CompTIA Network+ (N10-009)Network TroubleshootingMedium
Users report that internal web application URLs resolve to an old server's IP address even after the application was migrated to a new server three days ago. Other websites resolve correctly. Which action would MOST likely resolve this issue?
- AFlush the ARP cache on the affected client workstations
- BReconfigure the subnet mask on the new server
- CLower the TTL value and verify the updated A record propagated
- DRestart the DHCP service on the internal server
Show answer & explanationAnswer & explanation
Correct answer: C. Lower the TTL value and verify the updated A record propagated
When a DNS record's IP mapping changes but clients continue to resolve the old address, cached DNS records with a long TTL are usually the culprit. Verifying that the DNS A record was updated correctly and lowering the TTL for future changes addresses stale caching directly.
Why the other options are wrong
- A. ARP cache maps IP to MAC addresses on the local segment, not domain names to IPs.
- B. Subnet mask issues would cause routing problems, not incorrect DNS resolution.
- D. DHCP assigns client IP addresses; it is unrelated to DNS name resolution.
DNS Record Caching (TTL)
DNS resolvers cache records for a duration defined by Time To Live (TTL) to reduce lookups; stale caches cause outdated resolution after changes.
- TTL determines how long a resolver caches a DNS record before requerying
- Lowering TTL before a planned change speeds up propagation
- dig or nslookup can be used to verify current authoritative record values
Memory trick: Old TTL means old IP sticks around