Re: DNS settings changes for Sagemcom F@st 3864 v2 router


Well that is a piss poor answer considering i was given this sub quality  cheap modem for what is a business connection. I guess you gotta cut every corner possible to maximise the good old profit... even at the expense of customers.  Rubbish service 

Re: DNS settings changes for Sagemcom F@st 3864 v2 router


I just dug in to this one this morning out of frustration. Complete steps should be below:

  1. Open the router home page (e.g.
  2. Click "Advanced Settings" on the bottom left menu. This should take you to the "Sagecom" settings screen.
  3. On the left menu select "Management" followed by "Access Control".
  4. Right click on the whitespace between the Username/Password fields and the "Apply" button and select "View Frame Source" (this is in Chrome so it might be called something different for firefox etc.)
  5. Around lines 10-15 you should see passwords for various accounts. Copy the one in "pwdAdmin"
  6. in the address bar, browse to (where is the IP of your router)
  7. use admin as the username and use the password from pwdAdmin
  8. DNS settings are under "Advanced Settings" and then "DNS".

Considering there is even a warning about being a "proficient" user before messing with these settings, I'm surprised how much Optus Corp seems to want to keep this quiet. I can only asume that the moderators have been told not to give it away. 


Re: DNS settings changes for Sagemcom F@st 3864 v2 router


Hi GHunter

Thanks for your post! It is quite recent so I thought it might work...i'm trying to change the DNS settings to use OpenDNS as a filtering service. It worked before on a previous modem but is not working now. 

I  followed your script but I simply can't find the pwdadmin anywhere in the code even when I search for it.

Am I looking in the wrong place or is there a possibility that it is just is not there? I don't know anything about coding but I have managed to follow the instrcutions to bring the code up on the screen..

Also I don't quite follow the step which says use admin for the user and then copy over the password. Not that it matters as I can't find the password anyway!

I'd be grateful for any tips ...I'm about to give up on all this and try and find an alternative to OpenDNS to secure our internet for the kids. But i'm annoyed that Optus or Sagecom or both are making this soooooo hard!



Re: DNS settings changes for Sagemcom F@st 3864 v2 router


It's a bit of a disaster isn't it, if you want to change settings. Unfortunately in the version of the management tool I have there is no pwdAdmin variable listed in the code, I think they've hidden it in a cgi file "password.cgi" which I can't access. Looks like I'll be visiting the shop and buying a new router.



Re: DNS settings changes for Sagemcom F@st 3864 v2 router


@JLZ DNS settings can be changed through your laptop/desktop network configuration settings. It's not necessary to make the change using the Sagemcom modem management tool. If you need to change this setting via your modem settings then this should be the same password used to authenticate the service when it was originally activated. We can always reset this password.


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Re: DNS settings changes for Sagemcom F@st 3864 v2 router


Depending on how recently you got our modem from Optus, some or more of those steps have been disabled.


Try either of these addresses to log directly into the modem's super admin user (which unlocks all the settings that Optus have arbitrarily blocked)




Or, if that doesn't work, take a read through:


As a note, Optus, this is the most ridiculous crap to pull. The settings are there, you are the ones blocking them, don't pretend that you can't access them.

Re: DNS settings changes for Sagemcom F@st 3864 v2 router



this doesn't work.




Re: DNS settings changes for Sagemcom F@st 3864 v2 router


Thanks for your very useful reply. It's a crap trick of Optus to pull given the amount we pay them for such a slow NBN.

Re: DNS settings changes for Sagemcom F@st 3864 v2 router


Thanks so much for this!


Well done Optus.....


Re: DNS settings changes for Sagemcom F@st 3864 v2 router

[ Edited ]

This doesn't work on more recent modems - however the answer is indeed hidden in the whirpool thread posted by IFNI above. It's slightly technical... but only slightly! I'll sumarize the steps here because the whirpool thread is epic and confusing.


1. Visit the following link in your browser:

2. It will download a file called "dumpcfgdynamic.conf" to your computer

3. Find the file and rename the .conf to .html - and now open this in a sane browser like Firefox

4. You can now see a bunch of information that looks rather like computer code but is in fact what is known as XML

5. Search for the string "AdminPassword" near the top and you will see a string between the AdminPassword tags - in human language it is between the greater than and less than symbols and looks a bit like "LKJHhjhLJKHL=="  highlight and copy that to your clipboard (ctrl+c)
6. Navigate to the following website and paste the string in the box at the top and press the DECODE button below - a new string will appear in the box below the decode button - that is your admin password so now copy that
7. Now navigate back to and a password prompt will appear, username is "admin" and the password you just decoded in step 6.

8. You will have now gained access to all the routers advanced settings and can change things like the default DNS

9. Note you will need to enter the password *every* time you go to a new page, so you may want to paste it somewhere convenient


In my case all I wanted to do was block an insiduous and evil game called Roblox that my 12 year old daughter is addicted to - because it loads from a https:// address you cannot block it through the standard parental controls in the router. As such I had to open an account on OpenDNS and apply the new  DNS setting to the router - which you can only change if you access the advanced settings as an admin user - as outlined above. I tried to keep the steps as simple as possible because I'm sure there are many other parents out there who want to block things! I hope it helps somebody Smiley Happy


OpenDNS is a free service by Cisco - create an account here  and choose the "OpenDNS Home" option, not the family shield one. 


The above worked for me - I have a F@ST3864V2 router with the 8.353.21_F@ST5350_Optus Software (you can find this info after you click Advanced Settings)

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