Timothy E. Archer

This is Part 4 of 4 in my series of posts on some of the simple utilities one can use to test networking and DNS configurations. This post will concentrate on using the utility whois to determine the owner of a domain or IP address on the Internet.

Whois is a very simple utility to use and is included in most Linux distributions nowadays (and probably most other Unix variants too). If you’re a windows user, you’ll have to download a program to use whois, or just use one of the free web based utilities such as this one:
http://www.networksolutions.com/whois/index.jsp

The simplest way to use whois is to specify the command followed by either a domain name, or an IP address.

For example:
continue reading…

This is Part 3 of 4 in my series of posts on some of the simple utilities one can use to test networking and DNS configurations. This post will concentrate on using the utility dig to perform simple DNS server queries to ensure that your hostnames are resolving the way you expect them to.

Dig stands for domain information groper and is included in most Linux distributions nowadays (and probably most other Unix variants too). If you’re a windows user, you’ll have to download the dig program. One such site I’ve found for this program is http://pigtail.net/LRP/dig/

Much like nslookup, dig performs DNS lookups and displays the results from the queried name server. Most DNS administrators use dig to troubleshoot DNS problems because of its flexibility, ease of use and clarity of output. Dig tends to display its results in a format that DNS administrators recognize which resembles the setup for BIND. Other lookup tools tend to have less functionality than dig.

The most common things I use dig for are to:
continue reading…

This is Part 2 of 4 in my series of posts on some of the most simple utilities one can use to test networking and DNS configurations. This post will concentrate on using nslookup to perform simple DNS server queries to ensure that your hostnames are resolving the way you expect them to.

Nslookup stands for name server lookup and is included in unix and windows machines. Its most basic use is to lookup the IP address for a given hostname. I often also use it to perform reverse lookups (lookup the hostname for an IP address) and I also lookup who is configured as the MX (mail exchanger) server for a specific domain.

I’m not going to go into a detailed explanation of DNS, and all the different possible uses for nslookup, but rather I’ll show you some of the common things I do with it.

First and foremost, I use nslookup to query a nameserver to resolve a hostname to an IP address. To do this, you type the following command:

nslookup timarcher.com

And the output looks like:
continue reading…

Common tools that I find most programmers (and even some network admins!!) know nothing about are the basic networking and DNS related utilities. Typically a service will stop working or errors will crop up and I find it’s a DNS related issue rather than a programming issue. I find this to be especially true when dealing with email servers.

In any case, when diagnosing problems about why your program can’t talk to a server, printer, or client, or when trying to gather information about an IP address or hostname, I find a few tools extremely helpful: Ping, Dig, Whois, and Nslookup.

All of these tools are basic tools included with any Linux distro, and some are even included with your windows machine (ping & nslookup). Below I will describe the common ways I uses these tools in my day to day life. What I present below are extremely simple summaries. Once you’re comfortable with the basics, and if you’re on a unix platform, you should read the man pages about them to understand all the additional options they have.

This particular blog post will concentrate on the ping utility. I will then follow up with posts on the other tools nslookup, dig, and whois to complete the series of information.
continue reading…

When I setup my RedHat AS4 Linux server and connected it to the Internet, I soon saw in my logs that there were unauthorized people trying to login all day long. For the most part these attempted logins were from hacking scripts whose job is to try various common usernames and password until they find a combination that works. Frequently I would see entries in my /var/log/messages file that look like:

Apr  8 14:52:34 as1 sshd(pam_unix)[8217]: check pass; user unknown
Apr  8 14:52:34 as1 sshd(pam_unix)[8217]: authentication failure; logname= uid=0 euid=0 tty=NODEVssh ruser= rhost=111.111.111.111

While these scripts were never able to login, I did not like that fact that they were able to try to so easily.

My solution to stopping these hacking scripts from trying to login to my server was to just change the port that SSH listens on. It’s simply security through obscurity. I’m not here to argue on whether this will totally protect my server or not since I know there are multiple sides to the argument. You’ll find people who will suggest that I use public/private keys, firewalls, and VPN’s, and for an environment housing sensitive data I do agree with this. However, for my home server I was unwilling to spend any money. I wanted a solution that stopped my problem and took less than 5 minutes of effort.

Here’s how I did it on RedHat AS 4. continue reading…

Sure those ads from your ISP tell you what your maximum connection speed will be, but have you ever wondered what it really is at any point in time?

I just stumbled across a nifty little website that allows you to test your Internet Connection upload and download speeds – The Speakeasy Speed Test.

To test your own connection speed, go to the following URL: continue reading…