Selection of master node

Allowing MRP rings to share interfaces limits the nodes that can be designated as the master node. Any node on an MRP ring that does not have a shared interface can be designated as the ring master node. However, if all nodes on the ring have shared interfaces, nodes that do not have tunnel ports can be designated as the master node of that ring. If none of the nodes meet these criteria, you must change the rings’ priorities by reconfiguring the rings’ ID.
Note: Any node on an MRP ring that has two shared interfaces cannot be elected as the master node.

In Figure 2, any of the nodes on Ring 1, even S1 or S2, can be a master node since none of its interfaces are tunnel ports. However in Ring 2, neither S1 nor S2 can be a master node since these nodes contain tunnel ports.