Dynu DDNS: ddclients updates both IPv4 and IPv6 even when usev4=disabled.

[inevitable-commit]

I want to have only the IPv6 address tied to my domain address so I tried to disable updating entry for IPv4 address in ddclient's config. Still, entries for both get updated.

ddclient version: 4.0.0
OS: Arch Linux
Kernel: Linux 7.1.4-arch1-1
DDNS service provider: dynu.com
ddclient's config:

# /etc/ddclient/ddclient.conf

ssl=yes
daemon=300                      # check every 300 seconds
usev4=disabled
cmdv6="ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1"
usev6=cmdv6
syslog=yes                      # log update msgs to syslog
pid=/var/run/ddclient.pid                                # Record PID in file.                                      
force=yes
protocol=dyndns2
server=api.dynu.com                                      # IP update server.
login=[redacted]
password=[redacted]
zone=xubi.org
[redacted].xubi.org

[Erwin-Iosef]

What does ddclient --debug --verbose --foreground --force say?

[inevitable-commit]

sudo ddclient --debug --verbose --foreground --force
INFO:    [file /etc/ddclient/ddclient.conf]> file is accessible to ddclient group
INFO:    [file /etc/ddclient/ddclient.conf]> file is accessible to ddclient group
=== opt ====
opt{debug}                           : 1
opt{force}                           : 1
opt{foreground}                      : 1
opt{fw-banlocal}                     : CODE(0x555c9d6fabf0)
opt{help}                            : CODE(0x555c9da8abf0)
opt{if-skip}                         : CODE(0x555c9d6fabf0)
opt{list-devices}                    : CODE(0x555c9d6facf8)
opt{list-protocols}                  : CODE(0x555c9d6fae00)
opt{list-web-services}               : CODE(0x555c9d6faed8)
opt{quiet}                           : 0
opt{verbose}                         : 1
opt{version}                         : CODE(0x555c9d6fb028)
=== globals ====
globals{cmdv6}                       : ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1
globals{daemon}                      : 300
globals{debug}                       : 1
globals{force}                       : 1
globals{foreground}                  : 1
globals{login}                       : <redacted>
globals{password}                    : <redacted>
globals{pid}                         : /var/run/ddclient.pid
globals{protocol}                    : dyndns2
globals{quiet}                       : 0
globals{server}                      : api.dynu.com
globals{ssl}                         : 1
globals{syslog}                      : 1
globals{usev4}                       : disabled
globals{usev6}                       : cmdv6
globals{verbose}                     : 1
globals{zone}                        : xubi.org
=== config ====
config{[redacted].xubi.org}{cmdv6}        : ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1
config{[redacted].xubi.org}{daemon}       : 300
config{[redacted].xubi.org}{force}        : 1
config{[redacted].xubi.org}{host}         : [redacted].xubi.org
config{[redacted].xubi.org}{login}        : <redacted>
config{[redacted].xubi.org}{password}     : <redacted>
config{[redacted].xubi.org}{pid}          : /var/run/ddclient.pid
config{[redacted].xubi.org}{protocol}     : dyndns2
config{[redacted].xubi.org}{server}       : api.dynu.com
config{[redacted].xubi.org}{ssl}          : 1
config{[redacted].xubi.org}{syslog}       : 1
config{[redacted].xubi.org}{usev4}        : disabled
config{[redacted].xubi.org}{usev6}        : cmdv6
config{[redacted].xubi.org}{zone}         : xubi.org
=== recap ====
recap{[redacted].xubi.org}{atime}         : 1785037498
recap{[redacted].xubi.org}{backupmx}      : 0
recap{[redacted].xubi.org}{host}          : [redacted].xubi.org
recap{[redacted].xubi.org}{ipv6}          : [redacted]
recap{[redacted].xubi.org}{mtime}         : 1785037498
recap{[redacted].xubi.org}{status-ipv6}   : good
recap{[redacted].xubi.org}{wildcard}      : 0
DEBUG:   [[redacted].xubi.org][usev6=cmdv6 cmdv6=ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1]> found IPv6 address: [redacted]
INFO:    [[redacted].xubi.org]> update forced via 'force' option
INFO:    [dyndns2][[redacted].xubi.org]> setting IPv6 address to [redacted]
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> proxy    = <undefined>
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> protocol = https
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> server   = api.dynu.com
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> url      = nic/update?<redacted>
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]> curl config:
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  silent
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  include
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  user-agent="ddclient/4.0.0"
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  connect-timeout=120
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  max-time=120
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  request=GET
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  user="[redacted]"
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  url="https://api.dynu.com/nic/update?hostname=[redacted].xubi.org&myip=[redacted]"
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> CURL: /usr/bin/curl
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> CURL Tempfile: /tmp/ddclient_Qg3ahnVT4o
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]> reply:
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  HTTP/1.1 200 OK
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Date: Sun, 26 Jul 2026 3:45:30 GMT
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Server: Dynu Web Server
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  X-Powered-By: Dynu Dynamic DNS Service
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Content-Length: 5
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Content-Type: text/html; charset=UTF-8
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Connection: close
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  nochg
WARNING: [dyndns2][[redacted].xubi.org]> nochg: No update required; unnecessary attempts to change the current address are considered abusive
SUCCESS: [dyndns2][[redacted].xubi.org]> IPv6 address set to [redacted]
DEBUG:   > sleep 300
WARNING: > caught SIGINT; exiting

