Enabling/Disabling Firewall in Linux:

To enable the firewall in Linux OS first check the status by below command

service iptables status

For Enabling:

service iptables start

For Disabling:

service iptables stop

Next use below command to check the firewall config

chkconfig --list iptables

It should give the output as shown below if firewall is stopped

iptables        0:off   1:off   2:off   3:off   4:off   5:off   6:off

If you want to turn ON 345 segments then need to run

chkconfig iptables on 345