I was helping a friend of mine set up port forwarding on his router so that I could access his system remotely for tech support. We ran into a small problem right from the beginning. He did not know the password for his Netgear router configuration. He also did not have the manual any longer. After walking him through the reset procedure, it was time to login with the default password. Guess what? Neither one of us knew it (I use a Linksys router at home).

After some Googling, I found the Default Router Password Database. A straightforward name for a straightforward site. I just used the drop-down list for Netgear and found his router. I was able to successfully walk him through the port forwarding and then we promptly changed the password again.

With a site like the Default Router Password Database, it makes you want to take extra care to change those default passwords on your router. You did change your default password didn’t you?

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If you have ever heard networking geeks talk about subnetting or you are trying to learn it on your own, you may be wondering how anyone does all that subnetting magic binary math. Learning the math behind the subnetting is the key to a solid foundation. However, if you need to do subnetting really quickly (like for a certification exam), the following steps might help.

Most of the information for a subnetting question can be found by using the binary chart:

128 | 64   | 32   | 16   | 8     | 4     | 2     | 1     |
128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 |

The top of the chart is binary through 128. The bottom of the chart are the subnet mask values. (If you will notice, you get these values by first bringing down the 128, and then adding the next binary value to it e.g. 128+64=192, 192+32=224, 224+16=240 and so on.) Now here is the trick to using this chart:

Say you have a subnet mask of 255.255.248.0 Well, from this mask you know that the subnetting will be done in the third octet.

-Fill in 1’s in the chart until you reach 248 on the third octet from left to right. (That would be 8 ones in the first row, 8 ones in the second row, and 5 ones in the third row.) In CIDR notation this would be /21.

Now you know that this is a /21 subnet mask.

-Just do the same process if you do not know the decimal subnet and you do know how many bits you have borrowed. So if you had to borrow 5 bits from a class B address, then you would end up with a /21 (just fill in the 1’s).

Now comes the cool part. Finding your network increment. (In other words, knowing on which address the network begins and ends.)

-Having just filled in the 1’s on your chart you should see that you have stopped filling in 1’s at the 248 column in the third row of the binary chart.

-Now follow that column up until you get to the top row where the 8 is in the binary chart. Guess what? 8 is your network increment.

So you know that the Network ID’s are going to be multiples of 8. (*.*.8.*, *.*.16.*, *.*.24.* and so on.) This method works every time. It is a handy shortcut that has helped me on many networking tests. I hope that it helps you as well. Good luck with your certifications or other subnetting endeavors.

Happy Subnetting!

Technorati Tags: Networking, Subnetting, Easy Subnetting, Certification

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Google Query: create network diagrams with openoffice draw

Since I prefer to use Ubuntu Linux, I do not have access to Visio unless I boot my Windows VM. I often have to create Network Diagrams at work and I was looking for a way to do it without using Visio.

I eventually found some computer and networking equipment templates for Openoffice Draw at Lautman.net.

Since the graphics are just icons, all you need to do to use them in Openoffice Draw is copy and paste them into your diagram. It’s not a complete replacement for Visio. However, it does mean that I have to boot my Windows machine less often.

That alone, was worth the search effort!

Technorati Tags: OpenOffice, Network Diagrams

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