Transfer device and route addition method

A route addition method comprising:

• a first calculation step in which, on the basis of first topology information that is topology information on a network made up of a plurality of transfer devices, a redundant route calculator calculates a plurality of shortest routes from a first transfer device to a second transfer device among the plurality of transfer devices, and generates redundant route information that is information on the plurality of shortest routes, to register the generated redundant route information in an information storage;
• a first detection step in which a single point-of-failure detector detects a single point of failure on the basis of the redundant route information and generates second topology information that is topology information obtained by removing the single point of failure from the first topology information;
• a second calculation step in which, on the basis of the second topology information, the redundant route calculator calculates a candidate of an additional route to be added as a route from the first transfer device to the second transfer device, and generates additional route candidate information that is information on the candidate of the additional route;
• and
• a second detection step in which the single point-of-failure detector decides the additional route on the basis of the additional route candidate information, and generates additional route information that is information on the additional route, to register the generated additional route information in the information storage.