According to the VMware NSX 4.x Professional documents and tutorials, a RouterLink port is a logical port that connects a Tier-1 gateway to a Tier-0 gateway. This port is automatically created when a Tier-1 gateway is associated with a Tier-0 gateway from the NSX UI or API. The RouterLink port enables routing between the two gateways and carries all the routing protocols and traffic. There is no need to manually create a logical switch or segment for this purpose1.