Networking

Wireless Home Networking

Fix Connectivity Issues

It sounds crazy, but 95 percent of all Internet connectivity problems can be solved by power-cycling both the router and the modem. Turn them both off, and then turn the modem back on first. Once its "sync" or signal light comes on, turn on your router.

Use Encryption

You've probably heard this before, but it bears repeating: Always enable your router's wireless security! Wired Equivalent Privacy (WEP) encryption is the oldest (and weakest) form of security; the newer (and stronger) Wi-Fi Protected Access (WPA) and WPA-2 are the best protection available today for home users.

Update Your Router's Firmware

All routers include internal read-only chips with embedded instructions that can be updated by the manufacturer. Router manufacturers generally update a product's firmware to increase performance as well as to resolve bugs and security issues, so it's wise to keep your router's firmware up-to-date. Check the manufacturer's Web site for the latest updates.

Boost Your Wireless Signal

If walls and distance are causing wireless signal degradation, you can do a few things to boost it. Move your router to higher ground—the signal radiates downward. You can also try a signal extender (or repeater), which boosts the signal. Finally, high-gain antennas will work, but they only focus the signal in one direction.

Change Admin Password

Every router has a well-known default password that's used to access the router's browser-based configuration page. Most setup wizards will make you change this password, but not all do. If not, be sure to change it yourself to prevent unwanted hangers-on from changing your network's settings.

Go Back to Factory Settings

If you've lost or forgotten your router's login credentials, you can get around this predicament by resetting the router to its factory settings. Do this by holding down the button on the back of it for 30 seconds. Next, look in the manual for the default user name and password, and then change them on your router's browser-based configuration page.

Disable SSID Broadcast

Unless you disable it, your router broadcasts its service set identifier (SSID)—the name of your network—which allows your neighbors to see (and attempt to gain access to) your network. Instead, disable broadcasting, making the network appear as "SSID not broadcast." Access the unnamed network by typing in the SSID name when prompted.

Change the Default SSID

Change your pre-defined, default SSID—leaving it as "Linksys," for example, tells the world that you haven't configured your router, which invites attackers.

Filter by MAC Address

Every piece of networking gear includes a unique "fingerprint" called a media access control, or MAC, address. You can configure your router to filter connections using these addresses so that only your computers can connect to your network. Most routers will show you connected devices, so adding an adapter's MAC address is a one-click process.

Step Up to 5GHz

The majority of today's networks operate in the crowded 2.4GHz frequency range, which is shared by microwaves, cordless phones, and other home networks. To avoid possible interference, many new routers are capable of broadcasting at 5GHz, which has 23 wide-open channels as opposed to 2.4GHz's three non-overlapping channels.

Limit Your Number of DHCP Clients

Most people use their router as a DHCP server; when clients connect, the router dynamically assigns IP addresses from a large pool of addresses. Limiting that list to the number of clients in your home, however, will help prevent interlopers from hopping onto your network.

Use Your Router's Firewall

Two features make most hardware firewalls more powerful than software firewalls: stateful packet inspection (SPI) and network address translation (NAT). SPI examines packets' content and behavior before granting access, and NAT hides all PCs connected to the router from the Internet, "translating" their IP addresses into private ones that are unreachable from outside the firewall.

Change Your Channel

Wireless B and G (and some N) routers operate at the 2.4GHz frequency, which only has three non-overlapping channels: 1, 6 and 11. By default, your router will most likely be using one of these channels, and the bad news is so your neighbors' routers as well. If you experience dropped connections, sluggish performance or both, a good first step is to switch the channel. If it's set to channel 1, go to 11. If it's set to 6, try either 1 or 11 for best results.

Let Windows Control Your Wireless Networks

If a network adapter's software takes control of your wireless network, it can be difficult to put Windows back in charge. First, click Start, then Run, then type services.msc. Scroll down to Wireless Zero Configuration and start the service. Right-click your wireless connection, select view available networks, and then click advanced settings on the left. Click the wireless networks tab, and check "Use Windows to Configure my wireless network settings."

