ssh: Remember each host’s settings

ssh: Remember each host’s settings

When you start using ssh to connect to other linux-based computers, you’re probably only going to a handful of machines. Easy enough to remember the username and hostname, but this won’t do when you’re working on 5 or more servers, especially if some offer ssh on a non-default port.

~/.ssh/config

In this file, you can set all the options for each host, including the username, host or ip, port, even which key to use. Here’s an example:

#Contents of $HOME/.ssh/config
Host dev
HostName 192.168.0.1
User dev-deploy
Port 2222
IdentityFile ~/.ssh/id_rsa.deploy.key

Host prod
HostName www.example.com
User prod555deploy
Port 5899

Host www.example.com
User admin123
Port 5899

It’s that easy! To use this config information, simply ssh:

ssh prod

Happy Computing!

Internet Troubleshooting

What do you do when your internet connection goes does? Go get a board game or cards? Call your IT friend from work? Bang on the desk until the page loads? While most of these are good solutions, getting your connection running again is pretty simple. As long as nothing is wrong on your provider’s end, that is.

Perform each step by itself. Try to load a webpage after each step to see if it is working.

  1. Check your connections.
  2. Shutdown your computer and boot it up again.
  3. Unplug your router, if you have one, for 30 seconds then plug it back in.
  4. Unplug your cable/dsl modem for 30 seconds then plug it back in.
    Wait for the “Internet” or “DSL” or “Cable” light to light up.
  5. Repeat Step 3.
  6. Repeat Step 2.
  7. Open Control Panel -> Network Connections and Delete the “Local Area Connection”, then reboot.

If none of these steps fix your connection, there is probably a problem at your provider and you should call their tech support line.

Hint: Print this page and keep it by your computer so you have it when the internet does go out. Also, write the tech support number on the print out for convenience.

Networking Day 7: Extending your wifi range

General Wifi Range is 75 feet if the line from you to the router is completely open. Most of the time, you have lots of things between you and the router — walls, wires, pipes, etc. Many times you’ll find that 35 feet is where the signal gets tempermental.

Antennae
There are two basic types of wifi extender antennae. Both types connect to the same connector that your basic antenna uses. You may need an adapter though. Some laptops do not have a connector for an antenna, so double check before you go out and buy one for your laptop.

Unidirectional Antennae will boost the signal in one direction only. The best use is when you have a clear line of sight, but are a distance away.

Omnidirectional antennae will boost your signal in all directions. This is helpful if you have a router in the center of your home and the signal in the far corners isn’t all that.

Wireless Access Points
This is like having a second wireless router. If you don’t have a wireless router, you can add one of these to your network to give you wireless access.

There are many reasons why you would add an access point.

  1. If you want to limit access to the internet for your child, just take the power cord to bed with you.
  2. Place it on the porch for access outside.
  3. The list goes on.

Networking Day 6: Shared folders

Sharing a folder is an easy way to copy files from one computer to another. Windows shares work with Windows, MacOS and linux.

Setting your computer’s name
Right-click on My Computer and then click Properties. Under the name tab, you can setup the name. Your computer will reboot after you click OK. This step is not neccessary if you are using a static IP address.

Setting up a share on Windows
Sharing a folder is a snap. Right-click on a folder you want to share and then click “Sharing ans Security”. If you have never shared a folder before, click the link and tell it to enable sharing. Give the share a name. Check the box if you want other people to write to files or create files in this folder.

Connecting to a share on Windows
Click on the Start Button, then click on “Run…”. In the box type “\\COMPUTERNAME\” replacing COMPUTERNAME with the name of your computer or it’s IP address. Click OK and it will show you all the shares on that computer.

You can map a shared folder to a drive, like “Z:\”. Simply, right-click on a shared folder and select “Map Network Drive”. From that popup, select your drive letter. Click OK and you’re done. That drive will attempt to reconnect everytime the computer is booted.

Networking Day 5: Port Forwarding

Today is all about port forwarding.  This is needed when you want to make a specific service available to anyone on the internet.  That service could be a game, a web server, or even Yahoo Messenger.

Ports
Anytime you connect to a server, you are connecting to a specific port. The server listens on that port for incoming connections and respond appropriately. Different port numbers are for different services.  A few examples include:

  • 80 — http
  • 21 — ftp
  • 25 — smtp (sending email)
  • 110 — pop3 (recieving email)

Before you begin the setup, you should find out what port needs to be opened.  You can figure this out by the manual or a quick internet search.

Setting up a static IP
This is necessary for most port forwarding.  Please review Day 2: Subnets for information on selecting an IP address to use.  The static IP must be in the same subnet as the dynamic IP.

