Before you start
Objectives: learn where can you configure advanced DNS settings in XP.
Prerequisites: no prerequisites.
Key terms: dns, name, ip, server, wins, address, domain, netbios, resolution
DNS Usage
When we look at some IP address, we see four octets (grouping of eight bits). Every host on the network has its own IP address. For example, every website resides on a server. If we want to visit some website, we have to connect to the particular server which hosts the website that we want to visit. To do that, our computer has to know the IP address of that server. Instead of using IP addresses, we refer to websites using their names (for example www.google.com). For humans, names are a lot easier to use then to remember numbers like IP addresses. Solution for that problem is Domain Name Service, or DNS. We are using DNS to resolve names to IP addresses, because it’s the IP address that computers use to talk to one another. We can easily check that by pinging some host, for instance www.google.com. As a result, we will get back the IP address from the DNS server. As we can see, DNS serves have a very simple function. DNS takes user-friendly names, like www.google.com, and it converts it into a complex IP address, and vice-versa. This way we don’t have to remember IP addresses, and we can navigate the Web simply and easily.
FQDN
DNS name servers perform name resolution by resolving a Fully Qualified Domain Name (FQDN) into an IP address. A client asks its local name server for the IP address associated with the Fully Qualified Domain Name. For example, the client asks what is the IP address of www.google.com. The local name server checks its list, and if it finds the entry for www.google.com, it passes the information back. If the local name server can’t find the entry, it sends a fully qualified domain name to one of the DNS root servers. The DNS root server returns its referral to the local name server. The referral points to the name servers for the top-level of the DNS domain. The local name server sends an iterative query to one of the top-level domain name servers (.com in www.google.com case). The .com domain server responds with a referral to one of the Google name servers. The Google name server responds with the IP address of www.google.com. Now the client can contact the host which hosts the www.google.com website.
WINS
Microsoft first developed its own naming system. It was using NetBIOS names for hosts, and Windows Internet Name Service (WINS) to resolve names to IP addresses. NetBIOS name is a 15 character name that is used for identifying our computers on the network. All this is a part of Microsoft’s networking services, which Microsoft introduced with NT family of operating systems. It is continued on through the NT 4.0 family. With the Windows 2000 and Windows XP, Microsoft adopted the Domain Naming Service as its primary tool for resolving names to IP addresses while the rest of the Internet was always been using DNS. The problem that Microsoft had originally with DNS is that all of its entries had to be statically entered (DNS became a dynamic tool later). In WINS environment, a client would first get its IP address from DHCP server. Then the client would contact the WINS server, reporting its IP address. In this way, the WINS server has IP addresses of all clients on the local area network. So, WINS was the solution that solved this particular problem. With Windows 2000 the DNS service became more of a dynamic service. It could dynamically register clients and use that information to register the IP address. At that point Microsoft went back to using the DNS service as its primary name resolution service. Now, when we use Windows XP, it will automatically register its name with the DNS server. This simplifies the number of services that we have to run, because we don’t need a WINS server for our local area network. We still use WINS, but only for legacy machines that don’t understand that the DNS can now accept dynamic updates from clients. As we moved into the dynamic DNS, Microsoft had to adjust the names. Instead of being just a NetBIOS name, now we also add the domain information to the name structure as well. In order to find out who’s who on our network, we can use DNS using a FQDN instead of just a simple NetBIOS name that we used for WINS service.
Example Configuration
In order to configure Name Resolution Services on XP, we need to go to the connection properties and click the ‘Advanced…’ button on our TCP/IP configuration window. In advanced properties we can see current IP settings, DNS, WINS and Options tab.
Image 239.1 – Advanced TCP/IP Properties
Although most computers have a single IP address, and a single default Gateway, notice that on the IP Settings tab we can configure multiple addresses and gateways. Let’s open the DNS tab. Here we can edit DNS settings for our computer.
Image 239.2 – DNS Tab
The first thing that we would do on the DNS tab is to add additional DNS servers. Of course, the primary DNS server needs to be placed first on the list. If the first DNS server can’t be contacted, our system will try to contact the next DNS server on the list. Another thing that we can do here is to to append additional suffixes. Let’s say that we need to contact ‘host-pc’ using DNS. Let’s say that ‘host-pc’ is on ‘saadz26.sg-host.com’ domain. Let’s say that we want to access the ‘host-pc’ from the computer that is also on the ‘saadz26.sg-host.com’ domain. If we type only the name of the computer – ‘host-pc’, the DNS server will automatically look into the ‘saadz26.sg-host.com’ and try to locate the IP address for ‘host-pc’. Now, let’s say that we want to contact the ‘host2’ that is located on ‘utilizeothersystem.com’. If we type in only the name ‘host2’, our DNS server will also try to locate the computer in ‘saadz26.sg-host.com’. The DNS server will be unsuccessful in locating the ‘host2’, because it is located on ‘utilizeothersystem.com’. If ‘utilizeothersystem.com’ is a domain that we frequently use, and is in some relation with our primary ‘saadz26.sg-host.com’ domain, we can add ‘utilizeothersystem.com’ as an appended suffix. In this case, if we look for ‘host2’, our DNS server would first check ‘saadz26.sg-host.com’, and then, in case of failure, it would check the ‘utilizeothersystem.com’.
Let’s open the WINS tab. Here we can also add, remove, and control the order of our WINS servers. Once again, we have to put our primary WINS server at the top of the list. WINS servers are used for performing NetBIOS name resolution.
Image 239.3 – WINS Tab
Here we can also enable the LMHOSTS, and edit the NetBIOS settings. We have the ability to disable NetBIOS over TCP/IP, and we would do that if we are in an environment where we are using DNS only.
Troubleshooting
Windows XP supports two different types of name resolution services, DNS and WINS. Remember, when we mention DNS, we are talking about Fully Qualified Domain Names, ie. DNS is using FQDN to identify particular computer. An example of this might be ‘host1.utilizewindos.com’. On the other hand, WINS uses only NetBIOS names for name to IP resolution. NetBIOS names are simple names, and can contain only 15 characters. For example, NetBIOS name could be ‘host1’.
When troubleshooting name resolution services, first we have to check that everything is OK with TCP/IP. For example, if we pingsome IP address, and everything goes fine, we know that IP connectivity is OK. If we ping the name of the computer, and get an error, we know that we have problem with our name service.
Image 239.4 – PING
The next utility that we should run is ‘ipconfig /all‘. With this tool we can verify that the IP addresses for DNS or WINS are properly configured.
Image 239.5 – IPCONFIG
The next thing we can do is run the ‘nslookup‘ and see if we get an IP address from our DNS server.
Image 239.6 – NSLOOKUP
If all our settings are configured correctly, we should check the services related to name resolution (like ‘DNS Client’), and make sure that they are up and running. Another thing we can do is to try and re-register with our DNS server. To do that we have to enter ‘ipconfig /registerdns‘ in command prompt. For NetBIOS names we can use the ‘nbtstat -rr‘ to see name resolution status, and ‘nbtstat -RR‘ to re-register with the WINS server.
Image 239.7 – REGISTERDNS
We can also use the ‘ipconfig /flushdns‘ command to delete DNS cache, because sometimes we can have wrong information contained in it. For NetBIOS names we would use ‘nbtstat -R‘ command to do the same thing.
In the end, as a temporary solution we can use HOSTS file to configure DNS names, or LMHOSTS file for NetBIOS names.
Remember
We can have multiple DNS servers defined. The primary DNS server needs to be placed first on the list. WINS servers are used for performing NetBIOS name resolution.