DNAT problem / question

DNAT problem / question

[Arnauts, Bert]

Hello all,

I am still stuck with my DNAT. I updated the information that was
requested.
Could you please check my config, if I execute this I can not ping my
internal lan ip of this host 172.25.239.208 any more. I think this is
really wierd. I included all kinds of information, hopefully enough for
you guys to take a look at.

Cheers,

Bert

$IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT
--to-destination 11.0.0.16 $IPTABLES -t nat -A OUTPUT -d
172.25.239.220/27 -j DNAT --to-destination 11.0.0.16 

$IPTABLES -A INPUT   -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A OUTPUT  -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

$IPTABLES -N RULE_0
$IPTABLES -A OUTPUT -d 11.0.0.16  -m state --state NEW  -j RULE_0
$IPTABLES -A FORWARD -d 11.0.0.16  -m state --state NEW  -j RULE_0
$IPTABLES -A RULE_0  -j LOG  --log-level info --log-prefix "RULE 0 --
ACCEPT " 
$IPTABLES -A RULE_0  -j ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward

-----Original Message-----
From: netfilter-admin@lists.netfilter.org
[mailto:netfilter-admin@lists.netfilter.org] On Behalf Of Antony Stone
Sent: Monday, June 14, 2004 4:51 PM
To: netfilter@lists.netfilter.org
Subject: Re: DNAT question

On Monday 14 June 2004 3:35 pm, Arnauts, Bert wrote:

> Hello all,
>
> I want to DNAT some machines in another subnet.
> The target machines have ip's like 11.0.0.x/24
>
> My available lan ip's are 172.239.239.x/27 (255.255.255.224)
>
> These are my rules. Wich are apparently not working.

How are you trying to test the rules?   What tells you they're not
working?

Where are you testing from?

I am testing from a machine that can ping the nat box'es IP and I can
access all sorts of other systems services on that subnet.
(my nat box : 172.25.239.208)

> I created virtual interfaces on eth1, one for each DNAT'ed ip.

Can you ping one of those addresses fom a machine directly connected to
eth1, qand then check the arp cache (arp -an under Linux) to be sure
that the IP / MAC address link is working correctly?

Yes I can ping these addresses. (without my iptables) With my rules it
doesn't work anymore.

> What am I missing ? Forget about normal tables stuff, I only want this

> machine to do DNAT.

What does "iptables -L -t nat -nvx" show you for the packet / byte
counters?    see below
Does it look like netfilter thinks it's doing any NAT?    yes ... I
guess. see below

I also ripped something frowm fwbuilder, adepted it a little bit .. this
is my new script.


#!/bin/bash
LSMOD="/sbin/lsmod"
MODPROBE="/sbin/modprobe"
IPTABLES="/sbin/iptables"
LOGGER="/usr/bin/logger"
echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
echo 1800 > /proc/sys/net/ipv4/tcp_keepalive_intvl

$IPTABLES -P OUTPUT ACCEPT 
$IPTABLES -P INPUT   ACCEPT 
$IPTABLES -P FORWARD ACCEPT 

cat /proc/net/ip_tables_names | while read table; do
  $IPTABLES -t $table -L -n | while read c chain rest; do
      if test "X$c" = "XChain" ; then
        $IPTABLES -t $table -F $chain
      fi
  done
  $IPTABLES -t $table -X
done

MODULE_DIR="/lib/modules/`uname -r`/kernel/net/ipv4/netfilter/" 
MODULES=`(cd $MODULE_DIR; ls *_conntrack_*  *_nat_* | sed 's/\.o.*$//;
s/\.ko$//')` for module in $(echo $MODULES); do
  if $LSMOD | grep ${module} >/dev/null; then continue; fi
  $MODPROBE ${module} ||  exit 1
done

echo "Activating firewall script generated Thu Jun 10 15:03:22 2004 CEST
by root"

$IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT
--to-destination 11.0.0.16 $IPTABLES -t nat -A OUTPUT -d
172.25.239.220/27 -j DNAT --to-destination
11.0.0.16 

$IPTABLES -A INPUT   -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A OUTPUT  -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

$IPTABLES -N RULE_0
$IPTABLES -A OUTPUT -d 11.0.0.16  -m state --state NEW  -j RULE_0
$IPTABLES -A FORWARD -d 11.0.0.16  -m state --state NEW  -j RULE_0
$IPTABLES -A RULE_0  -j LOG  --log-level info --log-prefix "RULE 0 --
ACCEPT " 
$IPTABLES -A RULE_0  -j ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward



thx Antony !
(nice quote)

--
If the human brain were so simple that we could understand it, we'd be
so simple that we couldn't.

