help for open port in firewall

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Regular Contributor

I need some help for opening a port in WAN firewall.
My situation is a router cacade
internet FritzBox (LAN range: <-> WAN( Asus router (LAN range:
Additionally on the Asus router OpenVPN is running which connects to other routers.
Now on the Fritzbox I have connected a raspberry ( which I want to communicate to my NAS over the Asus router via OpenVPN.

Everything is working if I disable the WAN firewall on the Asus router but I do not want to disable it completely.
I want to make an exception only for for theRaspberry.
When Itry to mount my NAS ( on the Raspberry then I get the Asus syslog entry:

May 15 22:15:17 kernel: DROP IN=eth0 OUT=tun21 MAC=a8:...... SRC= DST= LEN=60 TOS=0x00 PREC=0x00 TTL=62 ID=47224 DF PROTO=TCP SPT=45328 DPT=445 SEQ=739216649 ACK=0 WINDOW=64240 RES=0x00 SYN URGP=0 OPT (021405....) MARK=0x8000000

On the Asus router I configure port fowarding for SMB using TCP and port 445 to destination but anfortunately this did not work.
Can someone help?
Last edited:


Very Senior Member
Where did come from?! All I see from the initial part of the description is two local networks; and (at least I assume they're /24, you weren't specific).

I assume we're talking about OpenVPN *server* here as well.


Regular Contributor
Yes the Asus router is the server and is LAN on a second Asus router connected via OpenVPN.
But this is not a problem. It is the WAN firewall which blocks the access.
The route is then

FriFritzBox (LAN range: <-> WAN( Asus router (LAN range: OpenVPN <-> Second Asus router (LAN range:
Raspberry ( <-> NAS (

But the problem is the WAN firewall when I disable it everything works well and the Raspberry cann connect to the NAS.
So I need to know how to enable this exception. Port forwarding seems not to work.


Regular Contributor
After a long search I find the solution.
I added WAN port fowarding of 445 (SMB).
And add the following iptable entry to accept fowarding of local adresses from eth0 to tun21:
iptables -Ie FORWARD 9 -t filter -i eth0 -o tun21 -p tcp -s -d -j ACCEPT
In my case I added this on the position 9 before the local chain "logdrop" where all unhandled packes gets dropped.

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