Network Time Protocol (NTP) allows routers on the network to synchronize their time settings with an NTP server. The %SYS-5-SYS_TIMECHNG: System time has changed to due to summertime message indicates that the system was switched to daylight savings time. This message is provided for informational purposes only.
This issue can result from one of these situations:
The NTP servers currently used do not provide the correct time.
There is a rogue NTP server that broadcasts the incorrect time.
When you use the third party NTP master server, which can only run Simple Network Time Protocol (SNTP), this uses SNTP a subnet of NTP for time synchronization. Both uses the same network-packet format. The main difference is SNTP does not provide the error-check and filtering functions that NTP provides. Cisco router and switches use NTP and allow for all error-checking and filtering functions provided by NTP Version 3.
Catalyst OS (CatOS) implements a simple NTP client, so most of the fields in the NTP packet are not checked for errors or abnormalities.
Cisco bug ID CSCef95980 is filed for this issue and requests a mechanism or feature that allows the system to ignore NTP broadcasts from servers with unreliable time.
CatOS release 8.4(2) and later have an enhancement that does not allow the Cisco Catalyst switch to accept NTP packets from rogue servers. In order to download and upgrade CatOS, refer to Cisco Downloads.
If the problem is due to the SNTP server, then you need a software that provides full NTP functions to the server to be able to do this, else you can choose a pubic NTP server.
Refer to these Cisco bug IDs for similar problems related to NTP: