Port Forwarding stop working since NBN transition


Hi there,


It seems like people are having issue with port forwarding with NBN. Not because they don't know how to setup but NBN should have been doing something fishy at backend to limit public IP addresses in each area. 


Port forwarding was working perfectly before NBN at my place and since transition to NBN HFC my port forwarding stop working. Have been looking around for the answer and can't find one yet. Some even went for Premium paid support and couldn't reach the resolution. Even the Premium support team is not trained well enough to understand the situation.


Again, I am just curious if someone has successfully done port forwaring on any NBN connection (even different ISPs). If yes, please enlighten me on how-to. It really has been a frustrating one as affected a lot of people using CCTV, media servers and VPN at home like me. 


Optus team, please provide me and others who having same issue since NBN transition. 




Re: Port Forwarding stop working since NBN transition

[ Edited ]

Hi @HotChilli 


Port forwarding is a function of the modem you have. Nothing to do with the internet or NBN or Optus. 


Your internet packet arrive tagged with a port number. (e.g. You can set up security on ports individually with rules depending on the modem's capabilities. Port forwarding is just an internal table that matches an external port number with a specific internal device in your local network using its MAC address or fixed IP address. For example:




I've had no issues port forwarding on the NBN (although I'm back off it for now having moved again). It can be a bit tricky to get set up despite its simplisity (and yes general support can't handle it.) The biggest issue is usually the need for a static external IP address. You generally need to pay $10 a month extra if it is even offered by your ISP (Optus don't). Alternatively you can set up DYDNS on a device in your network to track a variable external IP address


Good Luck


Peter Gillespie

Re: Port Forwarding stop working since NBN transition


Hi Peter,


Thanks a lot for your well detailed explanation. 


Yes, I think I can handle the NATTING and Port Forwarding from inside to outside network through gateway router. I am very familiar with all those technologies. 


My question was why my port forwarding is not working since moving over to NBN from my conventional Cable Broadband connection. It was seamlessly fine for my internal applications. 


I am not sure what NBN connection you are on right now but mine is NBN HFC. Optus technician installed NBN connection box for HFC in my premise. Connect to the basic wireless router but I replaced it with my own high-end Linksys router for broader range for wireless. Plus all configs are in place on Linksys so I don't need to reconfigure anything. 


Could you please share your setup at home if you don't mind? It might be different but I have seen a lot of people complain about the port forwarding issue after transition to NBN. Not sure how you have managed to do port forwarding on NBN. 


Also, for dynamic DNS, I have duckdns in place to handle it so assigning public IP address dynamic to me should not be an issue. 


Let me know what is your thought. And much appreciated for your assistance.

Re: Port Forwarding stop working since NBN transition


Hi HC,


I'm no expert but perhaps you are talking about some other functionality here (or I don't know everything about what port forwarding does.) My explanation related to packets ariving from outside (NBN) and being directed to inside (your local network). "Port Forwarding from inside to outside network" seems not what port forwarding is?


I'm not on NBN now (was on FTTP  about six months ago for a while) but my port forwarding settings are as in the image above. You set the port in question on your modem and then provide the internal IP address of the device you want to recieve the packets. As mentioned the NBN hasn't changed the underlying structure of the internet protocol, only the wires used to reach your home. Fundamentally, millions of packets (bits of data) turn up in the exact same format and ask to be let into you network. Port forwarding is just a standard way to address these packets to a particular machine - all of which is to say the NBN has no direct control over the data itseld that arrives at your house.


What might be happening is your new modem may be applying a different DHCP range to various devices? So the IP address in your port forwarding table might no longer match the IP address the device actually has? At this stage I would try some testing:


1) Reduce the issue to a single device. Solve that and the rest should be easy. So pick one to test.

2) Don't pick PC WAKE UP for a WIN10 PC - There's settings in WIN10 that interfere with this.

