Strikes my eyes instantaneously:
- SIP Transport = UDP ← not TCP ?
Will have a look at your other settings a little bit later …
@onyxnz: Same applies to your SIP settings also;
sorry I missed that in the first time - too tired, too late at night:
- SIP Transport = “UDP”
Hello Manfred,
Since I am a fresh user of this forum, the IPFire forum system is limiting my answers pretty much: I can not yet send you a private e-mail for the next two weeks. I can not yet send you more screenshots 
I even can reply only after a waiting time of 4H :(
Therefore, the information exchange might be a bit asymmetric.
I am using IPFire without any problems for several years now and therefore there was no need to join this forum. Now I have a problem and cannot communicate as I would need to do.
After this message I have to wait 15(!) hours before being allowed to send the next message.
How can I provide you the requested information within short time?
Here another setup screendump
BTW, SIP transport by TCP did not help either.
Thanks a lot in advance.
Seems the time delays are an anti-spam measure, it would make it difficult for new forums users trying to get timely support, maybe the rules can be relaxed a little, I would guess there are plenty of active users in the forums to catch and report spam instances?
Thanks to the hint of @anon33261557 I reached now the trust level basic by reading another topic 
Now I can upload more screeshots Here now the screen shots of my settings:
How can I send the more sensitive data by e-mail to @manfred_knick ?
Try clicking on his name and icon, it should give you a message option.
Quick Late Night Confirmation - just only for providing a proof:
- The moment I changed SIP Transport from “TCP” to “UDP”,
my ATA / FAX stopped working - Quite understandable:
It needs an (outgoing) TCP/IP connection to trigger off IP_NAT / Masquerading - Changing SIP Transport back to “TCP” restored working connections immediately
Hello Manfred,
Thanks a lot for your quick late night confirmation.
I tried it immediately this morning in Voice => Line 1 menu:
I did a reboot of the ATA SP112 after having set SIP Transport to TCP.
Unfortunately I do not even get a dial tone anymore (with UDP I am getting at least a dial tone).
In the connections list of IPFire I am getting a TCP connection to my ISP providers SIP proxy at TCP port 5060 (SYN_SENT):
All other parameters are identical with my sent yesterday’s setting.
In the IPFire’s Firewall log I see a lot of DROP_INPUTs for protocol 41
( Protocol 41 is a communication protocol which embeds internet protocol version 6 (IPv6) packets inside Internet protocol version 4 (IPv4) packets.)
My internet connection is IPv4 dual stack.
Addendum 9:57 am: My ISP provider Vodafon/UnityMedia is requiring for SIP messages UDP port 5060:
See also NTP_Provider_Interface_Spec_Unitymedia.pdf
Seems to be a ‘NoGo’ scenario IPFire requires TCP (without ALG) as proven by you; Vodafone/Unitymedia requires UDP.
Do I need now a port forward (what I want to avoid)?
Thanks for your help in advance!
Thanks you mention it !
Complete IPv4 plus IPv6 dual stack?
Or is it “Dual Stack Lite” = 4-in-6 tunneling ?
DS Lite is a completely different business -
which I have avoided under all circumstances.
I very much doubt the root of your problem resides in ATA configuration, now.
Please, provide detailed information about your ISP connection.
My cases are purely IPv4-based.
It does not matter if dynamically assigned or -in more complex ones- with a static IPv4.
@onyxnz : Please disclose your type of Internet Connection. Thanks!
Hi Manfred,
My internet connection should be a native IPv4 dual stack (how to check this?). It is definitively not “Dual Stack Lite” = 4-in-6 tunneling. I avoided this, too. I do NOT have a static IPv4 address, but a dynamic one. It basically changes when rebooting my cable modem once a day.
Please note that my internet provider Vodafone/Unitymedia is supporting for SIP only UDP port 5060.
See above.
As stated above, I have no real-life experience with DS Lite connections.
In order to figure out what may work at all, yes, I fear you have to statically open the minimal bunch of necessary ports permanently - but to your provider’s IP address only.
Hi Manfred,
To my best knowledge, I have a native IPv4 dual stack connection. But Unitymedia is requiring UDP as SIP transport protocol.
A test at https://ipv6-test.com/ tells me that my connection is IPv4. IPv6 is NOT supported.
According https://ipv6-test.com DNS is supported as follows:
Well, let’s figure that out.
I guess we are talking about a cable MoDem?
Which functionality does it provide? Pure Modem?
Or is it a MoDem + Router + added functionality (integrated switch / TV / etc ) ?
In the latter case: could you connect your ATA to the cable router directly,
but protect your PCs etc by IPFire as an internal second FW router?
How exactly is your WAN interface (“Red”) configured?
- (static) IPv6 ?
- (dynamic) IPv4 ? PPPoE ?
I have a pure cable modem Technicolor TC4400. The cable modem is directly connected to my IPFire router, a PC Engines APU1D hardware.
Where can I see the WAN configuration in IPFire? I guess it is (dynamic) IPv4 .
In the latter case: could you connect your ATA to the cable router directly,
but protect your PCs etc by IPFire as an internal second FW router?
This is not possible since the TC4400 modem has only one ‘working’ Ethernet port (the second is not working and only for 1Gbps connections). I don’t want to connect a switch between the modem and the router.
I tried also @onyxnz 's source NAT as shown above. It does not work either. I am puzzled 
Dual Stack = IPv4 + IPv6 , both fully implemented and provided in parallel
DS Lite = IPv6 connection only, tunneling IPv4 to IPv4 Internet Address Space
I guess you have been a customer of Unitymedia GmbH, Cologne,
before they were acquired by Vodafone Group in 2018 ?
AFAICR, old UnityMedia customers were forcibly transformed to DS Lite by Vodafone …
BTW:
Does your Cable MoDem provide analog ab via TAE or RJ11 ports,
so you can attach your analog Telephone directly by configuring “Voice over Cable” ?
BTW:
Does your Cable MoDem provide analog ab via TAE or RJ11 ports,
so you can attach your analog Telephone directly by configuring “Voice over Cable” ?
No it doesn’t provide TAE or RJ11 ports. Therefore I had to switch to SIP with the new TC4400 modem.
Yes, I’ve been a customer of Unitymedia GmbH, Cologne.
I am, however, not aware that I have been converted to DS Lite by Vodafone. See test result below. UnityMedia provided me a Dual Stack = IPv4 + IPv6 , both fully implemented and provided in parallel.
My telephone was working properly with ALG up to IPFire core 154.
Here the result of a dual stack test at IPv6-Test
IPFire → Main page → click upon “Internet” 
And have a look into the Web Configuration page provided by your TC4400 …
Thanks.
IPFire → Main page → click upon “Internet”
results in an error message
And have a look into the Web Configuration page provided by your TC4400 …
Here we go:
No IPv6 connection!
10.0.0.0 - 10.255.255.255 is private address space; c.f. RFC 1918