                                                     Please reply to the
list;
                                                           please don't
CC me.

------------------------------------------------------------------------
---------------------------------------------


[root@linuxrouter root]# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:E0:18:02:7E:9B  
          inet addr:11.0.0.3  Bcast:11.0.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4822 errors:0 dropped:0 overruns:0 frame:0
          TX packets:23 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:286513 (279.7 Kb)  TX bytes:6516 (6.3 Kb)
          Interrupt:5 Base address:0xd800 Memory:fb000000-fb000038 

eth1      Link encap:Ethernet  HWaddr 00:D0:B7:E0:1F:2C  
          inet addr:172.25.239.208  Bcast:172.25.239.223
Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7342 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2091 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:629297 (614.5 Kb)  TX bytes:342349 (334.3 Kb)
          Interrupt:11 Base address:0xd400 Memory:fa000000-fa000038 

eth1:1    Link encap:Ethernet  HWaddr 00:D0:B7:E0:1F:2C  
          inet addr:172.25.239.220  Bcast:172.25.255.255
Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:11 Base address:0xd400 Memory:fa000000-fa000038 

[root@linuxrouter root]# ping 11.0.0.16
PING 11.0.0.16 (11.0.0.16) 56(84) bytes of data.
64 bytes from 11.0.0.16: icmp_seq=1 ttl=128 time=0.261 ms


[root@linuxrouter root]# ping 172.25.239.220 PING 172.25.239.220
(172.25.239.220) 56(84) bytes of data.
64 bytes from 172.25.239.220: icmp_seq=1 ttl=128 time=0.264 ms


[root@linuxrouter root]# iptables -L -t nat -nvx Chain PREROUTING
(policy ACCEPT 16 packets, 3256 bytes)
    pkts      bytes target     prot opt in     out     source
destination         
      70    11224 DNAT       all  --  *      *       0.0.0.0/0
172.25.239.192/27  to:11.0.0.16 

Chain POSTROUTING (policy ACCEPT 19 packets, 6614 bytes)
    pkts      bytes target     prot opt in     out     source
destination         

Chain OUTPUT (policy ACCEPT 5 packets, 420 bytes)
    pkts      bytes target     prot opt in     out     source
destination         
       5      404 DNAT       all  --  *      *       0.0.0.0/0
172.25.239.192/27  to:11.0.0.16 

[root@linuxrouter root]# arp -an
? (172.25.239.201) at 00:30:05:11:F9:EA [ether] on eth1 ?
(172.25.239.193) at 00:60:47:40:F7:A5 [ether] on eth1 ? (11.0.0.16) at
00:E0:18:02:38:60 [ether] on eth0

[BRUBARNA7M] D:\some_crapy\windows_box>ping 172.25.239.220

Pinging 172.25.239.220 with 32 bytes of data:

Request timed out.

Ping statistics for 172.25.239.220:
    Packets: Sent = 1, Received = 0, Lost = 1 (100% loss), Control-C ^C

also ... even a ping to my normal host is not working anymore. (wich was
working without the tables)

[BRUBARNA7M] D:\some_crapy\windows_box>ping 172.25.239.208

Pinging 172.25.239.208 with 32 bytes of data:

Request timed out.

