Mailing List Archive: error - but I don't know where....

error - but I don't know where....

Aug 14, 2007, 2:59 AM

Post #1 of 3 (1801 views)

Hi *

I just try setup firewall. Config is following:

Desktop Firewll
(192.168.1.1) ------Eth0 Eth1(91.189.74.10)---------ISP

Script below is working OK for all LAN hosts, but not for for firewall PC itself (i tested it with i.e. ping www.ibm.com)
Commenting line "iptables -P INPUT DROP" allows to ping from firewall, but it effectivelly turning off firewall....
It is probably simple error - but I can't find where it is...
Can somebody verify thid script and tell me what is wrong ?

thx in advance

#Config area BEGIN--------------------------------------------------------------

LAN_intf=eth0
LAN_subnetwork=192.168.1.0/255.255.255.0

WAN_intf=eth1
WAN_ip=91.189.74.10

Open_WAN_TCP_ports=20,21,80,500,1352,4500
Open_WAN_UDP_ports=500,1352,4500,5060
Open_WAN_RTP_port_range=7070:7080

#Config area END----------------------------------------------------------------

#--Flushing all iptables tables-------------------------------------------------
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X

#--Setting up SNAT for outgoing to WAN DATA connections------------------------
iptables -t nat -A POSTROUTING -s $LAN_subnetwork -o $WAN_intf -j SNAT --to-source $WAN_ip

#--Allowing self access by loopback interface----------------------------------
iptables -A INPUT -i lo -p all -j ACCEPT

#--Allowing local access to LAN------------------------------------------------
iptables -A INPUT -i $LAN_intf -p all -j ACCEPT

#--Allowing WAN incoming traffic form already established connections----------
iptables -A INPUT -i WAN_intf -m state --state ESTABLISHED,RELATED -j ACCEPT

#--Allowing WAN incoming traffic for desired services--------------------------
#Open WAN TCP ports
iptables -A INPUT -p tcp -i $WAN_intf -m multiport --dport $Open_WAN_TCP_ports -j ACCEPT

#Open WAN UDP ports
iptables -A INPUT -p udp -i $WAN_intf -m multiport --dport $Open_WAN_UDP_ports -j ACCEPT

#Open VoIP UDP port ranges
iptables -A INPUT -p udp -i $WAN_intf --dport $Open_WAN_RTP_port_range -j ACCEPT

#--Drop all other incoming connection. Only above will be allowed-------------
iptables -P INPUT DROP

Re: error - but I don't know where.... [ In reply to ]

swifty at freemail

Aug 14, 2007, 4:02 AM

Post #2 of 3 (1706 views)

Permalink

warpme írta:
> Hi *
>
> I just try setup firewall. Config is following:
>
> Desktop Firewll
> (192.168.1.1) ------Eth0 Eth1(91.189.74.10)---------ISP
>
> Script below is working OK for all LAN hosts, but not for for firewall PC itself (i tested it with i.e. ping www.ibm.com)
> Commenting line "iptables -P INPUT DROP" allows to ping from firewall, but it effectivelly turning off firewall....
> It is probably simple error - but I can't find where it is...
> Can somebody verify thid script and tell me what is wrong ?
>
> thx in advance
>
>
> #Config area BEGIN--------------------------------------------------------------
>
> LAN_intf=eth0
> LAN_subnetwork=192.168.1.0/255.255.255.0
>
> WAN_intf=eth1
> WAN_ip=91.189.74.10
>
> Open_WAN_TCP_ports=20,21,80,500,1352,4500
> Open_WAN_UDP_ports=500,1352,4500,5060
> Open_WAN_RTP_port_range=7070:7080
>
>
> #Config area END----------------------------------------------------------------
>
>
>
>
> #--Flushing all iptables tables-------------------------------------------------
> iptables -F
> iptables -X
> iptables -t nat -F
> iptables -t nat -X
> iptables -t mangle -F
> iptables -t mangle -X
>
>
>
>
> #--Setting up SNAT for outgoing to WAN DATA connections------------------------
> iptables -t nat -A POSTROUTING -s $LAN_subnetwork -o $WAN_intf -j SNAT --to-source $WAN_ip
I would write like this:

iptables -t nat -A POSTROUTING ! -s $WAN_ip -o $WAN_intf -j SNAT
--to-source $WAN_ip
>
> #--Allowing self access by loopback interface----------------------------------
> iptables -A INPUT -i lo -p all -j ACCEPT
>
>
"-p all" not needed... And I would rather set up the OUTPUT rule than
the INPUT rule because the "lo" interface only accepts connections from
itself... if a new connection is made then first step is to send OUT
something to the other host... :D
iptables -A OUTPUT -o lo -j ACCEPT
>
> #--Allowing local access to LAN------------------------------------------------
> iptables -A INPUT -i $LAN_intf -p all -j ACCEPT
>
>
no need for "-p all"
>
> #--Allowing WAN incoming traffic form already established connections----------
> iptables -A INPUT -i WAN_intf -m state --state ESTABLISHED,RELATED -j ACCEPT
>
>
> #--Allowing WAN incoming traffic for desired services--------------------------
> #Open WAN TCP ports
> iptables -A INPUT -p tcp -i $WAN_intf -m multiport --dport $Open_WAN_TCP_ports -j ACCEPT
>
> #Open WAN UDP ports
> iptables -A INPUT -p udp -i $WAN_intf -m multiport --dport $Open_WAN_UDP_ports -j ACCEPT
>
> #Open VoIP UDP port ranges
> iptables -A INPUT -p udp -i $WAN_intf --dport $Open_WAN_RTP_port_range -j ACCEPT
>
>
For "ping" you need the following line:
iptables -A INPUT -p icmp -j ACCEPT
> #--Drop all other incoming connection. Only above will be allowed-------------
> iptables -P INPUT DROP
>
>
>
>