In this, there were mentions of valid IPv6 address address only. I just checked my Control Panel for DDNS on dynu and found another updated entry for IPv4 address which I had removed manually about 15hr ago. I don't know when in that 15 hr duration it got updated. This output is after I turned on this PC about an hour ago so catching the act of updating entry for IPv4 was missed I guess.

[Erwin-Iosef]

Try again after changing the ipv4 to something else in Dynu webconfig, looks like it understands ip4 is disabled for this host. Also btw if you want ddclient to get the ipv6 by itself you can use usev6=ifv6, ifv6=interfacename.

[Erwin-Iosef]

There is also this commit 126797c that adds Dynu support(which isn't included in 4.0.0), although I don't use it.

[inevitable-commit]

I think I found the problem. It is from dynu's side. When I removed IPv4 address from the dynu webconfig and ran the above command, I found a mention of my public facing IPv4 address in the dynu's response. I checked and found entry of that same IPv4 address in dynu webconfig. Here's the output (mention of IPv4 address is in 3rd last line):

sudo ddclient --debug --verbose --foreground --force
INFO:    [file /etc/ddclient/ddclient.conf]> file is accessible to ddclient group
INFO:    [file /etc/ddclient/ddclient.conf]> file is accessible to ddclient group
=== opt ====
opt{debug}                           : 1
opt{force}                           : 1
opt{foreground}                      : 1
opt{fw-banlocal}                     : CODE(0x55b573851d90)
opt{help}                            : CODE(0x55b573be1888)
opt{if-skip}                         : CODE(0x55b573851d90)
opt{list-devices}                    : CODE(0x55b573851e98)
opt{list-protocols}                  : CODE(0x55b573851fa0)
opt{list-web-services}               : CODE(0x55b573852078)
opt{quiet}                           : 0
opt{verbose}                         : 1
opt{version}                         : CODE(0x55b5738521c8)
=== globals ====
globals{cmdv6}                       : ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1
globals{daemon}                      : 300
globals{debug}                       : 1
globals{force}                       : 1
globals{foreground}                  : 1
globals{login}                       : <redacted>
globals{password}                    : <redacted>
globals{pid}                         : /var/run/ddclient.pid
globals{protocol}                    : dyndns2
globals{quiet}                       : 0
globals{server}                      : api.dynu.com
globals{ssl}                         : 1
globals{syslog}                      : 1
globals{usev4}                       : disabled
globals{usev6}                       : cmdv6
globals{verbose}                     : 1
globals{zone}                        : xubi.org
=== config ====
config{[redacted].xubi.org}{cmdv6}        : ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1
config{[redacted].xubi.org}{daemon}       : 300
config{[redacted].xubi.org}{force}        : 1
config{[redacted].xubi.org}{host}         : [redacted].xubi.org
config{[redacted].xubi.org}{login}        : <redacted>
config{[redacted].xubi.org}{password}     : <redacted>
config{[redacted].xubi.org}{pid}          : /var/run/ddclient.pid
config{[redacted].xubi.org}{protocol}     : dyndns2
config{[redacted].xubi.org}{server}       : api.dynu.com
config{[redacted].xubi.org}{ssl}          : 1
config{[redacted].xubi.org}{syslog}       : 1
config{[redacted].xubi.org}{usev4}        : disabled
config{[redacted].xubi.org}{usev6}        : cmdv6
config{[redacted].xubi.org}{zone}         : xubi.org
=== recap ====
recap{[redacted].xubi.org}{atime}         : 1785150599
recap{[redacted].xubi.org}{backupmx}      : 0
recap{[redacted].xubi.org}{host}          : [redacted].xubi.org
recap{[redacted].xubi.org}{ipv6}          : [redacted valid IPv6 address]
recap{[redacted].xubi.org}{mtime}         : 1785150599
