About DNS.

Today, the lab purchased a new router. Under the configuration of the O & M engineer, it was barely running (mainly the wireless route... I won't talk about it ).

The route is configured. However, there was another problem on everyone's computers, so they could not access the internet...

I have probably read that it is a common problem: I have obtained an IP address. It's okay with DHCP.

If the gateway is pinged, Google's DNS (8.8.8.8) cannot be pinged.

The arrow points to the so-called DNS server.

What is a DNS server?

DNS is a domain
Name System) is a core service of the Internet. It serves as a distributed database that maps domain names and IP addresses to make it easier for people to access the Internet, instead of remembering the number of IP address strings that can be directly read by machines.

Simply put, the IP address is equivalent to a person, and each person must have his/her own name. This is called a domain name. However, we want to find a person who just knows his name and network doesn't know who the person is. Therefore, we need a service that performs resolution conversion between IP addresses and domain names. This is what the DNS server does.

This technology is developed to facilitate user memory. An IPv4 IP address is composed of 32 digits, and is converted to an IP address of about the length of XXX. XXX in decimal format. However, the IP address in the future IPv6 protocol is composed of 128-bit binary numbers. Therefore, this technology is very necessary!

Configuration of a DNS server

In ubuntu, the path is/etc/resolv. conf.

Recommended DNS servers: 218.30.19.40 (DNS server of Xi'an Telecom) 8.8.8.8 (Google DNS)

Basically, these two are enough.

How does a DNS server work?

There are two main recursive and iterative approaches to work.

Recursion:

To put it bluntly, the host sends a domain name resolution request, which is passed up at the first level until a DNS parser can resolve the domain name you sent, the IP address pointed to by this domain name is passed to the client again.

Iteration type:

The working principle is to access a DNS server. If no query is found, the higher-level DNS server address is returned. Then, access the obtained DNS server address locally until the query results are displayed.

The above is my one-sided view of DNS...

There are still many defects.