For questions on connecting devices together so that they can communicate with each other, as well as on networking equipment such as routers and switches.

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692
votes
3answers
134k views

Transatlantic ping faster than sending a pixel to the screen?

John Carmack tweeted, I can send an IP packet to Europe faster than I can send a pixel to the screen. How f’d up is that? And if this weren’t John Carmack, I’d file it under “the interwebs being ...
328
votes
1answer
18k views

Ping faster than light

I just discovered very strange thing while testing my internet connection. My ping is smaller than it should be. For example ping time to Arizona State University is about 14ms. eryk@eryk-pc:~$ ping ...
147
votes
8answers
22k views

How do I get a static IP address for my teapot?

I maintain this teapot: It returns a 418 error when it is pinged, and it is pinged regularly by people arriving from the relevant Wikipedia page. (For those interested, and there appear to be a few ...
122
votes
10answers
109k views

Is it possible to ping an address:port?

I am not into networking, and I have the following question related to the Linux ping command. Can I only ping an address? For example: miner@raspberrypi ~ $ ping onofri.org PING onofri.org ...
111
votes
5answers
101k views

Connect to the host machine from a VirtualBox guest OS?

I'd essentially like to access my host computer from the guest in VirtualBox. Is there an IP address given for my host which I can use from the guest? Are there extra steps required to set this up? ...
110
votes
13answers
71k views

How to reliably keep an SSH tunnel open?

I use an SSH tunnel from work to go around various idotic firewalls (it's ok with my boss :)). The problem is, after a while the ssh connection usually hangs, and the tunnel is broken. If I could at ...
104
votes
4answers
15k views

What's the difference between 127.0.0.1 and 0.0.0.0?

I understand that 127.0.0.1 points to localhost, and so does 0.0.0.0 (correct me if I'm wrong). So, what's the difference between 127.0.0.1 and 0.0.0.0?
103
votes
13answers
41k views

What is the exact use of a MAC address?

I understand that IP addresses are hierarchical, so that routers throughout the internet know which direction to forward a packet. With MAC addresses, there is no hierarchy, and thus packet forwarding ...
99
votes
5answers
226k views

How can I list all IPs in the connected network, through Terminal preferably?

Using Ubuntu 10.10, I was wondering if there was a command line command that can list all the IPs of devices connected to the network? I would use this for example, to list all the computers ...
98
votes
2answers
199k views

What are CLOSE_WAIT and TIME_WAIT states?

When I do netstat -a on my Windows machine, I get a listing of the ports with one of the four states: LISTENING CLOSE_WAIT TIME_WAIT ESTABLISHED What do CLOSE_WAIT and TIME_WAIT mean/indicate?
95
votes
9answers
8k views

Why is dial up so slow?

On a dial-up Internet connection, why is the speed is limited to 56 kbits/s compared to a broadband Internet connection which may carry 10 times as much as dial up through that same telephone line? ...
92
votes
9answers
114k views

Disable “These files might be harmful to your computer” warning?

I keep getting this irritating warning when copying files over the network: These files might be harmful to your computer Your internet security settings suggest that one or more files may ...
88
votes
5answers
52k views

How can I find out where an email really came from?

How can I know where an email really originated from? Is there any way to find it out? I have heard about email headers, but I don't know where can I see email headers, for example in Gmail. Any ...
85
votes
7answers
6k views

Why do some RJ45 plugs have the lock release clip under a rubber cover?

Some RJ45 plugs have an exposed lock release clip, like this: However, others place the release clip under a rubber cover, like this: I find that the rubber cover is almost never anything but a ...
84
votes
2answers
6k views

How do web-servers “listen” to IP addresses, interrupt or polling?

I'm trying to understand the lower details of web servers. I am wondering if a server, say Apache, is continuously polling for new requests or If it works by some sort of interrupt system. If it is an ...
80
votes
12answers
110k views

How can I make the Windows VPN route selective traffic (by destination network)?

I want to use a Windows VPN but only for a particular network, so that it doesn't take over my entire network connection. e.g., Instead of the VPN becoming the default route, make it only the route ...
78
votes
5answers
7k views

Why did the IETF specifically choose 192.168/16 to be a private IP address class?

