ipv6 mode grayed out in server settings

ipv6 mode grayed out in server settings

Postby marcelser » 2020-09-02 15:41


I need to use ipv6 listening mode on a ultravnc server. I don't know if this is RC specific but why is ipv6 mode on all computers where I try it grayed out. The machines all have a ipv6 + ipv4 address in the network (I can see it in the router), nevertheless the admin option to enable ipv6 is grayed out and there absolutely no documentation whatsoever how make enable it make use of it.

Would be great if some of the devs could shed some light on it. The only bit of information I could find (but it's like 6 years old is some setting about "useipv6=1") but I don't know where this would be need to be set when the server is run as a service.


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Re: ipv6 mode grayed out in server settings

Postby Vort » 2020-10-15 15:11

Hello. RC binaries do not have IPv6 support.
But it can be enabled during build process.
However it is not enough, vncviewer.exe will not be able to process IPv6 address correctly without additional fixes.
I have made a fix for viewer and uploaded IPv6 capable binaries to github (only x64 and Win7+, but it is theoretically possible to make other variations).
To use them, you need to install UltraVNC_1_2_50_X64_Setup.exe (actually, and replace vncviewer.exe and winvnc.exe with the files from UltraVNC_1_2_51_X64_IPv6.zip.
Then open "c:\Program Files\uvnc bvba\UltraVNC\ultravnc.ini" with text editor and add two lines to its end:
Code: Select all

(you will need admin rights to do this)
Now winvnc.exe will start in IPv6 mode (this applies also to service mode).
To connect to your server with vncviewer.exe, you need to format your IPv6 address in specific way.
It should consist of 8 4-digit blocks, separated by :, but also at the end it should have :0.
Like this: 0225:9a7e:5c30:662e:317b:0ccb:0f93:e024:0
That's all, now client should be able to connect to server.
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Re: ipv6 mode grayed out in server settings

Postby Nanobot » 2020-10-15 17:59

Hi Vort,

thanks for your effort to support ipv6 with your patches. Nevertheless, according to my knowlegde 0225:9a7e:5c30:662e:317b:0ccb:0f93:e024 is not a valid format for an ipv6 address. According to this site


it is mandatory to enclose a literal ipv6 address in square brackets. This is due to the fact that the address itself and an optional port cannot be differentiated without the brackets. So the correct format of the ipv6 address in your example must be [0225:9a7e:5c30:662e:317b:0ccb:0f93:e024] or [225:9a7e:5c30:662e:317b:ccb:f93:e024], since leading 0s of each group may be truncated.

On the other hand, a canonical address which is resolved to an IPv6 address of course must not be enclosed by brackets, since it is not neccessary. So I would suggest that you to check if your patch against the vncviewer.exe is really correct. And with the elder versions ( ), where IPv6 is already supported, at least using a canonical address resolving to an ipv6 address worked fine for me. Using literal ipv6 addresses did not work for me but it doesn't bother me, since the servers I want to connect to already have canonical addresses for ipv6. The only problem with the version is that I had to enable ipv6 by manually editing ultravnc.ini in the way you mentioned.

If you ( for testing purposes ) need a free dyndns provider which supports ipv6 , you might have a look at https://freedns.afraid.org/

C.U. Nanobot
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Re: ipv6 mode grayed out in server settings

Postby Vort » 2020-10-16 04:35

The goal was to make a minimal change, which not breaks anything, but adds possibility to use IPv6 address (without DNS).
Right now fix is limited to a single function. Adding of correct parsing for IPv6 will for sure require more changes.
So, yes, you are right that use of square brackets is a good solution, same for zero compression support.
But I don't know yet if it is possible to implement it without breaking anything and how many changes it will require.
By the way, RFC2732 is related to URLs, which are not used here.
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Re: ipv6 mode grayed out in server settings

Postby Neustradamus » 2020-10-18 02:36

For example a https link in IPv6 is like https://[1fff:0:a88:85a3::ac1f]:1234....
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