1. First,add a new chain with a reasonable name:

iptables -N LOGGING

2. Next,insert a rule at the appropriate point (hence me using --line-numbers above). You could replace the existing REJECT at line 5 in its entirety as its functionality will be moved into the LOGGING chain (where I change it to a DROP anyway):

@L_301_0@

iptables -I INPUT 5 -j LOGGING

3. Add the actual logging rule next

iptables -A LOGGING -j LOG --log-prefix "DROP: " --log-level 7

iptables -A LOGGING -j DROP

service iptables save

service iptables restart

4. vi /etc/rsyslog.conf

kern.debug/var/log/iptables.log

service rsyslog restart

5. vi /etc/logrotate.d/syslog

add /var/log/iptables.log to list of filenames