Why did the Internet Engineering Task Force (IETF) choose 192.168/16 to be a private IP address classand not something else? Why specifically 192.168/16 and 10/8 and 172.16/12 and not 145.243/16 for ...
78
votes
10answers
190k views

Make Windows 7 ignore WiFi when ethernet is available

When I dock my Windows 7 laptop, I want it to prefer the wired ethernet connection over WiFi. This is a pretty straightforward thing to do on my Mac - I just reorder my network preferences, and it ...
77
votes
9answers
14k views

Can you grab any IP address on the Internet?

On a personal network (LAN) one can simply grab an IP address. If you choose the same IP address as an existing client, you get problems. There are companies like IANA and ICANN that are in charge of ...
74
votes
2answers
13k views

Why does Qatar use a single IP address when 800,000 IP addresses are allocated to it?

In discussions about IP address banning, IP 82.148.97.69 is often cited as an example. According to Wikipedia, this IP address is the public address of "the entire nation of Qatar". There are two ...
73
votes
7answers
212k views

Test if a port on a remote system is reachable (without telnet)

In the old days, we used telnet to see if a port on a remote host was open: telnet hostname port would attempt to connect to any port on any host and give you access to the raw TCP stream. These ...
72
votes
10answers
352k views

How to install Windows 7 from the network?

Is it possible to install Windows 7 (Current RTM Version) on a computer without using removable media like DVD or USB? The first thing that comes to my mind is through the network, but I don't have ...
70
votes
9answers
8k views

Are IP addresses with and without leading zeroes the same?

I have a security system and the network setting only allows a three-digit IP address. I can't set it to 192.168.2.100, instead I have to use 192.168.002.100. Are these two IP addresses different? Do ...
67
votes
6answers
32k views

Why is localhost IP 127.0.0.1?

I wondered what is the origin of the decision to make localhost's IP address 127.0.0.1. What is the "meaning" of 127? what is the "meaning" of 0.0.1?
65
votes
9answers
5k views

“Turn off router for 10 seconds” - Quantifiable? [duplicate]

Is there any quantifiable evidence to support power cycling routers for 10 seconds or any arbitrary amount of time, instead of just unplugging and plugging back in? This is related to troubleshooting ...
62
votes
6answers
221k views

How do I know what proxy server I'm using?

I need to know what the address for my proxy server is so I can configure another program to also use it. If I go into IE, Internet Properties, LAN Settings, then all I see is an automatic ...
61
votes
6answers
36k views

VirtualBox guest OS accessing local server on host OS

On my Ubuntu host I have my local webserver. I installed VirtualBox and Debian as a guest. I would like the Debian guest to be able to hit my webserver running on my Ubuntu host (for example, I just ...
61
votes
3answers
19k views

How do I diagnose and visualize high ping times to wifi router?

I'm seeing erratic and sometimes very long ping times to my wifi router that's just one hop away. Pinging 192.168.1.1 sometimes gives stretches of 400-800ms latencies. There are plenty of things to ...
60
votes
7answers
22k views

The locking clip/tab on my Ethernet cable's plug is broken. How can I fix it?

I have a 10 meter long Ethernet cable. One plug has the little locking clip missing, just like missing the part in red ellipse in the following picture. How can I fix it? Is this something I ...
60
votes
4answers
66k views

How to selectively route network traffic through VPN on Mac OS X Leopard?

I don't want to send all my network traffic down to VPN when I'm connected to my company's network (via VPN) from home. For example, when I'm working from home, I would like to be able to backup all ...
58
votes
8answers
9k views

IP address that is the equivalent of /dev/null

Is there an IP address that would result in any packet sent to be ignored (blackholed)? I know I can always set up a router with an IP address and then just have it ignore all packets sent to it, but ...
58
votes
8answers
42k views

What is the difference between various cable types like Cat 5, Cat 5e and Cat 6?

I'm just about to move house, so I'm going to have to disconnect and re-wire my network. Pretty much all the devices I have support Gigabit Ethernet. Should I go out and buy some decent network cables ...
57
votes
13answers
10k views

When I plug an Ethernet cable into my computer, is my computer directly connected to every server on the Internet?

