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how to access port forwarded server through internet ?

DISCUSSION J. Bakshi 3 participants 6 messages Mar 15, 2011 – Mar 16, 2011

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J. Bakshi

author
#0 lore raw

Dear list,

Here is a port forwarding issue. I have a linux router which have two NIC; one facing WAN and the other facing LAN. IP forwarding is active and this box is working as a gateway. This box has LAN IP 192.168.1.1

There is another box (webserver) 192.168.1.2 within the internal network and the router box has port forwarding to access the webserver.

```````````````````````````
iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080
iptables -A FORWARD -p tcp -m state --state NEW --dport 81 -i ${LAN_IFACE} -j ACCEPT
````````````````````````````

So within LAN I can access the 192.168.1.2 web server through 192.168.1.1:81 as port forwarding is there. But I can not access the same through internet. If I point at <domain-name>:81 throught internet ; the browser simply reports it can't connect to the service; though the other services running at that very server are quite accessible through internet. Have I missed something in my firewall rule ? Could anyone give any clue please ?

Thanks

#1 lore raw

Hello,
forwarding is enable?
can you try this;

#sysctl -w net.ipv4.ip_forward=1
#iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 19 lines · J. Bakshi

Dear list,

Here is a port forwarding issue. I have a linux router which have two NIC; one facing WAN and the other facing LAN. IP forwarding is active and this box is working as a gateway. This box has LAN IP 192.168.1.1

There is another box (webserver) 192.168.1.2 within the internal network and the router box has port forwarding to access the webserver.

```````````````````````````
iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080
iptables -A FORWARD -p tcp -m state --state NEW --dport 81 -i ${LAN_IFACE} -j ACCEPT
````````````````````````````

So within LAN I can access the 192.168.1.2 web server through 192.168.1.1:81 as port forwarding is there. But I can not access the same through internet. If I point at<domain-name>:81 throught internet ; the browser simply reports it can't connect to the service; though the other services running at that very server are quite accessible through internet. Have I missed something in my firewall rule ? Could anyone give any clue please ?

Thanks
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author
#2 lore raw

Hello Remzi,

Thanks for your kind response. Yes the forwarding is enable as I have it in my script

`````````````````
echo 1 >  /proc/sys/net/ipv4/ip_forward
`````````````````````

But no luck :-( here is the modified rule

iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080 iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 30 lines · On Tue, 15 Mar 2011 15:16:18 +0200 Remzi AKYÃœZ <[email protected]> wrote:

Hello,
forwarding is enable?
can you try this;

#sysctl -w net.ipv4.ip_forward=1
#iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 19 lines · J. Bakshi

Dear list,

Here is a port forwarding issue. I have a linux router which have two NIC; one facing WAN and the other facing LAN. IP forwarding is active and this box is working as a gateway. This box has LAN IP 192.168.1.1

There is another box (webserver) 192.168.1.2 within the internal network and the router box has port forwarding to access the webserver.

```````````````````````````
iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080
iptables -A FORWARD -p tcp -m state --state NEW --dport 81 -i ${LAN_IFACE} -j ACCEPT
````````````````````````````

So within LAN I can access the 192.168.1.2 web server through 192.168.1.1:81 as port forwarding is there. But I can not access the same through internet. If I point at<domain-name>:81 throught internet ; the browser simply reports it can't connect to the service; though the other services running at that very server are quite accessible through internet. Have I missed something in my firewall rule ? Could anyone give any clue please ?

Thanks
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author
#3 lore raw

Any clue please ?

Quoted 53 lines · On Tue, 15 Mar 2011 19:22:01 +0530 "J. Bakshi" <[email protected]> wrote:

Hello Remzi,

Thanks for your kind response. Yes the forwarding is enable as I have it in my script

`````````````````
echo 1 >  /proc/sys/net/ipv4/ip_forward
`````````````````````

But no luck :-( here is the modified rule

iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080 iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 4 lines · On Tue, 15 Mar 2011 15:16:18 +0200 Remzi AKYÃœZ <[email protected]> wrote:

Hello,
forwarding is enable?
can you try this;

Quoted 26 lines

#sysctl -w net.ipv4.ip_forward=1
#iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 19 lines · J. Bakshi

Dear list,

Here is a port forwarding issue. I have a linux router which have two NIC; one facing WAN and the other facing LAN. IP forwarding is active and this box is working as a gateway. This box has LAN IP 192.168.1.1

There is another box (webserver) 192.168.1.2 within the internal network and the router box has port forwarding to access the webserver.

```````````````````````````
iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080
iptables -A FORWARD -p tcp -m state --state NEW --dport 81 -i ${LAN_IFACE} -j ACCEPT
````````````````````````````

So within LAN I can access the 192.168.1.2 web server through 192.168.1.1:81 as port forwarding is there. But I can not access the same through internet. If I point at<domain-name>:81 throught internet ; the browser simply reports it can't connect to the service; though the other services running at that very server are quite accessible through internet. Have I missed something in my firewall rule ? Could anyone give any clue please ?

