Cisco Certified Support Technician (CCST) NetworkingIP ServicesHard
A network engineer is configuring a DNS server to handle a large number of internal domain names and their corresponding IP addresses. To improve query performance and reduce the load on the authoritative DNS servers, the engineer decides to implement a mechanism where the DNS server stores the results of previous queries for a specific duration. What is this mechanism called, and which parameter controls how long the results are stored?
- ADNS Zone Transfer; Zone Refresh Interval
- BDNS Recursion; Recursion Limit
- CDNS Caching; Time-to-Live (TTL)
- DDNS Forwarding; Forwarder Timeout
Show answer & explanationAnswer & explanation
Correct answer: C. DNS Caching; Time-to-Live (TTL)
DNS Caching stores the results of previous queries on the local DNS server. The Time-to-Live (TTL) value associated with each DNS record determines how long the cached entry remains valid before the server must query an authoritative server again.
Why the other options are wrong
- A. DNS zone transfer is for synchronizing zone data between authoritative servers; zone refresh interval relates to how often secondary servers check for updates.
- B. DNS recursion is the process of a server querying other servers on behalf of a client; recursion limit controls depth, not caching duration.
- D. DNS forwarding sends queries to another server; forwarder timeout is how long to wait, not about storing results.
DNS Caching & TTL
DNS Caching stores resolved domain names and their IP addresses on a local DNS server to speed up future queries. The Time-to-Live (TTL) value specifies how long these cached entries are considered valid.
- Improves DNS query performance.
- Reduces load on authoritative DNS servers.
- TTL impacts cache freshness and consistency.
Memory trick: Caching is like a speed-dial, and TTL is how long that number stays on the list.