Setting the public IP address is only necessary to support communication over WAN that involves Network Address Translation (NAT).

Typically, the address is the public address of the IP NAT router that provides access to the WAN.

By default, the DDS::DomainParticipant creating the transport will announce the IP addresses obtained from the NICs to other DomainParticipants in the system.

When this property is set, the DomainParticipant will announce the IP address corresponding to the property value instead of the LAN IP addresses associated with the NICs.

Note 1: Setting this property is necessary, but is not a sufficient condition for sending and receiving data over the WAN. You must also configure the IP NAT router to allow UDP traffic and to map the public IP address specified by this property to the DomainParticipant's private LAN IP address. This is typically done with one of the following mechanisms:

Port Forwarding: You must map the private ports used to receive discovery and user data traffic to the corresponding public ports (see DDS::RtpsWellKnownPorts_t). Public and private ports must be the same since the transport does not allow you to change the mapping.
1:1 NAT: You must add a 1:1 NAT entry that maps the public IP address specified in this property to the private LAN IP address of the DomainParticipant.

Note 2: By setting this property, the DDS::DomainParticipant only announces its public IP address to other DomainParticipants. Therefore, communication with DomainParticipants within the LAN that are running on different nodes will not work unless the NAT router is configured to enable NAT reflection (hairpin NAT).

There is another way to achieve simultaneous communication with DomainParticipants running in the LAN and WAN, that does not require hairpin NAT. This way uses a gateway application such as RTI Routing Service to provide access to the WAN.

WAN communication using RTI Routing Service

[default] null (the transport uses the IP addresses obtained from the NICs)