Disable File Sharing in Public

If you're in a public place with a Net connection, it's a good idea to disable File and Printer Sharing for Microsoft Networks. In the properties of your network adapter, uncheck the appropriate box. It's also a good idea to switch your notebook's wireless radio off if you aren't using it.

Sharing Files Among Computers on a Network

Sharing files and folders among computers on a network can seem very challenging if you've never tried it before. While complications certainly can arise, though, the basic process is simple enough most the time. Here's a short explanation on how to make sharing work on a Windows computer and on a Linux computer.

Setting up sharing on a Windows computer

If you have a folder on a Windows computer that you would like to access from other machines on the network, your first step should be to enable sharing on it. You simply need to go to Control Panel and then Network and Sharing, and then select Change Advanced Sharing Settings . When the Advanced Sharing Settings dialog box opens, you'll need to enable Network Discovery (to make sure that other computers on the network are able to see your computer) and also enable File and Print Sharing to actually make folders and files shareable. For added security, you may want to make use of the password option.

Once you have these basic settings done, your next step should be to enable sharing on the specific folders that you want to make accessible from other computers. Navigating to the folder that you plan to share, you need to right-click on it and then click onProperties . In the Folder Properties box that opens, you need to go to the Sharing tab and click on the Share button.

Accessing a shared folder on a Windows computer

On Windows Explorer, usually, you'll see a Network link on the pane on the left. Clicking on it will let you see all shared resources on your network that you have access to. If you don't see them, restarting both your computer and the computer that has the shared folder should get them talking to one another. Whatever shared resources you see, you can access them by double-clicking on them.

What if you don't see the shared resource you want?

While the basic method described above is straightforward enough, it doesn't always work. Computers sometimes have a hard time communicating with one another. In these cases, you may need to perform a search for the specific resource that you would like to access. To do this, you simply need to open up a Windows Explorer window and type the computer's name in the address bar in the format //name of computer . If the computer's name is dell , for instance, typing in //dell and hitting Entershould make it show up.

Sharing a folder on a Linux

Linux gives you a choice of multiple file managers. They mostly work the same way, though. To share a folder on Linux, you need to right-click on the folder, selectProperties and then go to Local Network Share . This is where you enable sharing. In some distributions of Linux, you may be prompted to okay an automatic software download at this point. Once you install the software, you can click on the Create Sharebutton and are good to go.

When you have a shared folder on a Windows computer that you would like to access on a Linux computer, the navigation process is similar to the way it works on Windows. You need to open a file manager window and click the Browse Network button. Linux will then give you the option to select a Windows network and workgroup. When you  make the choices necessary, you'll see all the shared Windows resources available on your network.

How to Set Up a Home Wireless Network on Windows 7, Windows Vista, or Windows XP

Setting up a home wireless network is easier than ever. Here is a quick guide to get you started.

1. Check that your computer’s operating system supports wireless networking.The new Windows 7 operating system comes prepared to support wireless networking. Windows Vista and Windows XP users will be able to set up a wireless network, but it is recommended that users first consult Microsoft’s homepage and download the applicable service packs in order to make the process easier. These updates should be free if you already have the operating system installed.

2. Sign up for broadband Internet service. Most Internet service providers (ISPs) will provide wireless options such as Digital Subscriber Line (DSL) or cable internet. They’re generally sold on a monthly subscription basis.

3. Purchase a wireless router, DSL modem, or cable modem. Check with your ISP as they may provide this as part of your subscription fees.

4. Plug one end of a network cable into your modem to connect it to the port labeled Internet, WAN, or WLAN on your router. Some newer modem models come with networking technology built in. Make sure the router and modem are turned off when you connect them.Once connected, turn on both devices.