Thanks
--
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#4 lore raw

Bakshi;

input interface maybe invalid.
can you try this;

iptables -t nat -I PREROUTING -i wan_intarface -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080

iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i wan_intarface -j ACCEPT

if this is failure, can you send yours active iptables rules ? (iptables-save> ipt_gw.txt )

Quoted 57 lines · J. Bakshi

Any clue please ?

Quoted 51 lines · On Tue, 15 Mar 2011 19:22:01 +0530 "J. Bakshi"<[email protected]> wrote:

Hello Remzi,

Thanks for your kind response. Yes the forwarding is enable as I have it in my script

`````````````````
echo 1>   /proc/sys/net/ipv4/ip_forward
`````````````````````

But no luck :-( here is the modified rule

iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080 iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 4 lines · On Tue, 15 Mar 2011 15:16:18 +0200 Remzi AKYÃœZ<[email protected]> wrote:

Hello,
forwarding is enable?
can you try this;

Quoted 25 lines

#sysctl -w net.ipv4.ip_forward=1
#iptables -A FORWARD -p tcp -m state --state NEW,ESTABLISHED --dport 81 -i ${LAN_IFACE} -j ACCEPT

Quoted 19 lines · J. Bakshi

Dear list,

Here is a port forwarding issue. I have a linux router which have two NIC; one facing WAN and the other facing LAN. IP forwarding is active and this box is working as a gateway. This box has LAN IP 192.168.1.1

There is another box (webserver) 192.168.1.2 within the internal network and the router box has port forwarding to access the webserver.

```````````````````````````
iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080
iptables -A FORWARD -p tcp -m state --state NEW --dport 81 -i ${LAN_IFACE} -j ACCEPT
````````````````````````````

So within LAN I can access the 192.168.1.2 web server through 192.168.1.1:81 as port forwarding is there. But I can not access the same through internet. If I point at<domain-name>:81 throught internet ; the browser simply reports it can't connect to the service; though the other services running at that very server are quite accessible through internet. Have I missed something in my firewall rule ? Could anyone give any clue please ?

Thanks
--
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#5 lore raw
In reply to J. Bakshi

My previous email was not sent to the list >_<

My answer is below.

Quoted 12 lines · J. Bakshi

Dear list,

Here is a port forwarding issue.  I have a linux router which have two NIC; one facing WAN and the other facing LAN. IP forwarding is active and this box is working as a gateway. This box has LAN IP 192.168.1.1

There is another box (webserver) 192.168.1.2 within the internal network and the router box has port forwarding to access the webserver.

```````````````````````````
iptables -A INPUT -p tcp -m tcp --dport 81 -j ACCEPT
iptables -A PREROUTING -t nat -i ${LAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080
iptables -A FORWARD -p tcp -m state --state NEW --dport 81 -i ${LAN_IFACE} -j ACCEPT
````````````````````````````
Quoted 4 lines

So within LAN I can access the 192.168.1.2 web server through  192.168.1.1:81 as port forwarding is there. But I can not access the same through internet. If I point at <domain-name>:81 throught internet ; the browser simply reports it can't connect to the service; though the other services running at that very server are quite accessible through internet. Have I missed something in my firewall rule ? Could anyone give any clue please ?

Thanks
--

You need another iptables rules for the WAN_IFACE

iptables -A PREROUTING -t nat -i ${WAN_IFACE} -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080

You can combine this new rule with the old rule by dropping the -i selector. I.e. :

iptables -A PREROUTING -t nat -p tcp --dport 81 -j DNAT --to 192.168.1.2:8080

Next, also add a proper FORWARD rule, since the FORWARD rule will be processed after NAT takes place:

iptables -A FORWARD -d 192.168.1.2 -p tcp --dport 8080 -j ACCEPT

This rule allows forwarding to the webserver (192.168.1.2) port 8080, no matter the incoming interface, be it WAN_IFACE or LAN_IFACE. No need to match the state here.

Finally, remember that since the packets do not actually end up in the firewall box, you don't need the -A INPUT rule there. It never gets matched.

Rgds,
--
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