By this I mean could I follow the Ethernet cable through thousands of miles of fiber optics and eventually get to Amazon's server, ESPN's server, and every other site's server? Thus, excluding the ...
55
votes
3answers
4k views

How can I turn off internet for roommates that haven't paid the bill this month?

I have several roommates who split my internet bill with me each month. On occasion they forget to pay me, and I have to pester them for the money. If after 3 days of pestering they still haven't ...
54
votes
8answers
169k views

Is there a good tool for monitoring network activity on Mac OS X? [closed]

Is there a good bit of software on Mac OS X that I can use to monitor incoming and outgoing network activity? Nothing too geeky, I just want something simple to use. I'm on version 10.6 (Snow ...
52
votes
7answers
73k views

What's the easiest way to sniff TCP traffic data on Linux?

I want a simple way to show all the TCP data (not the TCP headers or anything else) going over any interface on my Linux box. For instance, I want a magical command that if I do: ...
52
votes
9answers
141k views

How to do networking between virtual machines in VirtualBox?

I have two virtual machines in VirtualBox. I would like to do networking between them. For the moment I have the default configuration on both, but they seem to have the same IP-address 10.0.2.15. I ...
50
votes
2answers
5k views

Why was port 80 chosen as the default HTTP port and 443 as the default HTTPS port?

Why was port 80 chosen as the default HTTP port and 443 as the default HTTPS port? Is there a reason or was it is just defined that way?
49
votes
5answers
160k views

How can I scan the local network for connected devices? (Mac OS)

I'm basically looking for something like this but available on Mac. I am trying to connect a new workstation to our wireless multifunction printer and I'm having a hell of a time getting the device ...
49
votes
7answers
44k views

How to throttle bandwidth on a Linux network interface?

Is there a way to constrain the bandwidth on a NIC in linux? I'd like to be able to simulate an arbitrarily slow connection.
48
votes
6answers
6k views

Why is a router needed?

I‘ve been trying to figure out why a router is needed. I know a router can be used for DHCP and some other things, but I’m just thinking of networking with static IPs. So the following: Is it ...
48
votes
16answers
88k views

Why is 'ping' unable to resolve a name when 'nslookup' works fine?

On my Windows XP workstation, I can find the machine I want to connect to in DNS with nslookup: nslookup wolfman Server: dns.company.com Address: 192.168.1.38 Name: wolfman.company.com Address: ...
47
votes
4answers
163k views

List mapped network drives from the command line to text file

Is there a command that can be used from the command line to output a list of the mapped network drives on the local system and their location on the network to a text file? This will only be used on ...
46
votes
2answers
43k views

How can I rename a network in Windows 8?

I recently replaced my home router, and now Windows 8 seems to think that the main Ethernet network is called "Network 2", when it used to simply be called "Network". There is no "Network" ...
46
votes
7answers
69k views

Is there any benefit to using IPv6 on my home network?

I know that IPv6 is the future because there is only 4 billion IPv4 address, but on a home network, you are not going to have 4 billion users. So are there any other benefits that would make IPv6 on a ...
42
votes
4answers
24k views

Is there a way to find out what application using most of bandwidth in Linux?

I'm looking for an utility that could show me how much of a bandwidth each process are using. It should just print the data and exit as I want to feed that list into conky.
41
votes
2answers
29k views

Why is my “localhost” not 127.0.0.1? [duplicate]

When I use the Ping command to ping my localhost, it doesn't show up as 127.0.0.1. C:\Windows\system32>ping localhost Pinging GIGA [::1] from ::1 with 32 bytes of data: Instead, it shows up ...
40
votes
3answers
4k views

What's 24 in “192.168.15.0/24”?

What's the meaning of /24 in the following command? route add -net 192.168.15.0/24 192.168.8.10
39
votes
7answers
25k views

What is a external reliable IP address to ping to check if internet is available? [closed]

Is there any common always up server, which I can setup to ping in automatic mode to detect internet is available? Like Google or something? May be 8.8.8.8? My specific situation is that I am using ...
39
votes
8answers
184k views

How do you automatically detect a new network card in CentOS 6 / RedHat?

I'm using CentOS 6 in a virtual environment. When cloning a virtual version of CentOS, the old eth adapters are "removed" and replaced with new ones and net MAC addresses. However, the ifcfg-ethn ...