[nos-bbs] IPTABLES for TUN device

[Michael Fox - N6MEF]

Jose,

 

It looks like no one has responded to you yet.  That may be because you
asked a rather broad question.  You'll need to be much more specific about
iptables.

 

IPtables is for filtering (among other things).  For the best security, you
want to set a default policy of drop and then specify the specific traffic
that you want to allow.  So you need to define those traffic types first,
then translate to iptables rules.  If you define what you want, and take a
stab at writing the rules, there are probably several of us here who would
be happy to help you refine them.

 

If you're new to iptables, here's some background info to get you started:

 

Iptables has 3 principle filtering tables:  input, forward, output.  Input
is what traffic you want linux to accept coming in on that interface.  In
other words, this is traffic destined for linux that comes in on the tun0
interface.  Forward is for traffic you want linux to allow to pass through
from one interface to another.  This can be two way on the tun0 device.  For
example, you may want to allow certain ICMP traffic to go out from JNOS,
through Linux, to the internet, but not allow incoming traffic of that type
from the internet to reach JNOS.  So you need to define what traffic do you
want to allow linux to forward from other interfaces TO tun0  and what
traffic do you want linux to forward FROM tun0 to other interfaces.  Output
is for what traffic you want linux to be able to originate on that
interface.  

 

To specify the traffic types, you'll need to define if they're IP, TCP,
ICMP, etc., which ports (line TCP port 23 for default telnet, etc.), and
possibily which source and/or destination addresses to allow to send that
traffic.  For example, you may want to allow linux to forward telnet to JNOS
as long as it is from a 44.x address, but not from other addresses.

 

Once you have figured out what traffic you want to allow, here are three
good references to help write the rules:

 

https://help.ubuntu.com/community/IptablesHowTo

http://www.frozentux.net/iptables-tutorial/iptables-tutorial.html  (this is
how I learned - it has some good templates)

O'Reilly iptables pocket reference:
http://www.amazon.com/Linux-iptables-Pocket-Reference-Gregor/dp/0596005695/r
ef=sr_1_sc_1?ie=UTF8
<http://www.amazon.com/Linux-iptables-Pocket-Reference-Gregor/dp/0596005695/
ref=sr_1_sc_1?ie=UTF8&qid=1330745373&sr=8-1-spell>
&qid=1330745373&sr=8-1-spell  

 

Michael

N6MEF

 

 

From: nos-bbs-bounces at tapr.org [mailto:nos-bbs-bounces at tapr.org] On Behalf
Of Jose Ng Lee
Sent: Friday, March 02, 2012 11:20 AM
To: TAPR xNOS Mailing List
Subject: [nos-bbs] IPTABLES for TUN device

 

Hi,

 

Anyone can help me with a sample IPTABLES configuration that works with TUN
device.

 

Thanks,

Jose / HP2AT

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