Vision87 Corp has recently established their web and mail se

\"Vision87 Corp.\" has recently established their web and mail servers and intend to use the user friendly name vision87.com for both services. Assume that the web server load is distributed among 5 servers with a single canonical name web. vision87 akamai.net and IP addresses w_i for i elementof = {1, ...., 5} Moreover, there are 4 mail servers with canonical names m1. Vision87.akamai. net up to m4. M4. Vision87.akamai. net Let the IP addresses for these mail servers be denoted by m_i for i elementof {1, ....., 4}, respectively. The company has set up two authoritative name servers ns1.vision87.com and ns2.vision87.com with IP addresses denoted by n_1 and n_2 respectively. The company has registered its domain name in the DNS registrar, \"DNSREG Networks\". This registrar has 20 TLD name servers ns1. dnsreg.com up to ns20. dnsreg.com with IP addresses t_i for i elementof {1, ...., 20} respectively. Let root server.net be a dns root server with IP address r. Ignoring TTL field in the resource records, Suppose that a user clicks on a link in the web browser to receive the web page identified with the URL vision.com/index.html. Assume that DNS caches in the client host and local DNS server do not include any matching IP addresses for v ision87.com. Moreover, the local DNS cache does not include any IP address for TLD servers Specify the sequence of DNS query/responses until the local DNS server resolves an IP address for vicion87.com. In addition, assume that the round trip time for each DNS query and corresponding response between the local DNS server and some DNS server in the hierarchy is 5 msec. But the communication delay between the client host and local DNS server is negligible. The round trip time between the client host and vision87.com web server is 10 msec. Object transmission time and all nodal processing delays are also negligible. How much time elapses from the time the user clicks on the link until she receives the web page, if index.html does not contain any references to other objects and HTTP is non-persistent. index.html does not contain any references to other objects and HTTP is persistent. index.html refers to 12 other objects on vision87.com web server, HTTP is non-persistent and web browser is not supporting parallel TCP connections. index.html refers to 12 other objects on vision87.com web server, HTTP is non-persistent, and web browser is supporting up to 4 parallel TCP connections. index.html refers to 12 other objects on vision87 .com web server, HTTP is persistent, and web browser is supporting neither parallel TCP connections nor pipelining. index.html refers to 12 other objects on vision 87.com web server. HTTP is persistent and web browser is supporting up to 4 parallel TCP connections but not pipelining. index.html refers to 12 other objects on vision87.com web server, HTTP is persistent, and web browser is supporting pipelining.

Solution

Step 1: OS Recursive Query to DNS Resolver

Since the operating system doesn’t know where “www.vision87.com” is, it queries a DNS resolver. The query the OS sends to the DNS resolver DNSREG Networks has a special flag that tells it is a “recursive query.” This means that the resolver must complete the recursion and the response must be either an IP address or an error.

Step 2: DNS Resolver Iterative Query to the Root Server

The resolver starts by querying the root server rootserver.net for the IP of “www.vision87.com” . This query does not have the recursive flag and therefore is an “iterative query,” meaning its response must be an address, the location of an authoritative name server, or an error.

Step 3: Root Server Response

These root servers hold the locations of all of the top level domains (TLDs) such as .com, .de, .io, and newer generic TLDs such as .camera.

The root doesn’t have the IP info for “www.vision87.com,” but it knows that .com might know, so it returns the location of the .com servers.

Step 4: DNS Resolver Iterative Query to the TLD Server

Next the resolver queries one of the .com name servers for the location of vision87.com. Like the Root Servers, each of the TLDs have 4-13 clustered name servers existing in many locations. There are two types of TLDs: country codes (ccTLDs) run by government organizations, and generic (gTLDs). Every gTLD has a different commercial entity responsible for running these servers. In this case, we will be using the gTLD servers controlled by Verisign, who run the .com, .net, .edu, and .gov among gTLDs.

Step 5: TLD Server Response

Each TLD server holds a list of all of the authoritative name servers for each domain in the TLD. For example, each of the 13 .com gTLD servers has a list with all of the name servers for every single .com domain. The .com gTLD server does not have the IP addresses for vision87.com, but it knows the location of vision87.com’s name servers. The .com gTLD server responds with a list of all of vision87.com’s NS records. In this case vision87 has 2 name servers, “ns1. vision87.com” and        “ns2. vision87.com.”

Step 6: DNS Resolver Iterative Query to the vision87.com NS

Finally, the DNS resolver queries one of vision87 name server for the IP of “www. vision87.com.”

Step 7: vision87.com NS Response

This time the queried Name Server knows the IPs and responds with an A or AAAA address record (depending on the query type) for IPv4 and IPv6, respectively.

Step 8: DNS Resolver Response to OS

At this point the resolver has finished the recursion process and is able to respond to the end user’s operating system with an IP address.

Step 9: Browser Starts TCP Handshake

At this point the operating system, now in possession of www. vision87.com’s IP address, provides the IP to the Application (browser), which initiates the TCP connection to start loading the page.