시스템 관리자를 위한 20개의 Iptables 예제

방화벽 상태 표시

Type the following command as root:

# iptables -L -n -v

Sample outputs:

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Above output indicates that the firewall is not active. The following sample shows an active firewall:

# iptables -L -n -v

Sample outputs

• -L : List rules.
• -v : Display detailed information. This option makes the list command show the interface name, the rule options, and the TOS masks. The packet and byte counters are also listed, with the suffix 'K', 'M' or 'G' for 1000, 1,000,000 and 1,000,000,000 multipliers respectively.
• -n : Display IP address and port in numeric format. Do not use DNS to resolve names. This will speed up listing.

To inspect firewall with line numbers, enter:

iptables -n -L -v --line-numbers

To display INPUT or OUTPUT chain rules, enter:

iptables -L INPUT -n -v
iptables -L OUTPUT -n -v --line-numbers

Stop / Start / Restart the Firewall 

If you are using CentOS / RHEL / Fedora Linux, enter:

service iptables stop
service iptables start
service iptables restart

You can use the iptables command itself to stop the firewall and delete all rules:

iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT

Where, 

• -F : Deleting (flushing) all the rules.
• -X : Delete chain.
• -t table_name : Select table (called nat or mangle) and delete/flush rules.
• -P : Set the default policy (such as DROP, REJECT, or ACCEPT).

Delete Firewall Rules

To display line number along with other information for existing rules, enter:

# iptables -L INPUT -n --line-numbers
# iptables -L OUTPUT -n --line-numbers
# iptables -L OUTPUT -n --line-numbers | less
# iptables -L OUTPUT -n --line-numbers | grep 202.54.1.1

You will get the list of IP. Look at the number on the left, then use number to delete it. For example delete line number 4, enter:

iptables -D INPUT 4

Insert Firewall Rules

iptables -L INPUT -n --line-numbers

Ref

• http://www.cyberciti.biz/tips/linux-iptables-examples.html