directed to, but there are basically endless paths to any destination. If you were to start from your Ethernet connection, you would first hit your home router, then hit your ISP's routers. The ...


80

Ping the broadcast address (you can find it with ifconfig | grep broadcast) and then do an arp -a


79

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, ...


79

I think generally routers serve as an access point, DHCP, firewall and switch as an easy solution for people who don't know much about networking No, routers are a separate kind of device from APs and switches. "Router" is not just a generic name – it describes a specific function, routing IP packets between networks. In other words, you're ...


76

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 ...


75

This serverfault answer has good high-level guidance on what to do - so start with that. That last step is a real doozy though: presumably you (I mean, me) don't want to invest in dedicated hardware for this... Below are some good tools, first for understanding connectivity health within the local wifi network, and then to an internet endpoint. Wifi Tools ...



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