Ping statistics for 172.25.239.208:
    Packets: Sent = 1, Received = 0, Lost = 1 (100% loss),

you should think it is my firewall ... but I accept everything ... :(

[root@linuxrouter root]# iptables -L -nvx Chain INPUT (policy ACCEPT 0
packets, 0 bytes)
    pkts      bytes target     prot opt in     out     source
destination         
     557    72706 ACCEPT     all  --  *      *       0.0.0.0/0
0.0.0.0/0          state NEW,RELATED,ESTABLISHED 

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
    pkts      bytes target     prot opt in     out     source
destination         
     147    13879 ACCEPT     all  --  *      *       0.0.0.0/0
0.0.0.0/0          state NEW,RELATED,ESTABLISHED 
       0        0 RULE_0     all  --  *      *       0.0.0.0/0
11.0.0.16          state NEW 

Chain OUTPUT (policy ACCEPT 1 packets, 152 bytes)
    pkts      bytes target     prot opt in     out     source
destination         
     269    31752 ACCEPT     all  --  *      *       0.0.0.0/0
0.0.0.0/0          state NEW,RELATED,ESTABLISHED 
       0        0 RULE_0     all  --  *      *       0.0.0.0/0
11.0.0.16          state NEW 

Chain RULE_0 (2 references)
    pkts      bytes target     prot opt in     out     source
destination         
       0        0 LOG        all  --  *      *       0.0.0.0/0
0.0.0.0/0          LOG flags 0 level 6 prefix `RULE 0 -- ACCEPT ' 
       0        0 ACCEPT     all  --  *      *       0.0.0.0/0
0.0.0.0/0          

Re: DNAT problem / question

[Patrick Leslie Polzer]

On Fri, 18 Jun 2004 17:45:20 +0200
"Arnauts, Bert" <Bert.Arnauts@fujitsu-siemens.com> wrote:

> Could you please check my config, if I execute this I can not ping my
> internal lan ip of this host 172.25.239.208 any more. I think this is
> really wierd.
Why? These lines:

> $IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT
> --to-destination 11.0.0.16
> $IPTABLES -t nat -A OUTPUT -d
> 172.25.239.220/27 -j DNAT --to-destination 11.0.0.16 

are doing everything to keep ALL packets away from you ;)
All outgoing packets (statement 2) are redirected to 11.0.0.16
and all incoming are as well (statement 1)!
How do you expect ping to work with that? :-O


Kind regards,

Leslie

Re: DNAT problem / question

[Antony Stone]

On Friday 18 June 2004 5:06 pm, Patrick Leslie Polzer wrote:

> On Fri, 18 Jun 2004 17:45:20 +0200
>
> "Arnauts, Bert" <Bert.Arnauts@fujitsu-siemens.com> wrote:
> > Could you please check my config, if I execute this I can not ping my
> > internal lan ip of this host 172.25.239.208 any more. I think this is
> > really wierd.
>
> Why? These lines:
> > $IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT
> > --to-destination 11.0.0.16
> > $IPTABLES -t nat -A OUTPUT -d
> > 172.25.239.220/27 -j DNAT --to-destination 11.0.0.16
>
> are doing everything to keep ALL packets away from you ;)
> All outgoing packets (statement 2) are redirected to 11.0.0.16
> and all incoming are as well (statement 1)!
> How do you expect ping to work with that? :-O

Good point, but surely a ping packet sent to 172.25.239.220 (let's overlook 
the netmask for the time being...) would get redirected to 11.0.0.16, and 
provided that machine responds to the ping (and the reply goes back through 
netfilter's NAT table) the origianting client might see the reply?

However, I am certainly highly confused by what Bert is trying achieve here - 
perhaps the answers to a few questions would help:

1. How many interfaces does the netfilter machine have?   What are their IP 
addresses?

2. Where is machine 11.0.0.16?   How are packets routed to that frm the 
netfiler machine?

3. What address are you sending the ping packets from (and to)?   How is that 
client routed to the netfilter box?

4. What, in simple terms, are you trying to achieve with the two rules which 
Patrick has queried above?

Regards,

Antony.

-- 
"It would appear we have reached the limits of what it is possible to achieve 
with computer technology, although one should be careful with such 
statements; they tend to sound pretty silly in five years."

 - John von Neumann (1949)

                                                     Please reply to the list;
                                                           please don't CC me.

