OS-DDClient: Default GW is not always the right interface to send to Dyn DNS providers with Multi-WAN

[AegeanDad]

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Is your feature request related to a problem? Please describe. In a multi-WAN setting, where the default WAN gateway that the DDClient uses to connect to the dynamic DNS service provider differs from the WAN interface whose IP should be reported to the dynamic DNS service provider, the new plug-in fails to meet this requirement. User selects the "Check ip method" of Interface and "Interface to monitor" in the settings. With the new plug-in, the IP address reported to the service provider is always the outgoing WAN interface's IP in this setup. This causes issues in cases such as site-to-site VPNs where one or both sides have dynamic IPs or P2P applications where inbound traffic needs to be a specific WAN.

Describe the solution you'd like A clear and concise description of what you want to happen. Provide two options under the Check IP Method: 1. Specific interface IP; and 2. Default WAN GW IP. When option 1 is selected, refer to the Interface to monitor field to determine which interface to use.

Describe alternatives you've considered A user could create fw routing rules to route the dynamic DNS updates to the specific WAN whose IP is desired. However, with many different dynamic IP service providers, it is not trivial to find their public IP addresses or port numbers they use that would be necessary to create such rules.

Additional context N/A.