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explain DNS iterative search algorithm
The DNS iterative search algorithm is a process that DNS servers use to resolve domain names to IP addresses. It is a bottom-up approach, where the DNS server starts at the root of the DNS hierarchy and works its way down until it finds the authoritative DNS server for the domain name being queried.
The iterative search algorithm works as follows:
The DNS server receives a query for a domain name.
The DNS server checks its cache for the IP address of the domain name. If the IP address is in the cache, the DNS server returns it to the client.
If the IP address is not in the cache, the DNS server queries the root servers for the next level of the DNS hierarchy.
The DNS server receives a response from the root servers, which contains the IP addresses of the top-level domain (TLD) name servers.
The DNS server queries the TLD name servers for the next level of the DNS hierarchy.
This process continues until the DNS server reaches the authoritative DNS server for the domain name being queried.
The DNS server receives the IP address of the domain name from the authoritative DNS server and returns it to the client.
If the DNS server does not receive a response from any of the DNS servers it queries, or if the response does not contain the IP address of the domain name being queried, the DNS server returns an error to the client.
The iterative search algorithm is slower than the recursive search algorithm, but it is more reliable and scalable. It is also the only type of DNS query that can be used by DNS servers that are not authoritative for any domain names.
Here is an example of an iterative DNS query:
The client sends a DNS query for the domain name www.example.com to its local DNS server.
The local DNS server does not have the IP address of www.example.com in its cache, so it queries the root servers for the next level of the DNS hierarchy.
The root servers respond with the IP addresses of the top-level domain (TLD) name servers for the .com domain.
The local DNS server queries the .com TLD name servers for the next level of the DNS hierarchy.
The .com TLD name servers respond with the IP addresses of the authoritative DNS servers for the example.com domain.
The local DNS server queries the authoritative DNS servers for the IP address of www.example.com.
The authoritative DNS servers respond with the IP address of www.example.com.
The local DNS server returns the IP address of www.example.com to the client.
The iterative search algorithm is used by most DNS servers on the Internet today. It is a reliable and scalable way to resolve domain names to IP addresses.
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