Re: error - but I don't know where.... [ In reply to ]

warpme at o2

Aug 15, 2007, 5:38 AM

Post #3 of 3 (1709 views)

Permalink

Gaspar,

Thanx for trying help !
It looks like I found problem. Probably somewhere in file was non-ASCII
chars which are not visible in my editor and causing problem.
I rewrite manually script and now works as expected :-)
I also change little bit approach: default policy for FORWARD chain is
now DROP.
I'm allowing forwarding only new connections from LAN to WAN and accept
only already established
connections from WAN to LAN:
iptables -A FORWARD -i $WAN_intf -o $LAN_intf -m state --state
ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i $LAN_intf -o $WAN_intf -m state --state
NEW,ESTABLISHED,RELATED -j ACCEPT

BTW: I have some comments to Your hints (see inline):

br

Gáspár Lajos wrote:
> warpme írta:
>> Hi *
>>
>> I just try setup firewall. Config is following:
>>
>> Desktop Firewll (192.168.1.1) ------Eth0
>> Eth1(91.189.74.10)---------ISP
>>
>> Script below is working OK for all LAN hosts, but not for for
>> firewall PC itself (i tested it with i.e. ping www.ibm.com)
>> Commenting line "iptables -P INPUT DROP" allows to ping from
>> firewall, but it effectivelly turning off firewall....
>> It is probably simple error - but I can't find where it is...
>> Can somebody verify thid script and tell me what is wrong ?
>>
>> thx in advance
>>
>> #Config area
>> BEGIN--------------------------------------------------------------
>>
>> LAN_intf=eth0
>> LAN_subnetwork=192.168.1.0/255.255.255.0
>>
>> WAN_intf=eth1
>> WAN_ip=91.189.74.10
>>
>> Open_WAN_TCP_ports=20,21,80,500,1352,4500
>> Open_WAN_UDP_ports=500,1352,4500,5060
>> Open_WAN_RTP_port_range=7070:7080
>>
>>
>> #Config area
>> END----------------------------------------------------------------
>>
>>
>>
>>
>> #--Flushing all iptables
>> tables-------------------------------------------------
>> iptables -F
>> iptables -X iptables -t nat -F
>> iptables -t nat -X
>> iptables -t mangle -F
>> iptables -t mangle -X
>>
>>
>>
>>
>> #--Setting up SNAT for outgoing to WAN DATA
>> connections------------------------
>> iptables -t nat -A POSTROUTING -s $LAN_subnetwork -o $WAN_intf -j
>> SNAT --to-source $WAN_ip
> I would write like this:
>
> iptables -t nat -A POSTROUTING ! -s $WAN_ip -o $WAN_intf -j SNAT
> --to-source $WAN_ip
I'm understand advantage of such approach is that any non WAN_ip host
will be NAT'ed. But for non-LAN addressed hosts it will require
additional entries in routing table for packets received from WAN and
destinated to LAN host. Effectively it will require touch to firewall
- and by this I'm considering this as no beneficial.
>> #--Allowing self access by loopback
>> interface----------------------------------
>> iptables -A INPUT -i lo -p all -j ACCEPT
>>
>>
> "-p all" not needed... And I would rather set up the OUTPUT rule than
> the INPUT rule because the "lo" interface only accepts connections
> from itself... if a new connection is made then first step is to send
> OUT something to the other host... :D
> iptables -A OUTPUT -o lo -j ACCEPT
Well, default iptables policy for all chains is ACCEPT, so this rule is
redundant.
>
>>
>> #--Allowing local access to
>> LAN------------------------------------------------
>> iptables -A INPUT -i $LAN_intf -p all -j ACCEPT
>>
>>
> no need for "-p all"
Right !
>
>>
>> #--Allowing WAN incoming traffic form already established
>> connections----------
>> iptables -A INPUT -i WAN_intf -m state --state ESTABLISHED,RELATED -j
>> ACCEPT
>>
>>
>> #--Allowing WAN incoming traffic for desired
>> services--------------------------
>> #Open WAN TCP ports
>> iptables -A INPUT -p tcp -i $WAN_intf -m multiport --dport
>> $Open_WAN_TCP_ports -j ACCEPT
>>
>> #Open WAN UDP ports
>> iptables -A INPUT -p udp -i $WAN_intf -m multiport --dport
>> $Open_WAN_UDP_ports -j ACCEPT
>>
>> #Open VoIP UDP port ranges
>> iptables -A INPUT -p udp -i $WAN_intf --dport
>> $Open_WAN_RTP_port_range -j ACCEPT
>>
>>
> For "ping" you need the following line:
> iptables -A INPUT -p icmp -j ACCEPT
Well - it is not needed when only outgoing pings are allowed (my case).
I think incoming pings should be rather disabled - it will help to
protect host from potential DoS via ping flood.
>> #--Drop all other incoming connection. Only above will be
>> allowed-------------
>> iptables -P INPUT DROP
>>
>>
>>
>
>
>