DNS recursive query vs. Iterative query transcript

hello this is sunny welcome back today I want to talk about DNS recursive query and iterative query and their difference the goal of DNS is to resolve a fully qualified domain name to an IP address the process is called name resolution let me give you their definitions first the recursive query demands a name resolution or the answer it cannot be found the recursive query is between D has client and is local DNS server on the other hand the iterative query is between a local DNS server and other DNS servers the iterative query do not demand a name of resolution which means other servers are the DNS servers may provide a name resolution if they know or simply respond with a referral let me use an example to demonstrate the whole process of name resolution and I demonstrate there's two different queries suppose I want to go to a Google web server I type e www.google.com/mapmaker places first to say if there's any previous name resolution record of this google machine one place is my computer's cache memory the other place is a simple text file called hosts suppose there's no record either of these two locations my computer would ask my local Dean as a server I want to know IP address of a wwo com this initial query from my computer Dena's client to my local DNS server is recursive query because my computer demands a clear answer to resolve a name is the responsibility of my local DNS server let me assume that my local DNS server is brand new machine and it has no record of any IP address of www.bucks.edu starts remember during the iterative query other servers can simply provide a referral if they do not know the IP address of WWI comm keep in mind my local DNS server is looking for IP address of a Google web server a specific host at the very bottom of a name space pyramid specified by is a fully qualified domain name wwq com first my local server will go up to the root domain server because everybody knows the root domain server and asks do you know what's the IP address of WWI com routed arming servers are only responsible for the top level domain server Sacha's Homme de de de orc and etc thus the rooted dumbing server would reply I don't know the IP address of a wwo calm but I do know an IP address of a dot-com server here the wrote damming server gives referral they my local DNS server goes to dot-com server and asking the exactly same question do you know what's the IP address of group W wo comm the dot-com server and would reply I don't know IP address of this Google web server but I do know an IP address of Google DNS server under me and you can ask him here the dot-com server is also give a referral well my local DNS server never give up he finds that Google T as a server and asks the exact same question do you know what's the IP address of a www-where this time the answer is yes because Google DNS server shouldn't know any Google hosts IP address his response is like this here's one IP address you can use once my local DNS server guess is IP address it informs my computer which will use this IP a IP address you talk to the Google web server at at the same time my computer's save this IP address is a cache memory just in case it will use it again so does my local DNS server it has save this IP address is memory next time we any other computer in this network ask the same question and it would give this IP address directly from his memory without going through all those repetitive steps I mentioned about in summary Dean as recursive query is between and Dean as client which is my computer and my local DEA's server the local DNS server is responsible for answer the questions from diaz clients when this local DNS server could not resolve a new name from his own database it will make a trade query to other dear servers until it finds the answer I hope this video is helpful thank you very much and see you next time [Music]