In this video, explore a quick overview of how DNS works. This is not an exhaustive conversation as a certain amount of knowledge for this Cert Prep series is assumed.
- [Instructor] I won't spend too much time on how DNS name resolution works as that is a topic I will assume you know. However, just to make sure terminology we cover later makes sense, I'll skim it. DNS name space is a hierarchy. At the top is dot, which is the root of the tree. The levels right below it are the top level domains or TLDs, examples would be com, net, or org. Below the TLD is a domain which is a collection of hosts. An example of a domain would be redhat.com. Below the domain will be sub-domains such as access.redhat.com. These domains can then be sub-divided farther depending on the needs of the organization.
Deep within the organization would be the hosts, which have host names. For instance, if we had a server called rhhost1 in the access.redhat.com sub-domain. It's fully qualified domain name, or FQDN would be rhhost1.access.redhat.com. What is more important for us is that sections of a company's DNS tree can be divided up and given to one DNS server or another to manage. These sections don't have to correlate exactly to sub-domains and domains either. One DNS server could manage different portions depending on how the network is configured. For instance, DNS server one could manage the host and access.redhat.com and DNS server two could manage resolving the host directly under redhat.com.
DNS names inside of an organization can be managed by the DNS administrators themselves. But if that host has to be accessed from the internet by its DNS name, it needs to be registered with a domain registrar. This lets the rest of the world know who manages the resolution for that particular name. Not anyone can be a registrar, as they are licensed by ICANN or Internet Corporation for Assigning Names and Numbers. I mentioned that at the top of the tree are the root servers designated by the dot. There are not many of these servers running, but they do have mirrors to share the load. We can see where they are by looking at a file included in the binder package.
The file /var/named/named.ca. This lists both their IP version four addresses as well as IP version six addresses. It's important to note that the root servers only handle queries for the top-level domains. If you try to resolve access.redhat.com, the root server will tell you which DNS server to follow up with that manages that domain. The rest of the resolution process goes through other DNS servers. If the roots servers handled all DNS queries, they'd be overloaded in the first second of operation.
Note: This course also helps you study to pass the Red Hat Certified Engineer (RHCE) exam—the benchmark certification for Red Hat Enterprise Linux.
- Installing DNS clients
- Using host, nslookup, and dig
- Name resolution
- DNS roles
- Configuring DNS
- Apache web server features
- Apache commands and access control
- Configure Apache and virtual hosts
- Securing virtual hosts with SSL and TLS
- Running CGI scripts in Apache
- Configuring NGINX server blocks