Re: DNAT problem / question

[Antony Stone]

On Friday 18 June 2004 4:45 pm, Arnauts, Bert wrote:

> Hello all,
>
> I am still stuck with my DNAT. I updated the information that was
> requested.
> Could you please check my config, if I execute this I can not ping my
> internal lan ip of this host 172.25.239.208 any more. I think this is
> really wierd. I included all kinds of information, hopefully enough for
> you guys to take a look at.

It appears you have overlooked both of John Sullivan's postings on this (both 
more recent than mine).

> $IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT
> --to-destination 11.0.0.16
> $IPTABLES -t nat -A OUTPUT -d 172.25.239.220/27 -j DNAT --to-destination
> 11.0.0.16

You have specified an inappropriate combination of address and netmask with 
172.25.239.220/27 - the address 220 is not the base address of a /27 range, 
and it is possible (I am not certain) that this combination is confusing 
netfilter.

The /27 range within which address .220 falls is 172.25.239.192 (the braodcast 
address is 172.25.239.223), so firstly, try specifying that as your address 
range and see if it helps.

Secondly, do you really mean that you want all packets addressed to anywhere 
within the /27 range to be redirected instead to 11.0.0.16?   That is a valid 
rule, but seems like a slightly strange requirement.

Regards,

Antony.

-- 
"Linux is going to be part of the future. It's going to be like Unix was."

 - Peter Moore, Asia-Pacific general manager, Microsoft

                                                     Please reply to the list;
                                                           please don't CC me.

Re: DNAT problem / question

[Patrick Leslie Polzer]

On Fri, 18 Jun 2004 17:06:28 +0100
Antony Stone <Antony@Soft-Solutions.co.uk> wrote:

> You have specified an inappropriate combination of address and netmask with 
> 172.25.239.220/27 - the address 220 is not the base address of a /27 range, 
> and it is possible (I am not certain) that this combination is confusing 
> netfilter.
I don't think this is a problem. They'll be masked out anyway.

Leslie

Re: DNAT problem / question

[Rob Sterenborg]

> $IPTABLES -A INPUT   -m state --state NEW,
> ESTABLISHED,RELATED -j ACCEPT
> $IPTABLES -A OUTPUT  -m state --state NEW,
> ESTABLISHED,RELATED -j ACCEPT
> $IPTABLES -A FORWARD -m state --state NEW,
> ESTABLISHED,RELATED -j ACCEPT

I do not think you want this. Since you don't specify protocol and/or
port, you are accepting any packet that is NEW, RELATED or ESTABLISHED.
That means any packet.
This is the same as having a policy of ACCEPT for all filter chains with
no rules to block anything. If you want to filter anything, leave the
NEW out of the rules, or just set policy to ACCEPT and skip these rules.
(Btw, do you have policy set to DROP for INPUT, OUTPUT and FORWARD so
that these rules make sense ?)


Gr,
Rob

Re: DNAT problem / question (nfcan: addressed to exclusive sender for this address)

[Jim Laurino]

On 2004.06.18 11:45, Arnauts Bert  - Bert.Arnauts@fujitsu- 
siemens.com wrote:
> Hello all,
> 
> I am still stuck with my DNAT. I updated the information
> that was requested. Could you please check my config, if  
> I execute this I can not ping my internal lan ip of this  
> host 172.25.239.208 any more. I think this is really  
> wierd. I included all kinds of information, hopefully  
> enough for you guys to take a look at.
> 
> Cheers,
> 
> Bert
> 
> $IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27
> -j DNAT --to-destination 11.0.0.16

> $IPTABLES -t nat -A  OUTPUT -d 172.25.239.220/27
> -j DNAT --to-destination 11.0.0.16
>

The dest ip address/mask pattern looks odd.
I am not sure how this address matching works,
but the way I imagine it to work is that a mask
is generated and applied to an address to test
and then this is compared to the address given.
That is, I think the address given is not
masked. If this is so, then there might be a
failure to match destination addresses.

