IPTable - Configuration Examples

Owned by Marc Miller
Last updated: Jul 22, 2020 by Marc Miller
2 min read
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Purpose

Here are some additional iptables config files:

Examples

Restrict SSH Access to Campus Network

This file is similar to the iptables.base example, but set up to only allow SSH connections from the Campus Network

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*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [14039465:18394491353]
# Keep Current connections alive
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# Allow the UCSB Campus to ping the machine
-A INPUT -s 128.111.0.0/16 -p icmp -j ACCEPT
# Allow SSH Connections from Campus
-A INPUT -s 128.111.0.0/16 -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
# Allow the computer to talk to itself for its applications
-A INPUT -i lo -j ACCEPT
# Otherwise, drop the connection
-A INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT

In order to access it from the Campus Wireless or off Campus, you will need to use the Campus VPN.

Restrict a port to only your lab subnet

This is an example of how to restrict a port to a subnet

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*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [14039465:18394491353]
# Keep Current connections alive
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# Allow the UCSB Campus to ping the machine
-A INPUT -s 128.111.0.0/16 -p icmp -j ACCEPT
# Allow SSH Connections
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
# Allow connections to port 8475 for Lab machines
-A INPUT -s 128.111.43.0/24 -p tcp -m tcp --dport 8475 -j ACCEPT
# Allow the computer to talk to itself for its applications
-A INPUT -i lo -j ACCEPT
# Otherwise, drop the connection
-A INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT

In this example, -A INPUT -s 128.111.43.0/24 -p tcp -m tcp --dport 8475 -j ACCEPT line says to do the following:

Append this rule to INPUT chain, where Source is from 128.111.43.0/24 (Basically any computer coming from an IP address starting 128.111.43.*) trying to connect to TCP port 8475, allow the connection.

This example only puts in one port allowance, but multiple lines can be put in to allow others.

The important part here is limiting the access to the port in question to the subnet the lab is in, as most projects don't need to have the port fully open to the world if possible.

This, however, should not exclude the fact that any service running should not have some form of authentication with this up.

Having the Firewall restricting access to the port will mitigate other vulnerabilities some services may have even with authentication in place.

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