5. Connect your computer to an open network port on your router. Your computer will not stay directly connected to the router, but this step is necessary in order to set up the network. Make sure not to plug your computer into the Internet port, WAN port, or WLAN port. If your computer is turned on, it should automatically recognize the router and establish a connection.

6. Visit the URL indicated in the router’s packaging to configure your router.Different routers have different instructions for this configuration, so follow the directions that accompany your model.

7. Establish your network name and security settings. You can decide whether to add password protection to your connection.

8. Disconnect your computer from the modem. Your wireless internet should now be correctly configured and ready to use.

9. Connect your other computers, printers, and gaming systems to the network.This should be as easy as following the device’s configuration settings and selecting your established network. Consult your device’s specific instructions, as necessary.

By following these easy steps, your home wireless network will be up and running in no time.

View Your Computer's Important Network Information

Maybe just for your own information, but certainly when you're troubleshooting a network or Internet problem, you'll probably at some point need to know details about your computer's network connection.

Everything you'd want to know about your network connection is available somewhere in the Control Panel in Windows, but it's much easier to find, and much better organized, in the results from the ipconfig command.

 Open Command Prompt  and execute ipconfig /all.

What displays on screen next is everything important about your network connection i.e your IP address, hostname, DHCP server,DNS information, and much more.

Connect to a Wi-Fi router without entering the password

Most residential and some business-class routers support Wi-Fi Protected Setup (WPS), aimed to make securing and connecting to the Wi-Fi quicker and easier. Those routers that do support it usually have a WPS button somewhere on the router. You can push the router’s button and then within a limited amount of time, like a minute, you can initiate the connection of Wi-Fi devices supporting WPS. The Wi-Fi device automatically connects to the router and gets the security settings without you having to enter the WPA/WPA2 security passphrase.

WPS can help keep your network more secure by allowing you to set a very random, long, and complex passphrase on your router, but still allow quick and easy connections. However, do keep in mind that there was a major security hole found in WPS in late 2011 and you should see if a firmware update of your router patched it.

Some Wi-Fi devices, like USB adapters, may have physical buttons to initiate a WPS connection. However, with Windows 7 and later you can use the GUI to initiate connections if your wireless adapter supports WPS. You simply select the network from the usual network list in Windows and it will prompt you for the password while also saying “You can also connect by pushing the button on the router”. At that time, push the WPS button on the router and it should automatically connect.

Network Commands

netstat

Displays contents of /proc/net files. It works with the Linux Network Subsystem, it will tell you what the status of ports are ie. open, closed, waiting, masquerade connections. It will also display various other things. It has many different options.

tcpdump

This is a sniffer, a program that captures packets off a network interface and interprets them for you. It understands all basic internet protocols, and can be used to save entire packets for later inspection.

ping

The ping command (named after the sound of an active sonar system) sends echo requests to the host you specify on the command line, and lists the responses received their round trip time.

You simply use ping as:

ping ip_or_host_name

Note to stop ping (otherwise it goes forever) use CTRL-C (break).

Please note: Using ping/smbmount/ssh or other UNIX system programs with a computer name rather than IP address will only work if you have the computer listed in your /etc/hosts file. Here is an example:

192.168.1.100 new

This line says that their is a computer called “new” with IP address 192.168.1.100. Now that it exists in the /etc/hosts file I don't have to type the IP address anymore, just the name “new”.

hostname

Tells the user the host name of the computer they are logged into. Note: may be called host.

traceroute

traceroute will show the route of a packet. It attempts to list the series of hosts through which your packets travel on their way to a given destination. Also have a look at xtraceroute (one of severalgraphical equivalents of this program).

Command syntax:

traceroute machine_name_or_ip

tracepath

tracepath performs a very simlar function to traceroute the main difference is that tracepath doesn't take complicated options.

Command syntax:

tracepath machine_name_or_ip

findsmb

findsmb is used to list info about machines that respond to SMB name queries (for example windows based machines sharing their hard disk's).

