Default Rules in IPTables
Start the iptables firewall as shown below.
# service iptables status
Firewall is stopped.
# service iptables start
Applying iptables firewall rules: [ OK ]
Loading additional iptables modules: ip_conntrack_netbios_n[ OK ]
You can see the default rules under: iptables -> Filter Table -> RH-Firewall-1-INPUT Chain, as shown below. You can also use ‘iptables –list’ to view all the rules.
# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
1 RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
Chain RH-Firewall-1-INPUT (2 references)
num target prot opt source destination
1 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
2 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 255
3 ACCEPT esp -- 0.0.0.0/0 0.0.0.0/0
4 ACCEPT ah -- 0.0.0.0/0 0.0.0.0/0
5 ACCEPT udp -- 0.0.0.0/0 224.0.0.251 udp dpt:5353
6 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:631
7 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:631
8 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
9 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
10 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
IPTables Rules are stored in /etc/sysconfig/iptables
Please note that the iptables rules are stored in the /etc/sysconfig/iptables file. If you view this file, you’ll see all the default rules.
# cat /etc/sysconfig/iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
Temporarily delete all the firewall rules
Use ‘iptables –flush’ option to delete all the rules temporarily.
# iptables --flush
# iptables --list
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain RH-Firewall-1-INPUT (0 references)
target prot opt source destination
After the ‘iptables –flush’, if you restart the iptables, you’ll see all the default rules again. So, –flush is only temporary.
# service iptables stop
# service iptables start
# iptables --list
Permanently remove all the default firewall rules
Before deleting all the firewall rules, you’ll see the following in the /etc/sysconfig/iptables file.
# cat /etc/sysconfig/iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
First, flush all these rules temporarily, as we discussed above.
# iptables --flush
Next, save the current iptables (which is empty, as we just flushed it) to the /etc/sysconfig/iptables file for permanent use using ‘service iptables save’
# service iptables save
Saving firewall rules to /etc/sysconfig/iptables: [ OK ]
Finally, view the /etc/sysconfig/iptables to make sure there are no rules.
# cat /etc/sysconfig/iptables
# Generated by iptables-save v1.3.5 on Thu Oct 28 08:44:01 2010
*filter
:INPUT ACCEPT [102:7668]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [78:8560]
COMMIT
# Completed on Thu Oct 28 08:44:01 2010
Now, if you stop and start the iptables, you’ll not see the default rules anymore. So, remember to do ‘service iptables save’ to make the ‘iptables –flush’ permanent.
# service iptables stop
# service iptables start
# iptables --list