Cisco CCNA (200-301)IP ServicesHard
A network administrator is troubleshooting an issue where internal users cannot resolve external domain names. The router is configured with `ip name-server 8.8.8.8` and `ip domain-lookup`. Which command would the administrator use to verify if the router is successfully resolving domain names?
- Anslookup google.com
- Bping google.com
- Cshow ip dns
- Dshow host
Show answer & explanationAnswer & explanation
Correct answer: B. ping google.com
While `nslookup` is a common tool on end devices, on a Cisco router, the `ping` command with a domain name (e.g., `ping google.com`) directly leverages the router's configured DNS settings (`ip name-server` and `ip domain-lookup`) to resolve the name to an IP address before attempting to ping. This provides a direct test of the router's ability to perform DNS resolution.
Why the other options are wrong
- A. `nslookup` is a command-line utility found on operating systems like Windows, Linux, or macOS, but not directly on Cisco IOS for this purpose. The equivalent functionality on a router is usually integrated into commands like `ping` or `traceroute` when used with hostnames.
- C. `show ip dns` is not a standard Cisco IOS command. There are `show ip dns view` or `show ip dns server` for DNS server functionality, but not general client resolution status.
- D. `show host` displays the local hostname table on the router, which is for statically defined entries, not for dynamic DNS resolution.
Cisco Router DNS Resolution Test
Using Cisco IOS commands to test if a router can successfully resolve domain names configured with `ip name-server` and `ip domain-lookup`.
- `ping <hostname>` is the primary method to test DNS resolution on a router.
- Router must have `ip domain-lookup` enabled (default on many platforms).
- `ip name-server` specifies DNS server IP addresses.
Memory trick: To see if the router knows the name, just PING its domain game.