Command syntax:

findsmb

This would find all machines possible, you may need to specify a particular subnet to query those machines only.

nmap

“ Network exploration tool and security scanner”. nmap is a very advanced network tool used to query machines (local or remote) as to whether they are up and what ports are open on these machines.

A simple usage example:

nmap machine_name

This would query your own machine as to what ports it keeps open. nmap is a very powerful tool, documentation is available on the nmap site as well as the information in the manual page. 

Network Configuration Commands

ifconfig 

This command is used to configure network interfaces, or to display their current configuration. In addition to activating and deactivating interfaces with the “up” and “down” settings, this command is necessary for setting an interface's address information if you don't have the ifcfg script. 

Use ifconfig as either: 

ifconfig 

This will simply list all information on all network devices currently up. 

ifconfig eth0 down 

This will take eth0 (assuming the device exists) down, it won't be able to receive or send anything until you put the device back “up” again. 

Clearly there are a lot more options for this tool, you will need to read the manual/info page to learn more about them. 

ifup 

Use ifup device-name to bring an interface up by following a script (which will contain your default networking settings). Simply type ifup and you will get help on using the script. 

For example typing: 

ifup eth0 

Will bring eth0 up if it is currently down. 

ifdown 

Use ifdown device-name to bring an interface down using a script (which will contain your default network settings). Simply type ifdown and you will get help on using the script. 

For example typing: 

ifdown eth0 

Will bring eth0 down if it is currently up. 

ifcfg 

Use ifcfg to configure a particular interface. Simply type ifcfg to get help on using this script. 

For example, to change eth0 from 192.168.0.1 to 192.168.0.2 you could do: 

ifcfg eth0 del 192.168.0.1 

ifcfg eth0 add 192.168.0.2 

The first command takes eth0 down and removes that stored IP address and the second one brings it back up with the new address. 

route 

The route command is the tool used to display or modify the routing table. To add a gateway as the default you would type: 

route add default gw some_computer

Internet Specific Commands 

host 

Performs a simple lookup of an internet address (using the Domain Name System, DNS). Simply type: 

host ip_address 

or 

host domain_name 

dig 

The "domain information groper" tool. More advanced then host... If you give a hostname as an argument to output information about that host, including it's IP address, hostname and various other information. 

For example, to look up information about “www.amazon.com” type: 

dig www.amazon.com 

To find the host name for a given IP address (ie a reverse lookup), use dig with the `-x' option. 

dig -x 100.42.30.95 

This will look up the address (which may or may not exist) and returns the address of the host, for example if that was the address of “http://slashdot.org” then it would return “http://slashdot.org”. 

dig takes a huge number of options (at the point of being too many), refer to the manual page for more information. 

whois 

(now BW whois) is used to look up the contact information from the “whois” databases, the servers are only likely to hold major sites. Note that contact information is likely to be hidden or restricted as it is often abused by crackers and others looking for a way to cause malicious damage to organisation's. 

wget 

(GNU Web get) used to download files from the World Wide Web. 

To archive a single web-site, use the -m or --mirror (mirror) option. 

Use the -nc (no clobber) option to stop wget from overwriting a file if you already have it. 

Use the -c or --continue option to continue a file that was unfinished by wget or another program. 

Simple usage example: 

wget url_for_file 

This would simply get a file from a site. 

wget can also retrieve multiple files using standard wildcards, the same as the type used in bash, like *, [ ], ?. Simply use wget as per normal but use single quotation marks (' ') on the URL to preventbash from expanding the wildcards. There are complications if you are retrieving from a http site (see below...). 

Advanced usage example, (used from wget manual page): 

wget --spider --force-html -i bookmarks.html 

This will parse the file bookmarks.html and check that all the links exist. 

Advanced usage: this is how you can download multiple files using http (using a wildcard...). 

