Difficulty with iptables script to only allow 3 ports across the firewall

Difficulty with iptables script to only allow 3 ports across the firewall

[john]

First, thanks for taking the time to look.

I've been poking at this for almost 2 weeks and am quite stuck.

Here's the nutshell version of what I'm trying to do:

Client machine has an IP address of 192.168.100.101.  The only way I want this client to be able to communicate with machines on the 10.138.x.x network is via HTTPS (443), plus make DNS lookup requests.  I don't want PING, or any windows SMB type connections to succeed.  Just HTTPS and DNS.  Also, the linux box provides dhcp services to the 192.168.200.x network.

I think my fundamental understanding of iptables is wrong.

I 'think' the INPUT is what's allowed to the local machine (i.e. firewall box)
FORWARD is what's passed from NIC to NIC.
OUTPUT is what's allowed off the NIC.

Would anybody please give me a hand here?  I learn quickly by examples.  I've poked at a large number of websites, but am not making much headway.

Respectfully,

John

Here's my script as it sits.  It's driving me nuts that I can connect via SMB from the clients on the 192 network to windows SMB shares on the 10. network.


IPT="/sbin/iptables"

# THE NETWORK CONTAINING THE SITE SYSTEMS
DMZ_IP="10.138.2.117"
DMZ_IFACE="eth0"
DMZ_BROADCAST="10.138.2.255"

# THE IP RANGE FOR CLIENT COMPUTERS (disconnected network)
CLIENTS_IP="192.168.200.1"
CLIENTS_IP_RANGE="192.168.200.0/24"
CLIENTS_IFACE="eth1"

$IPT --flush
$IPT --table nat --flush
$IPT --delete-chain
$IPT --table nat --delete-chain

$IPT -A INPUT -j LOG --log-prefix "INPUT_PACKETS: "
$IPT -A FORWARD -j LOG --log-prefix "FORWARD_PACKETS: "
$IPT -A OUTPUT -j LOG --log-prefix "OUTPUT_PACKETS: "

$IPT --policy INPUT DROP
#$IPT --policy OUTPUT DROP


$IPT -A INPUT -p tcp --dport 22 -j ACCEPT
$IPT -A INPUT -p tcp --dport 80 -j ACCEPT
$IPT -A INPUT -p tcp --dport 443 -j ACCEPT
$IPT -A INPUT -p tcp --dport 53 -j ACCEPT
$IPT -A INPUT -p udp --dport 53 -j ACCEPT

#$IPT -A INPUT -p udp -j ACCEPT
#$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

#$IPT -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
#$IPT -A FORWARD -p tcp --dport 80 -j ACCEPT
$IPT -A FORWARD -p tcp --dport 443 -j ACCEPT
$IPT -A FORWARD -p udp --dport 53 -j ACCEPT
$IPT -A FORWARD -p tcp --dport 53 -j ACCEPT
$IPT -A FORWARD -p tcp --dport 445 -j DROP
$IPT -N LOGDROP
$IPT -A LOGDROP -j LOG
$IPT -A LOGDROP -j DROP
$IPT -A INPUT -j LOG
$IPT -A FORWARD -j LOG

$IPT --table nat --append POSTROUTING --out-interface $DMZ_IFACE -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

Re: Difficulty with iptables script to only allow 3 ports across the firewall

[Glenn Henshaw]

On 3-Jun-08, at 9:29 PM, john@langherd.com wrote:

> First, thanks for taking the time to look.
>
> I've been poking at this for almost 2 weeks and am quite stuck.
>
> Here's the nutshell version of what I'm trying to do:
>
> Client machine has an IP address of 192.168.100.101.  The only way I  
> want this client to be able to communicate with machines on the  
> 10.138.x.x network is via HTTPS (443), plus make DNS lookup  
> requests.  I don't want PING, or any windows SMB type connections to  
> succeed.  Just HTTPS and DNS.  Also, the linux box provides dhcp  
> services to the 192.168.200.x network.
>
> I think my fundamental understanding of iptables is wrong.
>
> I 'think' the INPUT is what's allowed to the local machine (i.e.  
> firewall box)
> FORWARD is what's passed from NIC to NIC.
> OUTPUT is what's allowed off the NIC.
>
> Would anybody please give me a hand here?  I learn quickly by  
> examples.  I've poked at a large number of websites, but am not  
> making much headway.
>
> Respectfully,
>
> John
>
> Here's my script as it sits.  It's driving me nuts that I can  
> connect via SMB from the clients on the 192 network to windows SMB  
> shares on the 10. network.
>
>
> IPT="/sbin/iptables"
>
> # THE NETWORK CONTAINING THE SITE SYSTEMS
> DMZ_IP="10.138.2.117"
> DMZ_IFACE="eth0"
> DMZ_BROADCAST="10.138.2.255"
>
> # THE IP RANGE FOR CLIENT COMPUTERS (disconnected network)
> CLIENTS_IP="192.168.200.1"
> CLIENTS_IP_RANGE="192.168.200.0/24"
> CLIENTS_IFACE="eth1"
>
> $IPT --flush
> $IPT --table nat --flush
> $IPT --delete-chain
> $IPT --table nat --delete-chain
>
> $IPT -A INPUT -j LOG --log-prefix "INPUT_PACKETS: "
> $IPT -A FORWARD -j LOG --log-prefix "FORWARD_PACKETS: "
> $IPT -A OUTPUT -j LOG --log-prefix "OUTPUT_PACKETS: "
>
> $IPT --policy INPUT DROP
> #$IPT --policy OUTPUT DROP

   try adding
  $IPT --policy FORWARD DROP
   this will drop any packets not explicitly listed

