For details on the vulnerability see : CVE-1999-0524
The remote host answers to an ICMP timestamp request.
This allows an attacker to know the date that is set on the targeted machine, which may assist an unauthenticated, remote attacker in defeating time-based authentication protocols.
All versions of Greenplum DB.
Greenplum Database(GPDB) clusters require ICMP to be enabled on the interconnect network.
GPDB uses "ping", which uses ICMP, to check that hosts are up and contactable within the cluster.