The difference between top-level, second-level, and third-level domain names
A complete domain name consists of two or more parts, each part is separated by an English period ".", and the right part of the last "." is called a top-level domain name (TLD, also known as a first-level domain name) , the left part of the last "." is called the second-level domain name (SLD), the left part of the second-level domain name is called the third-level domain name, and so on, each level of domain name controls the allocation of its next-level domain name
The composition of a domain name
Top-level domain name: A domain name consists of two or more word segments, and the rightmost one is the top-level domain name.
At present, the top-level domains that appear internationally include .com, .net, .org, .gov, .edu, .mil, .cc, .to, .tv and country or region codes, of which .com is the most common, .net,.org
.COM - - For business entities, it is the most popular top level domain name, anyone can register a .com domain name.
.NET - Originally used by Internet agencies such as ISPs, today anyone can register a .net domain name.
.ORG --- Designed for use by all kinds of organizations, including non-profit groups, today, anyone can register a .org domain name. Country code: Domain names with two letters such as cn (China), fr (France) and au (Australia) are called country code top-level domains (ccTLDs). Through ccTLDs, the country or region of the domain name holder can basically be identified. Detailed country codes can be found at www.icann.org.
Second-level domain name: The part on the left is the so-called second-level domain name. In cctv.com, cctv is the second-level domain name under the top-level domain name .com. cctv.com can also have the form of mail.cctv.com. Here the mail Can be called "host" or "subdomain"
//The network segment (private network address segment) that can be used by the LAN has three segments:
10.0.0.0~10.255.255.255 (Class A)
172.16.0.0~172.31.255.255 (Class B)
192.168.0.0~192.168.255.255 (Class C)
The domain name is an IP alias, which is easy to remember. The domain name is finally resolved into an IP address through DNS.
NAT (Network Address Translation) is network address translation, NAT can convert its local address into a global IP address