To cause iptables to function as a
basic packet filtering firewall, you need these commands:
iptables -F
iptables -N block
iptables -A block -m state --state
ESTABLISHED,RELATED -j ACCEPT
Obviously, that is the most basic and
essential iptables configuration. However, here are some others.
To list the current iptables rules
use:
iptables –L
To allow communication on a specific
port, SSH port 22 and HTTP port 80 for example use:
iptables –A INPUT –p tcp –dport ssh –j
ACCEPT
iptables –A INPUT –p tcp –dport 80 –j
ACCEPT
Also there are several flags that can
be passed to the iptables command. Below are listed the most common flags and
what they do. Several other flags exist but are not listed.
A: Append this rule to a rule chain
-L: List the current filter rules
-p: The connection protocol used
--dport: The destination port required
for the rule. A single port can be given or a range.
-i: Only match if the packet is coming
in on the specified interface.
-v: Verbose output
-s, --source: address source
specification
-d, --destination: address destination
specification
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