From part 1 to 3 we covered the whole TCP/IP structure as a whole in order to troubleshoot common problems connecting to the Internet, from part 4 to 6 I will cover DNS, DHCP, Default gateway, NAT, and Subnets in details. Let’s start with DNS (Domain Names Service) what’s DNS for? Let’s reverse time back to the seventies, and let’s imagine you and I are hanging out and you ask me where can you find information about troubleshooting Internet Problems?, I would tell you, go to 66.11.225.53 for my helpdeskgeek.com site or do a Google Search at 72.14.207.99 if you are like most people you won’t remember even the first two numbers from these addresses after a few minutes, that’s why DNS was develop to make this easier, you only need to type helpdeskgeek.com and DNS server automatically translate that to the IP address, is easier to remember names like google.com than an IP address right?

Back in the early days of the Internet when only a handful of people were fortunate to use the internet and the number of hosts were less than 100 on a network there used to be a list of names and IP addresses called the HOSTS.TXT file which was kept on a centralized location at Stanford Research Institute’s Network, everyone using the Internet would download this file locally to their machines , and it pretty much work well as long as the number of hosts were low and changes were infrequent, TCP/IP stacks still have this functionality though is seldom used with the Internet any more. But as the Internet grew bigger using this file was a pain, and the Internet needed a better way of managing name resolution, so in 1984 Paul Mockapetris introduced the DNS.

DNS is Hierarchical which means information is stored is related groups, these are some terms in DNS;

Tree a type of data structure with each element attached to one or more element directly beneath it. In DNS is called an inverted tree because is generally drawn with the root at the top of the tree.

Top Level Domain refers to the suffix attached to Internet Domain names, there are a limited numbers of defined suffixes and each represent a top-level domain, most popular top level domains are, .COM .NET .ORG .GOV. EDU etc.

Node a point where two or more lines in a tree intersect, in DNS a node can represent a top level domain a subdomain, or an actual network computer.

Fully Qualified Domain Name (FQDN) a domain name that includes all domains between the host and DNS is a FQDN for example www.helpdeskgeek.com is a fully qualified domain name.

Leaf an item at the very bottom of a hierarchical tree structure and it does not contain any other objects. In DNS this are called nodes.

Zone a DNS zone is a logical grouping of hostnames within DNS. For example www.helpdeskgeek.com is considered the forward look-up zone for Helpdesk Geek, is where the info about the helpdesk geek hosts is contained within DNS.

Basically everything in a computer is hierarchical, if you tell a typical user that he been working with a hierarchy since the first time he turned on a computer, he will tell you to stop smoking the peace pipe, and won’t have idea what are you talking about, since DOS 2 computers been using hierarchical file system. Why computers need hierarchical files system? Because storing files as alphabetical listing is inefficient, they need to be store in related groups. This is the way computers store files on the hard drive.

Enough of technical jargons and let’s get this in normal terms, how all this works? There are world DNS servers which provide resolution for top level domains like .COM.NET.ORG., so when you register a domain, let’s say you want to registry helpdeskgeek.com you query one of these DNS servers to see if it’s available, remember all objects on top domains need to be unique, so if someone else registered that domain you will get the notice that domain name is already taken, so how would .COM DNS hierarchy would look like?

Forward Lookup zone.

.COM

Helpdeskgeek
Everyone registering a domain name will be under .COM the same thing for .NET and .ORG domains. So less say you want to setup a network with your own DNS server you will put your top domain name in the forward lookup zone, which will look like this,

Forward Lookup zone

Helpdeskgeek.com

When you join computers to this network the full qualified name for the computer will be nelsonlap.helpdeskgeek.com, when you install a DNS server it automatically points to a top world domain name servers, which is addr.arpa.dns something like that, so you see the logic in computer communication? Let’s analyze, the first thing to notice is that all objects in a specific group are unique, like all computers joining the helpdeskgeek domain will need to be unique on the node group, otherwise you will have duplicate name conflicts. All these names are store in the DNS database, so when you want to access files shared in nelsonlap computer you type \\nelsonlap on the run command this name automatically get resolve to 192.168.10.50 and you are able to access the files. The same thing when accessing the Internet from your computer, let’s say you type www.google.com the query goes to helpdeskgeek.com and if helpdeskgeek.com doesn’t know the IP address for Google it will query the higher DNS on the line until it finds the DNS server which has the IP address for Google. I’m working on a document on how to setup DNS implemented in Active Directory on Windows 2003, subscribe to the geek so you don’t miss all this!

Wasn’t this document about troubleshooting? Yeah it is, but to troubleshoot something you need to have some understanding on how the thing works, otherwise you will be troubleshooting in the dark, if you have read this from the beginning you should have some idea how DNS works, so lets try some basic tools to check if DNS is functional, the first utility we will use is the PING, when you ping a computer you are sending ICMP (Internet Control Message Protocol) to a computer, let’s ping Google; go to START>RUN type CMD hit ENTER on the DOS prompt type ping google.com

From this sample you can see my DNS is functional for I get the IP address resolve for Google, is the first thing to look up when you are troubleshooting DNS, the rest of the information has to do with network latency.

The next to is NSLOOKUP.EXE is a standard command line tool provided in the most DNS server implementations, NSLOOKUP offers the capability to perform query testing of DNS servers and obtain detail responses at the command prompt from the command prompt les do s NSLOOKUP command, type nslookup google.com you should get something like this,

Please notice this query could not find my DNS server name, because I’m using a wireless router and the router already comes with a limited DNS server to resolve names, but I was able to get Google DNS server name and IP address which mean my DNS server is working.

 

The last utility we will use is flushdns type INCONFIG /FLUSHDNS, this simple command let you flush any DNS entries you might have on your computer cache, one scenario might be is when you change DNS servers and you still getting old DNS entries on a computer you flush the cache, and your computer should grab the new DNS settings. A flush command looks like this;

Well, I guess I made this a little too long, but there is so much things about DNS that I couldn’t stop writing, and I only have touched the tip of what is a DNS mechanism, in the future I will write the whole procedure on how to install, implement a DNS server. I hope this is being helpful to some of you, at least for me is being really helpful to pick my brain about this wonderful things. Next part will be DHCP. “˜til then.