This INTEGER, src or dst, is described exactly as its non-VI counterpart: source translation for outgoing packets, destination translation for incoming packets, scoped to a particular virtual interface. An admin picks 'dst' when publishing a server reachable through that specific VI, and 'src' when giving hosts behind that VI a consistent outbound address. For example, an admin publishing an internal DNS server reachable only via a partner-facing VI would set this object to 'dst' for that VI's static entry.