duduita opened a new issue, #2440: URL: https://github.com/apache/nuttx-apps/issues/2440
During NTP server querying through the `ntpclient.c`, different NTP server domain names (e.g., 0.uk.pool.ntp.org, 1.uk.pool.ntp.org) might resolve to the same set of IP addresses due to **DNS caching**. This can lead to **repeated queries to the same non-responsive IP addresses**, resulting in failures to obtain the correct time. For example, in the following, there are some logs that I added to `ntpclient.c`, in order to understand why the NTP was failing: ``` [ 51.046000] [25] (Info) '0.pool.ntp.org' resolved to: 216.238.113.58 [ 51.046000] [25] (Info) ntpclient.c-447-gethostbyname for 0.pool.ntp.org OK [ 51.046000] [25] (Info) ntpclient.c-480-Sending a NTP packet [ 51.055000] [25] (Info) ntpclient.c-509-sendto ret: 68 [ 51.056000] [25] (Info) ntpclient.c-515-Recv a NTP packet [ 56.055000] [25] (Info) ntpclient.c-521-recvfrom nbytes: -1 [ 56.056000] [25] (Info) '0.pool.ntp.org' resolved to: 216.238.113.58 [ 56.056000] [25] (Info) ntpclient.c-447-gethostbyname for 0.pool.ntp.org OK [ 56.056000] [25] (Info) ntpclient.c-480-Sending a NTP packet [ 56.063000] [25] (Info) ntpclient.c-509-sendto ret: 68 [ 56.063000] [25] (Info) ntpclient.c-515-Recv a NTP packet [ 61.065000] [25] (Info) ntpclient.c-521-recvfrom nbytes: -1 [ 61.066000] [25] (Info) '0.pool.ntp.org' resolved to: 216.238.113.58 [ 61.066000] [25] (Info) ntpclient.c-447-gethostbyname for 0.pool.ntp.org OK [ 61.066000] [25] (Info) ntpclient.c-480-Sending a NTP packet [ 61.075000] [25] (Info) ntpclient.c-509-sendto ret: 68 [ 61.075000] [25] (Info) ntpclient.c-515-Recv a NTP packet [ 66.075000] [25] (Info) ntpclient.c-521-recvfrom nbytes: -1 [ 66.076000] [25] (Info) '0.pool.ntp.org' resolved to: 216.238.113.58 [ 66.076000] [25] (Info) ntpclient.c-447-gethostbyname for 0.pool.ntp.org OK [ 66.076000] [25] (Info) ntpclient.c-480-Sending a NTP packet [ 66.085000] [25] (Info) ntpclient.c-509-sendto ret: 68 [ 66.085000] [25] (Info) ntpclient.c-515-Recv a NTP packet [ 71.085000] [25] (Info) ntpclient.c-521-recvfrom nbytes: -1 [ 71.086000] [25] (Info) '0.pool.ntp.org' resolved to: 216.238.113.58 [ 71.086000] [25] (Info) ntpclient.c-447-gethostbyname for 0.pool.ntp.org OK [ 71.086000] [25] (Info) ntpclient.c-480-Sending a NTP packet [ 71.095000] [25] (Info) ntpclient.c-509-sendto ret: 68 [ 71.095000] [25] (Info) ntpclient.c-515-Recv a NTP packet [ 76.095000] [25] (Info) ntpclient.c-521-recvfrom nbytes: -1 [ 76.095000] [25] (Info) ntpclient.c-563-ERROR: recvfrom() failed: 11 [ 76.095000] [25] (Info) ntpclient.c-589-The NTP client is terminating ``` To mitigate this issue, a possible option is to **flush the DNS cache after cycling through all configured NTP servers**, ensuring that subsequent DNS resolutions provide potentially new and responsive IP addresses, thereby increasing the likelihood of successful time synchronization. However, I cannot manipulate the DNS cache from the user space, unless I create an API for it. Overall, do you have a workaround or a hack that I can use in order to solve this NTP issue? Or at least to force a new IP resolution for an NTP hostname after some failures? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