3) Determine the external IP address of your modem. Use this actual number instead of any DYDNS figure to bypass that for the moment (the issue might be with DYDNS)

4) Confirm the device IP matches the port forwarding table IP

5) Have BOTH (TCP/UDP) modes enabled for port foerwarding

6) Check the modem has no security areas in deeper menus activated that might be interfering. 

7) I don't know how/if port forwarding works over wifi? Use a wired connection to test.

8) If still no luck, I suggest unplugging the new modem and getting the Optus one up and running. Just the basics and set a port forward as per above and see if that works.

9) And always using the external IP addresss for the testing phase.


Good Luck.


Peter Gillespie 

Re: Port Forwarding stop working since NBN transition


Hi Peter,


Very insightful response. Thank you for that. 


I have tried a few things based on what you responded previously. And after some trial and error, just noticed that all higher port numbers are blocked and all lower port numbers seems to be ok. Like port 80 or 443 can be forwarded to the internet while port 1194 blocked. Can we request or check with Optus support to remove the filter the ports by any chance? Never had that issue before on my previous cable broadband. 


Btw, I had also attempted with Optus router instead my own Linksys router and it remained the same issue. 


Again, much appreciated for your assistance, Peter. You are the best, mate!

Re: Port Forwarding stop working since NBN transition

[ Edited ]

Hi @HotChilli ,


Good find. So you have access to well known ports (as you'd expect). 


My understanding is Optus/NBN generally pass through all ports (I use 7878, 8989, 8800, 8080 and 6009 personally). Have you tried switching to some random high level ports on your test? Try 42756?


I'd still suspect the issue is something in your local setup. Antivirus, firewall, etc. Have you checked the modems security settings. Set to 'high'? Firewall enabled? Parental controls? - just guessing if those exist or not. (although switching routers would suggest that's not the issue.)


But otherwise yes, contact Optus and ask to get a specific port number 'unblocked'. You're main difficulty here will likely be getting hold of anyone who actually knows what you're talking about and can do something about it. 


Peter Gillespie

Re: Port Forwarding stop working since NBN transition


Hi Peter, 


Again, very educated discussion with you here and thanks for that as well. Yes, as you could guess, I have already contacted Optus Support for the port forwarding issue and they thought I was talking about porting home phone number from cable broadband to NBN HFC. So I had to explain really hard for what I wanted and eventually they agreed to call me back next day then still awaiting for the callback. 


Having said that, already attempted with any higher port numbers like 3389 and it worked thus I would imagine that Optus selectively block some hand-picked port numbers for no reason. Not necessarily only higher port numbers as I came to realise from my test runs. Tried both Optus provided router (Sagemcom which is very basic setup) and my BYO Linksys router for the tests, and all the same results. Weirdly enough Optus support said that they would also check with Sagemcom, the vendor for the blocked ports on device itself. I mentioned it should not be the case as I tested on both routers. 


As soon as I get something back from Optus Support, will update here for others to have the final resolution on this. But for now, still no luck. 




Re: Port Forwarding stop working since NBN transition


I've been having all sorts of trouble with port forwarding from my Synology NAS, where it worked fine with my old cable modem. 


It tells me to enable UPnP and check the modem can handle enough ports forwarded.


The Sagem F@ST 3864V3HP has UPnP on, but looks like it won't handle the number of ports


Add that to myriad issues with Wi-Fi and such, and a BYO router is best IMHO


At one point, 2.4 had no internet connection but 5 GHz did! 


Re: Port Forwarding stop working since NBN transition




Since my last post, there has been no communication back from Optus altough they promised to call me the next day. Obviously, Optus support fooled me to drag on and make me to give in with the issue. 


If there is Optus support or moderator can help me here, it would be great. Call and Chat to Optus Technical Support are hopeless at this point. Really frustrating for the simple query and they can reach to a resolution. 


Anyone here has ever successfully resolved the issue with Optus Support? Please let me know. It would be greatly appreciated.





Re: Port Forwarding stop working since NBN transition


Hi there, do you have a fault ticket number we can check?

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