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Consider a host at the domain abc.com with a local DNS server, dns.abc.com. Suppose the host wants to get an IP address for www.ibm.com. It is given that the authoritative name server for the domain ibm.com is ns.ibm.com.

With the aid of a diagram, explain how the host gets the IP address. Also, describe what messages are exchanged among the hosts involved in the process.

Answer :

Final answer:

The DNS resolution process involves several steps: the local host at abc.com sends a query to its local DNS server dns.abc.com which if can't resolve then sends query to Root and '.com' TLD servers that eventually point it to ns.ibm.com, the authoritative name server for ibm.com. The ns.ibm.com has the IP address for www.ibm.com and sends it back to dns.abc.com which then sends it to local host.

Explanation:

The mechanism that allows a host at domain abc.com to get the IP address for another domain like www.ibm.com is DNS resolution. It occurs in several steps:

  1. The local host first checks its local DNS cache. If the IP is not found, it proceeds with the next steps.
  2. The local host sends a DNS query to its job which is dns.abc.com.
  3. If dns.abc.com cannot resolve the query, it further requests the Root DNS server.
  4. The Root DNS server does not know the answer, but it knows where to find the information, which is the Top Level Domain (TLD) DNS server for '.com', and sends this information back to dns.abc.com.
  5. Then, dns.abc.com sends a query to the '.com' TLD DNS server.
  6. The '.com' TLD DNS server also doesn't have the IP, but it knows the authoritative DNS server (ns.ibm.com) for the ibm.com domain. It provides this information to dns.abc.com.
  7. Next, dns.abc.com sends a query to ns.ibm.com.
  8. The ns.ibm.com server knows the IP address for www.ibm.com, and sends this information back to dns.abc.com.
  9. Finally, dns.abc.com sends this information back to the local host. The IP information is also stored in dns.abc.com's cache for future queries, speeding up subsequent DNS resolutions for www.ibm.com.

Learn more about DNS resolution here:

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