Also, make sure that the DHCP on your router will not give out this IP address.  All routers will have a range of IP addresses.  If the range starts at “.100”, you can use “.99”. Also, if the range ends at “.199”, you can use “.200”.

Setting up the forwarding
Log into your router’s admin interface.  There should be “port forwarding” or “port address translation” in the menu, click this.  On this screen it should have somewhere you can enter the port and ip or a link to click to get to enter that information.  Enter the port and IP, click save, and you’re done.

Don’t forget to get your public IP address from a service like WhatIsMyIP.com.

Networking Day 4: Wireless Router Setup

A wireless router is a wired router with 1 or more antennae. You should complete the setup of the wired portion before continuing. The router’s admin tool will have a wireless setup section that we’ll be working in today.

Speeds
Most routers and devices use the “G” form of wifi. It’s technical name is 802.11G. It runs at up to 55 Mbps (megabits per second). The “B” form runs at up to 11 Mbps. The latest version, “N”, runs at up to 600 Mbps.

The speed of your connection will be the lower of the router and the device. So, if your router is “B” and your device is “G” or vice-versa, the fastest you’ll go is 11 Mbps. Just like many other things, you network is only as fast as its weakest link.

AP Name & Channel
The Access Point Name is the name that will identify the wireless network. It will only operate on the channel you select. If you notice that something is interfering with your signal, change the channel. 2.4GHz phones are bad interfering with wireless networks, but changing the channel does the trick most of the time.

Wireless Security
Under the wireless section of your router’s configuration, you can setup your security. WEP is the most common type of security used. It uses 128-bit encryption, the same level used by websites that take credit card payments.

Select WEP from the drop down menu and give it a 13 character password. The better the password, the better the security. A good mix of numbers, symbols, uppercase and lowercase letters is best. Try to use acronyms, like NASA or NFL, instead of words.

Windows and MacOS should have an icon next to the clock to setting it up. Tell it to connect to the AP name and it will ask for the password. Linux uses a utility called wpa supplicant which can be setup graphically or by the command prompt.

Where to purchase
You can get these anywhere. You don’t need all the fancy bells and whistles. The biggest question is whether you want wireless or not. If you’re going wireless, go with the “802.11G”.

One of the best places to purchase a used router is the flea market. It sounds a bit shady, but usually honest and good people work up there, and the price is 50% off the retail version.

Networking Day 3: General Router Setup

For almost all home networks, a router connects the local network to the internet via a cable/dsl modem. Most home routers have other features such as DHCP, a firewall, a de-militarized zone (DMZ) and port forwarding. Some even have a usb port to connect a printer for easy use from any computer.

The router actually has 2 IP addresses
Yes, the router has 2 IP address. One is the public IP address. This is the IP address that shows up to the outside world. WhatIsMyIP.com is one of the many sites that can tell you what your public IP address is.

The other is the local IP address. This is on the same subnet as all the computers on your network. This usually ends with a “.1”.

Configuring the router
Most routers can be configured directly from your web browser. All you have to do is type in the local IP of the router. You should be prompted to enter a username and password. These can be found in the manual along with the subnet IP of the router. If you don’t have the manual, you can download them from the manufacturer.

DHCP
DHCP hands out IP addresses automatically. Make sure this option is turned on. It makes life a lot easier. Also, make sure your computers are configured to use DHCP.

Configuring clients
Either set up DHCP on the computers that are connected or assign them a unique IP address in the subnet. I’d suggest going DHCP, as it makes life easier. If you’re brave enough to try static IP addresses, don’t turn off DHCP in the router, in case you mess up the IP address or subnet mask.

Cables
Standard routers use ethernet cables to connect computers to it and to connect it to the cable/dsl modem. These can be hazards if running across the floor. They can also be expensive. If you want to make your own, it’s fairly simple and inexpensive. Click here for wikiHow’s How to Make a Network Cable. You can even get ethernet wall jacks, they look just like phone jacks.

Where to purchase
You can get these anywhere. You don’t need all the fancy bells and whistles. The biggest question is whether you want wireless or not. If you’re going wireless, go with the “802.11G”.

One of the best places to purchase a used router is the flea market. It sounds a bit shady, but usually honest and good people work up there, and the price is 50% off the retail version.

Networking Day 2: Subnets

A subnet is just one small group of computers. What makes it special is that all the computers on the subnet can communicate with each other without a router. All the computers in your house should be on the same subnet.

Subnets can be difficult, but I’ll keep it easy as possible here.

Subnet mask
The subnet mask is used to determine if two computers are on the same subnet. In most home networks the subnet mask is “255.255.255.0”. That subnet mask means that the first three numbers in the IP address must be exactly the same for both computers to be in the same subnet. A subnet mask of “255.255.0.0” means the first two numbers must match.