recap{[redacted].xubi.org}{status-ipv6}   : good
recap{[redacted].xubi.org}{wildcard}      : 0
DEBUG:   [[redacted].xubi.org][usev6=cmdv6 cmdv6=ip -6 -o addr show dev enp3s0 scope global | awk '{print $4}' | cut -d/ -f1 | head -n1]> found IPv6 address: [redacted valid IPv6 address]
INFO:    [[redacted].xubi.org]> update forced via 'force' option
INFO:    [dyndns2][[redacted].xubi.org]> setting IPv6 address to [redacted valid IPv6 address]
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> proxy    = <undefined>
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> protocol = https
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> server   = api.dynu.com
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> url      = nic/update?<redacted>
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]> curl config:
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  silent
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  include
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  user-agent="ddclient/4.0.0"
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  connect-timeout=120
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  max-time=120
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  request=GET
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  user="[redacted]:[redacted]"
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][REQUEST]  url="https://api.dynu.com/nic/update?hostname=[redacted].xubi.org&myip=[redacted valid IPv6 address]"
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> CURL: /usr/bin/curl
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request]> CURL Tempfile: /tmp/ddclient_WwTm4vEqcy
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]> reply:
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  HTTP/1.1 200 OK
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Date: Mon, 27 Jul 2026 11:12:15 GMT
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Server: Dynu Web Server
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  X-Powered-By: Dynu Dynamic DNS Service
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Content-Length: 17
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Content-Type: text/html; charset=UTF-8
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Connection: close
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  good [redacted IPv4 address]
SUCCESS: [dyndns2][[redacted].xubi.org]> IPv6 address set to [redacted valid IPv6 address]
DEBUG:   > sleep 300

I again performed this test but didn't get any IPv4 related output. I did other tests and found that if the version of the IP address that is missing in the request matches the version of the IP address used by the host to establish the connection, dynu will use host's IP address of that connection. I found this by removing the IPv4 entry from dynu webconfig and disabling IPv6 on host (here disabling meant disabling IPv6 based traffic using firewall such that ddclient can still find valid IPv6 address) and got the response as above and found updated entry for IPv4(not intended) and IPv6(as intended).

Similarly, configured ddclient to use only IPv4, removed IPv6 entry from dynu webconfig and disabled IPv4 in host and ran the command and found updated entry for IPv6(not intended) and IPv4(intended) but no mention of IPv6 in the output. The piece of the output is:

DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  Connection: close
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]
DEBUG:   [dyndns2][[redacted].xubi.org][HTTP request][RESPONSE]  good [redacted IPv4 address]
SUCCESS: [dyndns2][[redacted].xubi.org]> IPv4 address set to [redacted IPv4 address]
DEBUG:   > sleep 300

My finding might need to be validated by others independently.

[Erwin-Iosef]

So dynu is the one that adds the missing protocol address and not ddclient in either case?

[inevitable-commit]

From my tests. yes.

