How does DNS work?

When any end device broadcast the query for asking IP address of any domain, like google.com, to the local DNS.

local DNS server gets the query, searches its cache and records if the related information is available on the server It then provides the ip address of particular domain to the end device so that end device can directly connect to the domain.

If the information is not available on the DNS’ caches or records, then it forwards the query to the IPS; on the IPS end, the same process is done by again. If the ISP also does not have the required information about google.com, as we know that every DNS server has an address of Root Hint, then this query is forwarded to the Root Server.

The Root Server has address of all the top-level domains like .com, .in, .org, .edu, etc. it searches in its catalog, and as soon as it gets the information about domain, it quickly sends to the top-level domain.

At the end of the top-level domain server, It searches for the IP address of Google.com and provides the IP address, and this address is forwarded to the end device so it can directly connect to Google.com.

The whole process is done with in a second.

                                              DNS Zones

DNS Zones is the most important component of DNS server that contains DNS record.

There are two types of DNS zones:

1. Forward Lookup Zones: It is used to resolve Fully Qualified Domain Name (domain name or Host Name) to IP address. It contains records like host name, CName, SVR, NS, MX, and SOA.

2. Reverse Lookup Zone: It is used to resolve IP address to Host Name (FQDN). It contains only one record, that is PTR.

                                                  DNS Record

DNS records are stored in DNS zones, forward lookup zones, and reverse lookup zones. By using all these record DNS servers, mostly resolve the queries.

There are mostly 7 types of records. Six records are stored in the forward lookup zone, and one is stored in the reverse lookup zone.

1. A record: It is also known as the host record. It is used to resolve FQDN to an IP address.

Also, there is an AAAA record that resolves IPV6 to hostname.

2. C Name record: This record is also known as Canonical; Alias record. It contains another name of device in a network.

3. NA record: Name Server record is used to transfer zones to authorised DNS server.

4. MX record: A Mail Exchanger record is used to locate a Microsoft mail server or Linux mail server.

5. SVR record: It is known as a Locator record. It locates local domain’s name and IP address in a local network.

6. SOA record: It is known as Start Of Authority. It contains information about the DNS zones and records stored in DNS server.

7. PTR: Pointer record is stored in reverse lookup zone It is used to resolve IP address to Hostname.

                                              DNS Query

When the client broadcasts the query asking the address of any destination to the DNS server, it is called a DNS query.

There are three types of DNS queries.

1. Recursive Query: When the DNS server resolves the queries by itself, this is called a recursive query, and this response is called an authoritative response.

2. Interative Query: When the DNS server resolves that query, which information is not saved in its DNS record and it takes help from other resources like another DNS server, root hint, etc., it is called an iterative query, and this response is a non-authoritative response.

3. Reverse Query: When the DNS takes a query of an IP address or hostname and returns the domain name or IP address associated with them, this is called a reverse query.

                                             Split DNS

Before understanding the Split DNS, we have to understand some facts:

Intranet is known as an internal corporate network, and extranet is known as an external network (Internet).

When we create two zones on one DNS server, the first zone is used for the internal network, and the second is used for the external network.

A method of creating two zones: internal hosts are redirected to the internal domain, and external hosts are redirected to the external domain.

                                             DNS Zones: There are three types of zones.

1. Primary Zone: The primary zone is created on the main server. It has all permissions to configure the primary zone, and it consists of all records, and it can create a new record also.
2. Secondary zone: A secondary zone cannot be created on the main DNS server. A secondary zone is created on another DNS server.

It has a full copy of the primary zone but in ready-only format. It can’t change or create new records. 

It also replicates the primary zone.

3. Stub Zone: It has only hostname records, CName records, and NS records in read-only format.