>
>
>
> $IPT -A INPUT -p tcp --dport 22 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 80 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 443 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 53 -j ACCEPT
> $IPT -A INPUT -p udp --dport 53 -j ACCEPT
>
> #$IPT -A INPUT -p udp -j ACCEPT
> #$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
>
> #$IPT -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
> #$IPT -A FORWARD -p tcp --dport 80 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 443 -j ACCEPT
> $IPT -A FORWARD -p udp --dport 53 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 53 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 445 -j DROP

    also add the following line to drop attempts to pass packets from  
DMZ to CLIENT
   $IPT -A FORWARD -i $DMZ_IFACE -j DROP
>
> $IPT -N LOGDROP
> $IPT -A LOGDROP -j LOG
> $IPT -A LOGDROP -j DROP
> $IPT -A INPUT -j LOG
> $IPT -A FORWARD -j LOG
>
> $IPT --table nat --append POSTROUTING --out-interface $DMZ_IFACE -j  
> MASQUERADE
> echo 1 > /proc/sys/net/ipv4/ip_forward
>
>

   I often use iptables -L -v to list the tables and see the packet  
counts for each filter. It helps to figure out where the packets go.

-- 
Glenn Henshaw                     Logical Outcome Ltd.
e: thraxisp@logicaloutcome.ca     w: www.logicaloutcome.ca

Re: Difficulty with iptables script to only allow 3 ports across the firewall

[Steven Ayre]

As a suggestion, I always place the ESTABLISHED,RELATED rules first.  
It has to check every packet against each rule in turn. Since most  
packets will be part of an established connection placing that rule  
first minimizes the amount of processing needed.

Steve on iPhone

On 4 Jun 2008, at 02:29, john@langherd.com wrote:

> First, thanks for taking the time to look.
>
> I've been poking at this for almost 2 weeks and am quite stuck.
>
> Here's the nutshell version of what I'm trying to do:
>
> Client machine has an IP address of 192.168.100.101.  The only way I  
> want this client to be able to communicate with machines on the  
> 10.138.x.x network is via HTTPS (443), plus make DNS lookup  
> requests.  I don't want PING, or any windows SMB type connections to  
> succeed.  Just HTTPS and DNS.  Also, the linux box provides dhcp  
> services to the 192.168.200.x network.
>
> I think my fundamental understanding of iptables is wrong.
>
> I 'think' the INPUT is what's allowed to the local machine (i.e.  
> firewall box)
> FORWARD is what's passed from NIC to NIC.
> OUTPUT is what's allowed off the NIC.
>
> Would anybody please give me a hand here?  I learn quickly by  
> examples.  I've poked at a large number of websites, but am not  
> making much headway.
>
> Respectfully,
>
> John
>
> Here's my script as it sits.  It's driving me nuts that I can  
> connect via SMB from the clients on the 192 network to windows SMB  
> shares on the 10. network.
>
>
> IPT="/sbin/iptables"
>
> # THE NETWORK CONTAINING THE SITE SYSTEMS
> DMZ_IP="10.138.2.117"
> DMZ_IFACE="eth0"
> DMZ_BROADCAST="10.138.2.255"
>
> # THE IP RANGE FOR CLIENT COMPUTERS (disconnected network)
> CLIENTS_IP="192.168.200.1"
> CLIENTS_IP_RANGE="192.168.200.0/24"
> CLIENTS_IFACE="eth1"
>
> $IPT --flush
> $IPT --table nat --flush
> $IPT --delete-chain
> $IPT --table nat --delete-chain
>
> $IPT -A INPUT -j LOG --log-prefix "INPUT_PACKETS: "
> $IPT -A FORWARD -j LOG --log-prefix "FORWARD_PACKETS: "
> $IPT -A OUTPUT -j LOG --log-prefix "OUTPUT_PACKETS: "
>
> $IPT --policy INPUT DROP
> #$IPT --policy OUTPUT DROP
>
>
> $IPT -A INPUT -p tcp --dport 22 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 80 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 443 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 53 -j ACCEPT
> $IPT -A INPUT -p udp --dport 53 -j ACCEPT
>
> #$IPT -A INPUT -p udp -j ACCEPT
> #$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
>
> #$IPT -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
> #$IPT -A FORWARD -p tcp --dport 80 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 443 -j ACCEPT
> $IPT -A FORWARD -p udp --dport 53 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 53 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 445 -j DROP
> $IPT -N LOGDROP
> $IPT -A LOGDROP -j LOG
> $IPT -A LOGDROP -j DROP
> $IPT -A INPUT -j LOG
> $IPT -A FORWARD -j LOG
>
> $IPT --table nat --append POSTROUTING --out-interface $DMZ_IFACE -j  
> MASQUERADE
> echo 1 > /proc/sys/net/ipv4/ip_forward
>
>
> --
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Re: Difficulty with iptables script to only allow 3 ports across the firewall