Notes: http doesn't support downloading using standard wildcards, ftp does so you may use wildcards with ftp and it will work fine. A work-around for this http limitation is shown below: 

wget -r -l1 --no-parent -A.gif http://www.website.com

This will download (recursively), to a depth of one, in other words in the current directory and not below that. This command will ignore references to the parent directory, and downloads anything that ends in “.gif”. If you wanted to download say, anything that ends with “.pdf” as well than add a -A.pdf before the website address. Simply change the website address and the type of file being downloaded to download something else. Note that doing -A.gif is the same as doing -A “*.gif” (double quotes only, single quotes will not work). 

wget has many more options refer to the examples section of the manual page, this tool is very well documented. 

Alternative website downloaders: You may like to try alternatives like httrack. A full GUI website downloader written in python and available for GNU/Linux 

curl 

curl is another remote downloader. This remote downloader is designed to work without user interaction and supports a variety of protocols, can upload/download and has a large number of tricks/work-arounds for various things. It can access dictionary servers (dict), ldap servers, ftp, http, gopher, see the manual page for full details. 

To access the full manual (which is huge) for this command type: 

curl -M 

For general usage you can use it like wget. You can also login using a user name by using the -u option and typing your username and password like this: 

curl -u username:password http://www.techzone/file 

To upload using ftp you the -T option: 

curl -T file_name ftp://ftp.techzone.com 

To continue a file use the -C option: 

curl -C - -o file http://www.site.com 

Remote Administration Commands

ssh 

Secure shell, remotely login on a machine running the sshd daemon. Once you are logged in you have a secure shell and are able to execute various commands on that computer such as copy files, reboot the computer, just like it was your own GNU/Linux PC. 

Or you can use ssh with a full hostname to connect to a remote machine (as in across the internet). 

Examples: 

ssh hostname 

Connect to a remote system with your current username, you will obviously need the password of the user on the other machine. 

ssh username@hostname 

Connect to a remote system with your a different username, you will obviously need the password of the user on the other machine. 

scp 

Secure copy, part of the ssh package. Allows you to copy files from one computer to another computer, use -r to copy recursively (copy entire directories and subdirectories). 

scp's syntax is always 

scp machineToBeCopiedFrom machineToBeCopiedTo 

Where either machine can be a local directory (on the current filesystem /) or a remote machine. Remote machines are usually machinesFullName:/directory (if you omit the directory part it will just assume the home directory of the username you are logging in with). 

The example below copies all files from the current directory (not including any directories), the command will login to “new” using the username of the person currently logged in on the localcomputer, the files will be copied to the root directory of the remote computer called “new” (which is probably on the LAN): 

scp * new:/ 

You could also copy files from another computer to another computer. Let's say you are on a computer called “p100”. And you want to copy files (and directories) from “hp166” (in the /tmp directory and anything below that) to “new” and put the files in new's temporary directory. You could do: 

scp -r hp166:/tmp new:/tmp 

Assuming you were logged in as “fred” you would need passwords for user “fred” on the computers hp166 and new. Add an user_name@ before the computer name to login under a different user name. 

For example to perform the above command with user “root” on hp166 and “anon” on new you would type: 

scp -r root@hp166:/tmp anon@new:/tmp 

To copy from a remote machine to a local computer you simply do things in reverse: 

scp remoteMachine:/mystuff/* . 

This will copy files on the remote machine in the directory “mystuff” to your local computer. 

Remote Machines: Please note that when working with a remote machine you need to have a : (colon) after the machine name even if you want the files in their home directory. Otherwise the command will fail. 

sftp 

Secure ftp, another part of the ssh package. This command is similar to ftp but uses an encrypted tunnel to connect to an ftp server and is therefore more secure than just plain ftp. 

The command usage is very similar to ftp (the command-line tool), sftp (once running) uses commands such as help (for help), put (send files to the server), get (download files from the server) and various others, refer to the manual page and internal documentation for further details.