A network technician is troubleshooting an issue where a workstation fails to connect to an internal web application after a recent server migration. The technician executes two command-line utilities on the client workstation and receives the following output:
C:\> nslookup portal.company.local
Server: dns01.company.local
Address: 10.10.5.2
Name: portal.company.local
Address: 10.10.20.100
C:\> ping portal.company.local
Pinging portal.company.local [10.10.5.50] with 32 bytes of data:
Request timed out.
Based on the diagnostic output, which of the following is the most likely cause of this discrepancy?
- A stale cached entry or static entry in the client workstation's local resolution files is overriding DNS server queries.Answer
- BThe DNS server is returning an incorrect IPv6 AAAA record instead of an IPv4 A record.
- CUDP port 53 traffic is blocked by a network firewall between the workstation and the DNS server.
- DThe nslookup tool failed because DNS queries must always use TCP protocol instead of UDP.
Answer
A stale cached entry or static entry in the client workstation's local resolution files is overriding DNS server queries.
The nslookup utility bypasses local system resolution mechanisms (such as the client DNS cache and local HOSTS file) and queries the designated DNS server directly, returning the updated IP address (10.10.20.100). In contrast, standard applications and utilities like ping rely on the operating system's DNS client service, which checks local cache and static HOSTS file entries first. The discrepancy indicates that the local workstation is resolving the host via a stale cached entry or static file entry.
Step-by-Step Solution
Key Concept
DNS Name Resolution Order and Client Resolver Cache vs. Direct Server Queries
Estimated Time:1m 30s