ICMP Timestamp Request and Timestamp Reply messages are used by network routers to synchronize their system clocks for time and date. When a router needs to synchronize its system time, it sends an ICMP Timestamp Request message to the other router. Once the ICMP Timestamp Request message is received by the other router, it will respond back with an ICMP Timestamp Reply message. Timestamp Reply message contains other router’s date and time.
ICMP Timestamp Request and Timestamp Reply messages are not used much these days, because there an entire protocol itself is dedicated for network device time synchronization. Network Time Protocol (NTP) is the standard protocol used for time synchronization.
ICMP Timestamp Request message Type is 13 and ICMP Timestamp Reply message Type is 14. Please click next link to know more about Type and Code fields in ICMP header