Here are some examples:

IP AddressIP AddressSubnet maskSame
subnet?
192.168.0.3192.168.0.205255.255.255.0Yes
192.168.0.3192.168.1.3255.255.255.0No
172.16.1.33172.16.33.1255.255.255.0No
172.16.1.33172.16.33.1255.255.0.0Yes
192.168.0.3192.168.0.134255.255.0.0Yes

Subnet notation
In binary, the subnet mask is a string of 1’s followed by a string of 0’s and 255 is eight 1’s in binary. So the netmask “255.255.255.0” is 24 1’s followed by 8 0’s in binary. An IP address in subnet notation is the IP address immediately followed by a forward slash and the number of 1’s in the subnet mask.

Here are some examples:

IP AddressSubnet maskSubnet notation
192.168.0.3255.255.255.0192.168.0.3/24
192.168.1.233255.255.0.0192.168.1.233/16
172.16.10.3255.255.255.0172.16.10.3/24
172.16.10.3255.255.0.0172.16.10.3/16

The gateway
If a subnet is connected to another network, such as the internet, you need a router. A router acts as a gateway for a subnet. It’s IP address usually is “.1” or “.0.1” inside a subnet. So 172.16.10.3/24 would be 172.16.10.1 and 172.16.10.3/16 would be 172.16.0.1.

That’s basic subnets
This is the easy subnetting. Of course, the full subnetting involves masks of “255.255.196.0”, notations of “172.16.33.34/19”, etc. There’s no need to do all that. Most of the time you are safe using the subnet mask of “255.255.255.0”, unless you want to connect more than 253 computers. Why not 255 or 256 you ask? It’s a long story.

Come back tomorrow for how to set up a router.

Networking Day 1: Intro

A home network can allow multiple computers to share files, a printer, as well as an internet connection. For the most part they are fairly simple to setup. This series of posts will help you setup your home network and understand what is happening within the network.

This post covers the basics of networking. If you know what IP addresses and DHCP are, you can skip to the next post.

Here are the simple facts:

  • A network is two or more computers connected together.
  • Each computer on the network is assigned a unique address.
  • The internet is one huge network consisting of many smaller networks.
  • Almost all modern networks, including the internet, use the TCP/IP protocol.

This guide’s networks will use the TCP/IP protocol.

IP Addresses
Using TCP/IP, each computer’s unique address is an IP address. An IP address looks like 192.168.0.145. It’s just 4 sets of numbers separated by a period. These numbers range from 0 to 255. You can set the IP address for a computer manually. This is call a static IP.

DHCP
A dynamic IP address is one that is assigned via a DHCP server. The DHCP server takes care to make each IP address unique. Most, if not all, routers, cable modems and DSL modems have a DHCP server built into them.

Wired vs. Wireless
On a wired network, every computer is connected via a cable to a cental point. On a wireless network, every computer is connected wirelessly to an access point. A hybrid network is when some computers are connected via a cable and others are connected wirelessly.

You are the architect
When designing a network, you are the architect. You have complete control over every bit of data that travels over your network.

Home Networks

Now that high speed internet is the norm, more and more people have a home network. A home network is nothing but 2 or more computers connected together via a router. There is more to it than this, but it all boils down to being that simple. To see how it works, let’s trace the internet connection.

If you have cable internet, the signals come into your house over the cable lines. The cable modem converts these signals into an ethernet (looks like a wide phone jack) connection.

If you have DSL internet, the signals come into your house over the phone lines. The DSL modem converts these signals into an ethernet (looks like a wide phone jack) connection.

From the ethernet connection, the internet travels to your router. The router does several important things. It acts as a firewall, blocking people on the internet from accessing your home network. It provides any computer directly connect with a unique IP address which helps the router know what computer is sending/receiving data from the interent.

An IP address is a set of 4 numbers, each 0-255, which identifies a computer on a network. The router uses something called a subnet which is just a group of IP addresses. Most routers use the subnet 192.168.0, which includes all the addresses from 192.168.0.1 to 192.168.0.254. The router is the 192.168.0.1. These addresses might not be the same as your router is using because every router is different.

Because the router has a firewall, you don’t need a firewall on any computer connected to the router, wired or wireless. That means that Windows won’t have to work as hard to protect your computer because you can turn Windows’ firewall off.

A home network isn’t limited to only having computers. A printer can be connected to the network instead of to a computer. After installing the printer software to a computer connected to the network, you can print from another room! A VOIP (Voice Over IP) phone, such as ViaTalk or Vonage, can be connected to the router as well. The list doesn’t stop there either.