Dragon is Garp’s son. No direct interactions have been shown, but he seems casual about the idea of his own son being a Revolutionary and wanted by the World Government.
Garp seems to have communicated with Dragon at least once since the Loguetown Arc due to Garp knowing of Dragon’s role in saving Luffy from Smoker. However, this can be disputed since it is most likely that Smoker reported the incident so it’s only natural that Garp would find out. Garp denied Luffy and Dragon’s relationship from the world in the hopes to protect his grandson, but by the time Sengoku made it public, Garp simply states that Luffy already has such a reputation that his connection to Dragon is irrelevant.
Garp and Dragon have different assessments of the East Blue. While Garp perceives it as a rather peaceful place, Dragon expresses his disgust with Garp’s view of “peace” as nothing more than a form of oppression authorized by the law in places, such as Tequila Wolf and the Goa Kingdom, where common people that are put into horrible living conditions.
Ultimately, Dragon has a extremely different ideology from his father, while Garp takes pride and contentment in being a Marine serving the World Government, Dragon absolutely despised the World Government to the point of becoming a Revolutionary and seek to overthrow them.