masc2008 commented on PR #3460:
URL: https://github.com/apache/nuttx-apps/pull/3460#issuecomment-4296440895
@zhhyu7 it's not a good method to use ping to check if DNS server is
reachable. Here is the reason:
A DNS server is only required to answer DNS queries on port 53 over UDP/TCP.
Replying to ping means replying to ICMP Echo, which is separate and optional.
So a DNS server may:
- answer DNS normally
- ignore or block ping
- be behind a firewall that drops ICMP
If you want to test DNS reachability, use a DNS query like nslookup, dig,
or host, not ping.
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