Time not synchronized. ErrorCode=-659

We have 2 machines between firewalls and when we try to sync the
databases, we get the following error:

ndsconfig add -t LDAP -n ou=test.o=test -a cn=admin.o=test -S ldapedir11 -
d /novell/eDirectory/ldapedir11/data -b 1025 -L 1026 -o 1028 -O 1029 -p
192.168.1.24:1025

.....

Warning: The machine hosting the target server has time ahead of the time
on this machine. Configuration will continue,however,Directory Services
may have trouble modifying objects.
Time not synchronized. ErrorCode=-659

ERROR -659: Setup for NDS installation failed.
Stopping the service 'ndsd'... Done.

Does anyone know which services/ports it's trying to use? any ideas?

tks in advance,

Roberto