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Difficulty: Very hardDNS Lookup and Name Resolution Roles in Enterprise Networks

An enterprise client workstation attempts to access an external web application at `app.partner.example.net` for the first time. Arrange the steps of the complete DNS resolution process in the correct chronological order, starting from the client's initial lookup request to the final IP address retrieval.

  1. 1The client operating system inspects its local hosts file and DNS resolver cache for an existing mapping of app.partner.example.net.
  2. 2The client host issues a recursive DNS query over UDP port 53 to its configured internal primary DNS resolver.
  3. 3The internal recursive DNS server issues an iterative DNS query for app.partner.example.net to a DNS root name server.
  4. 4The DNS root name server returns a referral response containing the IP addresses of the .net Top-Level Domain (TLD) authoritative servers.
  5. 5The internal recursive DNS server queries the .net TLD name server and receives a referral to the authoritative DNS server for partner.example.net.
  6. 6The internal recursive DNS server queries the partner.example.net authoritative server, receives the A record, caches the entry, and sends the IP address answer to the client host.

Answer

The correct sequence begins with the client host checking its local resolver cache and hosts file, followed by sending a recursive query to the local internal DNS resolver. The internal resolver then performs iterative queries starting at the root server, proceeding to the .net TLD server, and finally querying the authoritative server for partner.example.net before caching the record and returning the resolved IP address to the client.
The proper sequence follows standard operating system and DNS protocol operational order: local client cache and hosts file check -> client recursive query to the local internal DNS resolver -> internal resolver iterative query to the root name server -> root referral to the TLD server -> TLD referral to the domain authoritative server -> authoritative answer returned, cached by the internal resolver, and forwarded to the client.

Step-by-Step Solution

1
Check local OS resolution mechanisms.
The host OS scans the local `hosts` file and client DNS cache for `app.partner.example.net`.
Local lookup prevents unnecessary network overhead if the IP address is already known locally.
2
Transmit recursive query from client host to configured DNS server.
A UDP port 53 recursive query is sent to the internal enterprise DNS resolver.
The client delegates name resolution responsibility entirely to its configured local DNS server.
3
Initiate iterative resolution from the DNS root hierarchy.
The internal DNS server queries a DNS root hint server (`.`).
When resolving an un-cached external FQDN, the recursive resolver starts lookups at the root zone.
4
Process root referral response.
The root server responds with NS and glue A records for the `.net` TLD servers.
Root servers maintain delegation points for top-level domains.
5
Query TLD name server for domain authority.
The `.net` TLD server provides NS records pointing to authoritative servers for `partner.example.net`.
TLD servers maintain delegations for secondary registered domains under their top-level domain.
6
Fetch definitive record from authoritative server and respond to client.
The authoritative server responds with the `A` record, which the internal server caches and forwards to the requesting client.
Only authoritative name servers hold the master resource records for the targeted domain.

Key Concept

DNS Lookup and Name Resolution Roles in Enterprise Networks
Estimated Time:2m 0s
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DNS Lookup and Name Resolution Roles in Enterprise Networks

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