netlib: support checkipconnectivity when use reslov.conf

[zhhyu7]

Summary

Improve netlib_check_ipconnectivity() to support DNS nameservers from resolv.conf via dns_foreach_nameserver(), instead of relying on the compile-time CONFIG_NETDB_DNSSERVER_IPv4ADDR macro.

Impact

• Add dns_ping_callback() to iterate over all configured DNS nameservers and ping each one until a reply is received.
• When ip is NULL, use dns_foreach_nameserver() to dynamically resolve and ping DNS servers at runtime, replacing the previous #ifdef CONFIG_NETDB_DNSSERVER_IPv4ADDR compile-time approach.
• When ip is provided, ping the specified address directly (behavior unchanged).
• Fix missing newline at end of file.

Testing

Verify netlib_check_ipconnectivity(NULL, ...) pings DNS servers from resolv.conf and ram.

[masc2008]

@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.

And we need move further:
It's not good practice to just check network connectivity via ping ipv4 address, the device may just have an IPv6 address only.

[zhhyu7]

@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.

And we need move further: It's not good practice to just check network connectivity via ping ipv4 address, the device may just have an IPv6 address only.

@masc2008, You're right. Regarding NTP, I think we should directly remove the netlib_check_ipconnectivity check from the ntpclient file, because we already have backoff behavior to avoid screen flooding. Meanwhile, I will add a new patch later to select a more appropriate IP address for the check, such as DRaddr, and also add support for IPv6 addresses.

[masc2008]

thanks! Good job HongYu!👍

…

On Wed, 22 Apr 2026 at 21:39, zhhyu7 ***@***.***> wrote: *zhhyu7* left a comment (apache/nuttx-apps#3460) <#3460?email_source=notifications&email_token=AEIQS6OZIYF2Y6WWNXTS7F34XDDRLA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIMRZGY3DONJUGIYKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJNLQOJPWG33NNVSW45C7N5YGK3S7MNWGSY3L#issuecomment-4296675420> @zhhyu7 <https://github.com/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. And we need move further: It's not good practice to just check network connectivity via ping ipv4 address, the device may just have an IPv6 address only. @masc2008 <https://github.com/masc2008>, You're right. Regarding NTP, I think we should directly remove the netlib_check_ipconnectivity check from the ntpclient file, because we already have backoff behavior to avoid screen flooding. Meanwhile, I will add a new patch later to select a more appropriate IP address for the check, such as DRaddr, and also add support for IPv6 addresses. — Reply to this email directly, view it on GitHub <#3460?email_source=notifications&email_token=AEIQS6OZIYF2Y6WWNXTS7F34XDDRLA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIMRZGY3DONJUGIYKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJNLQOJPWG33NNVSW45C7N5YGK3S7MNWGSY3L#issuecomment-4296675420>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEIQS6OGLDI3RFJ5NLGD2ID4XDDRLAVCNFSM6AAAAACYCBRKC6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DEOJWGY3TKNBSGA> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[cederom]

Thank you @zhhyu7 :-) I agree with @masc2008 remarks please todo in a free moment :-)