RE: Port forward

Eugene Joubert <eugenej@xxxxxxxxxxxxxxx> · Tue, 4 Feb 2003 15:20:39 +0200

Title: Message

If you 
port forwarding happens from outside your linux box going inside your network 
you should telnet from an external address to your linux ip on port 25. Also 
with every PREROUTING entry you would have to have an entry in your FORWARD 
chain. This is if your FORWARD default policy is set to drop. If you have the 
default policy on your FORWARD chain set to ACCEPT then you DON'T have to 
specifically add it.

eg 
iptables -A FORWARD -p tcp -i eth0 -o eth1 -s 0/0 --dport 25 -j 
ACCEPT

Hope 
this helps

PS: 
Remeber you have to come in from outside your network to test this 
rule

  -----Original Message-----
From: ASC - Ronald 
  Roeleveld [mailto:r.roeleveld@ascinternational.nl] 
Sent: 04 02 2003 
  15:11 PM
To: 'Eugene Joubert'
Cc: 
  'netfilter@lists.netfilter.org'
Subject: RE: Port 
  forward

  Thanks a lot everyone for the 
  emails...
  I 
  did iptables -t nat --list and it now gives me this 
output:
  DNAT       tcp  
  --  
  anywhere             
  anywhere           tcp 
  dpt:smtp to:192.168.22.6:25
  But 
  when I tried to telnet from another machine to 192.168.22.5 port 25 (the ip of 
  the netfilter firewall/router) it didn't work at all..Do there has to be a 
  line somewhere that says it's allowed to forward these 
  connections?

  Regards,

  Ronald.

    -----Original Message-----
From: Eugene Joubert 
    [mailto:eugenej@centratel.co.za]
Sent: dinsdag 4 februari 2003 
    11:41
To: 'ASC - Ronald Roeleveld';       
Subject: 
    RE: Port forward

    remember that you are using DNAT so you would have to specify the -t 
    nat switch in your line.

    eg 

    iptables -t nat -A PREROUTING -p tcp -s 0/0 --dport 25 -i eth0 
    -j DNAT --to 192.168.22.6:25

    Hope this helps

      -----Original Message-----
From: ASC - Ronald 
      Roeleveld [mailto:r.roeleveld@ascinternational.nl] 
Sent: 04 02 
      2003 12:31 PM
To: 
      'netfilter@lists.netfilter.org'
Subject: Port 
      forward

      Hi 
      all,

      Iam trying to 
      set up a port forward for several hours now, but I don't seem to get it 
      working right.
      When I type 
      the following command:
      iptables -A 
      PREROUTING -p tcp --destination-port 25 -i eth0 -j DNAT --to-destination 
      192.168.22.6:25
      I get this 
      output:
      iptables: 
      Invalid argument
      I did do 
      iptables -X PREROUTING so the chain does exist.
      Can anyone 
      please help me out..
      What I want is 
      that all incoming connections on eth0 on port 25 are routed to another 
      machine on the internal network 192.168.22.6

      Thanks in 
      advance,

      Ronald Roeleveld 
System 
      Administrator 
      ASCINTERNATIONAL 
Vlietweg 17c, 2266 KA, Leidschendam, The 
      Netherlands 
Tel. +31 
      (0)70 3178400, Fax +31 (0)70 3204760
E-mail: r.roeleveld@ascinternational.nl, 
      Website: http://www.ascinternational.nl 