Re: [LARTC] Buggy netfilter?

["Roy" <roy@xxx.lt>]

Netfilter is working ok in this case,

but this place of your setup
>--- ip route settings ---
>
>Just like in the Adv-Routing-HowTo (4.2.1. Split access), except
for the
>different IP addresses.

may not work as you want (i dont have idea what is there)

anyway I am not iproute2 specialist, and prefer to use netfilter for this
purpose

probably eth0 is yor default gateway.

but as I see your problem is that you want to map 2 external addreses into
one internal.
but you are doing do this in one direction only, reverse is default gateway,

because routing takes place "inside" nat so routing code should always see
internal network address.
you should either mark packets and route them with iptables ROUTE in the
postrouting chain
(I am not completely sure in what I said , but i think it is more or less
correct)

or you have much more simple way to assign second address to your server.
and nat 2 interfaces into 2 diferent addreses.
server software will take care of everything then.
but you will need to dnat these 2 adderses back into real ones again


----- Original Message ----- 
From: "Gludovátz Gábor" <ggabor@sopron.hu>
To: "Roy" <roy@xxx.lt>; <lartc@mailman.ds9a.nl>
Sent: Thursday, April 01, 2004 9:33 AM
Subject: Re: [LARTC] Buggy netfilter?




Roy wrote:

>You mail is little hard to undersatnd what you need.
>
>what this configuration is supposed to do?
>
>

I would like to connect to my firewall and to the machines behind it
(with DNAT) from the Internet.
The firewall has 2 Internet providers, one with a broadband DSL (ppp0)
connection, one with a cabel connection (eth0).

I can connect to my firewall through both connections, but DNAT operates
only on eth0.

However ppp0 DNAT should work as well, because  the packets go the same
route inside the netfilter. An iptables log event is also fired, but in
the end the ppp0 packets get lost, while the eth0 packets get forwarded
to the target machine (behind the firewall).

The ppp0 packets cannot be tracked down as they entered the firewall.
tcpdump sees only ppp0 pockets coming in, but nothing goes back, and
nothing goes out on the inner interface (eth2) to the target.

With eth0 everything works well.
ppp0 mtu is reduced as well, so I don't have more ideas what else to try
to make this configuration work.


>----- Original Message ----- 
>From: '"'Gludovátz Gábor'"'
<ggabor@sopron.hu>
>To: <lartc@mailman.ds9a.nl>
>Sent: Wednesday, March 31, 2004 11:53 PM
>Subject: [LARTC] Buggy netfilter?
>
>
>Or am I doing something really wrong.
>
>
>2 public interfaces (eth0 and ppp0), with 2 public IP
addresses.
>
>I can ping and connect to both interface's IP address. I can
login with
>ssh, anything on _both_ IP address.
>
>But iptables DNAT works only for eth0.
>
>Here are my settings:
>
>(ppp is initialized with 'pptp provider.ip')
>
>--- /etc/ppp/options ---
>
>nodefaultroute
>noipdefault
>name ''"''adsluser@provider''"''
>linkname ''"''adsl''"''
>noauth
>debug
>mtu 1400
>mru 1400
>
>--- ip route settings ---
>
>Just like in the Adv-Routing-HowTo (4.2.1. Split access), except
for the
>different IP addresses.
>
>--- iptables ---
>
>iptables -t nat -N ROUTING1
>iptables -t nat -N ROUTING2
>
>iptables -t nat -A PREROUTING -p tcp -i eth0 -j ROUTING1
>iptables -t nat -A PREROUTING -p tcp -i ppp0 -j ROUTING1
>
>iptables -t nat -A ROUTING1 -p tcp -j ROUTING2 -s
$clientip1/32
>iptables -t nat -A ROUTING1 -p tcp -j ROUTING2 -s
$clientip2/32
>
>iptables -t nat -A ROUTING2 -p tcp -j LOG  --dport 3389
--log-prefix
>''"''FW: MSTSC connection attempt ''"'' --log-level
warn
>iptables -t nat -A ROUTING2 -p tcp -j DNAT --dport 3389
--to-destination
>192.168.100.23:3389
>
>---
>
>eth2 is the 3rd interface, with access to our 192.168.100.*
private network.
>
>
>-- The result: --
>
>I can reach both interfaces (from the Internet), I can connect
through
>them to the firewall.
>
>But DNAT works only with the eth0 interface.
>
>Strange: iptables LOG rule is fired for ppp0 and eth0
connections,
>but eth0 connections are successful, and at the same
time:
>ppp0 connections are just waiting without anything coming
back.
>
>But as you can see, the packets for both go the same way in
iptables.
>
>--- tcpdump ---
>
>If I go through ppp0, nothing can be seen on the inner interface
(eth2).
>The packets seem to get lost somewhere, so nothing (nothing at
all) goes
>back to the client, who tries to connect.
>
>
>
>Thanks in advance
>

-- 
 Gábor GLUDOVÁTZ <gabor@gludovatz.com>  /  +36 (70) 520 31 62
  http://www.gludovatz.com/  ...
... .. .. . .


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