[Martin]

On Wed, 2008-06-04 at 01:29 +0000, john@langherd.com wrote:
> First, thanks for taking the time to look.
> 
> I've been poking at this for almost 2 weeks and am quite stuck.
> 
> Here's the nutshell version of what I'm trying to do:
> 
> Client machine has an IP address of 192.168.100.101.  The only way I want this client to be able to communicate with machines on the 10.138.x.x network is via HTTPS (443), plus make DNS lookup requests.  I don't want PING, or any windows SMB type connections to succeed.  Just HTTPS and DNS.  Also, the linux box provides dhcp services to the 192.168.200.x network.
> 
> I think my fundamental understanding of iptables is wrong.
> 
> I 'think' the INPUT is what's allowed to the local machine (i.e. firewall box)
> FORWARD is what's passed from NIC to NIC.
> OUTPUT is what's allowed off the NIC.
> 
> Would anybody please give me a hand here?  I learn quickly by examples.  I've poked at a large number of websites, but am not making much headway.
> 
> Respectfully,
> 
> John
> 
> Here's my script as it sits.  It's driving me nuts that I can connect via SMB from the clients on the 192 network to windows SMB shares on the 10. network.
> 
> 
> IPT="/sbin/iptables"
> 
> # THE NETWORK CONTAINING THE SITE SYSTEMS
> DMZ_IP="10.138.2.117"
> DMZ_IFACE="eth0"
> DMZ_BROADCAST="10.138.2.255"
> 
> # THE IP RANGE FOR CLIENT COMPUTERS (disconnected network)
> CLIENTS_IP="192.168.200.1"
> CLIENTS_IP_RANGE="192.168.200.0/24"
> CLIENTS_IFACE="eth1"
> 
> $IPT --flush
> $IPT --table nat --flush
> $IPT --delete-chain
> $IPT --table nat --delete-chain
> 
> $IPT -A INPUT -j LOG --log-prefix "INPUT_PACKETS: "
> $IPT -A FORWARD -j LOG --log-prefix "FORWARD_PACKETS: "
> $IPT -A OUTPUT -j LOG --log-prefix "OUTPUT_PACKETS: "
> 
> $IPT --policy INPUT DROP
> #$IPT --policy OUTPUT DROP
> 
> 
> $IPT -A INPUT -p tcp --dport 22 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 80 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 443 -j ACCEPT
> $IPT -A INPUT -p tcp --dport 53 -j ACCEPT
> $IPT -A INPUT -p udp --dport 53 -j ACCEPT
> 
> #$IPT -A INPUT -p udp -j ACCEPT
> #$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> 
> #$IPT -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
> #$IPT -A FORWARD -p tcp --dport 80 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 443 -j ACCEPT
> $IPT -A FORWARD -p udp --dport 53 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 53 -j ACCEPT
> $IPT -A FORWARD -p tcp --dport 445 -j DROP
> $IPT -N LOGDROP
> $IPT -A LOGDROP -j LOG
> $IPT -A LOGDROP -j DROP
> $IPT -A INPUT -j LOG
> $IPT -A FORWARD -j LOG
> 
> $IPT --table nat --append POSTROUTING --out-interface $DMZ_IFACE -j MASQUERADE
> echo 1 > /proc/sys/net/ipv4/ip_forward
[...]

You can be a bit more strict using source and destination

$IPT -A FORWARD -s 192.168.100.101 -d 10.138.x.x -m tcp --dport 443 -j
ACCEPT

$IPT -A FORWARD -s 192.168.100.101 -d 10.138.x.x -m udp --dport 53 -j
ACCEPT

$IPT -A FORWARD -s 192.168.100.101 -j LOG #To see if there is another
attemp of connection
$IPT -A FORWARD -s 192.168.100.101 -j DROP


You probably will need the reverse rules (from 10.138.x.x to
192.168.100.101).


Cheers


Martin

Re: Difficulty with iptables script to only allow 3 ports across the firewall

[john]

-----Original Message-----
From: Glenn Henshaw [mailto:thraxisp@logicaloutcome.ca]
Sent: Tuesday, June 3, 2008 11:03 PM
To: john@langherd.com
Cc: netfilter@vger.kernel.org
Subject: Re: Difficulty with iptables script to only allow 3 ports across the firewall

" try adding $IPT --policy FORWARD DROP this will drop any packets not explicitly listed "

This worked perfectly.  Thanks a million.

John