Domain Names are hierarchical and each part of a domain name is referred to as either the root, top level, second level or as a sub-domain. To allow computers to properly recognize a fully qualified domain name, dots are placed between each part of the name. All resolvers treat dots as separators between the parts of the domain name. The fully qualified domain name is split into pieces at the dots and the tree is searched starting from the root of the hierarchichal tree structure. All resolvers start their lookups at the root, therefore the root is represented by a dot and is often assumed to be there, even when not shown. The resolver navigates it's way down the tree until it gets to the last, left-most part of the domain name and then looks within that location for the information it needs. Information about a host such as its name, its IP address and occasionally even it's function are stored in one or more zone files which together compose a larger zone often referred to as a domain. Within the hierarchy, you will start resolution at the top level domain, work your way down to the second-level domain, then through zero, one or more sub-domains until you get to the actual host name you want to resolve into an IP address. It is traditional to use different DNS servers for each level of the DNS hierarchy. The root of all DNS entries is handled by the DNS servers at the InterNIC [well, sort of, but we'll get to that later --InetD ]. The InterNIC points the Top Level Domains (TLDs) to the top level domain name servers maintained by all registrars such as Network Solutions, Register.Com, OpenSRS and many others. [Please note that InetDaemon does not endorse ANY registrar--they all suck, some more than others. --InetD ]. Next come each domain's server will delegate to the DNS server at the next lower level in the hierarchy. For example, in the figure below, .edu is the top level domain, berkeley is the second level domain, and .cs is the sub-domain of berkeley. Eos is the host name. A DNS server would store the IP address of the host where its name resides in the tree.  Bookmark this page and SHARE:
In the first post for this series, I described DNS being both hierarchical and decentralized. In this post, we will dive into what that really means. DNS is HierarchicalHierarchy is obtained through levels of domains, starting at the root server (represented by a period "."). You may have heard of top-level domains (TLDs) before. Some examples of TLDs include:
They are called top-level domains because well, they are at the top level (excluding the root)! Organizations can register second-level domains under any valid TLD. Because DNS is hierarchical, that means that two separate second-level domains can both use the same third-level domain For example, mail.google.com and mail.yahoo.com are both allowed because the uniqueness of the third level domain is limited to the scope of the second-level domain. This was not possible under the predecessor hosts.txt system. Root Zone ServersIn the above graphic, I introduced a new DNS concept called the root server. The root is the base of the DNS hierarchy tree. While I described it as a single point, it is actually more than that. In reality, the root server is called the Root Zone servers. It's called the Root Zone because there are actually 13 Root servers. These servers are spread out geographically and are the starting place for traversing DNS via resolution. ICANN appoints operators for these 13 root servers. There are 12 total operators.
You may be asking yourself, how do hosts and resolvers know about these 13 root servers? The answer is simple: they're hardcoded! You can view the locations of all the root zone servers here. DNS is DecentralizedThis hierarchical structure of domain levels permits decentralization too. DNS is decentralized in terms of not a single party is responsible for providing the nameservers at each level. At each second-level domain, there are a set of nameservers. These nameservers are used during resolution to provide the IP addresses of third+ level domains within the scope of that specific second-level domain. Since the scope is limited to that particular second-level domain, the registry of the TLD does not need to operate this, and instead, the responsibility is given to the second-level domain registrant to provide this functionality. If the domain registrant does not want the responsibility of providing their own nameservers, there exist third-party companies that offer managed DNS services. Cloudflare is one of the largest managed DNS providers. Most registrars also offer this service. ObservationsWe can make a few observations about DNS from the fact that it is both hierarchical and decentralized. Firstly, DNS is scalable due to its hierarchy. By having "zones" of TLDs, the infrastructure for each zone can be spread out and independently scaled. This is great because some TLDs have more registrations than others. Secondly, since the hierarchy begins with the root, and the root is represented by a period, the fully qualified domain name (FQDN) technically ends with a period too. This is official and was documented in RFC 1034. You can try it out in your browser and verify that it still works:
Finally, FQDNs are parsed from right to left. This is because the root starts on the right-hand side, and the lowest level is on the left-hand side.
The Domain Name System (DNS) has a hierarchical inverted tree structure. The DNS hierarchical inverted tree structure is called the DNS namespace. The DNS namespace tree has a unique root and large number of sub-trees. A domain is a subtree of the DNS name space. A Domain can further divided in to sub-domains. In Domain Name System (DNS) inverted tree structure, top is called the Root. The Root is represented by an empty string "". After the Root, the next layer in the DNS hierarchy is called as TLDs (Top Level Domains). Examples of TLDs (Top Level Domains) are edu., net., org., com., gov., etc. The second level in the DNS hierarchy is made up of the business names or organization names. At the second level in the DNS hierarchy, an organization has control over its own name resolution and is authoritative to its own DNS database. Example cisco.com, microsoft.com. omnisecu.com A Fully Qualified Domain Name (FQDN) identifies the hosts or Sub-domains inside the DNS hierarchy. pc15.tek.omnisecu.com. is a Fully Qualified Domain Name (FQDN), which identifies a computer, under the Sub-domain tek.omnisecu.com. Fully Qualified Domain Name (FQDN) is made up of individual labels separated by dots "." (period). There are DNS Servers operating at different levels of DNS Namespace hierarchy. ICANN has the overall control of DNS Servers operating at Root Level and Top Level Domains Level. Click the following link view the IP Addresses (IPv4 or IPv6) and Fully Qualified Domain Name (FQDN) of Root Level DNS Servers. When we register a domain name, (for example omnisecu.com) we control the DNS namespace within omnisecu.com. There is a delegation within within Root Level DNS Servers, pointing to .com. TLD DNS Servers. There is also a delegation within .com TLD DNS Servers, pointing to the DNS servers of omnisecu.com. No other subdomain can be named omnisecu under .com TLD, within the whole DNS namespace. Now, we control the responsibility of name resolution of omnisecu.com. We can install our own DNS Servers for serving DNS name queries for our domain, omnisecu.com. We can create Resource Records inside the delegated portion of omnisecu.com., create subdomains under omnisecu.com and delegate control of newly created subdomains to other DNS Servers. |
What is at the top of the hierarchy tree of domains?
zusammenhängende Posts
Urheberrechte © © 2024 frojeostern Inc.
