This is the OCID of the route table that is used to route the traffic as it enters a VCN through this attachment.
For information about why you would associate a route table with a DRG attachment, see:
[Transit Routing: Access to Multiple VCNs in Same Region](https://docs.cloud.oracle.com/iaas/Content/Network/Tasks/transitrouting.htm) * [Transit Routing: Private Access to Oracle Services](https://docs.cloud.oracle.com/iaas/Content/Network/Tasks/transitroutingoracleservices.htm)
Indicates whether the VCN CIDRs or the individual subnet CIDRs are imported from the attachment. Routes from the VCN ingress route table are always imported.
Specifies the update details for the VCN attachment.