A route distribution establishes how routes get imported into DRG route tables and exported through the DRG attachments.
A route distribution is a list of statements. Each statement consists of a set of matches, all of which must be True in order for the statement's action to take place. Each statement determines which routes are propagated.
You can assign a route distribution as a route table's import distribution. The statements in an import route distribution specify how how incoming route advertisements through a referenced attachment or all attachments of a certain type are inserted into the route table.
You can assign a route distribution as a DRG attachment's export distribution. Export route distribution statements specify how routes in a DRG attachment's assigned table are advertised out through the attachment. When a DRG attachment is created, a route distribution is created with a single ACCEPT statement with an empty match criteria (empty match criteria implies match ALL). Exporting routes through VCN attachments is unsupported, so no VCN attachments are assigned an export distribution.
The two auto-generated DRG route tables (one as the default for VCN attachments, and the other for all other types of attachments) are each assigned an auto generated import route distribution. The default VCN table's import distribution has a single statement with empty match criteria statement to import routes from each DRG attachment type. The other table's import distribution has a statement to import routes from attachments with the VCN type.
The route distribution is always in the same compartment as the DRG.