Verify the client-side settings: In some cases, the client-side settings may be causing the frequent disconnections. Check the client's configuration and ensure that it is not set to disconnect after a certain period of inactivity.

Monitor the system resources: If the SSL VPN server is experiencing high resource utilization, it may result in frequent disconnections. Monitor the server's CPU, memory, and disk usage to identify any resource bottlenecks.

Enable SSL VPN debugging: Enable SSL VPN debugging on the server to capture more detailed logs of the disconnection events. This can help in identifying the cause of the issue, such as network connectivity issues or authentication problems.

Contact the vendor support: If the issue persists and you are unable to identify the cause, it may be necessary to contact the vendor's support for further assistance. Provide them with the SSL VPN configuration and any relevant logs to help them troubleshoot the issue.

Review firewall and NAT configurations: Incorrect firewall or NAT configurations can cause issues with the SSL VPN connections. Verify that the necessary ports and protocols are allowed through the firewall and that the NAT translations are set up correctly.

Yes, there is a workaround to set the destination as DDNS in a DNAT rule, even if your public IP address changes. You can do this by creating a DNS alias for your DDNS hostname.

For example, if your DDNS hostname is my-ddns-hostname.example.com, you can create a DNS alias for it called my-public-ip. Then, you can use the DNS alias as the destination in your DNAT rule.

To create a DNS alias, you will need to contact your DNS provider. Once you have created the DNS alias, you will need to update your DNAT rule to use the DNS alias instead of the specific public IP address.

Here is an example of a DNAT rule that uses a DNS alias as the destination:

nat destination {
  from any to any
  rule my-ddns-rule {
    destination-address "my-public-ip"
    destination-port 80
    to-address 192.168.1.100
    to-port 80
    protocol tcp
  }
}

If your public IP address changes, your DNS provider will automatically update the DNS alias my-public-ip to point to the new public IP address. This means that you will not need to manually update your DNAT rule.

Note: Some DNS providers may charge a fee for creating DNS aliases.

Another workaround is to use a reverse proxy server. A reverse proxy server is a server that sits in front of your web server and forwards traffic to it. You can configure the reverse proxy server to use your DDNS hostname as its public IP address.

To do this, you will need to install and configure a reverse proxy server on your network. Once you have configured the reverse proxy server, you will need to update your DNAT rule to forward traffic to the reverse proxy server instead of your web server.

Here is an example of a DNAT rule that forwards traffic to a reverse proxy server:

nat destination {
  from any to any
  rule my-reverse-proxy-rule {
    destination-address 192.168.1.100
    destination-port 80
    to-address 192.168.1.101
    to-port 80
    protocol tcp
  }
}

When you receive traffic on your public IP address, your router will forward the traffic to the reverse proxy server. The reverse proxy server will then forward the traffic to your web server.

If your public IP address changes, you will only need to update the reverse proxy server configuration. You will not need to update your DNAT rule.

Which workaround is better?

The best workaround for you will depend on your specific needs and requirements.

If you are only hosting a single website, then using a DNS alias may be the simplest solution. However, if you are hosting multiple websites or if you need more control over how traffic is forwarded, then using a reverse proxy server may be a better option.