I think a /27 mask is meant to select a
contiguous group of 27 addresses, that is
5 bits. I think masking the 5 low bits of
a number like 220 or 208 gives 192 (xC0)
and a rule like .192/27 would match addresses
in the range 192-223 (xC0-xDF),
where .220/27 might match nothing.

Of course, the code might be written another
way, where this would not be a problem.

You could try logging what is happening
or looking at the counts to see if the
rules are matching. I think this will do it:

iptables -L -t nat -nvx

Jim

RE: DNAT problem / question

[Arnauts, Bert]

 

-----Original Message-----
From: netfilter-admin@lists.netfilter.org
[mailto:netfilter-admin@lists.netfilter.org] On Behalf Of Antony Stone
Sent: Friday, June 18, 2004 6:15 PM
To: netfilter@lists.netfilter.org
Subject: Re: DNAT problem / question

On Friday 18 June 2004 5:06 pm, Patrick Leslie Polzer wrote:

> On Fri, 18 Jun 2004 17:45:20 +0200
>
> "Arnauts, Bert" <Bert.Arnauts@fujitsu-siemens.com> wrote:
> > Could you please check my config, if I execute this I can not ping 
> > my internal lan ip of this host 172.25.239.208 any more. I think 
> > this is really wierd.
>
> Why? These lines:
> > $IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT 
> > --to-destination 11.0.0.16 $IPTABLES -t nat -A OUTPUT -d
> > 172.25.239.220/27 -j DNAT --to-destination 11.0.0.16
>
> are doing everything to keep ALL packets away from you ;) All outgoing

> packets (statement 2) are redirected to 11.0.0.16 and all incoming are

> as well (statement 1)!
> How do you expect ping to work with that? :-O

Good point, but surely a ping packet sent to 172.25.239.220 (let's
overlook the netmask for the time being...) would get redirected to
11.0.0.16, and provided that machine responds to the ping (and the reply
goes back through netfilter's NAT table) the origianting client might
see the reply?

However, I am certainly highly confused by what Bert is trying achieve
here - perhaps the answers to a few questions would help:

1. How many interfaces does the netfilter machine have?   What are their
IP 
addresses ?

[root@linuxrouter root]# ifconfig eth1:1 172.25.239.207 netmask
255.255.255.224 broadcast 172.25.239.223 up
[root@linuxrouter root]# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:E0:18:02:7E:9B  
          inet addr:11.0.0.3  Bcast:11.0.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:234000 errors:0 dropped:0 overruns:0 frame:0
          TX packets:117 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:13367392 (12.7 Mb)  TX bytes:5082 (4.9 Kb)
          Interrupt:5 Base address:0xd800 Memory:fb000000-fb000038 

eth1      Link encap:Ethernet  HWaddr 00:D0:B7:E0:1F:2C  
          inet addr:172.25.239.208  Bcast:172.25.239.223
Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:234540 errors:0 dropped:0 overruns:0 frame:0
          TX packets:685 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:13429554 (12.8 Mb)  TX bytes:69016 (67.3 Kb)
          Interrupt:11 Base address:0xd400 Memory:fa000000-fa000038 

eth1:1    Link encap:Ethernet  HWaddr 00:D0:B7:E0:1F:2C  
          inet addr:172.25.239.207  Bcast:172.25.239.223
Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:11 Base address:0xd400 Memory:fa000000-fa000038 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:57 errors:0 dropped:0 overruns:0 frame:0
          TX packets:57 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:6489 (6.3 Kb)  TX bytes:6489 (6.3 Kb)

2. Where is machine 11.0.0.16?   How are packets routed to that frm the 
netfiler machine?

machine 11.0.0.16 is in the same physical network.

3. What address are you sending the ping packets from (and to)?   How is
that 
client routed to the netfilter box?

in both ways. From the 172. network. and from the 11. network. Pinging
goes fine, until I execute my script

4. What, in simple terms, are you trying to achieve with the two rules
which Patrick has queried above?

In fact the problem is that I have in a internal network only limited
ip's, I have everything in the 172.25.239.0/27 network. Which gives me
only 20 something ip's. What I need are 40-50 ip's that need to talk to
each other. (all in the 11 network) But I still want to have access to
some (20) of these boxes from the outside world (our intranet).
Therefore I just want to do ip aliasing : meaning 172.25.239.207 should
be the alias for 11.0.0.16 for example.