[Erwin-Iosef]

@inevitable-commit this is a mere guess but can you check with disabling ipv4 wildcard alias in Dynu if you haven't already?

[inevitable-commit]

I already had disabled it.

[Erwin-Iosef]

Last guess, try setting usev4=disabled globally, i.e at the top of the config.

[DustyRah]

The parameters are myip and myipv6. If you want ipv6 to be updated, the URL should contain myipv6=[your IPv6 address] and your request should come over IPv6 net.

If your IP update request is coming over IPv4 net, you can set myip=no and myipv6=[your IPv6 address].

The details are on Dynu website at https://www.dynu.com/en-US/DynamicDNS/IP-Update-Protocol

[Erwin-Iosef]

For me it works instantly with usev4=disabled and usev6=ifv6, ifv6=[interfacename] set globally.
EDIT: Although ddclient does fail to pick up new address changes, that's a separate issue.

[Erwin-Iosef]

If the suggestions this far doesn't help, I'd try using the git master at this point since it's got improved Dynu support added.

[inevitable-commit]

I didn't know about "using IP address from which the request originates" being an intended behavior. My apology.

So, I used the main branch and it works for my use case. However, if the user wants to use IPv4 only, this same problem occurs i.e. dynu using request originating address for IPv6 because 126797c doesn't include myipv6=no in the request when usev6=disabled.

I tried fixing it with following changes but "Prefer Revert and Redo, Not Fix". I also don't know Perl:

diff --git a/ddclient.in b/ddclient.in
index f408d7b..0d455e8 100755
--- a/ddclient.in
+++ b/ddclient.in
@@ -4425,6 +4425,7 @@ sub nic_dynu_update {
             $url .= "&myip=$ipv4"   if $ipv4;
             $url .= "&myip=no"      if !$ipv4 && $ipv6;  # prevent server auto-detecting v4
             $url .= "&myipv6=$ipv6" if $ipv6;
+            $url .= "&myipv6=no"    if !$ipv6 && $ipv4;  # prevent server auto-detecting v6
             my $reply = geturl(
                 proxy    => opt('proxy'),
                 url      => $url,
@@ -4433,6 +4434,9 @@ sub nic_dynu_update {
             );
             next if !header_ok($reply);
             (my $body = $reply) =~ s/^.*?\n\n//s;
+            # When updating entries for both IPv4 and IPv6, dynu will update both but acknowledge
+            # only one of them. Here, for that case, a good response from dynu will be treated as
+            # successful entry update for both IP version.
             my ($status) = split(/\s/, $body);
             $status //= 'unknown';
             if ($status eq 'nochg') {
diff --git a/t/protocol_dynu.pl b/t/protocol_dynu.pl
index 7cdff50..34b0f30 100644
--- a/t/protocol_dynu.pl
+++ b/t/protocol_dynu.pl
@@ -24,7 +24,7 @@ my @test_cases = (
         desc => 'IPv4 only, good',
         cfg => {'myhome.dynu.net' => {wantipv4 => '192.0.2.1'}},
         resp => ['good'],
-        wantquery => 'hostname=myhome.dynu.net&myip=192.0.2.1',
+        wantquery => 'hostname=myhome.dynu.net&myip=192.0.2.1&myipv6=no',
         wantrecap => {
             'myhome.dynu.net' => {'status-ipv4' => 'good', 'ipv4' => '192.0.2.1', 'mtime' => $ddclient::now},
         },

Looked further in the https://www.dynu.com/en-US/DynamicDNS/IP-Update-Protocol and found a solution for making Version 4.0.0 work as I wanted to. The doc lists three servers as:
IPv4 only server: api-ipv4.dynu.com
IPv6 only server: api-ipv6.dynu.com
IPv4 and IPv6 server: api.dynu.com

So,

protocol=dyndns2
server=api-ipv6.dynu.com

works for me. However, with 4.0.0, this solution will not work when a host tries to update an entry for an IP version that it can't use.

[Erwin-Iosef]

Maybe you should do a pull request so these changes can help everyone.