Thx,

Bert

RE: DNAT problem / question

[Arnauts, Bert]

Hello all,

thx already for the hints, but I am still in a strugle. I changed my
destination ip to 207, because 220 could cause problems. Forgive me that
I don't understand why. 
Anyway, these rules give even a more confusing result.
I am still not able to access my 11.0.0.16 box through the
172.25.239.207 DNAT'ed alias. (not pingable, not nothing)
I also can not connect anymore to my netfilter box anymore after
executing this script, BUT my active ssh connection stays open ! ? I am
still on my machine remotly, but I can not ping it anymore ?? :(

Any more ideas ?

------------------------------------------------------------

echo "Activating firewall script generated Thu Jun 10 15:03:22 2004 CEST
by root"

$IPTABLES -t nat -A PREROUTING -d 172.25.239.207/27 -j DNAT
--to-destination 11.0.0.16

$IPTABLES -A INPUT   -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A OUTPUT  -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

$IPTABLES -N RULE_0
$IPTABLES -A OUTPUT -d 11.0.0.16  -m state --state NEW  -j RULE_0
$IPTABLES -A FORWARD -d 11.0.0.16  -m state --state NEW  -j RULE_0
$IPTABLES -A RULE_0  -j LOG  --log-level info --log-prefix "RULE 0 --
ACCEPT "
$IPTABLES -A RULE_0  -j ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward 

execution of this script gives me this : (why is there 192 ? in stead of
207 ?)

[root@linuxrouter root]# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         
DNAT       all  --  anywhere             172.25.239.192/27  to:11.0.0.16


Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
[root@linuxrouter root]# 



-----Original Message-----
From: netfilter-admin@lists.netfilter.org
[mailto:netfilter-admin@lists.netfilter.org] On Behalf Of Antony Stone
Sent: Friday, June 18, 2004 6:15 PM
To: netfilter@lists.netfilter.org
Subject: Re: DNAT problem / question

On Friday 18 June 2004 5:06 pm, Patrick Leslie Polzer wrote:

> On Fri, 18 Jun 2004 17:45:20 +0200
>
> "Arnauts, Bert" <Bert.Arnauts@fujitsu-siemens.com> wrote:
> > Could you please check my config, if I execute this I can not ping 
> > my internal lan ip of this host 172.25.239.208 any more. I think 
> > this is really wierd.
>
> Why? These lines:
> > $IPTABLES -t nat -A PREROUTING -d 172.25.239.220/27 -j DNAT 
> > --to-destination 11.0.0.16 $IPTABLES -t nat -A OUTPUT -d
> > 172.25.239.220/27 -j DNAT --to-destination 11.0.0.16
>
> are doing everything to keep ALL packets away from you ;) All outgoing

> packets (statement 2) are redirected to 11.0.0.16 and all incoming are

> as well (statement 1)!
> How do you expect ping to work with that? :-O

Good point, but surely a ping packet sent to 172.25.239.220 (let's
overlook the netmask for the time being...) would get redirected to
11.0.0.16, and provided that machine responds to the ping (and the reply
goes back through netfilter's NAT table) the origianting client might
see the reply?

However, I am certainly highly confused by what Bert is trying achieve
here - perhaps the answers to a few questions would help:

1. How many interfaces does the netfilter machine have?   What are their
IP 
addresses?

2. Where is machine 11.0.0.16?   How are packets routed to that frm the 
netfiler machine?

3. What address are you sending the ping packets from (and to)?   How is
that 
client routed to the netfilter box?

4. What, in simple terms, are you trying to achieve with the two rules
which Patrick has queried above?

Regards,

Antony.

--
"It would appear we have reached the limits of what it is possible to
achieve with computer technology, although one should be careful with
such statements; they tend to sound pretty silly in five years."

 - John von Neumann (1949)

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